Covalent organic frameworks (COFS) for removing toxic perfluoroalkyl and polyfluoroalkyl substances and / or humidity and / or temperature detection

Abstract

Provided are covalent organic frameworks (COFs). The COFs may be used to bind or capture perfluorinated compounds, such as, for example, perfluorooctanoic acid (PFOA). The COFs may assemble and form nanoparticles suitable in methods of the present disclosure. Additionally, COFs may be used as fluorescent indicators to detect perfluorinated compounds, or temperature and / or humidity. COFs of the present disclosure may have the following structure: (I) wherein each R is independently (II) or (III) and each R' is independently (IV) or (V) wherein at least one R is (VI) or (VII) wherein each R is independently (VIII) or (IX) each R' is independently (X) or (XI) wherein at least one R is (XII).

Description

Attorney Docket No.: 058636.00795 COVALENT ORGANIC FRAMEWORKS (COFS) FOR REMOVING TOXIC PERFLUOROALKYL AND POLYFLUOROALKYL SUBSTANCES AND / OR HUMIDITY AND / OR TEMPERATURE DETECTION CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 633,767, filed April 13, 2024, the disclosure of which is incorporated herein in its entirety by reference. BACKGROUND OF THE DISCLOSURE

[0002] The emergence of the persistent, bio-accumulative, and toxic organic pollutants, perfluorinated and polyfluorinated substances (PFAS) and their derivatives, has led to widespread contamination of surface and groundwater worldwide, with detrimental consequences for human health and the environment. Among these pollutants, perfluorooctanoic acid (PFOA) stands out, having been detected in the majority of human serum samples from exposed populations worldwide, with water being the primary exposure pathway. Efficient detection and removal of PFOA from water resources is vital for minimizing human exposure. Material design plays a crucial role in developing systems that can simultaneously detect and adsorb PFOA.

[0003] Conventional sensing methods such as Liquid Chromatography-Mass Spectrometry (LC-MS) and High Precision Liquid Chromatography (HPLC), while accurate and reliable, are complex, expensive, and time-consuming. Rapid and cost-effective PFOA sensing technologies are urgently needed to overcome these challenges. Consequently, there’s been a significant increase in research and development focused on new materials for selective sensing of hazardous substances. In the quest for efficient detection of water contaminants, fluorescence-based sensors have gained significant attention for their inherent advantages over their non-emitting counterparts. These advantages include rapid response times, high sensitivity at low contaminant concentrations, and visual detection capabilities. Designing an efficient fluorescent sensing material entails maximizing sensor-analyte interactions by optimizing the chemistry, density, and distribution of active groups within the material to mitigate diffusion limitations and improve analyte interactions. These characteristics are essential for effective sensing and are equally important for developing an efficient adsorbent, highlighting the potential of simultaneously integrating sensing and adsorption properties in materials designed to mitigate water contamination issues.

[0004] Research on PFAS adsorption using common materials such as activated carbon (AC) and ion exchange resins has provided valuable insight into the main interaction mechanisms between PFAS and adsorbents. This knowledge is key for the development of materials that optimize these interactions while overcoming the challenges faced by conventional adsorbents. These adsorbents rely primarily on hydrophobic interactions with the fluorinated alkyl chains of PFAS, which are particularly effective in activated carbon (AC). Additionally, they rely on electrostatic interactions and ion exchange processes to target the polar functional groups of PFAS, especially in ion exchange resins. Despite widespread use, these adsorbents have significant limitations, including slow adsorption kinetics, low PFAS uptake capacity, and harsh recycling conditions. For this reason, the molecular design of adsorbents has been crucial in developing PFAS-specific materials that exploit both hydrophobic and electrostatic interactions. Recent studies have focused on the development of hydrophobic aminated materials and charged fluorinated materials, designed to maximize interactions with PFAS molecules. These studies have demonstrated promising results, significantly improving the adsorption capacity and efficiency compared to conventional materials. Such advancements highlight the potential of tailored adsorbents in effectively addressing PFAS contamination.

[0005] While designing adsorbents that harness both hydrophobic and electrostatic interactions is crucial, it is equally important that these adsorption sites are abundant and accessible to optimize the adsorption kinetics and capacity of emerging contaminants. Therefore, porous and open structures that are stable in aqueous environments are preferred for this purpose. This need is particularly evident when developing adsorbents for long-chain PFAS like PFOA and PFOS, which tend to form aggregates on the adsorbent surface via hydrophobic interactions of their fluorinated tails. While these aggregates can block the adsorption sites within the pores, and hinder diffusion and accessibility, they can alternatively boost PFAS adsorption capacity through cooperative adsorption. Consequently, the challenge lies in engineering materials with tailored physicochemical properties, striking a balance surfacween hydrophobic and electrostatic traits within an open, porous, and stable framework leveraging PFOA aggregation with an unimpeded access to adsorption sites inside the porous network.

[0006] Covalent-organic frameworks (COFs) are a class of porous crystalline materials composed of light elements (for example, C, H, O, N, etc.) formed by covalent bonding of organic building blocks into extended porous and ordered 2D and 3D structures. The structure of COFs can be tailored by the rational choice of their organic building blocks,which has contributed to their use in many applications such as gas storage, water treatment, sensing, drug delivery, and catalysis. The inherent hydrophobic nature of COFs’ main backbone makes them suitable for the adsorption of PFAS via hydrophobic interactions. In addition, the introduction of cationic moieties into their building units allows for better sensing and adsorption of PFOA through electrostatic host-guest interactions between the charged COF channels and the anionic head groups of PFOA and other anionic PFAS. In a recent study, cationic COFs were synthesized and used as adsorbents for the PFOA derivatives GenX (Qmax= 680 mg^g–1) and HFPO-TA (Qmax= 1076 mg^g–1) that reached adsorption equilibrium in 10–20 hours. However, this is not suitable for real-life applications such as point-of-use gravity filtration systems that require fast kinetics. Additionally, although there are few reports on the use of COFs in fluorescence sensing, the synthesis and application of cationic COFs for the simultaneous fluorescence sensing and adsorption of PFOAs is rarely investigated.

[0007] Further, development of optical-based sensors to detect changes in “environmental properties” such as temperature and humidity has attracted considerable interest because of their significant impact on both the human health / life and industrial sector. Relative humidity (RH)—the concentration of water vapor in the air—has received considerable attention in scientific research due to its importance in all industries, from predictive maintenance in construction and infrastructure, humidity control in the textile industry, humidity monitoring in agriculture, and production and storage in the food industry, to all aspects of water sensing in healthcare facilities, pharmaceutical processing, and drug storage. To date, known moisture-sensitive organic materials have been limited to small organic molecules, supramolecular nanostructures polymeric materials, and metal organic frameworks (MOFs). However, the lack of long-range order in smaller molecular units and polymeric materials would compromise either stability, reusability, or precise tunability. MOFs on the other hand, do not suffer from the above problems because they are crystalline, tunable networks. Nevertheless, even those that are hydrolytically stable have shown significant performance decline upon extended exposure to moisture, posing a challenge to their potential commercial applications. To address these challenges, covalent organic frameworks (COFs) have been developed in recent years to serve as multivariate sensors for various types of external stimuli via the florescence response. COFs are light materials, offer excellent thermal and chemical stability, coupled with tunable porosity and selectivity for guest molecules, making them outstanding candidates for sensing. Real-time on-site humidityvisualization with high sensitivity and accuracy using fluorescent or optical signals via a color-changing mechanism in a thermochromic luminophore is therefore a desired powerful tool in this regard. Although some progress has been made in COF materials as fluorescent water sensors, research in the area of COF water sensors is still in its infancy. Moreover, the majority of optical sensors based on COFs are often fabricated for specific applications and focus on a single function. In addition to humidity (RH) detection, there is a growing demand for temperature detection through fluorescence as a non-invasive method. Thus, the need for temperature sensors is equally necessary. The development of temperature sensors which can operate over a wide temperature range and especially under extreme conditions, such as high or low temperatures, pose a great challenge because organic-based luminescent materials may encounter diminished stability or suppressed sensor sensitivity at low temperatures, which can adversely affect their overall performance and reliability. To date, fluorescent 2D and 3D COFs have been developed to exhibit luminescence at either room temperature or higher temperatures. Luminescent materials capable of emitting light at low temperatures hold significant potential for various applications, such as temperature sensors for products that need to be cooled or frozen. The concept of a dual-function COF sensor that is sensitive to both temperature and humidity is new and has not been widely explored. Therefore, there is an urgent need to develop an advanced, readable sensor that can monitor both temperature and RH in a single intelligent system. For real-world applications, solid-state fluorescent probes are a much more practical alternative. However, most COFs exhibit poor luminescence under wet conditions. This is either due to their inherent hydrophobic nature leading to poor polar interactions with atmospheric moisture or competition with non- radiative pathways causing effects such as aggregation-caused quenching (ACQ). BRIEF SUMMARY OF THE DISCLOSURE

[0008] Described herein are cationic COFs (e.g., TG-PD COF) that comprise guanidinium cores that introduces well-distributed positively charged adsorptive sites in its structure. These cationic sites are capable of creating electrostatic interactions with electron- rich species thereby enabling simultaneous fluorescence sensing and adsorption of perfluorinated compounds (e.g., PFOA) from water. The uniformly distributed, abundant, and accessible cationic guanidinium moieties help to increase the TG-PD COF’s interactions with the anionic heads of perfluorinated compounds (e.g., PFOA) and enhance selectivity. The applied design principle yielded a COF capable of detecting and removing perfluorinated compounds (e.g., PFOA molecules) from water in seconds, even at environmentally relevantconcentrations, with high uptake capacity leveraging cooperative adsorption through PFOA aggregation. In addition, the mechanisms underlying both detection, and rapid removal through computer simulations was investigated. These results suggest that tailored cationic COFs represent a significant advance in the detection and removal of persistent anionic pollutants from water.

[0009] In an aspect, a COF of the present disclosure is suitable to capture perfluorinated compounds, such as, for example perfluorooctanoic acid (PFOA). Other perfluorinated compounds may be captured. Such a COF may form hollow, tube-like nanoparticles.

[0010] A COF for capturing perfluorinated compounds (e.g., PFOA) may have the following structure: ,R is independently.disclosure may be made from the following monomers:and .The may the following structure: ,groups are either formyl groups or are attached to an additional triamino guanidinium group, such as in the following structure: ,, rious examples, at least 10%, 11%, 12%, 13%, 14%, 15%, 6%, %, 8%, 9%, 0%, %, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or greater than 99% of the R groups are . or substantially all of the R groups are: .the present disclosure provides an indicator. The indicator may comprise a porous membrane and a COF disposed thereon. The COF may have the following structure: ,R is independently, is . onfigured to fluoresce in the presence of perfluorinated compounds (e.g., PFOA).

[0012] In an aspect, the present disclosure provides filters. Filters may comprise a porous membrane and a COF disposed thereon. The COF may have the following structure: ,R is independently.the present disclosure provides kits. The kit may comprise a filter or indicator of the present disclosure, wherein the filter or indicator comprises a COF with thefollowing structure: , R is independently, is .the present disclosure provides COFs suitable for humidity and temperature sensing. A suitable COF may have the following structure: ,R is independentlywherein at least one R is . be made from the following monomers:and.The resulting COF may comprise the following structure: ,groups are either formyl groups or are attached to an additional triamino guanidinium group, such as in the following structure: ,examples, at least 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%,32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or greater than 99% of the R groups are . aspect, the present disclosure provides methods for detecting humidity, thepresence and / or temperature. The method may comprise contacting a COF having the following structure: ,R is independentlycontacting the medium with the COF, the COF may change color. The COF changing color from yellow to red indicates an increase in humidity or temperature.

[0016] The COF changing color from red to yellow indicates a decrease in temperature or humidity. Fluorescence may further be used. Fluorescence of the medium may be measured and compared to a control. A difference relative to the control can be used to determine the presence or absence of water or the relative temperature of the medium. In various examples, fluorescence can also be used ratiometrically for more accurate,quantitative sensing. By tracking the intensity ratio between a responsive emission band and a stable internal reference, this method minimizes background interference and enables precise detection of humidity or temperature changes.

[0017] In an aspect, a COF having the following structure: , R is independently, ispresence or absence of water in an organic medium (e.g., organic solvent). For example, the COF can be dispersed in a solvent to form a sample, and the fluorescence of the sample can be measured. The fluorescence can be then compared to a control and a change in fluorescence can be used to determine the absence or presence of water. For example, the method can be used to detect tract amounts of water (e.g., about 0.03 wt% v / v). Various organic solvents can be used. For example, the organic solvent may be tetrahydrofuran (THF).

[0018] In an aspect, the present disclosure provides indicators comprising a COF having the following structure: ,R is independentlyd . be a reusable. The indicator may be in the form of an article ofmanufacture that can be regenerated and reused. In various examples, the indicator may be a substrate having a plurality of COFs disposed thereon. In various examples, the indicator may be a cloth, fabric, or paper. BRIEF DESCRIPTION OF THE FIGURES

[0019] For a fuller understanding of the nature and objects of the disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying figures.

[0020] Figure 1 shows synthesis, chemical structure, and morphology of the TG-PD COF a) sonochemical synthesis of TG-PDCOF, b-c) SEM and HRTEM images of TG-PD COF, d) Experimental (black) and simulated PXRD (red) patterns of TGH+-PD COF, e) Geometrically optimized crystal structure of TG-PDCOF.

[0021] Figure 2 shows photophysical properties of the TG-PD COF and its PFOA sensing efficiency a) Normalized photoluminescence (PL) spectra (λex = 365 nm) of TG- PDCOF dispersion in water with the stepwise addition of PFOA, b) Linear plot of normalized PL intensity (λmax= 365 nm) as a function of PFOA concentration, c) Bar graph illustrating the comparative fluorescence intensity of TG-PDCOF in the presence of different analytes, where I0 is the initial intensity of TG-PDCOF, and I is the final intensity in response to each analyte, d) Solid state13C CP / MAS NMR spectra of PFOA (black line), TG-PDCOF (green line) and TG-PDCOF and PFOA (red line). Asterisks denote spinning side bands. e) Overlay of the two-dimensional1H-13C HETCOR solid-state NMR spectra of pure PFOA (red contour, red dotted circle) and PFOA bound to TG-PD COF (black contour, gray oval). Insetshows the simplified chemical structures of TG-PD COF and PFOA. Intramolecular1H-13C correlation from pure PFOA is shown by green arrow and inter-molecular correlation between PFOA and TG-PD COF is shown by red arrow. Upfield chemical shiftthe carbonyl carbon from PFOA upon binding to TG-PD COF is shown by green arrow.

[0022] Figure 3 shows adsorption performance of the TG-PD COF. a) Schematic representation of the PFOA adsorption experiments with the COF suspension. Created in BioRender. (2023) BioRender.com / m60h920. b) Adsorption kinetics at two different concentrations of PFOA and TG-PD COF and in the absence of COF. c) Adsorption isotherm of PFOA onto TG-PD COF. d) Schematic representation of the PFOA adsorption experiment with the TG-PD column. Created in Biorender (2024) BioRender.com / u27r837. e) PFOA adsorption at two different influent concentrations with respect to water filtrate volume using the TG-PD column.

[0023] Figure 4 shows PFOA adsorption mechanisms and COF regeneration a–c) The elemental mapping of TG-PD COF at different PFOA concentrations d) A graphical representation of PFOA adsorption onto the TG-PD COF at increasing PFOA concentrations in water e) The effect of temperature increase on the equilibrium PFOA adsorption capacity f) The removal efficiency of PFOA through 5 different regeneration cycle ([PFOA]= 0.2 mg^L–1, [COF]= 100 mg^L–1).

[0024] Figure 5 shows PFOA adsorption process from computer simulations. a) All- atom MD simulation setup of TG-PD COF with PFOA molecules. b) Snapshot taken from simulation at different time points to show the process. c-e) Time evolution of the density profiles along the long axis of the simulation box (z-axis) depicted in b for PFOA, water, and total charge, computed from simulation data averaged over a time interval of dt=0.1 ns.

[0025] Figure 6 shows Binding site and energetic analysis. a) Major surface atom types used for radial distribution function (RDF) analysis. b-g) RDF of the COF-PFOA atom pairs. RDFs of water-PFOA and water-COF atom pairs are shown in Figure 61 and 62. h) Change in the number of hydrogen bonds between water-water, PFOA-water, COF-water, and the total system due to PFAO adsorption. i) Non-bonded energy change during adsorption process is partitioned into van der Walls and electrostatic terms. We consider total energy change, and the energy change due to PFOA-COF interactions. j) A cartoon of the COFs of the present disclosure capturing PFOA in water.

[0026] Figure 7 shows a cartoon of the COFs of the present disclosure capturing PFOA in water.

[0027] Figure 8 shows FTIR analysis of TG-PD COF and its precursors. Stacked FTIR spectra of the as-synthesized TG-PD COF (green line), phenanthroline-2,9-dicarbaldehyde (PD, blue line) and triamino guanidium hydrochloride salt (TGl, black line).

[0028] Figure 9 shows solid state13C CP / MAS NMR spectral analysis. One-dimensional13C CP / MAS NMR spectrum of TG-PD. Spinning side bands are shown by asterisks.

[0029] Figure 10 shows thermogravimetric analysis (TGA) of TG-PD COF. TGA profile of TG-PD COF showing the thermal stability of the COF, the profile was recorded at a scan rate of 5 °C / min.

[0030] Figure 11 shows SEM (a, b, and c) and HRTEM (d, e, and f) images of TG-PD COF. Both microscopic analyses clearly confirm the hollow tubular morphology.

[0031] Figure 12 shows comparison of experimental and simulate PXRD pattern of TG-PD COF.

[0032] Figure 13 shows a) N2 adsorption isotherms of TG-PD COF, surface area measurements were performed by activating the samples at 85 °C for 24 hours under high vacuum, b– c) Top and side view of inclined stacking of TG-PD COF.

[0033] Figure 14 shows water contact angle of TG-PD COF.

[0034] Figure 15 shows change in the emission spectra of TG-PD COF suspensions in the presence of different analytes.

[0035] Figure 16 shows variation in the emission spectra of suspended TG-PD COF upon the addition of 11×10⁻⁷ M PFOA in the presence of equal amounts of various interfering analytes.

[0036] Figure 17 shows (a) schematic illustration for the synthesis of TG-DFP COF: (i) Microwave (MW) assisted synthesis in 1, 4-dioxane: H2O (1: 1); Simulated crystal structure shown in a spacing filling / capped sticks eclipsed model in (b) Top view and (c) Side view, Cl^ions were omitted for clarity.

[0037] Figure 18 shows a microscopic analysis of TG-DFP COF: a, b, and c) SEM and HRTEM images of TG-DFP COF at different magnifications (in c, inset displays the lattice fringes). d) AFM images of powder (inset displays the height profile).

[0038] Figure 19 shows an analysis of versatile reversible thermochromic properties: (a) Photographs of TG-DFP COF powder at temperatures of 25 and 100 °C (under different humidity conditions); (b) Dynamic vapor sorption (DVS) isotherm of TG-DFP COF powder at 298K; (c-d) operando diffuse-reflectance (DRUV) spectroscopic investigations of TG-DFP COF at different temperatures under constant RH flow (RH=18 %), the temperature interval is 1.5 °C between spectra; (e) Evolution of the FTIR spectra of TG-DFP COF recorded versus the temperatures under dry argon flow (spectra subtracted from the spectrum of thesample collected at different temperatures, the temperature interval is 4.5 °C between spectra; (f) digital images of optical handwriting on the Whatman 40 filter paper with thermochromic TG-DFP COF. The images depicted in the top and bottom views correspond to the paper strip exposed to temperatures of 25 °C and 100 °C, respectively.

[0039] Figure 20 shows (a-b) 3D-isosurface plots for single layer fragment, in gas phase and aqueous solution respectively.

[0040] Figure 21 shows fluorescence thermo / hydrochromism: (a) variable temperature solid-state fluorescence spectra (^ex= 365 nm) from TG-DFP iCOF heating under air in the wide range of temperature; (b) CIE coordinates corresponding to the emission color observed at each temperature; (c) images of a filter paper strip coated with fluorescent TG-DFP COF showing its thermos / hydrochromic fluorescence response before and after exposure to two different temperatures under a UV lamp (365 nm).

[0041] Figure 22 shows solid-state humidity sensing: (a) solid-state, diffuse reflectance spectra (DRS) of TG-DFP COF at different humidity level; (b) humidity dependence of optical density measured on TG-DFP COF; (c) plot of the absorbance band at 530 nm as a function of different RH percentages (RH%); (d) humidity-dependent emission spectra of TG-DFP COF after exposure to different RHs (inset: photographs of TG-DFP COF powder under different humid conditions under a 365 nm UV-lamp); (e) linear plot of fluorescence intensity as a function RH; f) optical images of the reversible color change in day-light (top) and under UV light (bottom panel) of a cotton fabric coated with TG-DFP COF powder between humid and dry air.

[0042] Figure 23 shows (a) an emission spectral change in stirred suspension of activated TG-DFP COF in dry THF upon incremental addition of aliquots of water (% v / v); (b) fluorescence decay profile of TG-DFP COF in THF after addition of water; (c) non-linear fitting curve of fluoresce intensity against different concentrations of water content; (d) photographs showing ratiometric fluorescence color change of the activated TG-DFP COF coated test strip when exposed to THF solutions containing different amounts of water (0-0.8 wt %).

[0043] Figure 24 shows stacked FTIR spectra of the as-synthesized TG-DFP COF (blue line), triamino guanidium hydrochloride salt (TGH.Cl, red line), and 2,6-diformyl pyridine (DFP, black line).

[0044] Figure 25 shows stacked one-dimensional13C CP / MAS spectra of (a) TG-DFP COF, (b) TGH.Cl, and (c) 2, 6-diformylpyridine. Spinning side bands are shown by asterisks.

[0045] Figure 26 shows stacked one-dimensional13C CP / MAS spectra of (a) TG-DFP COF, (b) TGH.Cl, and (c) 2, 6-diformylpyridine. Spinning side bands are shown by asterisks.

[0046] Figure 27 shows (a) comparison of the experimental PXRD (redline) and simulated PXRD (black line) patterns of TG-DFP COF, (b) computational simulated crystal structure of TG-DFP COF.

[0047] Figure 28 shows SEM (a, b, c, d) images of TG-DFP COF at different magnifications. SEM images showing the stacked sheets on top of each other.

[0048] Figure 29 shows HRTEM images of exfoliated TG-DFP COF material at different magnifications.

[0049] Figure 30 shows AFM images of exfoliated TG-DFP COF stacked nanosheets at different magnifications.

[0050] Figure 31 shows dynamic vapor sorption (DVS) isotherm of TG-DFP COF powder at 298 K at different cycles, inset showing the complete adsorption / desorption at 0% humidity.

[0051] Figure 32 shows an Operando UV-VIS setup used to carry out the study of optical response in presence of humidity.

[0052] Figure 33 shows an operando IR in DRIFTS mode to investigate the study of vibrational spectral changes response in presence of humidity.

[0053] Figure 34 shows (a-b) Tauc plots (derived from the solid-state UV-Vis spectra) for TG-DFP COF at 100 ^C and 25 ^C.

[0054] Figure 35 shows evolution of the normalized band intensity at 500 nm as function of temperature under dry argon and RH 18 %. Evolution of the absorbance of TG- DFP COF vs the temperature under dry Argon is irreversible and perfectly reversible under constant humidity. Quasi-linear evolution between 20 and 70 °C showing potential application as thermosensitive material.

[0055] Figure 36 shows (a-b) UV-Vis spectra at variable temperature under dry-argon flow. The temperature interval corresponds to 1.5 °C per spectrum.

[0056] Figure 37 shows UV-Vis spectra of TG-DFP under dry Argon, (a-b) and 18% RH (c-d) versus the temperature: Data Subtracted from the spectrum collected at T=20 °C. The temperature interval corresponds to 1.5 °C per spectrum.

[0057] Figure 38 shows plot of the surface bands of TG-DFP COF as a function of temperature in DRIFTS mode and the corresponding evolution of the water band area. TPD (thermal programed desorption) analysis of TG-DFP COF using DR-FTIR confirms the waterdesorption as a function of temperature in a similar temperature range of that observed in the thermochromism measurement.

[0058] Figure 39 shows (a-b) TGA and DSC thermograms of TG-DFP COF.

[0059] Figure 40 shows a 3D isosurface plot of electron density difference S0-S1. A significant depletion of electron density was observed on the guanidinium subunit, accompanied by an increase in electron density on the pyridine ring during the excitation process.

[0060] Figure 41 shows temperature dependance on HOMO and LUMO molecular orbitals for the TG-DFP COF fragment in implicit aqueous solution computed at three temperatures 293 K, 325 K and 363 K. Orbital isosurfaces are constructed using iso-value of 0.02.

[0061] Figure 42 shows (a-b) wide angle fitting diffraction profiles at two representative temperatures, 35 ^C and 100 ^C.

[0062] Figure 43 shows Plots of (a) d-spacing, (b) peak intensity, (c) peak width as a function of temperature, plots obtained from wide-angle PXRD data.

[0063] Figure 44 shows (a-b)13C CP / MAS spectra of TG-DFP COF (as synthesized) and regenerated COF.

[0064] Figure 45 shows solid-state photoluminescence emission spectra of TG-DFP COF over a wide temperature range.

[0065] Figure 46 shows a luminescence regeneration study of the TG- DFP COF coated paper strip. The photos are taken under UV lamp irradiation at 365 nm.

[0066] Figure 47 shows florescence images of TG-DFP COF coated paper strip (a) at 298 K, (b) dipped in liquid N2.

[0067] Figure 48 shows reversible / irreversible thermochromic effect of TG-DFP COF coated fabric examined under an open atmosphere and in glove box.

[0068] Figure 49 shows detailed regeneration study of COF coated paper strip: fluorescence regeneration analysis of TG-DFP COF coated paper strip was carried out by removing the COF-coated paper strip from the solvent and immediately drying it using a heat gun at 100 °C for 1 minute. The fluorescent color was restored under dry conditions.

[0069] Figure 50 shows PXRD analysis of the regenerated TG-DFP COF powder after water sensing applications.

[0070] Figure 51 shows (a) emission spectra of TG-PD drop-cast films after immersion in aqueous solutions of PFOA at different concentrations. (b) Variation in fluorescence intensity with PFOA concentration. Excitation wavelength: 365 nm.

[0071] Figure 52 shows DNP enhanced15N CP / MAS solid-state NMR spectra of TG- PD COF (bottom, blue line) and PFOA bound to TG-PD COF (top, red line).

[0072] Figure 53 shows Stacked one-dimensional19F solid-state NMR spectra of pure PFOA (bottom, blue line) and PFOA bound to TG-PD COF (top, red line). Asterisks denote spinning side bands.

[0073] Figure 54 shows HOMO-LUMO energy diagrams of (i) TG-PDCOF, (ii) TG- PDCOF and PFOA and (iii) TG-PDCOF and OA (right).

[0074] Figure 55 shows adsorption kinetics data fitting for high PFOA and COF concentrations using (a) the pseudo-1stand (b) pseudo-2ndmodels, and for low PFOA and COF concentrations using (c) the pseudo-1stand (d) the pseudo 2ndmodels.

[0075] Figure 56 shows a picture of the column adsorption experiments.

[0076] Figure 57 shows (a) variation of zeta potential with PFOA concentration in the adsorption solutions; (b) variation of the pH value of the adsorption solution as a function of the initial PFOA concentration.

[0077] Figure 58 shows elemental mapping of TG-PD COF at different PFOA concentrations.

[0078] Figure 59 shows adsorption isotherm data fitted to the (a) Langmuir model for the whole PFOA concentration range; (b) Freundlich model for the whole PFOA concentration range; (c) Langmuir model for PFOA concentration below 600 mg / L; (d) Freundlich model for PFOA concentration higher than 600 mg / L.

[0079] Figure 60 shows (a) a comparison of PXRD pattern of as synthesized TG-PD COF, and regenerated COF after PFOA treatment, (b) SEM image of regenerated TG-PD COF.

[0080] Figure 61 shows PFOA adsorption process (a) Number of PFOA molecules binding to the COF in time. (b) Number of water molecules inside the COF in time, inset shows the environment of the PFOA when solvated in water and bound to the COF.

[0081] Figure 62 shows radial distribution function (RDF) of water atoms OW and HW with PFOA select atoms. (a, b) bound state computed from the last 3 ns. (c, d) unbound state computed from the first 3 ns.

[0082] Figure 63 shows radial distribution functions (RDFs) between the atoms of the TG-PD COF with water molecules (HW and OW). (a) displays the RDF between thehydrogen atoms of water (HW) and the three carbon atoms in the COF, labeled as (C1, C2, and CR). (b) the RDF between the oxygen atoms of water (OW) and the three carbon atoms in the COF, labeled as (C1, C2, and CR). (c) presents the RDF between the hydrogen atoms of water (HW) and hydrogen atoms in the COF, denoted as (Hb, H, and HHB). (d) illustrates the RDF between the oxygen atoms of water (OW) and hydrogen atoms in the COF, denoted as (Hb, H, and HHB). (e) the RDF between the hydrogen atoms of water (HW) and the nitrogen atoms in the COF, labeled as (N2, N3, and NR) is depicted. (f) shows the RDF between the oxygen atoms of water (OW) and the nitrogen atoms (N2, N3, and NR) in the COF.

[0083] Figure 64 shows radial distribution functions (RDFs) between TG-PD COF atoms, with PFOA select atoms. (a) shows the RDF between the three carbon atoms in the COF (C1, C2, and CR) and the C2 atom in PFOA. (b) presents the RDF between the hydrogen atoms in the COF (Hb, H, and HHB) and the C2atom in PFOA. (c) shows the RDF between the nitrogen atoms in the COF (N2, N3, and NR) and the C2 atom in PFOA. (d) illustrates the RDF between the hydrogen atoms in the COF (Hb, H, and HHB) and the C3atom in PFOA. (e) the RDF between the carbon atoms in the COF (C1, C2, and CR) and the C3 atom in PFOA is depicted. (f) presents the RDF between the nitrogen atoms in the COF (N2, N3, and NR) and the C3 atom in PFOA.

[0084] Figure 65 shows change in the number of hydrogen bonds between water- water in time during PFAO adsorption.

[0085] Figure 66 shows change in the number of hydrogen bonds between COF-water in time during PFAO adsorption.

[0086] Figure 67 shows change in the number of hydrogen bonds between PFOA- water in time during PFAO adsorption. DETAILED DESCRIPTION OF THE DISCLOSURE

[0087] Although claimed subject matter will be described in terms of certain examples, other examples, including examples that do not provide all of the benefits and features set forth herein, are also within the scope of this disclosure. Various structural, logical, process step, and electronic changes may be made without departing from the scope of the disclosure.

[0088] As used herein, unless otherwise indicated, “about”, “substantially”, or “the like”, when used in connection with a measurable variable (such as, for example, a parameter, an amount, a temporal duration, or the like) or a list of alternatives, is meant to encompass variations of and from the specified value including, but not limited to, those withinexperimental error (which can be determined by, e.g., a given data set, an art accepted standard, etc. and / or with, e.g., a given confidence interval (e.g.90%, 95%, or more confidence interval from the mean), such as, for example, variations of + / -10% or less, + / -5% or less, + / -1% or less, and + / -0.1% or less of and from the specified value), insofar such variations in a variable and / or variations in the alternatives are appropriate to perform in the instant disclosure. As used herein, the term “about” may mean that the amount or value in question is the exact value or a value that provides equivalent results or effects as recited in the claims or taught herein. That is, it is understood that amounts, sizes, compositions, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error, or the like, or other factors known to those of skill in the art such that equivalent results or effects are obtained. In general, an amount, size, composition, parameter, or other quantity or characteristic, or alternative is “about” or “the like,” whether or not expressly stated to be such. It is understood that where “about,” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0089] Ranges of values are disclosed herein. The ranges set out a lower limit value and an upper limit value. Unless otherwise stated, the ranges include the lower limit value, the upper limit value, and all values between the lower limit value and the upper limit value, including, but not limited to, all values to the magnitude of the smallest value (either the lower limit value or the upper limit value) of a range. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a numerical range of “0.1% to 5%” should be interpreted to include not only the explicitly recited values of 0.1% to 5%, but also, unless otherwise stated, include individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5% to 1.1%; 0.5% to 2.4%; 0.5% to 3.2%, and 0.5% to 4.4%, and other possible sub-ranges) within the indicated range. It is also understood (as presented above) that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. Ranges can be expressed herein as from “about” one particular value, and / or to “about” another particular value. Similarly, when values are expressed as approximations, by use of the antecedent“about, it will be understood that the particular value forms a further disclosure. For example, if the value “about 10” is disclosed, then “10” is also disclosed.

[0090] The articles “a” and “an” are used in this disclosure to refer to one or more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.

[0091] As used herein, unless otherwise stated or indicated, “s” refers to second(s), “min” refers to minute(s), and “h” refers to hour(s).

[0092] As used herein, unless otherwise stated, the term “group” refers to a chemical entity that is monovalent (i.e., has one terminus that can be covalently bonded to other chemical species), divalent, or polyvalent (i.e., has two or more termini that can be covalently bonded to other chemical species). The term “group” also includes radicals (e.g., monovalent and multivalent, such as, for example, divalent radicals, trivalent radicals, and the like). Illustrative examples of groups include: . The present disclosure provides(COFs). Also provided are methods of making the COFs and methods of using the COFs.

[0094] In an aspect, a COF of the present disclosure is suitable to capture a perfluorinated compounds, such as, for example, perfluorooctanoic acid (PFOA). Such a COF may assemble to form hollow, tube-like nanoparticles.

[0095] A COF for capturing perfluorinated compounds (e.g., PFOA) may have the following structure: ,R is independently, is . disclosure may be made from the following monomers:and. The resulting COF may comprise the following structure: ,groups are either formyl groups or are attached to an additional triamino guanidinium group, such as in the following structure:, , examples, at least 10%, 11%, 12%, 13%, 14%, 15%,22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or greater than 99% of the R groups are . or substantially all of the R groups are: .of the present disclosure may have various structural and chemical features. For example, the resulting nanoparticle may have a P21 space group. The COFs and nanoparticles may porous and have some degree of crystallinity. For example, the COFs and nanoparticles may be partially crystalline, substantially crystalline, or crystalline.

[0097] Additionally, the COFs may form tube-like nanoparticles that are hollow. Additionally, the COFs and nanoparticles may act as “turn-on” fluorescent sensors for perfluorinated compounds (e.g., perfluorooctanoic acid (PFOA)). The COFs may have a low detection limit of perfluorinated compounds. For example, the detection limit may be in the nanomolar range. For example, the detection limit may be 4.5 nM or about 4.5 nM. The nanoparticles of the present disclosure may comprise honeycomb (hcb) type layers, with chlorine anions located in the pores.

[0098] The COFs of the present disclosure may be readily dispersible in water. Without intending to be bound by any particular theory, it is considered that the cationic character of the guanidinium enhances the COF’s dispersibility in water. PFOA molecules, with their long-tail fluorinated carbon atoms, are highly hydrophobic in nature. The hydrophobic-hydrophilic interaction is the key factor in the selective sensing of PFOA by TG-PD COF. With its long alkyl fluorocarbon tail, PFOA exhibits a strong hydrophobic binding interaction with the TG-PD COF. In contrast, OA, which lacks fluorination, has lower hydrophobicity, which reduces its binding interaction with COFs of the present disclosure.

[0099] In an aspect, the COFs and / or nanoparticles of the present disclosure may be used to capture and / or detect the presence of perfluorinated compounds (e.g., PFOA). For example, perfluorinated compounds (e.g., PFOA) may be captured upon contact with the COFs and / or nanoparticles. For example, the perfluorinated compound can be longer aliphatic chain perfluorinated compounds (e.g., having six or more carbon atoms). Without intending to be bound by any particular theory, it is considered that longer aliphatic chain perfluorinated compounds exhibit strong hydrophobic interactions via their fluorinated tails and electrostatic interactions via their anionic head groups. Compounds with shorter chains or lacking sufficient fluorination may show reduced binding affinity and thus lower sensing or adsorption efficiency.

[0100] The COFs and / or nanoparticles may be used to capture and / or detect perfluorinated compounds (e.g., PFOA) in a medium, such as, for example, water or other aqueous media. The method may comprise contacting a medium comprising or suspected of comprising perfluorinated compounds (e.g., PFOA) with COFs and / or nanoparticles of the present disclosure. Upon contact with the COFs and / or nanoparticles, the perfluorinated compounds (e.g., PFOA) may bind via hydrophobic interactions to the COFs and / or nanoparticles. The resulting binding results in a change in fluorescence, which can be measured and compared to a control sample without perfluorinated compounds (e.g., PFOA).The change in fluorescence may be indicative of the presence of perfluorinated compounds (e.g., PFOA) bound to the COFs and / or nanoparticles. perfluorinated compounds (e.g., PFOA) may bind to the COFs and / or nanoparticles within seconds, minutes, or in an hour.

[0101] The same COF may be used repeatedly (e.g., the COF may be regenerated after use). Following contacting the COF with perfluorinated compounds (e.g., PFOA) and perfluorinated compounds (e.g., PFOA) binds to the COF, the COF may be regenerated by soaking the COF bound with perfluorinated compounds (e.g., PFOA) in an organic medium, such as, for example, methanol or the like. The COF may then be reused to capture perfluorinated compounds (e.g., PFOA) 1, 2, 3, 4, 5, or more times.

[0102] In an aspect, the present disclosure provides an indicator. The indicator may comprise a porous membrane and a COF disposed thereon. The COF may have the following structure: ,R is independently.to fluoresce in the presence of perfluorinated compounds (e.g., PFOA). It is expected that upon binding to a perfluorinated compound, there is a blue shift in fluorescence.

[0103] The indicator may comprise various porous membranes. These porous membranes provide an effective substrate for immobilizing the COF or nanoparticles and facilitating interaction with the target analyte, perfluorinated compounds (e.g., PFOA), in liquid samples. The membrane may serve as the structure support for the COF and facilitate the diffusion of analytes while retaining stability and integrity. Examples include, but are not limited to, polyethersulfone (PES) membranes, polytetrafluoroethylene (PTFE) membranes, cellulose acetate (CA) membranes, nylon membranes, combinations thereof, and the like. Additional examples include, but are not limited to, Mixed Matrix Membranes (MMMs) and other composite membranes, which combine COFs with polymeric or inorganic supports to enhance stability, processability, and performance. For example, PES membranes may have a porosity of 0.1 to 0.2 µm, including all µm values and ranges therebetween. PES membranes may have a desirable mechanical strength, desirable chemical resistance, and desirable thermal stability. For example, PTFE membranes may have a porosity of 0.1 to 0.2 µm, including all µm values and ranges therebetween. PTFE membranes may have desirable chemical inertness, desirable hydrophobicity, and desirable thermal stability. For example, CA membranes may have a porosity of 0.1 to 0.2 µm, including all µm values and ranges therebetween. CA membranes may have desirable biocompatibility, desirable hydrophilicity, and are cost-effective. For example, nylon membranes may have a porosity of 0.1 to 5.0 µm, including all µm values and ranges therebetween. Nylon membranes may have a desirable tensile strength, desirable chemical resistance, and desirable durability. In various examples, the membrane has a porosity consistent with a microfiltration membrane, ultrafiltration membrane, or nanofiltration membrane. In various examples, the membrane has a porosity consistent with a nanofiltration membrane.

[0104] In an aspect, the present disclosure provides filters. Filters may comprise a porous membrane and a COF disposed thereon. The COF may have the following structure: ,R is independentlyeach R' is independently , is . filters are contemplated. The filter can be a screw-on filter for afaucet, a water filter for a house, an in-line filter, an active bed in gravity filters (a point of use filter), a filter for a syringe, or the like. In other examples, the COF could be formulated as a powder or granulated powder. These formulations could be used to increase the efficacy of perfluorinated compound (e.g., PFOA / PFAS) removal. Filters may be used for removal of perfluorinated compounds (e.g., PFOA) from liquid samples. In various examples, a filter has a higher quantity of COF or nanoparticles to maximize adsorption capacity for efficient removal of perfluorinated compounds (e.g., PFOA).

[0106] The filter may also comprise a COF adsorbent bed (whether in a column setting or on a membrane) and water flows through the COF layer rather than being mixed with it for a certain period of time (unless batch experiments are being conducted for research purposes but in real life applications water flows through the COF layer). The filter may have a larger surface area or specific configuration optimized for filtration purposes, ensuring effective removal of perfluorinated compounds (e.g., PFOA) contaminants from the liquid stream. In various embodiments, the filter does not include fluorescence-based detection components.

[0107] In an aspect, the present disclosure provides kits. The kit may comprise a filter or indicator of the present disclosure, wherein the filter or indicator comprises a COF with the following structure: ,R is independentlyd .may further comprise a flow cell. The flow cell may be configured such that liquid interacts with the indicator or filter when the liquid is passed through the flow cell.

[0109] In an aspect, the present disclosure provides COFs suitable for humidity and temperature sensing. A suitable COF may have the following structure: ,R is independentlybe made from the following monomers: and .The resulting COF may comprise the following structure: ,groups are either formyl groups or are attached to an additional triamino guanidinium group, such as in the following structure: ,examples, at least 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%,48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or greater than 99% of the R groups are . COF may be at least partially crystalline. For example, the COF is mostlycrystalline, or crystalline.

[0111] This material displays remarkable sensitivity to two crucial environmental factors: humidity and temperature. These parameters have an impact on its optical properties, and thus the COF can serve as a solid-state sensor for rapid and accurate measurement of temperature and humidity. The water sensitivity of this COF material can be used for detecting trace amounts of water in organic solvents.

[0112] The COFs of the present disclosure have desirable optical and spectral properties. For example, a COF having the following structure: ,R is independently,powder when dry and at temperatures around room temperature andlower. Upon contact with water and / or heat, the COF changes color to deep red. Additionally, there is a corresponding change in fluorescence.

[0113] In aspect, the present disclosure provides methods for detecting humidity, the presence of water, and / or temperature. The method may comprise contacting a COF having the following structure: , R is independentlythe medium with the COF, the COF may change color. The COF changing color from yellow to red indicates an increase in humidity or temperature. The COF changing color from red to yellow indicates a decrease in temperature or humidity. Fluorescence may further be used. Fluorescence of the medium may be measured and compared to a control. A difference relative to the control can be used to determine the presence or absence of water or the relative temperature of the medium. In various examples, fluorescence can also be used ratiometrically for more accurate, quantitative sensing. By tracking the intensity ratio between a responsive emission band and a stable internal reference, this method minimizes background interference and enables precise detection of humidity or temperature changes.

[0114] In an aspect, a COF having the following structure: , R is independentlythe presence or absence of water in an organic medium (e.g., organicsolvent). For example, the COF can be dispersed in a solvent to form a sample, and the fluorescence of the sample can be measured. The fluorescence can be then compared to a control and a change in fluorescence can be used to determine the absence or presence of water. For example, the method can be used to detect tract amounts of water (e.g., about 0.03 wt% v / v). Various organic solvents can be used. For example, the organic solvent may be tetrahydrofuran (THF).

[0115] In an aspect, the present disclosure provides indicators comprising a COF having the following structure:, is reusable. The indicator may be in the form of an article of manufacture that can be regenerated and reused. In various examples, the indicator may be a substrate having a plurality of COFs disposed thereon. In various examples, the indicator may be a cloth, fabric, or paper.

[0116] The steps of the method described in the various embodiments and examples disclosed herein are sufficient to carry out the methods of the present invention. Thus, in an embodiment, the method consists essentially of a combination of the steps of the methods disclosed herein. In another embodiment, the method consists of such steps.

[0117] The following Statements present various examples of the present disclosure. Statement 1. A covalent organic framework (COF), comprising the following structure: ,R is independentlywherein at least one R is .to Statement 1, wherein at least 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or greater than 99% of the R groups are .to Statement 1 or Statement 2, wherein the COF comprises the following structure:of the preceding Statements, wherein the COF is porous and at least partially crystalline.Statement 5. A COF according to Statement 4, wherein the COF is substantially crystalline or crystalline. Statement 6. A nanoparticle comprising the COF according to any one of Statements 1 to 5. Statement 7. A nanoparticle according to Statement 6, wherein the nanoparticle has a hollow, tube-like morphology. Statement 8. An indicator for detecting perfluorinated compounds (e.g., perfluorooctanoic acid (PFOA)) in a liquid, comprising: a porous medium; a COF according to any one of Statements 1 to 5 or a plurality of nanoparticles according to Statements 6 or 7 disposed on the porous medium; and wherein the indicator is configured to fluoresce in the presence of perfluorinated compounds (e.g., PFOA). Statement 9. An indicator according to Statement 8, wherein the porous medium comprises polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF), cellulose acetate, nylon, or porous silica gels, Mixed Matrix Membranes (MMMs), other composite membranes that combine COFs with polymeric or inorganic supports to enhance stability, processability, and performance, or any combination thereof. Statement 10. A kit for detecting one or more perfluorinated compounds (e.g., PFOA) in a liquid, the kit comprising: an indicator according to Statement 8 or Statement 9; and a flow cell containing the indicator, the flow cell configured such that liquid interacts with the indicator when the liquid is passed through the flow cell. Statement 11. A kit according to Statement 10, further comprising a fluorometer configured to measure a fluorescence of the indicator. Statement 12. A kit according to Statement 10 or Statement 11, further comprising a filter for removing perfluorinated compounds (e.g., PFOA) from the liquid. Statement 13. A kit according to claim 12, wherein the filter comprises: a porous medium; a COF according to any one of Statements 1 to 5 or a plurality of nanoparticles according to Statements 6 or 7 disposed on the porous medium disposed on the porous medium. Statement 14. A kit according to any one of Statements 10 to 13, wherein the flow cell is a syringe. Statement 15. A filter for removing one or more perfluorinated compounds (e.g., PFOA) from a liquid, the filter comprising: a porous medium; a COF according to any one ofStatements 1 to 5 or a plurality of nanoparticles according to Statements 6 or 7 disposed on the porous medium. Statement 16. A method for capturing one or more perfluorinated compounds (e.g., PFOA) comprising contacting a COF according to any one of Statements 1 to 5 or a plurality of nanoparticles according to Statements 6 or 7 with a liquid comprising or suspected of comprising one or more perfluorinated compounds (e.g., PFOA) such that a dispersion of the COF or nanoparticle with the liquid is formed, wherein following the contacting, the perfluorinated compounds (e.g., PFOA) binds to the COF or nanoparticle. Statement 17. A method according to Statement 16, further comprising measuring the fluorescence of the dispersion and comparing the fluorescence of a control dispersion. Statement 18. A method according to Statement 16 or Statement 17, further comprising measuring the pH of liquid following contacting with the COF or nanoparticle. Statement 19. A covalent organic framework (COF), comprising the following structure: , wherein each R is independently.according to Statement 19, wherein at least 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%,62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or greater than 99% of all the R groups are .COF according to Statement 19 or Statement 20, wherein the COF comprises the following structure:to any one of Statements 19 to 21, wherein the COF is porous and at least partially crystalline. Statement 23. A COF according to any one of Statements 19 to 22, wherein the COF is substantially crystalline or crystalline. Statement 24. A method for determining the humidity or temperature of a medium comprising contacting a COF according to any one of Statements 19 to 23 with a medium or substrate and observing the COF for a change in color. Statement 25. A method according to Statement 24, wherein the COF changing color from yellow to red indicates an increase in humidity or temperature. Statement 26. A method according to Statement 24, wherein the COF changing color from red to yellow indicates a decrease in temperature or humidity. Statement 27. A method according to any one of Statements 24 to 26, further comprising measuring fluorescence of the medium and comparing the fluorescence of the medium to a control.Statement 28. A method for determining if water is present in an organic solvent at trace levels comprising contacting the organic solvent with a dry, yellow COF according to any one of Statements 19 to 21 and observing if the COF changes color or measuring the fluorescence of the solvent relative to a control. Statement 29. An indicator comprising a COF according to any one of Statements 19 to 21.

[0118] The following examples are presented to illustrate the present disclosure. They are not intended to be limiting. EXAMPLE 1

[0119] This example provides an example of COFs of the present disclosure and uses thereof.

[0120] The contamination of water by per- and polyfluorinated substances (PFAS) is a pressing global concern due to their harmful effects on human health and the environment. To address the simultaneous challenges of detection and removal of perfluorooctanoic acid (PFOA) from water, a cationic covalent-organic framework (COF), TG-PD COF, is presented in this study. TG-PD COF is synthesized by a simple sonochemical method and characterized by a distinct hollow tube-like morphology. The COF exhibits remarkable selectivity and sensitivity to PFOA, with a detection limit as low as 4.5 nM, and a significant adsorption capacity exceeding 2600 mg^g-1. Removal of PFOA is achieved within seconds, with the COF retaining its efficacy over multiple adsorption cycles. Our results show a unique adsorption behavior characterized by two distinct phases leveraging PFOA molecules’ aggregation through hydrophobic interactions. The design of TG-PD COF was engineered to harness both hydrophobic and electrostatic interactions, while its large pores and open structure significantly facilitate rapid adsorption kinetics preventing blockage of internal adsorption sites by PFOA aggregates, a common limitation of conventional materials. Computer simulations were performed to decipher the mechanism underlying the PFOA sensing, adsorption, and charge transfer dynamics of the TG-PD COF. This study presents TG-PD COF as a multifunctional material that seamlessly integrates highly efficient sensing and adsorption capabilities. The comprehensive understanding of the adsorption mechanism positions the COF design strategy described herein as a promising solution for combating PFAS contamination in water bodies worldwide.

[0121] Presented herein is a cationic COF, TG-PD COF, featuring guanidinium cores that introduces well-distributed positively charged adsorptive sites in its structure. Thesecationic sites are capable of creating electrostatic interactions with electron-rich species thereby enabling simultaneous fluorescence sensing and adsorption of PFOA from water. The uniformly distributed, abundant, and accessible cationic guanidinium moieties help to increase the TG-PD COF’s interactions with the anionic heads of PFOA and enhance selectivity. The applied design principle yielded a COF capable of detecting and removing PFOA molecules from water in seconds, even at environmentally relevant concentrations, with high uptake capacity leveraging cooperative adsorption through PFOA aggregation. In addition, the mechanisms underlying both detection and rapid removal through computer simulations were investigated. These results suggest that tailored cationic COFs represent a significant advance in the detection and removal of persistent anionic pollutants from water.

[0122] The synthesis of TG-PD COF (Figure 1a) involved a simple sonochemical method, in which triamino guanidinium chloride TGH•Cl (42.3 mg, 0.30 mmol) and 2,9- diformyl 1, 10-phenanthroline PD (106.2 mg, 0.45 mmol) were combined in a mixture of 1,4- dioxane and water (1:1, v:v). The resulting mixture underwent ultrasonication for one hour at room temperature using a high power (40 %, 550 W) ultrasonic probe in continuous mode with a 3 mm microtip. The orange-colored product was subsequently purified by ethanol washing and dried at 120 °C for 12 hours.

[0123] Confirmation of the successful formation of the imine bond (-C=N) in TG-PD COF was achieved by Fourier transform infrared (FT-IR) spectroscopy and solid-state13C cross-polarization magic-angle spinning (CP / MAS), and the results are shown in Figure 8. The emergence of a new stretching vibration at 1625 cm−1, indicative of imine (– C=N) bonds, along with the disappearance of the band at 1701 cm–1, corresponding to −CHO groups in PD, provided evidence for the formation of TG-PD COF. Moreover, the13C CP / MAS NMR spectrum of TG-PD COF showed a signal at ~147 ppm, providing additional confirmation of the formation of the –C=N bond (Figure 9). Another signal observed at 152 ppm in the NMR spectrum was attributed to the C atom of the guanidinium moiety. The TG-PD COF demonstrated thermal stability up to approximately 200 °C (Figure 10). The weight loss observed before 100 °C is mainly attributed to the desorption of water from the COF surface. Subsequent weight loss beyond 200 °C is attributed to the thermal decomposition of the COF network. The morphology of TG-PD was investigated using scanning electron microscopy (SEM) and high-resolution transmission-electron microscopy (HRTEM). SEM images revealed a hollow tube-like morphology with open-ended sides as shown in Figure 1b and Figure 11. HRTEM analysis further confirmed the hollow nature ofTG-PD COF, as evidenced by the presence of an inner interior region covered by two outer rigid shells with a largely rough surface, as shown in Figure 1c and Figure 11.

[0124] PXRD analysis was conducted to verify the formation of the 2D organic network and confirm its periodic nature (Figure 1d). For this purpose, a crystal structure model was simulated and geometrically optimized, based on the formation of extended layers through the covalent bonding between TG and DP building blocks (Figure 1e, Figure 12). The structure model consists of TG units acting as three connected nodes linked by DP moieties, forming honeycomb (hcb) type layers, with chlorine anions located in the pores. A model in the monoclinic P21 space group was optimized, with cell parameters a = 39.36 Å, b = 23.67 Å, c = 4.19 Å, β = 131.97°, where the covalent layers extend along the ab plane, and are stacked in an inclined fashion along the c direction. The calculated PXRD pattern is in excellent agreement with the experimental one. Thus, the experimental PXRD pattern show several diffraction lines, including a distinct peak centered at 2θ = 4.6°, which was assigned to the (110) diffraction plane of the COF network, followed by broader signals, spanning the 2^ range of 7 – 11^, that are mainly attributed to the (020), (220), and (310) planes. Additionally, a relatively sharp intense peak was observed at 2θ = 27°, which corresponds to the (11-1) reflexion. As expected for a two-dimensional, layered COF, where the interlayer interactions are not covalent, the peaks are broad, which is indicative of the limitations in the size crystalline domains. Nevertheless, this is comparable to most reported guanidinium-based 2D COFs. Regarding the correspondence between the calculated and experimental pattern, the calculated position of the most intense reflections according to our model are in good agreement with the experimental pattern. The list of the most intense diffraction lines (I >5%), and their corresponding d spacing values, hkl indexes, and 2^ position is shown in the following table (Table 1).

[0125] The BET surface area analysis of the TG-PD COF was conducted (Figure 13), and the calculated surface area was around 13 m²^g-1. This is likely due to the presence of a large number of counter anions within the COF network, which may block the COF pores. Similar observations have also been noted in other reported guanidinium-based COFs. Furthermore, the lower BET value can be attributed to several factors, such as disorderly distributed anions, and an imperfectly defined stacking sequence as consequence of the use of phenanthroline units Figure 13.

[0126] Photophysical properties and PFOA detection. Despite its hydrophobicity, with a water contact angle of 112⁰ (Figure 14), despite having a contact angle characteristicof hydrophobic materials, the material forms a relatively stable dispersion after just a few minutes of sonication, owing to its ionic nature, and its photophysical properties in water were investigated. In aqueous medium, TG-PD COF possesses an emission band with a maximum centered around 575 nm upon excitation at 365 nm. This emission is caused by intramolecular charge transfer (ICT) from the phenanthroline to the guanidinium moiety. After adding different concentrations of PFOA to the TG-PD COF dispersion, the fluorescence intensity showed a linear increase with increasing PFOA concentration (Figure 2a). By fitting the linear data and using the 3σ / slope method, a limit of detection (LOD) for PFOA of 1.8 µg^L-1, showing competitive PFOA sensitivity (Figure 2b). While it is not the most sensitive of the materials listed in Table 2, it offers a detection capability in the environmentally relevant concentrations range, making it a viable option for the detection of PFOA in the environment.

[0127] Interestingly, the TG-PD COF exhibits remarkable selectivity for the PFOA molecule. Control experiments were conducted to assess the sensing ability of TG-PD COF with other isostructural fluorinated and non-fluorinated strong acids (trifluoroacetic acid (TFA), propionic acid, and perfluorohexanoic acid). TG-PD COF showed a very weak response to these acids, probably due to their lower hydrophobic character (Figure 2c, Figure 15). Also tested was NaCl and Na₂SO₄ for selectivity studies, considering that these salts might be present in contaminated water (Figure 2c). However, they did not show any noticeable response with TG-PD COF in water. It is important to note that the PFOA molecules, with their long-tail fluorinated carbon atoms, are highly hydrophobic in nature. The hydrophobic-hydrophilic interaction is the key factor in the selective sensing of PFOA by TG-PD COF. With its long alkyl fluorocarbon tail, PFOA exhibits a strong hydrophobic binding interaction with the TG-PD COF. In contrast, OA, which lacks fluorination, has lower hydrophobicity, which reduces its binding interaction with TG-PD COF. To further understand the sensitivity of TG-PD, an additional experiment was conducted in which equal quantities of interfering analytes were added along with PFOA. As shown in Figure 16, TG- PD exhibited a turn-on signal even in the presence of other analytes, indicating that the presence of interfering substances does not significantly affect its performance.

[0128] In water, when TG-PD COF and PFOA are in close proximity, large aggregates form as a result of the strong electrostatic interactions between the sensor and analyte molecules. In the aggregated state, the nonradiative intramolecular motions are restricted, which in turn leads to an enhancement in fluorescence. This phenomenon, knownas aggregation-induced emission (AIE), is responsible for the observed “turn-on” fluorescence when TG-PD COF interacts with PFOA. To confirm this hypothesis, zeta potential (ζ) measurements were performed to follow the change in surface charge of the TG- PD COF as the PFOA concentration increased (Figure 57a). The zeta potential was calculated from DLS measurements. Initially, the COF suspension showed a positive zeta potential (+24 mV). Upon additions of PFOA, the surface charge significantly decreased to –19.95 mV. This notable change in the zeta potential values is strong evidence of the electrostatic interaction between the sensor and the analyte. It is known that in aggregates, the restriction of intramolecular rotation prevents nonradiative decay, causing fluorescence enhancement.

[0129] To assess the practical applicability of the COF material, solid-state fluorescence sensing experiments were conducted. In the solid state, an efficient fluorescence “turn-on” response to PFOA was observed (Figure 51). Solid-state PFOA sensing was conducted by depositing TG-PD COF powder onto a 2 cm portable filter paper. The paper- based sensor serves as a suitable substrate that allows for the uniform dispersion of the COF powder and the formation of a stable, uniform film. The emission intensity of TG-PD COF varied linearly with the concentration of PFOA, and a LOD of 12 ^g L^1was calculated in the solid state (Figure 51b).

[0130] To further elucidate the sensing mechanism and determine the interaction sites, a thorough13C CP / MAS NMR spectral analysis was performed (Figure 2d) on TG-PD COF before and after exposure to PFOA. After binding of PFOA with the COF, the carbonyl carbon of PFOA is upfield shifted by ~ 3.4 ppm. The reason for this significant change in chemical shift could be attributed to the presence of strong hydrogen bonding or deprotonation of the carboxyl group as the electronic environment of the carbonyl carbon is changed. The loss of the proton and the formation of the carboxylate anion can decrease the electron-withdrawing effect, leading to increased shielding of the carbonyl carbon and, consequently, an upfield shift in the NMR signal. This was further supported by the observed ~ 3.5-fold fluorescence enhancement of the TG-PD COF upon interaction with PFOA, which clearly confirms the presence of strong interactions between the two species. This was also confirmed by two-dimensional1H-13C HETCOR (Heteronuclear correlation) solid-state NMR experiments on pure PFOAbound to TG-PD COF. Figure 2e shows the overlay of the two-dimensional1H-13C HETCOR solid-state NMR spectra of pure PFOA (red contours) and PFOA bound to TG-PD COF (black contours). The spectrum of pure PFOA is mainly characterized by the presence of an intramolecular1H-13C correlation peak (indicated by a reddotted circle) between the carboxyl carbon atom (~ 165.4 ppm) and the carboxyl proton (~ 9.6 ppm). On the other hand, the spectrum from PFOA bound to TG-PD COF is characterized by the presence of intramolecular1H-13C correlation peaks appearing mainly from the aromatic protons from the TG-PD COF (~ 6.3 ppm) and the carbon atoms from the TG-PD COF (from 115 to 155 ppm) and1H-13C correlation peaks between the aromatic protons from the TG-PD COF (~ 6.3 ppm) and the carbon atoms from the bound PFOA (111 and 163 ppm). The presence of intermolecular1H-13C correlation peaks between the aromatic protons from the TG-PD COF (~ 6.3 ppm) and the carbon atoms from the bound PFOA (111 and 163 ppm) indicate the presence of very strong interactions between PFOA and TG-PD COF and their close proximities in space. It is also worth noting that the spectrum from PFOA-bound TG-PD COF is characterized by the systematic absence of intramolecular1H-13C correlation peak between the carboxyl carbon and the carboxyl proton (13C ~ 165.4 / 1H ~ 9.6 ppm) indicating the possible deprotonation of the carboxyl protons. Furthermore,1H-13C HETCOR spectra also reveal significant upfield changes in the chemical shifts (~ 3.4 ppm) for the carbonyl carbon (highlighted by green arrow) of the PFOA between the free and bound state, indicating that the carbonyl group of PFOA is the major point of interaction between the PFOA and the TG-PD COF. To monitor the changes in15N chemical shifts upon PFOA binding, DNP-enhanced15N solid-state NMR experiments were performed on TG-PD COF before and after binding to PFOA (Figure 52). The spectrum from pure TG- PD COF is characterized by the presence of peaks appearing mainly from the imine (~ 322.4 ppm) and from NH nitrogen atoms (~ 142.7 ppm). The spectrum from PFOA-bound TG-PD COF also reveals peaks appearing mainly from the imine (~ 315.5 ppm) and from NH nitrogen atoms (~ 144 ppm). However,15N spectrum from PFOA-bound TG-PD COF reveals an upfield chemical shift of around 6.9 ppm for the imine nitrogen atoms and downfield chemical shift changes of about 1.3 ppm for the NH nitrogen atoms. The upfield shift of the imine nitrogen atoms can be attributed to the increase in electron density at these sites. When PFOA binds to the COF, the guanidine group can act as a hydrogen bond acceptor, interacting with the deprotonated carboxylate group of PFOA. This interaction can increase the electron density on the imine nitrogen atoms, leading to greater shielding and an upfield shift for imine nitrogen in the NMR spectrum. Conversely, the downfield shift of the NH nitrogen atoms indicates a decrease in electron density at these sites. The hydrogen bonding interaction between the guanidine group and the PFOA carboxylate can withdraw electron density from the NH nitrogen atoms, deshielding them and causing a downfield shift in the NMR signal.

[0131] Furthermore,19F MAS solid-state NMR experiments were performed to better understand the interaction between PFOA and TG-PD COF. Figure 53 shows the19F solid- state NMR spectra of pure PFOA (bottom, blue line) and TG-PD COF treated with PFOA (top, red line). The19F spectrum obtained from the free PFOA is well resolved and reveals mainly chemical shifts from the terminal -CF3 groups (~ –83 ppm) and from the backbone - CF2groups (between –120 to –130 ppm). Compared to the19F spectrum of free PFOA, the spectrum of TG-PD COF treated with PFOA is relatively broad and shows chemical shifts from the terminal -CF3groups (~ –82 ppm) and from the backbone -CF2groups (between – 110 to –130 ppm). The appearance of the well-resolved19F peaks from the pure PFOA could be attributed to the presence of dynamics to sufficiently average out the anisotropic NMR interactions. On the other hand, the appearance of the broad19F peaks from the TG-PD COF treated with PFOA could be ascribed to the lack of dynamics and aggregation of PFOA due to the preferential binding of the PFOA with the TG-PD COF.

[0132] Finally, to gain a deeper understanding of the sensing mechanism and the selectivity of TG-PD COF, computational analysis was conducted (Figure 54) on the COF with PFOA in the gas phase (further details below). For band gap calculations, octanoic acid (OA) was selected due to its close structural similarity to PFOA. The band gap of TG-PD COF with octanoic acid (OA) is observed to be 1.92 eV, which is larger than both the pristine TG-PD COF and the TG-PD COF with PFOA. This larger band gap suggests a weaker interaction between TG-PD COF and OA compared to the interaction with PFOA.

[0133] PFOA Adsorption experiments. Adsorption studies were conducted to assess the efficiency of the cationic TG-PD COF in removing PFOA from water. Unless otherwise stated, all adsorption experiments were carried out at 24 °C using an adsorbent suspension (Figure 3a). The concentrations of PFOA in these experiments were determined by HPLC- MS, and further details are outlined in the methods section.

[0134] Kinetic studies were conducted at different PFOA and TG-PD COF concentrations to assess their influence on adsorption efficiency (Figure 3b). Notably, at higher PFOA and adsorbent concentrations ([COF] = 400 mg^L–1, [PFOA] = 0.2 mg^L–1), PFOA was rapidly adsorbed by the TG-PD COF, with 96% of PFOA adsorbed within the seconds required for sampling and COF filtration from the solution. This remarkable performance of the TG-PD COF reflects rapid and efficient PFOA removable capabilities, outperforming previous studies with similar conditions (Table 3).

[0135] To evaluate the efficiency of the TG-PD COF in removing PFOA at environmentally relevant concentrations, a kinetic study was conducted at a lower concentration ([COF]=100 mg^L–1, [PFOA]= 1 µg^L–1). Notably, even at such concentrations, nearly 50% of the PFOA was adsorbed within a minute, with an adsorption equilibrium corresponding to 83% PFOA removal achieved within one hour. The rapid adsorption kinetics achieved by the TG-PD COF highlights its potential for practical applications, where it is essential to swiftly adsorb PFAS contaminants during the brief contact period with the adsorption bed.

[0136] The kinetic study data were fitted with pseudo-first-order and pseudo-second- order kinetic models (Figure 55). The experimental data exhibited a better fit with the pseudo-second order model, suggesting that chemisorption is the rate-limiting step in adsorption. The apparent rate constant was calculated to be 11470 g^mg–1^min–1for the high concentration kinetics study, and 2535 g^mg–1^min–1for the low concentration study. Notably, the adsorption kinetics results reported herein at this low concentration exceed the exemplary reports on PFOA adsorption in the literature (Table 3). Nevertheless, direct comparisons with the existing literature are difficult, particularly with regard to the apparent rate constant, due to the prevalent use of highly concentrated PFOA solutions.

[0137] To determine the maximum adsorption capacity of TG-PD COF, adsorption isotherm experiments were conducted across a wide range of initial PFOA concentrations from 0.2 mg^L–1to 1000 mg^L–1, with the concentration of TG-PD COF remaining constant at 100 mg^L–1in all experiments (Figure 3c). The resulting adsorption isotherm showed two distinct regions separated by an initial PFOA concentration approximately at 600 mg^L–1. Starting from the onset of the isotherm data up to around 600 mg^L–1, where the equilibrium adsorption capacity slightly exceeded 1000 mg^g–1, the adsorption capacity showed an asymptotic increase with increasing PFOA concentration. Interestingly, the trend of PFOA adsorption showed a significant increase at PFOA concentration higher than 600 mg^L–1instead of reaching a saturation point and plateau. This observation is consistent with the two- stage adsorption isotherms reported for the adsorption processes of ionic surfactants on oppositely charged adsorbents. The initial phase involves “head-on” adsorption at lower PFOA concentrations, which is primarily driven by the electrostatic interactions between anionic head of PFOA and the cationic guanidium moieties in the COF structure. Due to the high surface charge, the PFOA anions must be oriented with their charged heads towards the oppositely charged COF surface, while their tails extend into the water mass.

[0138] While the PFOA concentration in the bulk solution remains below the critical micellization concentration (CMC), a significant local concentration near the COF surface promotes the formation of PFOA molecular aggregates, attributed to hydrophobic interactions among the PFOA tails. This localized aggregation phenomenon triggers a cooperative adsorption process, leading to a PFOA uptake exceeding 2600 mg^g–1, which is an exceptional capacity for PFOA uptake using COF-based adsorbents.

[0139] In order to assess the performance of the COF in removing PFOA from water under more realistic conditions, adsorption columns containing 3 mg of COF were prepared. Water containing two different concentrations of PFOA flowed through the columns at a rate of around 100 µL^min-1(Figure 3d, Figure 57). Remarkably, complete removal of PFOA was achieved throughout the filtration of 20 mL of water with PFOA concentrations of 1 µg^L-1and 200 µg^L-1(Figure 3e). The PFOA concentration in the filtrate was below the HPLC-MS detection limit, which is in the ng / L (50 ppt) range. This further demonstrates the TG-PD COF's effectiveness in the rapid and complete removal of PFOA in conditions similar to gravity filters.

[0140] Other studies in the literature using various adsorbents have investigated the effects of PFAS aggregation on increased adsorption over time or at increased mass concentrations and highlighted their influence on the adsorption isotherm. However, the remarkable increase in the uptake capacity demonstrated in the isotherm in this study is not only more pronounced, but also results in a significantly higher adsorption capacity compared to these reports. The interplay of hydrophobic and electrostatic forces between the TG-PD COF and the PFOA molecules leads to a synergistic effect that uses the two most potent mechanisms known for the efficient extraction of PFOA from aqueous media. Moreover, the unique open architecture of the TG-PD COF prevents blockage of the internal adsorption sites by PFOA aggregates, a common limitation with other adsorbents. Additionally, the periodic distribution of adsorption sites within the COF and its large pore size provide unobstructed access to these sites within the porous structure, optimizing the PFOA adsorption process.

[0141] To further investigate the observed two-phase adsorption phenomenon shown in the isotherm (Figure 3c), zeta-potential measurements were performed to follow the change in surface charge of the TG-PD COF as the PFOA concentration increased (Figure 57a). Initially, the COF suspension exhibited a positive zeta potential (+24 mV), which is due to the presence of positively charged guanidinium moieties. After the introduction of a lowPFOA concentration (1 µg^L–¹), a significant decrease in the surface charge to about –0.8 mV was observed, indicating preferential adsorption on the outer surface of the TG-PD COF, leading to neutralization of the surface. As the PFOA concentrations continued to increase, the surface charge of the COF suspension was effectively neutralized, suggesting adsorption within the porous structure of the TG-PD COF following the saturation of the outer surface up to a PFOA concentration of around 200 mg^L–1. Notably, when the PFOA concentration was further increased up to 1000 mg^L–1, the surface charge decreased significantly to –19.95 mV. This phenomenon could be due to the aggregation of PFOA molecules on the COF surface via tail-to-tail hydrophobic interactions, induced by the increased concentration of PFOA molecules in the vicinity of the COF surface. This observation aligns well with the sudden increase in adsorption capacity observed in the isotherm, further suggesting that the formation of PFOA aggregates causes this abrupt increase in adsorption capacity.

[0142] Additionally, the pH of the solution (Figure 57b) shows a progressive decrease with increasing PFOA concentration, indicating the ionization of the PFOA molecules and the release of H3O+. Even at the highest PFOA concentration, the pH continued to decrease, indicating progressive ionization of the PFOA molecules, facilitating their adsorption onto the COF structure in their anionic state.

[0143] Scanning transmission electron microscopy (STEM), specifically utilizing high-angle annular dark field (HAADF) imaging, was used to study COF suspensions at varying PFOA concentrations (0, 600, and 1000 mg^L–1). This technique provided detailed Z- contrast images, allowing accurate identification of the locations of the fluorine atoms within the COF structure (Figure 4a-c). At a higher magnification, elemental mapping showed the dispersion of fluorine atoms throughout the COF material. At 600 mg^L–1, the fluorine atoms were evenly distributed across the COF, whereas at 1000 mg^L–1, while still uniformly distributed, fluorine also formed aggregates on the COF surface. The analysis showed a qualitative increase in fluorine content from 12.4% to 16.1% within the COF matrix as the PFOA concentration increased from 600 mg^L–1to 1000 mg^L-1, as documented in Table 4 and Figure 58. This is further supported by the stable chlorine concentrations observed by STEM, indicating that the adsorption of PFOA anions leads to an increased negative charge within the suspension. Aggregation, driven by hydrophobic interactions, marks a distinct phase in PFOA adsorption, as illustrated schematically in Figure 4d.

[0144] The effect of temperature on PFOA adsorption by the TG-PD COF was investigated at a PFOA concentration of 200 mg^L-1and a COF concentration of 100 mg^L-1(Figure 4e). Increasing the adsorption temperature from 24 °C to 50 °C led to a significant decrease in COF adsorption capacity by almost 40 %. A further increase in the temperature to 80 °C led to a slight increase in adsorption, but still about 33 % lower than that at 24 °C. This decrease in adsorption capacity with increasing temperature indicates a predominant influence of enthalpic forces in the adsorption process. However, the subsequent increase in adsorption at higher temperatures implies that entropic contributions become more dominating, which is consistent with observations reported for surfactants.

[0145] The isothermal data were fitted using both the Langmuir and Freundlich models, as shown in Figure 59. Attempting to fit the entire data set to either the Langmuir or Freundlich model did not yield satisfactory linear fits, indicating that the adsorption process cannot be fully characterized as monolayer or multilayer adsorption over the entire range of PFOA concentrations. Upon dividing the adsorption isotherm dataset at a threshold of 600 mg^L–1, where aggregation is expected to occur, it was observed that the data points below 600 mg^L–1fit the Langmuir model well. This suggests that monolayer adsorption predominates at lower PFOA concentration ranges. Conversely, data points above 600 mg^L–1show a better fit with the Freundlich model, indicating a multilayer adsorption process within this PFOA concentration range. Although the maximum adsorption capacity, Qmax, of the TG-PD COF is higher than 2600 mg^L–1, its calculation was not pursued due to safety concerns, which prevented experiments at higher PFOA concentrations. Further details on the safety considerations regarding experimental work involving PFOA can be found in the supporting information file and in literature.

[0146] Regeneration experiments were carried out to evaluate the reusability of the TG-PD COF over several adsorption cycles. The COF was soaked in methanol overnight before being reused for PFOA adsorption at a concentration of 10 mg^L–1(Figure 4e). Notably, the COF effectively desorbed the PFOA in methanol and maintained its adsorption efficiency throughout five regeneration cycles, without any reduction in adsorption performance. Finally, we assessed the stability of the regenerated TG-PD COF. The unchanged PXRD pattern and SEM images after regeneration clearly confirm the stability of the TG-PD COF adsorbent (Figure 60).

[0147] Computer Simulations. To gain deeper insights on the mechanism and the thermodynamics factors governing the adsorption of PFOA, Molecular Dynamics (MD) simulations were conducted. A 12-layer COF structure was constructed and solvated with water and ions to mimic experimental conditions, as depicted in Figure 5a. Details regardingthe parameters of the MD simulation setup can be found in the methods section. The convergence of the adsorption process was monitored by calculating the PFOA uptake, which stabilized after approximately 200 ns, as depicted in Figure 61a. A time evolution of the adsorption process at various time are shown in (Figure 5b).

[0148] First, the accuracy of the molecular simulations was assessed by comparing the number of PFOA molecules adsorbed by the TG-PD COF with the experimental data. The simulations show that out of 290 PFOA molecules initially present in the simulation box, 280 were adsorbed by the COF upon reaching equilibrium. This translated to a removal capacity of 96% at a bulk PFOA concentration of 900 mg^L–1, in a COF concentration of 374 mg^L–1. This computational estimate closely matches the experimental findings at a corresponding PFOA concentration, where the equilibrium uptake was nearly 2300 mg^g–1(Figure 3b), compared to 2310 mg^g–1obtained from the simulation.

[0149] Subsequently, simulations were employed to elucidate the mechanism of PFOA adsorption. Snapshots captured at various time points provide qualitative insights into the dynamics of the adsorption process (Figure 5b). Changes occurring throughout the adsorption process were tracked by examining the density profiles of PFOA, water molecules, and the total charge along the long axis of the simulation box, as depicted in Figure 5c-e. To guide the eye, the COF-solvent interface was highlighted with dashed lines in the density profiles.

[0150] Findings from the temporal evolution of the average density profiles reveal a significant shift in the distribution of components upon adsorption of PFOA by the TG-PD COF. The first notable change is observed when PFOA forms a layer on the surface of the COF between t=1-10 ns, resulting in a peak in the PFOA density profile (compare Figure 5b with Figure 5c). This accumulation of PFOA at the interface leads to a drastic shift in water density (Figure 5d). As the COF adsorbs PFOA molecules, a significant displacement of water molecules occurs from the COF to the bulk (Figures 5d, Figure 61b). Upon reaching equilibrium, water in the bulk reaches a density of almost 0.98 g^cm-3, while the density of water inside the COF decreases to ~0.34 g^cm-3, indicating a substantial dehydration at the COF-PFOA interface. The binding of PFOA to the COF leads to the displacement of approximately 22 water molecules per adsorbed PFOA molecule. This displacement stems from PFOA molecules occupying positions previously held by water within the COF and stripping of water molecules from the solvation shell of PFOA (Figure 61b). To interpret the zeta-potential measurements shown in Figure 57a, the average charge density along thelongitudinal axis (z) was computed. These findings reveal a positive surface charge for the COF at low PFOA loadings, which transitions to neutral and then to a negative surface charge distribution at high PFOA loadings (Figure 5e), consistent with the observations in Figure 57a.

[0151] To unravel the molecular mechanism underlying the exceptional PFOA uptake capacity, the specific interactions between PFOA, water, and the COF were examined using the radial distribution function (RDF). This analysis was conducted over the final 500 ns of the simulation, where equilibrium was achieved (Figures 6a–g and Figures 61–63). RDF peaks at shorter interatomic distances reveals specific binding sites between certain atom pairs, whereas the absence of peaks suggests a lack of interaction between pairs. Based on this, we observe a weak interaction between water and PFOA, with no specific binding observed between them (Figure 62). In contrast, interactions between water and the COF were involved in weak hydrogen bonds between the aliphatic hydrogens of the COF and the oxygen atoms of water molecules (Figure 63). The interactions between PFOA and the COF on the other hand were characterized by strong electrostatic forces at the binding sites, specifically between the positively charged nitrogen and aliphatic hydrogens of the COF and the negatively charged oxygen groups of PFOA, as well as the fluoride atoms (Figure 64).To better understand the nature of the PFOA-COF interactions, the changes were investigated in the number of hydrogen bonds, ∆^^^^, and the changes in the non-bonded energy terms∆^^௩ௗ௪, and ∆^^^^^^ using the first and last three nanoseconds of the simulation, representingthe states of PFOA in its unbound and bound states respectively (Figures 5b, and Figure 65– 67). Each term was partitioned into the different species, namely water, PFOA, and COF. The results are summarized in Figures 6h-i.

[0152] It was observed that the process of PFOA adsorption causes a rise in the total number of hydrogen bonds, primarily governed by water-water hydrogen bonds. As PFOA molecules bind, the displaced water moving to bulk starts forming more hydrogen bonds with other water molecules. While the number of hydrogen bonds between water molecules increases, the count of COF-water and water-COF hydrogen bonds decreases (Figure 6h and Figures 65–67). Nonetheless, the acquired hydrogen bonds during water displacement outweigh the losses, providing an enthalpic and entropic contribution to the PFOA adsorption process. A second contributor to the PFOA-COF stability was found to be the change in the non-bonded interactions between PFOA and COF (Figure 6i). The charge distribution of the PFOA and the cationic nature of the COF resulted in a dramatic reduction of the electrostatic energy upon PFOA adsorption into the pores in addition PFOA-COF form favorableinteractions via dispersion forces. Overall, these simulations propose that the enthalpic gain resulting from the interactions between PFOA and COF, supported by the increase in the number of hydrogen bonds of displaced water, serve as the driving force for PFOA adsorption by the COF.

[0153] In conclusion, this disclosure presents a novel approach to mitigate PFOA contamination by designing and synthesizing a multifunctional cationic covalent-organic framework (COF), TG-PD COF, which seamlessly integrates PFOA sensing and removal capabilities. TG-PD COF exhibits high sensitivity for PFOA sensing, achieving a detection limit as low as 1.8 µg^L-1through its fluorescence-based “Turn-On” sensing mechanism triggered by PFOA binding. Detailed investigations elucidate the charge transfer mechanism responsible for this performance. The adsorption performance is equally efficient, with rapid adsorption kinetics demonstrated even at environmentally relevant concentrations. The observed two-phase adsorption isotherm, attributed to the aggregation of PFOA molecules, culminates in a remarkable equilibrium uptake of over 2600 mg^g–1at the highest PFOA concentration tested. Adsorption column tests have also revealed complete PFOA removal at environmentally relevant concentrations. The COF's physicochemical properties, designed to harness both hydrophobic and electrostatic interactions, increase its efficiency in removing PFOA. In addition, the large pores and open structure prevent blockage of internal adsorption sites by PFOA aggregates and enable rapid adsorption kinetics. Molecular Dynamics simulations validate our experimental results and shed light on the intricate interactions between PFOA, water, and TG-PD COF at the atomic level. This study not only presents an innovative material, but also provides profound insights into its interactions at the atomic- level, serving as a valuable guide for further research in this field.

[0154] Materials. All chemicals and starting materials were procured from Sigma- Aldrich and utilized without additional purification. The synthesis of 2,9-diformyl 1,10- phenanthroline (PD) and triamino guanidium hydrochloride salt (TGH•Cl) followed previously documented procedures in the literature. Silica gel 60F (Merck 9385, 0.040– 0.063 mm) was employed for column chromatography. Amine analytes, including ammonium hydroxide (28.0–30.0%), methyl amine (2 M in THF), hydrazine hydrate (80%), pyridine (99%), 1-naphthylamine (99%), cadaverine (95%), diethylamine (99.5%), and triethylamine (99.5%) were obtained from Sigma Aldrich and utilized without further purification.

[0155] Characterization. Solution state nuclear magnetic resonance (NMR) spectroscopy was conducted at 25 °C using a Bruker Avance III spectrometer operating at frequencies of 500 MHz for 1H and 125.0 MHz for13C nuclei. All chemical shifts are expressed in ppm relative to the signals corresponding to the residual non-deuterated solvents (CDCl3 = 7.26 ppm). Simultaneous decoupling of proton nuclei was employed for all13C NMR spectra. Coupling constant values (J) are given in hertz (Hz). The proton spectrum multiplicity was denoted as follows: s (singlet), d (doublet), dd (doublet of doublets), t (triplet), q (quartet), qt (quintet), sx (sextet), m (multiplet), and a broad signal is indicated by br (broad). Magic Angle Spinning (MAS) solid-state NMR experiments were carried out on a Bruker Avance-HD 600 MHz spectrometer operating at a static field of 14.1 T using a 4.0 mm MAS probe in the double channel mode. Samples were packed into 4.0 mm zirconia rotors and were spun at a MAS frequency of 14 kHz. Cross-Polarization Magic Angle Spinning (CP / MAS) NMR experiments were performed using a standard linearly ramped cross-polarization pulse sequence.13C chemical shifts were externally referenced to the adamantane CH2 signal at 38.48 ppm on the TMS scale. NMR data were processed using TopSpin software.

[0156] Fourier transform infrared (FTIR) analyses were conducted using the Agilent 670-IR spectrometer. Thermogravimetric analysis (TGA) was carried out on the TA SDT Q600 instrument. Scanning electron microscopy (SEM) imaging was performed with the FEI Quanta 450FEG apparatus. Transmission electron microscopy (TEM) analysis of the COF material was conducted using a FEI-Titan 300 microscope, with samples prepared on carbon- coated copper grids and allowed to dry overnight after spotting a drop of dispersed TG-PD network. Surface area measurements were performed on a Micromeritics 3Flex gas sorption analyzer. Samples (20–50 mg) underwent degassing at 85 °C for 24 h followed by backfilling with N2. Adsorption isotherms were generated incrementally by exposure to ultrahigh-purity nitrogen up to 1 atm using ultrahigh-purity nitrogen in a liquid nitrogen bath, and surface area was determined employing BET adsorption models provided in the instrument software (Micromeritics ASAP 2020 V4.00). Powder X-ray diffraction (PXRD) analyses were carried out utilizing the PANalytical X’Pert PRO MP X-ray diffractometer equipped with a focusing elliptical mirror and a fast-high resolution detector (PIXCEL) using radiation with a wavelength of 0.15418 nm. UV–Visible spectroscopy (UV–Vis) was conducted on the Cary 5000 UV–Vis–NIR spectrophotometer. Emission spectra in water at room temperature were recorded using a Perkin Elmer LS55 Fluorescence Spectrometer. Dynamic light scatteringmeasurements were executed with a Malvern Zeta sizer NanoSeries to determine the size and zeta-potential of the nanoparticles.

[0157] Quantum Mechanical Calculations. To compute point charges and the HUMO-LUMO levels, NWChem was utilized. The geometry of the structures was optimized using the Hartree Fock method and a 6-31G* basis set. Charges were computed by fitting the electrostatic potential using the ESP module. To compute energy levels, we employed the B97-D functional by assigning a 6-311G** basis set for all atoms.

[0158] PFOA Adsorption Experiments. All adsorption experiments of PFOA were performed in batch mode using 20 mL glass scintillation vials at 24 ^C. The experiments were conducted on a stirring hot plate at 500 revolutions per minute (rpm) stirring rate. Prior to PFOA adsorption experiments, the vacuum-dried COF adsorbent was rehydrated by adding a precalculated mass of COFs to a scintillation vial with a precalculated volume of DI water to yield the required adsorbent concentration as a suspension. The COF suspensions were then sonicated for 30 min to disperse small aggregates. Then, the experiments were conducted by adding suitable volumes of the PFOA solution, DI water, and the COF adsorbent suspension to a 20 mL glass scintillation vial to generate the required concentrations of the PFOA solution and the COF suspension. Samples were collected in 1 mL volumes and filtered with a 0.2 μm syringe filter. Control experiments were conducted using samples that did not contain the COF adsorbent to account for PFOA losses due to other factors. These samples were collected for the control experiments in the same manner. All adsorption experiments were performed in triplicate.

[0159] Kinetic Adsorption Studies. Batch kinetic experiments were performed at both high and low concentrations of the PFOA and COF adsorbent. For experiments conducted at high concentration, the adsorbent dose was 400 mg L-1, while the PFOA concentration was 0.2 mg L-1. Prior to the measurements, the COF adsorbent was rehydrated by combining 8 mg of adsorbent with 16 mL of DI water in a 20 mL glass scintillation vial yielding a 500 mg^L-1suspension. The suspension was sonicated for 30 minutes to disperse any small aggregates. Then, 4 mL of a 1 mg^L-1PFOA solution was added to each suspension.1 mL samples were collected in HPLC vials and filtered using a 0.2 µm syringe filter. Samples were collected at predetermined times (0, 0.1, 0.5, 1, 5, 10, 30 min and 22 h), where the time 0 sample was taken prior to the addition of the COF suspension and the 0.1 min sample was taken immediately following the addition of the COF suspension. Control experiments were performed in the exact same manner but without the addition of the COF suspension. Thevolume of DI water added to the control experiment was higher to compensate for the water not added from the COF suspension and to achieve the required final PFOA concentration. The removal efficiency of PFOA at different experimental times was calculated by Equation 1: ^^^^^^^^ ^^^^^^^^^^^^^^ % ൌ ^^బି^^^^బ^^ 100 Equation 1 Where ^^^(mg^L–1) residual concentration of PFOA in the stock solution andcapacity was determined by Equation 2: ^^^^ ௧ൌ బି^^^ ^ಲEquation 2 Where ^^௧(mg^g–1) is the mass of PFOA adsorbed on the COF adsorbent at any time t (min); ^^^(mg^L–1) is the PFOA average concentration in the control experiments; ^^௧(mg^L–1) is the concentration of PFOA in the sample at time t (min); and ^^^(mg^L–1) is the concentration of adsorbent. The data from the adsorption kinetics were fitted against the pseudo-first-order and pseudo-second-order adsorption models in a linearized form represented by Equation 3 and Equation 4 respectively: Pseudo-first order model: ln^^^^ െ ^^௧^ ൌ ln^^^^^ െ ^^^^^ Equation 3Pseudo-second order model: ௧^௧ ொ^ ൌ^మொ^మ^ொ^Equation 4 Where ^^ is time, ^^^(mg^g-1) is the mass of PFOA adsorbed on the COF adsorbent at equilibrium, ^^^(min−1) is the moduli of the pseudo-first order model and ^^ଶ(g^mg-1^min-1) is the rate constant of adsorption.

[0160] Isotherm Adsorption Studies. Adsorption isotherm experiments were performed in 20 mL glass vials at 24 °C on a stirring hot plate (500 RPM) with magnetic stir bars. The COF adsorbent dose was fixed at 100 mg^L–1for all the experiments and the initial concentration of the PFOA was varied with increments at 0.2, 1, 10, 20, 30, 50, 100, 200, 400, 600, 800, and 1000 mg^L–1. The experiments were stirred for 22 h to reach the equilibrium, then 1 mL samples were collected and filtered using 0.2 μm syringe filters to remove any remaining COF. Control experiments to account for PFOA losses were performed under the same conditions except for the addition of adsorbents, and samples were collected at 22 h. All adsorption isotherm experiments were performed in triplicate. Langmuir adsorption and Freundlich isotherm fits were generated by Non-linear Least Square Regression in Equation 5 and Equation S:Langmuir model: ^^ ^ ^^ொ^ ൌொ^^^ ^ொ^ Equation 5Freundlich model: ln^^^ ^ ൌ ln ^^^ ^൫ ^൯ ^^ln ^^^^^ Equation 6Where ^^^(mg^L–1) is the equilibrium of the PFOA in the solution following orption, ^^^(mg^g–ads1) is the adsorption capacity of the COF adsorbent, ^^^(L^mg–1) is a Langmuir-adsorption-affinity constant; ^^^is a Freundlich empirical constant which corresponds to the relative adsorption capacity of the adsorbents; and ^ ^ is a Freundlich-adsorption-intensity constant. n is an indicator of the intensity of the adsorption.

[0161] Column Adsorption Studies. The COF column adsorption experiments were conducted using glass droppers as columns, allowing for controlled, small-scale experiments for safety, given the high concentrations of PFOA involved (Figure 56). A cotton layer was first inserted at the bottom of the column to support the COF and prevent it from exiting with the water. A 1000 mg^L–1TG-PD COF suspension was used to form the COF bed. Specifically, 3 mL of the suspension was pipetted into the column to create a COF bed with exactly 3 mg of COF, and the suspension was allowed to settle. While the water exited through the cotton layer, the TG-PD COF particles settled on top of it. DI water was flushed through the column until clear water was collected from the filtrate end. Subsequently, 1 mL of the PFOA solution was pipetted into the dropper and discarded before sample collection. Then, 20 mL of each PFOA solution was continuously pipetted from the influent side, and the filtrate was collected in 1 mL volumes, placed in HPLC vials, and analyzed using HPLC- MS. This setup minimized contact and leak risks with the PFOA solution during the column tests.

[0162] Elemental Mapping. High resolution transmission electron microscopy (HRTEM) images were collected using a Talos F200X STEM equipped with a CETA 16M camera and a lattice-fringe resolution of 0.14 nm at an accelerating voltage of 200 kV. The samples were prepared on holey carbon film mounted on a copper grid. A drop of diluted particle solution was spotted on the grid and dried overnight at room temperature (298 K). The obtained images of periodic structures were analyzed using TIA software. Chemical mapping was carried out in STEM-EDAX mode while the energy-dispersive X-ray analysis (EDAX) was performed using a super-X EDS detector. The system has superior sensitivity with resolution of ≤ 136eV / Mn-Kα for 10 kcps at zero-degree sample tilt. The detector provides quick data even for low intensity EDS signals. The data is the sum of 4 detectorsand the collection time for the elemental maps in fast mapping mode can be reduced to minutes from hours. The data was analyzed using Velox analytical software. The samples for the HRTEM study were prepared on holey carbon film mounted on a copper grid.

[0163] Regeneration Studies. Adsorption Experiments: 20 mg of the COF adsorbent was added to a glass vial with 20 mL DI water to yield a 1 g^L–1suspension. The suspensions were sonicated for 30 min to disperse small aggregates. Then, the adsorbent solution (2 mL, 1 g^L–1) was passed through a 10 mL syringe fitted with a 0.2 μm filter to pack the adsorbent into the filter. A PFOA solution (2 mL, 10 mg^L–1) was then passed through the syringe for 10 seconds and the PFOA concentration of the filtrate was measured by LC-MS.

[0164] Desorption Experiments: To desorb the PFOA from the COF adsorbent packed in the syringe filter, 2 mL of DI water was passed through the filter, followed by 10 mL of methanol in 10 seconds. The DI water and methanol leaving the filter were collected in a 20 mL scintillation vial. The mixture (water + methanol) was volatilized in a vacuum oven and the remaining solid was mixed with DI water and analyzed using LC-MS to determine the quantity of the desorbed PFOA.

[0165] Molecular modelling setup for the COF Simulations. The COF unit cell was obtained from PXRD extended along each axis, forming a supercell of 2×2×12. The framework was then placed in a periodic box measuring 82.9×50.2×163.4 ų, with 63.4 Å extra space along the z-axis to create the bulk phase.290 PFOA molecules were randomly added to the simulation box. Later, the box was solvated with water molecules, and Na+ions were introduced to neutralize the system. The TIP3P model was employed to represent the water molecules, while the Dreiding force field was utilized for representing PFOA and COF. PFOA charges were derived from QM calculations implemented in NWchem, while the Gasteiger method was adopted for the COF. This force field combination provides an experimentally consistent depiction of the adsorption process, as demonstrated in our previous studies.

[0166] Quantum Mechanical Calculations. To compute point charges and the HUMO-LUMO levels, we utilized NWChem. The geometry of the structures was optimized using the Hartree Fock method and a 6-31G* basis set. Charges were computed by fitting the electrostatic potential using the ESP module.

[0167] Molecular Dynamics Simulations. The simulations were performed using GROMACS. The simulation system was first optimized using the steepest descent for 500steps. Then the equations of motion were solved using the leapfrog integrator with a timestep of 1 fs in an NVT ensemble. The velocity rescaling was used to keep the temperature at 298 K. Long-range interactions were treated with a cut-off of 1 nm for both electrostatic and van der Waals interactions. The Particle Mesh Ewald Summation method was used to compute electrostatic interactions. Data recorded every 5 ps was used for the analysis.

[0168] Figure 8 shows TG-PD COF FTIR analysis

[0169] Figure 9 shows TG-PD COF solid state13C CP / MAS NMR spectral analysis.

[0170] Figure 10 shows TG-PD COF solid state13C CP / MAS NMR spectral analysis Thermogravimetric Analysis (TGA).

[0171] Figure 11 shows TG-PD COF SEM and HRTEM.

[0172] Figure 12 shows TG-PD COF PXRD pattern.

[0173] Table 1: d spacing values, hkl indexes, and 2^ position of the TG-PD COF. I(%) d (Å) (hkl)2^ (^)1 1 4 11 4

[0174] F

[0175] Figure 14 shows TG-PD COF water contact angle measurements.

[0176] Figure 15 shows TG-PD COF emission spectra in the presence of different analytes.

[0177] Table 2: Comparison of PFOA-sensor materials. No Materials Detection of Media Mode of LOD )2 Guanidinocalix[5]arene PFOA HEPES Fluorescence buffer “Turn-on” 26.4 Fluorescence 2 heranalytes.

[0179] Figure 51 shows TG-PD COF solid state emission spectra in presence of different PFOA concentrations.

[0180] Figure 52 shows TG-PD COF DNP enhanced15N CP / MAS solid-state NMR spectra.

[0181] Figure 53 shows stacked one-dimensional19F solid-state NMR spectra of pure PFOA and PFOA@TG-PD.

[0182] Figure 54 shows HOMO-LUMO energy diagrams.

[0183] Research Limitations for Safety: while conducting research on the adsorption of PFOA, it is imperative to take into account the safety aspects associated with handling high concentrations of PFOA. PFOA is a persistent organic pollutant, recognized for its bioaccumulation and environmental persistence. The handling of PFOA, especially at high concentrations, raises several safety concerns that must be addressed to ensure the well-being of researchers and the environment. These safety hazards are summarized below and could also be found in other reports. Given these safety concerns, the decision to limit the concentration of PFOA in experimental setups is a prudent one. Continuing experiments at PFOA concentrations higher than 1000 mg / L may exacerbate the risks mentioned below, and the marginal benefits of such an extension may not justify the potential hazards.

[0184] Toxicity and Health Risks: PFOA is known for its potential adverse health effects. Exposure to PFOA has been linked to various health issues, including developmental problems, liver toxicity, and potential carcinogenic effects.

[0185] Environmental Impact: Given its environmental persistence, it is essential to assess the necessity of working with highly concentrated PFOA solutions since anyaccidental release into the environment would cause adverse effects. Additionally, the disposal of PFOA must be conducted with utmost care. All PFOA waste is collected and disposed of according to local environmental regulations.

[0186] Laboratory Safety Measures: Human exposure to PFOA at high concentrations is potentially detrimental to human health, and it could occur through different exposure pathways. Therefore, working with high concentrations of PFOA necessitates stringent laboratory safety protocols. This includes using fume hoods to avoid inhalation, having spill containment measures in place, and ensuring that all containers and pipettes used are adequately sealed and labeled. Regular monitoring for any accidental release or contamination should be part of the routine.

[0187] Handling and Storage: Proper storage of PFOA solutions is essential. Chemicals should be stored in clearly labeled, sealed containers in designated safety cabinets. Inventory logs should be maintained, and access to these chemicals should be restricted to trained personnel only.

[0188] Emergency Response Plan: A well-defined emergency response plan should be in place in case of accidental spills or exposure. This plan should include steps for containment and cleanup of spills, first aid measures in case of exposure, and emergency contact information.

[0189] Training and Awareness: Regular training sessions on the hazards associated with PFOA and the proper handling techniques are essential for all personnel involved in the research. This training should cover the use of PPE, spill response, waste disposal, and emergency procedures.

[0190] Cross-Contamination: This could be minimized with strategies like increased renewal of disposable items, double gloving, and assignment of lab coats for specific tasks to reduce cross-contamination and minimize personal exposure.

[0191] In conclusion, while the study of PFOA adsorption is critical for environmental remediation efforts, the safety of researchers and the protection of the environment are paramount. Limiting PFOA experiments to concentrations below 1000 mg / L is thus considered a proper decision to avoid increasing the potential safety risks associated mentioned above. The marginal benefits of extending experiments beyond this concentration may not justify the hazards.

[0192] Table 3: Maximum adsorption capacity (Qmax), adsorption rate constant (Kobs), and PFOA kinetics concentration in this study and other reports in the literature.Q [PFOA] in orbent max k Ads obs –1 –1kinetics Year (mg^g ) (g^mg ^h–1) (μg^L–1) 24 22 20 20 1918 18 17 17 1615 15 15 14 1414 12111109090908

[0194] Figure 56 shows a photograph of the column adsorption experiments.

[0195] Figure 57 shows the change in zeta-potential and pH with increasing PFOA concentrations.

[0196] Table 4: The atomic fraction of carbon, fluorine, and chlorine at different PFOA concentrations in the adsorption solution, as measured by STEM. PFOA Concentration Carbon Atomic Fluorine Atomic Chlorine Atomic

[0198] Figure 59 shows adsorption isotherms model fitting.

[0199] Figure 60 shows PXRD of TG-PD COF before and after regeneration.

[0200] Figure 61 shows PFOA adsorption on TG-PD COF modelling with time.

[0201] Figure 62 shows radial distribution function of water atoms with PFOA atoms.

[0202] Figure 63 shows radial distribution function of TG-PD COF atoms with water atoms.

[0203] Figure 64 shows radial distribution function of TG-PD COF atoms with PFOA atoms.

[0204] Figure 65 shows hydrogen bonds between water-water molecules.

[0205] Figure 66 shows hydrogen bonds between COF-water molecules.

[0206] Figure 67 shows hydrogen bonds between PFOA-water molecules. EXAMPLE 2

[0207] This example provides an example of COFs of the present disclosure and uses thereof.

[0208] Visual sensing of humidity and temperature by solids plays an important role in our everyday life and in industrial processes. Due to their hydrophobic nature, most COF sensors often exhibit poor optical response when exposed to moisture. To overcome this challenge, we set out to improve the optical response to moisture by incorporating H-bonding ionic functionalities into the COF network. A highly sensitive COF, consisting of guanidinium and diformylpyridine linkers (TG-DFP), capable of detecting changes in temperature and moisture content was fabricated. The hydrophilic nature of the framework enables enhanced water uptake, allowing the trapped water molecules to form a large number of hydrogen bonds. Despite the presence of non-emissive building blocks, the H-bonds restrict internal bond rotation within the COF, leading to reversible fluorescence and solid- state optical hydrochromism in response to relative humidity and temperature.

[0209] To improve the water tolerance of COF fluorophores, a luminescent ionic covalent organic frameworks (iCOFs) equipped with highly polar or charged hydrogen- bonded guanidinium functional groups was made. These hydrogen bonds block the pathway of non-radiative energy decay by restricting intramolecular bond rotation (RIR), which enhances fluorescence. Using these COFs, it was hypothesized that the introduction of H- bonded ionic electron-deficient moieties into the iCOF networks could improve the polarity of the iCOF surface, and thus the luminescence properties at intermediate humidity, by preventing the molecular motion of the iCOF network.

[0210] To test this hypothesis, the guanidinium-based covalent organic framework (TG-DFP, Figure 17a) was obtained by the condensation of triamino-guanidinium hydrochloride salt (TGH•Cl) with diformylpyridine (DFP). The incorporation of guanidinium linkers into the iCOF backbone leads to multiple H-bonding sites within the framework. The H-bonding ability and the hydrophilic nature of TG-DFP iCOF offers several advantages, including improved water uptake, visible thermochromism, significant fluorescence enhancement under humid conditions or at low temperatures, and its potential use as a fluorescent chemosensor for trace amounts of water in organic solvents. Additionally, monitoring the complex structural changes caused by changes in humidity or temperature using conventional UV-Vis or spectrofluorometric methods poses a significant challenge. In contrast to previous work reported on COF humidity or temperature sensors, the method for monitoring real-time structural alteration in response to change in humidity or temperature utilizes state-of-the-art operando UV-Vis and operando FTIR techniques in DRIFTS mode, providing superior accuracy.

[0211] Synthesis and Characterization. The formation of TG-DFP COF was confirmed by Fourier transform infrared (FT-IR) spectroscopy and solid-state13C nuclear magnetic resonance (13C NMR) spectroscopy (Figure 25 and 26). The absence of the C=O stretching vibration band at 1723 cm⁻¹ and appearance of a new band at 1629 cm⁻¹ in the FT- IR spectra of TG-DFP COF provides confirmation of the formation of a -C=N bond. Additionally, the disappearance of the N-H stretching vibration band at 3185 cm⁻¹, which is associated with the amino group in TGH, serves as further evidence of the formation of an imine bond. The solid-state13C NMR spectrum (Figure 26) of TG-DFP COF also exhibited a peak at 165 ppm, indicative of the carbon atoms within the -C=N bonds. To elucidate the crystal structure (Figure 17b) of the synthesized TG-DFP COF, powder X-ray diffraction (PXRD, Figure 27) analysis of the solid sample was recorded. The PXRD pattern agrees well with our previous results on TTA-DFP gel. As shown in Figure 27, the experimental PXRD pattern of TG-DFP COF shows its first peak at 5.13°, which corresponds to the (200) plane. In the wide-angle region, the reflection at 2θ = 28.79° associated with the (003) plane corresponds to the adjacent π-π stacking of the 2D layers (Figure 17c). Using the self- consistent charge density functional tight-binding method (SCC-DFTB) within DFTB+ 17.1, geometry optimization was performed. The COF structure formed in the hexagonal space group P3, following a triangular sequence arrangement. The unit cell parameters were determined as follows: a = 37.273 Å, b = 35.525 Å, and c = 12.30 Å. Compared to other reported hexagonal COFs, the observed PXRD pattern has relatively weak intensity. Thisphenomenon can be attributed to the electrostatic repulsion between the polar triaminoguanidinium units in the two layers and the intercalated chloride ions. This repulsion significantly hampers the organized π-π stacking over longer distances. This type of PXRD pattern is common in other guanidinium-based COFs previously documented. The morphology of TG-DFP COF was studied by scanning electron microscopy (SEM, Figure 28), high-resolution transmission electron microscopy (HR-TEM, Figure 29), and atomic force microscopy (AFM, Figure 30). SEM, HR-TEM, and AFM images show that TG-DFP COF, as a powder, has a sheet-like morphology (Figure 18a–d, Figure 28–30). High- magnification HR-TEM images confirm the presence of ordered and oriented crystal lattice fringes within the TG-DFP COF. This phenomenon is attributed to the stacked 2D layers with a stacking distance of 0.37 nm (Figure 18c), with the π-π stacking spacing closely matching the experimental wide-angle PXRD data. A thorough examination of the AFM images (Figure 18d and Figure 30) revealed that the thickness of the TG-DFP nanosheets is about 26 nm (as shown in Figure 18d), indicating the presence of a COF network consisting of multiple layers of stacked sheets.

[0212] Thermochromism in TGDFP COF: As synthesized, TGDFP COF has a visibly yellow color. Once heated to 100 °C, the COF material showed a drastic and clearly visible color change from yellow to deep red (Figure 19a). When the sample is cooled at ambient temperature, the original color returned, changing from red-to-yellow. The reversible color change in response to temperature is attributed to the adsorption and desorption of water trapped in the COF network. To confirm this phenomenon, water adsorption studies were conducted. The water vapor adsorption characteristics of TG-DFP COF were evaluated using a IGAsorp vapor sorption analyser from Hiden, Isochema. The water vapor adsorption behaviour of the fully activated TG-DFP COF material exhibits a type I isotherm, (Figure 19b), with a maximum water uptake capacity of 23 wt% at RH = 98% and T = 298 K, which is comparable to recently reported water-adsorbing porous COFs. In addition, the water desorption curve is governed by a moderate hysteresis and incomplete desorption upon reducing the relative humidity to 0%, where 4% of water uptake is retained by the COF with a total working capacity of 18.7 wt% (Figure 31). The observed hysteresis reflects the relatively strong interaction between the framework and the free and intermediate water molecules that preferentially desorb whereas, the un-desorbed water molecules signify the presence of the more polar guanidinium sites. The occupied sites are further verified by the second and the third cycles, collected at equilibrium, where a full desorption of the water adsorbed with a total working capacity of 18 wt% was observed. To understand themechanism of the thermochromic color change, operando optical diffuse-reflectance (DRUV-DRIFTS) spectroscopic measurements (Figure 19c-d, Figure 32-33) were performed. The synthesized COF showed a π-π* CT absorption at λmax = 494 nm. Upon incremental heating of the sample, this band was batho- and hyper-chromically shifted (50 nm), leading to an intense absorption band centered at λmax = 553 nm. Moreover, the band gap of TG-DFP COF at 100 °C (ΔE = 1.83 eV, calculated from the Tauc plot, Figure 34) is lower than that of the COF at 25 °C (ΔE = 2.22 eV, Figure 34). The temperature-induced color changes were fully reversible with no significant colour bleaching observed after four consecutive cycles (Figure 35).

[0213] This result clearly indicates the robustness of the iCOF structure towards exposure and changes in both moisture and temperature. The thermally induced color change is possibly associated with the reversible sorption of water molecules from the iCOF network, with water molecules playing a crucial role in thermochromism. To confirm this mechanism, UV-VIS spectra at variable temperature under dry-argon flow was recorded. Interestingly, the color change was not reversible under Argon (Figure 36–37), confirming the role of coordinating waters on the observed thermochromism of the iCOF. To directly observe the effect of temperature on water sorption, a thermally programmed desorption analysis was performed on TG-DFP iCOF in diffuse reflectance infrared Fourier transform (DRIFT) spectral mode (Figure 19e). From the analysis of DRIFT, it is evident that the prepared TG- DFP iCOF has a broad peak at 3378 cm^1, which is due to hydrogen-bonded water molecules adsorbed within the framework. The proportional decrease of the intensity of this band with increases in temperature confirmed the thermal desorption of water. At the thermochromic transition temperature (100 °C), this band disappeared completely. The plot of the corresponding evolution of the water band area (Figure 38) as a function of temperature clearly confirms the gradual desorption of water in a similar temperature range than that observed in the thermochromism measurement. To quantitatively measure the coordinating waters within the COF network, thermal analyses (TG / DSC, Figure 39) were performed. Thermogravimetric analysis (TGA), as depicted in Figure 39, revealed a two-step weight loss pattern. The initial weight loss of 13.3% occurred between 37 to 106 °C (Figure 39a) and was attributed to the removal of weakly adsorbed water. Subsequently, a weight loss at 295 °C was observed, corresponding to the degradation of the framework. From the TGA analysis, it was calculated that 39.2 water molecules are present per unit cell. DSC analysis reveals a large endothermic peak at 99.6 °C (∆H = 680.2 J g^1, Figure 39b), corresponding to theremoval of water molecules that are bound to the COF network, this finding is further supported by the decreased intensity of the OH stretching vibration of hydrogen-bonded water molecules at higher temperatures (3378 cm^1). To shed light on the electronic structure of TG-DFP, TD-DFT calculations on the TG-DFP single layer fragment capped with Hydrogen atoms were performed. All electronic structure calculations were carried out at the level of PBE / 6-311G using the Gaussian16 program. The choice of PBE functional and basis sets 6-311G is based on a previous study that showed experimentally consistent HOMO- LUMO energy gaps for a similar framework. To elucidate the hydration effect, the implicit continuum solvation model was incorporated to mimic non-specific binding of water molecules (dielectric constant was used here for pure water) to the framework. In addition, to account for specific binding consistent with experimental observation, a water molecule was explicitly positioned close to the guanidine subunit. The optimized geometries and their corresponding orbitals are shown in Figure 20. These calculations indicated that the HOMO orbitals mostly lie on the pyridine ring, whereas LUMO orbitals are localized over the guanidine subunit. The computed HOMO-LUMO gap of 2.114 eV agrees reasonably well with our experimental value 1.83 eV. In addition, it was found that the computed HOMO- LUMO gap in presence of water is larger than the gas phase (Figure 20a vs 20b) which supports the observation of the red shift in the absorption spectra upon heating (Figure 19c– d). To understand the changes in the charge distribution, the difference in electron density was computed between the ground S0 and first excited single S1 states (Figure 40). A significant depletion of electron density was observed on the guanidine subunit, accompanied by an increase in electron density on the pyridine ring during the excitation process. Consequently, this analysis suggests a substantial charge transfer character in the lowest energy optical transition. To access temperature dependance on the HOMO and LUMO orbitals, a similar approach that was previously used was adopted. Molecular dynamics simulations were performed at three different temperatures 293, 325, and 363 K using a semi empirical and tight binding quantum mechanical method xTB-GFN2 and with implicit water as solvent. All MD simulations were performed for 10 ps with a time step of 2 fs using xTB tight binding platform. From the MD trajectory, the structure close to the mean RMSD was extracted and the HOMO-LUMO orbitals at the level of PBE / 6-311G were computed using the Gaussian16 program. Figure 41 shows the HOMO-LUMO orbitals and the corresponding energy gaps at three different temperatures. It was observed that the HOMO-LUMO gapsdecreases with increase temperature and agree qualitatively with the experimental observations of the redshift in the absorption spectra.

[0214] To verify any structural changes at the thermochromic transition temperature, we recorded PXRD at several temperatures from 30 ^C to 100 ^C, concentrating on the wide- angle region. The raw diffraction profiles at two representative temperatures, 35 ^C and 100 ^C, are shown in Figure 42. At all temperatures, the pattern remained the same, exhibiting primarily two diffuse peaks centered at spacings 0.42 nm (Peak 1) and 0.34 nm (Peak 2), with no significant temperature dependence (Figures 42a–b). While the peak width and peak intensity are essentially thermally invariant for Peak1 (Figures 43a–c), substantial increases and large decreases were seen for the width and intensity, respectively, for Peak 2. The spacings proved not to be temperature dependent, even up to 100 ^C, an indicator that the crystal structure remained intact, while the behavior of the width and the intensity (seen for Peak 2) clearly indicated that the extent of correlation notably weakens with increasing temperature. To check the stability of the thermally treated TG-DFP COF,13C CP / MAS NMR was performed (Figure 44). No significant changes in NMR signals were observed upon thermal treatment, clearly indicating stability under extreme conditions. Interestingly, due to the high hydrophilicity of TG-DFP COF, the material disperses well in water without aggregating. The homogeneously dispersed solution was used as a thermochromic ink for optical labeling of a low-cost filter paper (Figure 19f). When thermally heated, the handwritten letters (NYUAD) undergo a distinct color change. The paper strip coated with the iCOF is easily folded / portable and can be regenerated after several rounds of thermal annealing.

[0215] Fluorescent hydrochromic behavior of TGDFP COF: To investigate the effect of temperature on luminescence (Figure 21a), the solid-state luminescence of TG-DFP COF was measured at a wide range of temperatures (-15 °C to 105 °C, Figure 45). It is a challenge to design and develop materials that exhibit luminescence enhancement under extreme conditions while maintaining their inherent properties. Interestingly, at -15 °C, the powder TG-DFP emits a strong yellow fluorescence (λem = 550 nm, Figure 21a, inset) under excitation with a 375 nm light, which is due to charge transfer from the DFP to the guanidinium moiety (TGH+). Although the monomers DFP and TGH+are non-emissive, the TG-DFP COF is highly emissive at very low temperatures. At low temperatures, the reduced molecular motion within the iCOF networks stabilizes the hydrogen bonds. This stabilization in turn, can lead to a reduction in non-radiative relaxation pathways, thereby promotingradiative processes that lead to a remarkable increase in emission intensity. When the temperature is increased gradually, the weak H-bonds are disrupted, the emission intensity decreases dramatically, and a large bathochromic shift of emission maximum (λem = 550 nm) occurs. This large hypo / bathochromic shifts can be detected visually. The chromaticity coordinate (CIE) also shows a large degree of color change in the solid-state in the temperature range of -15°C to 105 °C (Figure 5b, Table 5). The hypochromic shift at high temperature is due to the disruption of H-bonds as the temperature increases. Moreover, upon cooling the sample, the yellow emission is regenerated, showing the reversible thermofluorochromic behavior of the COF (Figure 46). The TG-DFP COF material can further be used for smart anticounterfeiting applications, the handwritten letters (Figure 21c) and numbers on a commercial filter paper showed a bright yellow emission at low temperature and the emission intensity of the pattern quenches instantaneously upon heating. The reason measurements were recorded down to -15°C is because the instrument used for the luminescence study is not capable of operating below -15°C. However, the luminescence could be enhanced below -15°C. To investigate this phenomenon, a coating of TG-DFP COF material was applied to Whatman 40 filter paper and immersed it in liquid nitrogen. The TG- DFP COF coated paper showed a pronounced luminescent emission at cryogenic temperatures (Figure 47).

[0216] TG-DFP COF as an Optical hygro-sensor: Next, we tested the humidity- dependent optical properties at constant temperature (25 °C) and humidity between 0 and 20% of RH. The activated TGDFP-COF showed an absorption onset at 530 nm (Figure 22a). As shown by diffuse reflectance spectroscopy (DRS), the band decreases significantly with the increase of RH in the range of 0-20 RH%, while no detectable change was observed at values higher than 20 RH% (Figure 22b). Figure 22c shows how the optical density of TGDFP-COF changes as a function of humidity. As the RH increases, the optical density decreases. In addition, the effects of humidity on the photoluminescence of TG-DFP COF in the solid state were investigated. As shown in Figure 22d, TG-DFP COF shows an enhancement of fluorescence in response to an increase in humidity from ∼10 to ∼90 RH% for excitation at 375 nm. In response to the high humidity (RH = 90%), the COF material showed a significant change in emission color (inset Figure 22e). The plot of emission intensity as a function of RH shows a nonlinear relationship over the entire RH range (Figure 22e). The different impacts of humidity on the absorption and photoluminescence of the COF material can be attributed to the distinct ways in which moisture interacts with the material’s electronic and structural properties. For example, swelling due to moisture absorption canalter the structural integrity of COFs. This change may not greatly affect the electronic transitions responsible for absorption. However, the same structural changes can have a more profound effect on the processes that govern photoluminescence, such as the alignment of energy levels and the efficiency of electron-hole pair recombination. Other factors can be related to the competition of radiative and non-radiative pathways, solvation of the excited states and / or variation of the refractive index under various conditions.

[0217] For applications in daily life, such as the production of responsive textiles, TG-DFP COF was synthesized in the presence of cotton fabric (2 cm ^ 2cm). The obtained cotton fabric was uniformly covered with the TG-DFP material. The composite showed excellent reversible response to moisture, which is visually detectable (Figure 22f). At high humidity (RH = 90%), the color of the cotton fabric is light yellow and slowly changes to red when heated in a temperature-controlled oven at 80 ^C, decreasing RH from 90% to 10% (Figure 22f). Under UV light, the fabric shows a rapid and reversible fluorescent color change. Under humid conditions, the COF-coated fabric shows bright yellow fluorescence (Figure 22f, top panel), but in dry atmosphere, the fabric is almost non-emissive (Figure 21f, bottom panel). Overall, TG-DFP COF has the potential to be an effective platform for developing rapid and reversible RH sensing system with remarkable stability. The color changes of the cotton fabric are primarily determined by the relative humidity or a combination of temperature and humidity. In Figure 22f, the COF-coated fabric was heated at 100 °C in an open atmosphere and the color change was reversible. However, after the fabric was activated at 100 °C and then placed it in a glove box, the color change was irreversible under glove box-controlled atmosphere (nitrogen). This observation confirms the influence of adsorbed water from atmospheric humidity on the observed thermochromism of the iCOF. Evidence for this observation is provided in Figure 48.

[0218] TG-DFP COF for Visual Water Sensing Applications in Organic Solvent: The enhancement of luminescence caused by water prompted us to quantify trace amounts of water in organic solvents. The detection of water in THF was tested by gradually increasing the water content in 3 mL of THF containing 5 mg of TG-DFP COF as suspension. When the water content was increased up to 0.8 wt.% (v / v), a significant increase in emission intensity was observed, accompanied by a slight blue shift in the emission spectra to lower wavelengths (Figure 23a). When a trace of water is added to TG-DFP COF, dispersed in THF, the excited state lifetime value increases from 0.28 ns to 0.48 ns (Figure 23b), clearly indicating that there is a significant interaction between the framework and the watermolecules. The detection limit for water is 0.03 wt.% (v / v) (Figure 23c), which is sufficient for detecting trace amounts of residual water in dry solvents. It was assumed that the iCOF network in dry THF is fully saturated with the organic solvent. Upon gradual addition of water, the water molecules displace the THF molecules, leading to the formation of hydrogen bonds with the guanidinium linker throughout the network. This displacement reduces the non-radiative pathway and eventually increases the emission intensity. Unlike conventional COFs used to detect water, TG-DFP iCOF can detect trace amounts of water in organic solvents through a fluorescence “turn-on” mechanism. The distinct “turn-on” detection of moisture in organic solvents is of great importance for industrial applications.

[0219] To investigate the practical utility of the solid TG-DFP iCOF material, several iCOF-supporting test strips were fabricated from commercially available Whatman filter paper. After immersing these strips in THF solutions containing different amounts of water (0–0.8% v / v) and illuminating the paper strips with 365 nm UV light, an abrupt color change can be seen when the COF strip is exposed to an increasing amount of water (Figure 23d). To test the reusability of the sensor, the wet paper strip were heated with a heat gun, and its fluorescent color was restored. These results suggest that the COF-coated paper strip could serve as an efficient and recyclable portable water sensor. For reusability of the TG-DFP coated COF paper strip, the paper strip was subjected to heating at 100 °C for 1 minute inside a glass vial (Figure 49). Further, the PXRD data of the regenerated COF powder isolated by scratching the iCOF-coated filter paper were subsequently recorded and show identical patterns to the original TG-DFP iCOF (Figure 50).

[0220] In summary, a strategy to enhance the optical and photoluminescent properties of ionic COFs in the solid state were developed by limiting the nonradiative transitions through the incorporation of a H-bonding guanidinium building block. The optical and fluorescent response can be reversibly modulated by the presence of adsorbed water molecules in the iCOF channels. Unlike conventional single-function COF sensors, our strategically designed TG-DFP iCOF sensor offers ultra-fast sensitivity and dual functionality. It serves as a responsive system that can monitor both temperature and humidity simultaneously, under constant humidity and temperature, respectively. Interestingly, the iCOF material described herein shows changes in its fluorescence spectral properties over a wide temperature range, especially below room temperature. The fluorescence properties at temperatures below room temperature have not been studied for any other COF material. Due to the ease of preparation of our iCOF and the rapid optical response, we have developed a portable COF-coated test strip made of plain paper. This teststrip is capable of visualizing extremely low water content (0.03% v-v) in organic solvents. This work provides a unique route to the development of a multifunctional, color-tunable fluorescence, and optical iCOFs-based sensor for humidity and temperature.

[0221] Materials and Methods. All reagents and starting materials were purchased from Sigma-Aldrich and used without further purification. Deionized water was obtained from a Millipore Gradient Milli-Q water purification system. Thin-layer chromatography (TLC) was performed on silica gel 60 F254 (E. Merck). The plates were inspected under the UV light. Column chromatography was performed on silica gel 60F (Merck 9385, 0.040– 0.063 mm). Routine nuclear magnetic resonance (NMR) spectra were recorded at 25 °C on a Bruker Avance spectrometer, with a working frequency of 500 and 125 MHz for1H, and 151.0 MHz for13C nuclei. All chemical shifts are reported in ppm relative to the signals corresponding to the residual non-deuterated solvents (CD3CN: ^ = 1.94 ppm, CD3OD: ^ = 3.31 ppm, D2O: δ = 4.97 ppm and DMSO-d6: δ = 2.50 ppm). Coupling constant values (J) are given in hertz (Hz), the multiplicity is abbreviated in the following way: s (singlet) and d (doublet). The FTIR spectra were recorded using a Thermo Nicolet 6700 spectrometer equipped with an MCT detector. The mass changes of the same sample were continuously monitored by a SETSYS-B Setaram microbalance (resolution= 1^^g). The gas flow composition was analyzed by a Pfeiffer Omnistar GSD301 mass-spectrometer. All solid-state NMR experiments were carried out on a Bruker Avance-HD 600 MHz spectrometer operating at a static field of 14.1 T, resonating at 150.0 MHz for13C, using a 4.0 mm MAS probe. Thermogravimetric analysis (TGA) was performed on TA SDT Q600. Scanning electron microscopy (SEM) images were obtained from FEI Quanta 450FEG. The topography of the TG-DFP COF material was analyzed by dynamic atomic force microscopy (5500 Atomic Force Microscope; Keysight Technologies Inc., Santa Rosa, CA). Topography, phase, and amplitude scans were acquired simultaneously. Silicon cantilevers (NanosensorsTM, Neuchatel, Switzerland) with resonant frequencies of 250–300 kHz and force constants of 100–130 Nm-1were used. The set point value was kept at 2.5 V. AFM scans were collected at 1024 points / lines with scan speed of 0.20 at fixed scan angle of 0o. Scan artifacts were minimized by acquiring a typical scan at an angle of 90ounder identical image acquisition parameters. GwyddionTM free software (version 2.47), SPM data visualization and analysis tool were used for post-processing the AFM scans. Size and morphology of the TG-DFP COF film was determined with a TEM (FEI-Titan 300) microscope. Samples were prepared on a carbon-coated copper grid. A drop of dispersed gelnetwork was spotted on the grid and allowed to dry overnight. Powder X-ray diffraction (PXRD) measurements were carried out using the PANalyticalX’Pert PRO MP X-ray diffractometer consisting of a focusing elliptical mirror and a fast-high resolution detector (PIXCEL) with the radiation wavelength of 0.15418 nm.

[0222] UV-VIS operando measurements: The optical response of TG-DFP was conducted under continuous flow using Operando UV-VIS spectroscopy equipped with a Cavy 4000 UV-Vis spectrophotometer using a high temperature reaction chamber (HVC) running under Varian’s easy-to-use Cary WinUV software. Heating of the sample from 20 °C to 95 °C was carried out using a Eurotherm 2408 temperature regulator with a rate of 1.5 °C.min-1with a time resolution of 1 spectrum.min-1. Argon continuously flowed through the sample at a total flow rate of 10 cc min-1. For experiments involving different relative humidity (RH %), water was added at a specific flow rate to achieve the desired RH %. In this study, the measurement of the optical responses versus the temperature has been performed under operando conditions under flow (10 ml / min) of initially dry Ar. The quantity of the humidity in the flow (controlled by the temperature of the saturator and calculated using Antoine equation) is therefore maintained at various temperature. This was ensured by monitoring the stability of the water level during the measurement using on-line spectrometer at the outlet of the cell.

[0223] DRIFTS measurements: Diffuse reflectance FTIR (DRIFT) spectra were recorded on a Brüker IFS 66 V spectrometer in the 4000-600 cm-1range (resolution 4 cm-1, 64 scans / spectrum) with a time resolution of 1 spectrum.min-1using a Thermo Spectra-Tech high-temperature cell. Heating of the sample was carried out from 10 °C to 140 °C with a rate of 1 °C.min-1. The sample was under continuous flow of Argon with a flow rate = 5 cc.min-1.

[0224] Synthesis of 2,6-diformylpyridine (DFP): 2,6-diformylpyridine (DFP) was synthesized according to published procedures with no modification.

[0225] Synthesis of Triaminoguanidiniumchloride: Triaminoguanidinium chloride (TGH.Cl) was synthesized according to published procedures with no modification.

[0226] Synthesis of TG-DFP COF: To an aqueous solution (0.5 mL) of TGH.Cl (8.46 mg, 0.06 mmol), a mixed solution of 2, 6-diformylpyridine (DFP) (12.15 mg, 0.09 mmol) and 1,4-dioxane (2 mL) was slowly added. The resulting mixture was stirred under microwave irradiation of 2.45 GHz at 100 °C for 30 minutes and subsequently cooled to room temperature. The precipitate was collected by centrifugation and washed with anhydrousethanol five times and with water twice. The powder was dried at 120 °C under vacuum overnight to yield the yellow-colored product.

[0227] Table 5: “x” and “y” values for the chromaticity coordinate (CIE) plots. Temperature X-Coordinate Y-Coordinate Intensity-15 °C 0.33 0.49 8.7 x 103° 033333ribed with respect to one ormore particular embodiments and / or examples, it will be understood that other embodiments and / or examples of the present disclosure may be made without departing from the scope of the present disclosure.

Claims

CLAIMS 1. A covalent organic framework (COF), comprising the following structure: , R is independently. to claim 1, wherein at least 10% of the R groups are .

3. The COF according to claim 1, wherein the COF comprises the following structure: .

4. The COF according claim 1, wherein the COF is porous and at least partially crystalline.

5. The COF according to claim 4, wherein the COF is substantially crystalline or crystalline.

6. A nanoparticle comprising the COF according to claim 1.

7. A nanoparticle according to claim 6, wherein the nanoparticle has a hollow, tube-like morphology.

8. An indicator for detecting one or more perfluorinated compounds in a liquid, comprising: a porous medium; a COF according to claim 1, or a plurality of nanoparticles comprising a COF according to claim 1, disposed on the porous medium; and wherein the indicator is configured to fluoresce in the presence of one or more perfluorinated compounds.

9. The indicator according to claim 8, wherein the porous medium comprises polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF), cellulose acetate, nylon, or porous silica gels, or any combination thereof.

10. A kit for detecting one or more perfluorinated compounds in a liquid, the kit comprising:an indicator according to claim 8; and a flow cell containing the indicator, the flow cell configured such that liquid interacts with the indicator when the liquid is passed through the flow cell.

11. The kit according to claim 10, further comprising a fluorometer configured to measure a fluorescence of the indicator.

12. The kit according to claim 10, further comprising a filter for removing one or more perfluorinated compounds from the liquid.

13. The kit according to claim 12, wherein the filter comprises: a porous medium; the COF, or the plurality of nanoparticles comprising the COF, disposed on the porous medium disposed on the porous medium.

14. A kit according to claim 10, wherein the flow cell is a syringe.

15. A filter for removing one or more perfluorinated compounds from a liquid, the filter comprising: the porous medium; the COF, or the plurality of nanoparticles, disposed on the porous medium.

16. A method for capturing one or more perfluorinated compounds comprising contacting a COF according to claim 1, or a plurality of nanoparticles comprising a COF of claim 1, with a liquid comprising or suspected of comprising one or more perfluorinated compounds such that a dispersion of the COF or nanoparticle with the liquid is formed, wherein following the contacting, the one or more perfluorinated compounds bind to the COF or nanoparticle.

17. The method according to claim 16, further comprising measuring the fluorescence of the dispersion and comparing the fluorescence of a control dispersion.

18. The method according to claim 16, further comprising measuring the pH of liquid following contacting with the COF or nanoparticle.

19. A covalent organic framework (COF), comprising the following structure: , R is independently.

20. The COF according to claim 19, wherein at least 10% of all the R groups are22. The COF according to claim 19, wherein the COF is porous and at least partially crystalline.

23. The COF according to claim 19, wherein the COF is substantially crystalline or crystalline.

24. A method for determining the humidity or temperature of a medium comprising contacting a COF according to claim 1 with a medium or substrate and observing the COF for a change in color.

25. The method according to claim 24, wherein the COF changing color from yellow to red indicates an increase in humidity or temperature.

26. The method according to claim 24, wherein the COF changing color from red to yellow indicates a decrease in temperature or humidity.

27. The method according to claim 24, further comprising measuring fluorescence of the medium and comparing the fluorescence of the medium to a control.

28. A method for determining if water is present in an organic solvent at trace levels comprising contacting the organic solvent with a dry, yellow COF according to claim 19 and observing if the COF changes color or measuring the fluorescence of the solvent relative to a control.

29. An indicator comprising a COF according to claim 19.

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