Molecularly confined hydration in thermoresponsive hydrogels for efficient atmospheric water harvesting

Abstract

Described are compositions for use as and methods for generating water harvesting material. The disclosed compositions can include a thermoresponsive gel network, a hygroscopic material, a copolymer, a photothermal agent, a crosslinking agent, or any combination thereof to generate or for use as an atmospheric water harvesting material. The disclosed compositions and methods advantageously allow for the efficient sorption and desorption of atmospheric moisture in low relative humidity environments. The atmospheric water harvesting material can be useful for generating potable water in environments for example, where access to clean water is limited.

Description

MOLECULARLY CONFINED HYDRATION IN THERMORESPONSIVE HYDROGELS FOR EFFICIENT ATMOSPHERIC WATER HARVESTINGCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of and priority to U.S. Provisional Application No. 63 / 518,996, filed on August 11, 2023, and titled “MOLECULARLY CONFINED HYDRATION IN THERMORESPONSIVE HYDROGELS FOR EFFICIENT ATMOSPHERIC WATER HARVESTING,” the content of which is herein incorporated by reference in its entirety for all purposes.FIELD

[0002] This invention is in the field of atmospheric water harvesting. This invention relates generally to atmospheric water harvesting hydrogels and related methods of making and using atmospheric water harvesting hydrogels.BACKGROUND

[0003] Water scarcity is a pressing global issue, requiring innovative solutions such as atmospheric water harvesting (AWH), which captures moisture from the air to provide potable water to many water-stressed areas. Thermoresponsive hydrogels, a class of temperature-sensitive polymers, demonstrate potential for atmospheric water harvesting as matrices for hygroscopic components, like salts, predominantly due to their relatively energy-efficient desorption properties compared to other sorbents. However, challenges such as limited swelling capacity due to the salting-out effect and difficulty in more complete water release hinder the effectiveness of conventional hydrogel sorbents. Synthesis of an atmospheric water harvesting material with improved efficiency and sustainability remain a consistent need. The present disclosure satisfies this need and offers other advantages as well.SUMMARY

[0004] Described herein are atmospheric water harvesting hydrogel compositions and methods for making and using atmospheric water harvesting hydrogels. The disclosed compositions and methods advantageously allow for the efficient sorption and desorption of atmospheric moisture. Atmospheric water harvesting hydrogels described herein can be useful in environments where access to potable water is limited.

[0005] In a first aspect, compositions for use as or for generating an atmospheric water harvesting material are described. In some examples, compositions of this aspect may be referredto as hybrid hydrogels or hybrid hydrogel compositions. An example composition of this aspect comprises a thermoresponsive gel network and a hygroscopic material dispersed throughout the thermoresponsive gel network. The thermoresponsive gel network may include a thermoresponsive polymer and a crosslinking agent. In some examples, the thermoresponsive polymer can include hydroxypropyl cellulose (HPC), poly(N-isopropylacrylamide) (PNIPAM), poly(N,N-diethylacrylamide) (PDEAM), poly(N-vinylcaprolactam) (PVCL), poly(N- isopropylmethacrylamide) (PNIPMAM), poly(N,N-dimethylacrylamide) (PDMA), or any combination thereof. The crosslinking agent may be selected from glutaraldehyde, epichlorohydrin, diepoxy compounds, polyisocyanates, divinyl sulfone, formaldehyde, or any combination thereof. The crosslinking agent and thermoresponsive gel network may confine a hygroscopic material within the gel network resulting in a charged polymer network loaded with salt ions. In some examples, the hygroscopic material can include a hygroscopic salt, lithium chloride, magnesium chloride, calcium chloride, or any combination thereof.

[0006] The water harvesting material described herein may efficiently absorb water and desorb water due, in part, to the composition within the thermoresponsive gel network. The thermoresponsive gel network may comprise a matrix of crosslinked microgel structures. In some examples, the crosslinked microgel structures can have a cross-sectional dimension of from 50 nm to 500 pm.

[0007] In a second aspect, methods for making a water harvesting material are described. In some examples, methods of this aspect may be useful for making any suitable water harvesting material or composition described herein, such as hybrid hydrogels. An example method of this aspect comprises adding a thermoresponsive polymer solution to a solution of a hygroscopic material to generate a mixture. The reaction may further include mixing the thermoresponsive polymer solution and the hygroscopic material solution at an elevated temperature for a time sufficient to ensure adequate mixing of solution. In some examples, the hygroscopic material may include a hygroscopic salt, lithium chloride, magnesium chloride, calcium chloride, or any combination thereof. The thermoresponsive polymer may include hydroxypropyl cellulose (HPC), poly(N-isopropylacrylamide) (PNIPAM), poly(N,N-diethylacrylamide) (PDEAM), poly(N- vinylcaprolactam) (PVCL), poly(N-isopropylmethacrylamide) (PNIPMAM), poly(N,N- dimethylacrylamide) (PDMA), or any combination thereof.

[0008] Subsequent to the adequate mixing of the thermoresponsive polymer and hygroscopic material, a crosslinking agent may be added. In some examples, the crosslinking agent may beglutaraldehyde, epichlorohydrin, diepoxy compounds, polyisocyanates, divinyl sulfone, formaldehyde, or any combination thereof.

[0009] The method may further include adjusting the pH of the mixture of the therm oresponsive polymer solution, hygroscopic solution, and crosslinking agent. For example, in events wherein the pH is greater than 7.0, a Lewis acid may be added to the solution to reduce the pH to 7.0. In some examples, the pH may be below 7.0, a Lewis base may be added to raise the pH to 7.0. The resulting water harvesting material is subsequently collected from the mixture. In some examples, the collected water harvesting material may include a microgel structure comprising the thermoresponsive polymer. The microgel structure may allow for adequate sorption of atmospheric water. For example, the micro gel structure may have a cross-sectional dimension of from 50 nm to 500 pm.

[0010] In a third aspect, compositions for use as or for generating an atmospheric water harvesting material are described. In some examples, compositions of this aspect may be referred to as copolymer hydrogels or copolymer hydrogel compositions. An example composition of this aspect comprises a copolymer comprising a first monomer and a second monomer. The first monomer may be a thermoresponsive monomer and may be selected from N-isopropyl acrylamide, N,N-di ethyl acrylamide, N-isopropylmethacrylamide, N-vinylcaprolactam, or any combination thereof. The second monomer may be an ionic monomer loaded with salt ions. For example, the second monomer may be a cationic vinyl monomer, an anionic vinyl monomer, a zwitterionic vinyl monomer, or any combination thereof.

[0011] In some examples, the ionic monomer is the cationic vinyl monomer and may be 2- (methacryloyloxy)ethyltrimethylammonium chloride (METAC), [2- (methacryloyloxy)ethyl]trimethylammonium methosulfate (METAMS), vinylbenzyl trimethylammonium chloride (VBTAC), or any combination thereof. In some examples, the ionic monomer is an anionic vinyl monomer selected from acrylic acid (AA), methacrylic acid (MAA), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), or any combination thereof. In some examples, the ionic monomer is a zwitterionic polymer selected from comprises 2- methacryloyloxyethyl phosphorylcholine (MPC), sulfobetaine methacrylate (SBMA), carboxybetaine methacrylate (CBMA), N-(3-Sulfopropyl)-N-(methacryloxyethyl)-N,N- dimethylammonium betaine (SPE), or any combination thereof.

[0012] The composition of this aspect may further include a photothermal agent. The photothermal agent may be added to the mixture to induce desorption of the absorbed water under sun exposure or light exposure. For example, the light for increasing the temperature of the waterharvesting material may be in the range of from 400 nm to 1750 nm. In some examples, the photothermal agent may be selected from carbon black, active carbon, polypyrrole:poly(styrene sulfonate), polyaniline: poly (styrene sulfonate), poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), or any combination thereof. The composition of this aspect may result in a bifunctional polymeric network or matrix of crosslinked microgel structures between the copolymer and the photothermal agent. A crosslinking agent may be included in the composition and may be selected from comprises N,N'-methylenebis(acrylamide) (BIS), ethylene glycol dimethacrylate (EGDMA), divinylbenzene (DVB), trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate (PETA), polyethylene glycol) diacrylate (PEGDA), glycidyl methacrylate (GMA), or any combination thereof. The composition of this aspect may optionally include the addition of a catalyst for increasing the rate of reaction in the polymer network. The catalyst may be selected from ammonium persulfate (APS), potassium persulfate (KPS), sodium persulfate (NaPS), azo- bis-isobutyronitrile (AIBN), benzoyl peroxide (BPO), 2, 2'-azobis(2 -methylpropionitrile) (AIBN), 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50), 2,2'-azobis[2-(2-imidazolin-2- yl)propane] dihydrochloride (VA-044), or any combination thereof.

[0013] In a fourth aspect, methods for making a water harvesting material are described. In examples, methods of this aspect may be useful for making any suitable water harvesting material or composition described herein, such as copolymer hydrogels. An example method of this aspect comprises mixing a thermoresponsive polymer, an ionic monomer loaded with salt ions, and a photothermal agent in water to generate a first mixture. The method of this aspect may further include mixing a surfactant and a solvent to generate a second mixture that may be subsequently combined with the first mixture under the addition of a tertiary amine.

[0014] In some examples, the thermoresponsive monomer and may be selected from N- isopropyl acrylamide, N,N-di ethyl acrylamide, N-isopropylmethacrylamide, N-vinylcaprolactam, or any combination thereof. The second monomer may be an ionic monomer loaded with salt ions. For example, the second monomer may be a cationic vinyl monomer, an anionic vinyl monomer, a zwitterionic vinyl monomer, or any combination thereof.

[0015] In some examples, the ionic monomer is the cationic vinyl monomer and may be 2- (methacryloyloxy)ethyltrimethylammonium chloride (METAC), [2- (methacryloyloxy)ethyl]trimethylammonium methosulfate (METAMS), vinylbenzyl trimethylammonium chloride (VBTAC), or any combination thereof. In some examples, the ionic monomer is an anionic vinyl monomer selected from acrylic acid (AA), methacrylic acid (MAA), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), or any combination thereof. In someexamples, the ionic monomer is a zwitterionic polymer selected from comprises 2- methacryloyloxyethyl phosphorylcholine (MPC), sulfobetaine methacrylate (SBMA), carboxybetaine methacrylate (CBMA), N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N- dimethylammonium betaine (SPE), or any combination thereof.

[0016] The method of this example may include adding the tertiary amine to the mixture via a drop wise addition method. The tertiary amine may be selected from tetraethylenediamine, N,N,N’,N’ -tetramethylhexanediamine (TMHDA), or N,N,N’,N’-tetramethyl-l,3-butadiamine. The method of this example may optionally include adding a crosslinking agent to the second mixture prior to combining the first mixture with the second mixture. The crosslinking agent may be added to the mixture to strengthen the polymer hydrogel. In some examples, the crosslinking agent may be N,N'-methylenebis(acrylamide) (BIS), ethylene glycol dimethacrylate (EGDMA), divinylbenzene (DVB), trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate (PETA), polyethylene glycol) diacrylate (PEGDA), glycidyl methacrylate (GMA), or any combination thereof.

[0017] The method of this example further includes freeze-drying the mixture for a first time to generate a freeze-dried powder of the water harvesting material. The resulting freeze-dried powder is submerged in a solution comprising the hygroscopic material. In some examples, the hygroscopic material may be a hygroscopic salt, such as, lithium chloride, magnesium chloride, calcium chloride, or any combination thereof. The resulting ion-loaded polymer networks may be washed in a solvent bath and subsequently freeze-dried for a second time to generate the water harvesting material. In some examples, the water harvesting material may comprise small microgel structures ranging in size from 50 nm to 500 pm.

[0018] In a fifth aspect, examples of methods of using water harvesting materials are described herein, such as for purposes of harvesting water, which may be used directly after harvesting or subjected to one or more purification processes after harvesting. An example of the method of using the water harvesting material may include providing any water harvesting material described herein and subsequently exposing the water harvesting material to water for a duration of time sufficient to cause the water harvesting material to absorb water. In some examples, exposing the water harvesting material to water may comprise exposing the water harvesting material to air or gas having a relative humidity of from 10% to 100% (e.g., from 10% to 20%, from 20% to 30%, from 30% to 40%, from 40% to 50%, from 50% to 60%, from 60% to 70%, from 70% to 80%, from 80% to 90%, or from 90% to 100%). It will be appreciated that the time required to absorb 50% water efficiently is dependent upon the environment the atmospheric water harvestingmaterial is located within. For example, the time required to absorb water in a 30% relative humidity environment may be from about 20 minutes to about 50 minutes. In an environment, with a relative humidity of 60%, the atmospheric water harvesting material may absorb 50% water by weight of the hydrogel in less time than an environment of 30% relative humidity. For example, the atmospheric water harvesting material, when exposed to environments comprising a relative humidity of 60 %, may absorb water in less than 20 minutes to reach 50 % uptake by weight of the hydrogel.

[0019] To desorb the water from the atmospheric water harvesting material, heat may be applied to the material. In some examples, heating the water harvesting material may include using light for increasing the temperature of the surface of the water harvesting material. For example, the light may be at a wavelength of from about 400 nm to 1750 nm. The desorbed water may further be collected. In some examples, the desorbed water is treated to generate clean or drinkable water. The treatment may include any known steps or methods known to those skilled in the art for cleaning water to produce a safe drinkable water source. In some examples, the method described above may be repeated upon desorption of the collected water to re-expose the water harvesting material to air or gas having a relative humidity of from 10 % to 100 % to re-absorb water.

[0020] Without wishing to be bound by any particular theory, there can be discussion herein of beliefs or understandings of underlying principles relating to the invention. It is recognized that regardless of the ultimate correctness of any mechanistic explanation or hypothesis, an embodiment of the invention can nonetheless be operative and useful.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 A, FIG. IB, and FIG. 1C provide a schematic for the process and characteristics of an atmospheric water harvesting sorbent material. FIG. 1 A provides an illustration of a typical sorbent-based atmospheric water harvesting process; FIG. IB provides a schematic representation of two moisture capture mechanisms: 1) Salt Deliquescence including a three-step process involving hygroscopic salts, including chemisorption, crystallization, and deliquescence, which requires elevated temperatures for complete desorption of salt hydrates; 2) Confined Hydration - molecularly confined hygroscopic sites enable water capture within the molecular mesh, allowing for water release at lower temperatures due to conformational changes in the thermoresponsive gel network without the involvement of crystal hydrates; and FIG. 1C provides a qualitative comparison of salt-contained sorbents, highlighting key performance factors for atmospheric water harvesting sorbents, in accordance with some embodiments of the present disclosure.

[0022] FIG. 2A, FIG. 2B, FIG. 2C, FIG. 2D, and FIG. 2E provide illustrations of the basic properties and characterization of copolymer hydrogels. FIG. 2A provides a schematic representation of copolymer structure and compositions; FIG. 2B provides example Fourier- transform infrared spectroscopy (FT-IR) spectra for monomers and copolymers; FIG. 2C provides example x-ray diffraction (XRD) patterns of thermoresponsive zwitterionic microgel (TZMG) with varying copolymerization ratios; FIG. 2D provides an example graph of the swelling ratios of hydrogels in 4 M LiCl solution; and FIG. 2E provides an example graph of the phase transition temperatures of hydrogels with different copolymerization ratios, in accordance with some embodiments of the present disclosure.

[0023] FIG. 3A, FIG. 3B, FIG. 3C, FIG. 3D, FIG. 3E, FIG. 3F, and FIG. 3G provide example graphs of the atmospheric water harvesting performance of thermoresponsive zwitterionic microgels. FIG. 3 A provides a schematic representation of the inverse mini-emulsion polymerization process and subsequent scanning electron microscopy (SEM) images and elemental mapping of as-prepared thermoresponsive zwitterionic microgel, scale bar is 50 pm; FIG. 3B provides a graph illustrating the water uptake of thermoresponsive zwitterionic microgels at various relative humidity (RH) levels; FIG. 3C provides a graph of the static water vapor sorption-desorption performance at different RH for TZMG-1.0; FIG. 3D provides a graph of the desorption curves for TZMG-1.0 at different temperatures; FIG. 3E provides a graph of the evaporation behavior of thermoresponsive zwitterionic microgels and pure LiCl hydrated with 1 g g’1; FIG. 3F provides a graph of the cycling performance of TZMG-1.0; and FIG. 3G provides graphs of the comparison of desorption performance of TZMG-1.0 with reported salt- contained / gel based evaporation-based materials, in accordance with some embodiments of the present disclosure.

[0024] FIG. 4 provides example scanning electron microscopy images of photothermal- responsive zwitterionic microgel (PZMG)-1 (panel a) and PZMG-4 (panel b) hydrogels, in accordance with some embodiments of the present disclosure.

[0025] FIG. 5A, FIG. 5B, FIG. 5C, and FIG. 5D provide example graphs of the performance or PZMGs. FIG. 5A provides a schematic illustration of the PZMG synthesis process, Scale bar is 1 cm; FIG. 5B provides a graph of the ultraviolet-visible-near-infrared (UV-Vis-NIR) spectra of PZMGs with varying polypyrrole (Ppy) content, and the normalized spectral solar irradiance density of air mass 1.5 global tilt solar spectrum, PZMG 1 to 4 corresponds to PZMG with 15 vol%, 10 vol%, 5 vol%, and 2 vol% of 0.1 g / mL Ppy: polystyrene sulfonate(PSS) solution; FIG. 5C provides a graph of the time-dependent surface temperature and the infrared (IR) thermalimages of PZMG-1 under different light intensities; and FIG. 5D provides a graph of the water vapor sorption curve under 60% RH and desorption curve under 1 sun of PZMG-1, and sorptiondesorption rates (green dots) of PAMG-1, in accordance with some embodiments of the present disclosure.

[0026] FIGS. 6 A, FIG. 6B, FIG. 6C, and FIG. 6D provide representations of testing methods for water absorption and desorption. FIG. 6A provides an image of the homemade solar-driven atmospheric water harvesting system; FIG. 6B provides a graph of the water uptake and release at different RH levels; FIG. 6C provides a graph of the cycling performance of PZMG at 60 % RH; and FIG. 6D provides a graph of the collected water quality assessed by inductively coupled plasma mass spectrometry (ICP-MS), in accordance with some embodiments of the present disclosure.

[0027] FIG. 7 provides a schematic illustration of the homemade water vapor sorption system, in accordance with some embodiments of the present disclosure.

[0028] FIG. 8 provides a schematic of the hydrophobic interaction of the methyl group and hydrogen bonding breakage induce the phase transition.

[0029] FIG. 9A provides a graph of the saturated water content of [2- poly(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (PDMAPS) hydrogel swelling in deionized water and LiCl solution with different concentrations, in accordance with some embodiments of the present disclosure; FIG. 9B provides a graph of the thermogravimetric analysis curve of thermoresponsive zwitterionic microgels, in accordance with some embodiments of the present disclosure.

[0030] FIG. 10A and FIG. 10B provide graphs of the static vapor sorption-desorption performance of thermoresponsive zwitterionic microgels (FIG. 10A) and the weight change rate in the sorption and desorption process of thermoresponsive zwitterionic microgels (FIG. 10B), in accordance with some embodiments of the present disclosure.

[0031] FIG. 11 provides a graph of the temperature dependent desorption behavior of TZMG-1.0 under sorption conditions of 30 % RH at 25 °C and desorption conditions of 60°C and water vapor pressure of 3.17 kPa, in accordance with some embodiments of the present disclosure.

[0032] FIG. 12 provides a graph of the static sorption-desorption properties of poly-N- isopropylacrylamide-LiCl (PNIPAM-LiCl), in accordance with some embodiments of the present disclosure.

[0033] FIG. 13 A and FIG. 13B provide graphs of the differential scanning calorimetry of pure LiCl (FIG. 13 A) and PNIPAM-LiCl and PDMAPS-LiCl (FIG. 13B), in accordance with some embodiments of the present disclosure.

[0034] FIG. 14A and FIG. 14B provide graphs of a scatter plot of water uptake at 60 % RH vs. time to reach equilibrium (FIG. 14 A) and a corresponding bar graph of the vapor sorption rate (FIG. 14B), in accordance with some embodiments of the present disclosure.

[0035] FIG. 15 provides a graph of the cycling performance of PZMG at 30 % RH, in accordance with some embodiments of the present disclosure.DETAILED DESCRIPTION

[0036] Described herein are atmospheric water harvesting (AWH) material compositions, such as atmospheric water harvesting hydrogels, and methods relating to the formation and use of atmospheric water harvesting materials. The disclosed compositions and methods allow for a more sustainable and efficient hydrogel system for harvesting water from the atmosphere. In some examples, a hybrid hydrogel class of microgels comprise a thermoresponsive gel network comprising a thermoresponsive monomer and a crosslinking agent, along with a hygroscopic material, such as a hygroscopic salt or another hydrogel loaded with salt ions. In some examples, a copolymer hydrogel class of microgels comprise a copolymer of a thermoresponsive monomer and an ionic monomer loaded with salt ions, a photothermal agent, and a crosslinking agent. These classes of microgels are useful as atmospheric water harvesting materials suitable in all weather conditions. By placing the atmospheric water harvesting material in an environment suitable for removing water from the environment, an efficient method for harvesting water in environments where for example, access to water is limited, may be improved. One or more surfactants and crosslinking agents can be incorporated into the atmospheric water harvesting to facilitate the formation of a stable hydrogel material. One or more methods may be suitable for generating the microstructure hydrogels as described below. The atmospheric water harvesting material described herein may be capable of repeated use for capturing water from surrounding environments.

[0037] The disclosed materials and methods allow for efficient all-weather atmospheric water harvesting. This can be achieved because the hybrid microgels can store water molecules, confine hygroscopic ions, and release pure water upon mild heating or exposure to solar radiation, achieving an energy efficient water release. In addition, the microgel configuration provides for ultrafast water harvesting, at least in part, due to shortened water diffusion distance.

[0038] In general the terms and phrases used herein have their art-recognized meaning, which can be found by reference to standard texts, journal references and contexts known to those skilledin the art. The following definitions are provided to clarify their specific use in the context of the invention.

[0039] “Thermoresponsive monomers” refers to a monomer that exhibits conformational changes in response to temperature stimuli. In some examples, temperature stimuli may correspond to a temperature of from 60 °F to 200 °F. Thermoresponsive monomer may refer to a monomer that exhibits a drastic or discontinuous changes in their physical properties in response to thermal stimuli. Thermoresponsive monomers belong to a class of stimuli -responsive materials which change their properties continuously with environmental conditions (e.g., temperature). Thermoresponsive monomers may display a gap in their temperature-composition diagram when compared to other monomers.

[0040] “Temperature stimuli” refers to direct temperature increase or indirect temperature increase, such as from the sun or from a chemical reaction or exposure to heat from another source.

[0041] “Zwitterionic” refers to a polymer that comprises at least one pair of oppositely charged groups in their repeating units.

[0042] “Co-polymer” refers to a polymer derived from more than one species of monomer.

[0043] “Cycling” refers to the repeated absorption and subsequent desorption of water from a hydrogel. For example, a first absorption and a first desorption refer to 1 cycle while a first absorption followed by a first desorption and subsequently re-hydrating via a second absorption and re-desorbing via a second desorption may refer to 2 cycles.

[0044] “Harvesting” refers to the collection of water from surround environments. As used herein the water may include rainwater, flood water, freshwater, fog, humid air that includes water or any other water capable of being harvested.

[0045] “Atmospheric” refers to the atmosphere of the earth. As used herein, atmospheric may refer to any environment within the earths’ atmosphere, including 0% relative humidity to 100% relative humidity.

[0046] “Microgel structures” refers to the formation of micron sized particles during the formation of a hydrogel, such as a hydrogel comprising a thermoresponsive polymer and a hygroscopic material. The microgel structures can include an ionic monomer loaded with salt ions, a crosslinking agent, a photothermal agent, or any combination thereof, that upon chemical crosslinking, the resulting hydrogel is comprised of the micron sized particles. The microgelstructure may be micron sized spheres, rods, discs, or any other shape resulting in a diameter of or cross-sectional dimension from 1 micron to 1000 micron.Atmospheric water harvesting hydrogel use, compositions, and properties

[0047] FIG. 1 A provides an illustration of a sorbent-based atmospheric water harvesting process. As illustrated, humid air may be removed of dust or other small particulate matter. Particulate matter removal may include removal of particulate matter ranging in sizes from 2.5 micron to 10 micron in size. For example, the dust may be in a size range of from 2.5 micron to 5 micron, from 5 micron to 7.5 micron, or from 7.5 micron to 10 micron in size. The methods used for dust removal may include any known methods of dust removal, for example, by passing the air through a HEPA filter.

[0048] Following dust removal, the humid air may come in contact with the atmospheric water harvesting hydrogel to undergo sorption to the hydrogel. In some embodiments, the hydrogel described herein may be in an environment where dust removal from the air does not happen prior to exposure to the hydrogel. In some embodiments, sorption may be performed under ambient temperatures and pressures. For example, sorption to the hydrogel may be performed at temperatures of from about 25 °C to about 30 °C. In some embodiments, the time required for the hydrogel to attain an 80% saturated water uptake may be from about 20 minutes to about 3 hours. For example, from about 25 minutes to about 30 minutes, from about 30 minutes to about 35 minutes, from about 35 minutes to about 40 minutes, from about 40 minutes to about 45 minutes, from about 45 minutes to about 50 minutes, from about 50 minutes to about 55 minutes, from about 55 minutes to about 60 minutes, from about 60 minutes to about 70 minutes, from about 70 minutes to about 80 minutes, from about 80 minutes to about 90 minutes, from about 90 minutes to about 100 minutes, from about 100 minutes to about 110 minutes, from about 110 minutes to about 120 minutes, from about 120 minutes to from about 130 minutes, from about 130 minutes to from about 140 minutes, from about 140 minutes to about 150 minutes, from about 150 minutes to about 160 minutes, from about 160 minutes to about 170 minutes, or from about 170 minutes to about 180 minutes. In some embodiments, the time required to attain an 80% saturated water uptake may be dependent upon the relative humidity of the atmosphere in which the hydrogel may be disposed.

[0049] Subsequent to undergoing sorption, the atmospheric water harvesting hydrogel described herein may undergo desorption, or release of the collected water. Desorption from the atmospheric water harvesting hydrogel may be performed under increased temperature. For example, desorption may occur under temperatures of from 50 °C to about 80 °C (e.g., about 50 °C to about60 °C, from about 60 °C to about 70 °C, or from about 70 °C to about 80 °C). In some embodiments, desorption from the atmospheric water harvesting hydrogel may be from sun exposure. For example, desorption of the water may be performed by irradiating the atmospheric water harvesting device under sunlight. For example, sunlight exposure may include natural exposure to sun light, or a system incorporating artificial sunlight or concentrated sunlight or concentrated artificial sunlight, generally herein referred to as “sun exposure”. In some embodiments, the sun exposure may be conducted or otherwise performed under 1 sun (e.g., the intensity of natural sunlight), or higher intensity. In some embodiments, the sun exposure may be conducted or otherwise performed under up to 5 sun. For example, the sun exposure may be conducted or otherwise performed under 1 sun, 2 sun, 3 sun, 4 sun, or up to 5 sun. The water desorbed from the hydrogel described herein may be collected into a structure designed for holding liquids and further purified to generate a potable water that can be readily accessible.

[0050] FIG. IB provides a schematic representation of two moisture capture mechanisms: 1) Salt Deliquescence may refer to a three-step process involving hygroscopic salts, including chemisorption, crystallization, and deliquescence, which requires elevated temperatures for complete desorption of salt hydrates. In some embodiments, the hydrogel described herein may undergo salt deliquescence as part or all of the mechanism for release of the absorbed water from the hydrogel. The second moisture capture mechanism may be referred to as confined hydration. The process includes molecularly confined hygroscopic sites, enabling water capture within the molecular mesh and allowing for water release at lower temperatures due to conformational changes in the thermoresponsive gel network without the involvement of crystal hydrates. In some embodiments, the moisture capture mechanism of the hydrogel described herein may include at least some of or all of confined hydration. In some embodiments, the mechanism of moisture capture of the hydrogel described herein may include both salt deliquescence and confined hydration.

[0051] The atmospheric water harvesting material may include a thermoresponsive gel network. The thermoresponsive gel network may include a thermoresponsive polymer. In some embodiments, the thermoresponsive polymer includes hydroxypropyl cellulose, poly(N- isopropyl acrylamide) (PNIPAM), poly(N,N-diethylacrylamide) (PDEAM), poly(N- vinylcaprolactam) (PVCL), poly(N-isopropylmethacrylamide) (PNIPMAM), or poly(N,N- dimethylacrylamide) (PDMA). In some embodiments, the hygroscopic material can include lithium chloride, magnesium chloride, calcium chloride or any other suitable salt material known by those skilled in the art. In some embodiments, the hydrogel described herein comprises a thermoresponsive polymer that is hydroxypropyl cellulose and a hygroscopic material that islithium chloride. FIG. 2B provides example FT-IR spectra for monomers and copolymers of certain of the hydrogels described herein.

[0052] In some embodiments, the hydrogel described herein may include microgel structures that are composed of the therm oresponsive polymer and hygroscopic material. In some embodiments, the microgel structures may have a diameter or cross-sectional dimension of from 50 nm to 500 microns. For example, the microgel structures may have diameters of from 50 nm to 100 nm, from 100 nm to 200 nm, from 200 nm to 300 nm, from 300 nm to 400 nm, from 400 nm to 500 nm, from 500 nm to 600 nm, from 600 nm to 700 nm, from 700 nm to 800 nm, from 800 nm to 900 nm, from 900 nm to 1 micron, from 1 micron to 100 micron, from 100 micron to 150 micron, from 150 micron to 200 micron, from 200 micron to 250 micron, from 250 micron to 300 micron, from 300 micron to 350 micron, from 350 micron to 400 micron, from 400 micron to 450 micron, or from 450 micron to 500 micron.

[0053] The hydrogel described herein may further include a crosslinking agent. In some embodiments, the crosslinking agent can include divinyl sulfone, N,N'-methylenebis(acrylamide) (BIS), ethylene glycol dimethacrylate (EGDMA), divinylbenzene (DVB), trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate (PETA), polyethylene glycol) diacrylate (PEGDA), glycidyl methacrylate (GMA), glutaraldehyde, epichlorohydrin, diepoxy compounds, polyisocyanates, or formaldehyde. In some embodiments, the crosslinking agent may be included in an amount of from about 1 wt.% to about 20 wt.% by weight of the hydrogel. For example, the crosslinking agent may be included in an amount of from about 1 wt.% to about 5 wt.%, from about 5 wt.% to about 10 wt.%, from about 10 wt.% to about 15 wt.%, or from about 15 wt.% to about 20 wt.%.

[0054] In an alternate embodiment, the atmospheric water harvesting hydrogel may include a thermoresponsive monomer, a crosslinking agent, a photothermal agent, and an ionic monomer loaded with salt ions. FIG. 2A provides a schematic representation of copolymer structure and compositions of the hydrogel described herein. In some embodiments, the photothermal agent includes carbon black, active carbon, polypyrrole: poly (styrene sulfonate), polyaniline: poly (styrene sulfonate), or poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate). The photothermal agent may be added to the thermoresponsive monomer and an ionic monomer loaded with salt ions from about 1 wt.% to 20 wt.% by volume of the thermoresponsive-zwitterionic hydrogel.

[0055] The atmospheric water harvesting hydrogel described herein may comprise a co-polymer system that includes two monomers in combination to form the hydrogel. In some embodiments, the thermoresponsive monomer may include N-isopropylacrylamide, N,N-diethylacrylamide, N-isopropylmethacrylamide, or N-vinylcaprolactam. In some embodiments, the ionic monomer is loaded with salt ions. In some embodiments, the ionic monomer is a monocharged monomer. In some examples, the ionic monomer may be a cationic vinyl monomer, an anionic vinyl monomer, or a zwitterionic vinyl monomer. In some embodiments, the cationic vinyl monomer may include 2-(methacryloyloxy) ethyltrimethylammonium chloride (METAC), [2- (methacryloyloxy)ethyl]trimethylammonium methosulfate (METAMS), or vinylbenzyl trimethylammonium chloride (VBTAC). In some embodiments, the anionic vinyl monomer may include acrylic acid (AA), methacrylic acid (MAA), or 2-acrylamido-2-methylpropane sulfonic acid (AMPS). In some embodiments, the zwitterionic vinyl monomer may include 2- methacryloyloxyethyl phosphorylcholine (MPC), sulfobetaine methacrylate (SBMA), carboxybetaine methacrylate (CBMA), or N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N- dimethylammonium betaine (SPE). FIG. 2C provides example XRD patterns of thermoresponsive zwitterionic microgel with varying copolymerization ratios. In some embodiments, the mole ratio of the ionic monomer loaded with salt ions to thermoresponsive polymer may be from about 1 :0.1 to 1.0: 1.0. For example, the mole ratio may be about 1.0:0.1, about 1.0:0.2, about 1.0:0.3, about 1.0:0.4, about 1.0:0.5, about 1.0:0.6, about 1.0:0.7, about 1.0:0.8, about 1.0:0.9, or about 1.0: 1.0.Method of producing atmospheric water harvesting hydrogels

[0056] Methods of making atmospheric water harvesting hydrogels according to some embodiments described herein may include adding, to a solution of a thermoresponsive gel network including a thermoresponsive polymer, a solution of a hygroscopic material to generate a mixture. The mixture may be comprised of a mole ratio of thermoresponsive polymer to hygroscopic material from about 1.0:0.1 to about 1.0: 1.0. For example, the mole ratio may be about 1.0:0.1, about 1.0:0.2, about 1.0:0.3, about 1.0:0.4, about 1.0:0.5, about 1.0:0.6, about 1.0:0.7, about 1.0:0.8, about 1.0:0.9, or about 1.0: 1.0. In some embodiments, the mixture may be further combined with a crosslinking agent. The crosslinking agent may be any one of N,N'- methylenebis(acrylamide) (BIS), ethylene glycol dimethacrylate (EGDMA), divinylbenzene (DVB), trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate (PETA), poly(ethylene glycol) diacrylate (PEGDA), or glycidyl methacrylate (GMA). Optionally, a catalyst may be added to the mixture. In some embodiments, the catalyst may be ammonium persulfate (APS), potassium persulfate (KPS), sodium persulfate (NaPS), azo-bis-isobutyronitrile (AIBN), benzoyl peroxide (BPO), 2,2'-azobis(2-methylpropionitrile) (AIBN), 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50), or 2,2'-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride (VA-044). The catalyst may be added to the mixture in a concentration of from about 0.1 M to about 1.0 M. For example, the catalyst may be added at a concentration of from about 0.1 M to about 0.2 M, offrom about 0.2 M to about 0.3 M, of from about 0.3 M to about 0.4 M, of from about 0.4 M to about 0.5 M, of from about 0.5 M to about 0.6 M, of from about 0.6 M to about 0.7 M, of from about 0.8 M to about 0.9 M, or of from about 0.9 M to about 1.0 M. The solution may be prepared in water. In some embodiments, the water may be fresh water, deionized water, tap water, or any chemically inert water. The water may be further treated after desorption to produce clean water. In some embodiments, the clean water may be potable water or drinking water.

[0057] Following the initial mixing of the components, the mixture pH may be adjusted. The pH may be adjusted by adding, to the thermoresponsive polymer mixture, an acid or base component. For example, when the thermoresponsive polymer mixture has a pH of above 7, an acid may be added to the mixture. When the thermoresponsive polymer mixture has a pH of below 7, a basic solution may be added to the mixture. The initial mixing of the polymer and hygroscopic material may be heated to a temperature of from about 30 °C to 50 °C for a period of time to induce crosslinking and collapse of the polymer into a coil to generate the microgel structure. In some embodiments, the heating of the mixture may be from about 30 °C to 50 °C for about 1 minute to about 24 hours. Subsequent to heating the mixture for a sufficient time period to induce the transition of the polymer network, the resulting hydrogel may be comprised of microgel structures, increasing the total surface area of the hydrogel and provide an efficient method of absorbing more water than previously produced methods. In some embodiments, the microgel structures may have a diameter or cross-sectional dimension of from 50 nm to 500 microns. For example, the microgel structures may have diameters from 50 nm to 100 nm, from 100 nm to 200 nm, from 200 nm to 300 nm, from 300 nm to 400 nm, from 400 nm to 500 nm, from 500 nm to 600 nm, from 600 nm to 700 nm, from 700 nm to 800 nm, from 800 nm to 900 nm, from 900 nm to 1 micron, from 1 micron to 100 micron, from 100 micron to 150 micron, from 150 micron to 200 micron, from 200 micron to 250 micron, from 250 micron to 300 micron, from 300 micron to 350 micron, from 350 micron to 400 micron, from 400 micron to 450 micron, or from 450 micron to 500 micron.

[0058] Any suitable method, including methods known in the art, may be used for forming the hydrogels described herein. The examples provided are not set forth to limit the scope of the disclosed hydrogels but to provide examples of methods for producing a hydrogel as described according to the compositions disclosed herein. For example, the method for forming the hydrogel described herein may include mixing a thermoresponsive monomer, an ionic monomer loaded with salt ions, and optionally a photothermal agent in an aqueous solution, such as water, to generate a first mixture. A surfactant and a solvent may be mixed to generate a second mixture. In some embodiments, the surfactant may be sorbitan monooleate, sorbitan trioleate, sorbitan monolaurate, polyvinyl alcohol, polyvinylpyrrolidone, or any suitable surfactant. In some embodiments, thesurfactant is food safe or food grade. In some embodiments, the solvent may be cyclohexane, mineral oil, paraffin oil, hexadecane, isooctane, or any suitable solvent. The first mixture may undergo a purge with an inert gas for 15 minutes, such as nitrogen gas, and then combined with the second mixture and a tertiary amine. In some embodiments, the tertiary amine may be tetraethylenediamine, N,N,N’,N’ -tetramethylhexanediamine (TMHDA), or N,N,N’,N’- tetramethyl-l,3-butadiamine. The tertiary amine may be added to the mixture for a second time after a sufficient amount of time has passed to provide adequate mixing. After a period of time (e.g., from about 12 hours to 36 hours) the combined mixture may be washed with a solvent followed by precipitation by acetone and subsequently washed in water solution. In some embodiments, the solvent may be an organic solvent, or the solvent used in the second mixture. For example, the solvent in water solution may include cyclohexane, acetone, and / or water. The washed mixture may undergo a free-drying process for a first time to generate a freeze-dried powder of the water harvesting material. Upon complete freeze-drying, the powder may be submerged in a solution comprising the hygroscopic material and freeze-dried for a second period of time to generate the water harvesting hydrogel.

[0059] In some embodiments, the combining of the first mixture and the second mixture with the tertiary amine may be performed via drop-wise addition. In some embodiments, the method described herein may be referred to as water-in-oil microdroplet formation. The microdroplets formed via the method described herein may produce a thermoresponsive gel network microgel structure having a diameter or cross-sectional dimension of from 50 nm to 500 microns. For example, the microgel structures may have diameters from 50 nm to 100 nm, from 100 nm to 200 nm, from 200 nm to 300 nm, from 300 nm to 400 nm, from 400 nm to 500 nm, from 500 nm to 600 nm, from 600 nm to 700 nm, from 700 nm to 800 nm, from 800 nm to 900 nm, from 900 nm to 1 micron, from 1 micron to 100 micron, from 100 micron to 150 micron, from 150 micron to 200 micron, from 200 micron to 250 micron, from 250 micron to 300 micron, from 300 micron to 350 micron, from 350 micron to 400 micron, from 400 micron to 450 micron, or from 450 micron to 500 micron.Methods of using the atmospheric water harvesting material

[0060] The water harvesting material described herein may be used in all weather conditions, such as in dry air conditions or humid environments. For example, the atmospheric water harvesting material may be used in environments where the relative humidity may be below 30% relative humidity (RH). In some embodiments, the atmospheric water harvesting may be employed in environments where the RH may be from about 10% RH to about 100 % RH. For example, theenvironment or atmosphere may be from 10% RH to about 30% RH, from about 30% RH to about 45% RH, from about 45% RH to about 60% RH, from about 60% RH to about 75% RH, from about 75% RH to about 90% RH, or from about 90% RH to about 100% RH.

[0061] The atmospheric water harvesting material may be exposed to the environments for a period of time sufficient to allow at least 50% saturated water uptake. In some embodiments, the time required for at least 50% saturated water uptake may be dependent upon the relative humidity of the environment the atmospheric water harvesting may be disposed. The atmospheric water harvesting material described herein may be used to capture water from the surrounding environment to generate potable water without the use of electricity. In some embodiments, the atmospheric water harvesting may be re-used (e.g., re-hydrated) more than once so as to absorb and desorb water more than once from the surrounding environment (e.g., up to 100 times, or up to 1000 times, or more). For example, the atmospheric water harvesting may be used at least 1 time, at least 2 times, at least 3 times, at least 4 times, at least 5 times, at least 6 times, at least 7 times, at least 8 times, at least 9 times, at least 10 times, at least 11 times, at least 12 times, at least 13 times, at least 14 times, at least 15 times, at least 16 times, at least 17 times, at least 18 times, at least 19 times, at least 20 times or more without losing efficiency in water collection. Desorption of water from atmospheric water harvesting materials described herein may be performed via increasing the surface temperature of the hydrogel, such as via exposure to a light source having a wavelength of from about 400 nm to about 2500 nm. In some embodiments, the light exposure may be artificial light or natural light.

[0062] Atmospheric water harvesting materials described herein may be placed in cool environments, such as outside or in the shade to allow absorption of water to the hydrogel structures described herein. In some embodiments, the cool environments may be an area with a temperature of about 5 °C to 20 °C lower than the surrounding environment. For example, the surrounding environment may be at an elevated temperature, while the shade is about 5 °C to 20 °C lower than the surrounding environment. Other cool environments can include overnight exposure where temperatures are cooler than daytime exposure. For example, the atmospheric water harvesting material described herein may be placed outside and absorb water overnight and desorb the water upon sun exposure from the daytime heat or the direct sunlight. Other such examples may have a temperature difference of about 5 °C to 40 °C. In some embodiments, the atmospheric water harvesting materials described herein may be adhered to a surface such as a plastic surface or metal surface as a support to allow placement in the cool environments. In some embodiments, the atmospheric water harvesting materials described herein may be in any suitable shape to allow maximum absorption of water from the surrounding environment, such as a thinsheet, a cylindrical shape, a cube, or any other suitable shape to allow maximum surface area exposure.

[0063] The invention may be further understood by the following non-limiting examples.EXAMPLE 1 : ATMOSPHERIC WATER HARVESTING HYDROGELS OVERVIEW

[0064] Addressing the escalating global challenge of limited access to potable water necessitates the exploration of more abundant water sources and the advancement of innovative water production methods. In contrast to other water treatment techniques, such as seawater desalination, atmospheric water harvesting (AWH) has emerged as a decentralized approach, providing considerable potential for domestic implementation, regardless of geographical and hydraulic limitations. Sorbent-based atmospheric water harvesting (SAWH) exhibits a unique advantage of versatile functionality across diverse relative humidity (RH) levels, retaining efficacy even at levels as low as 15% RH. In a practical sorbent-based atmospheric water harvesting process, steps may include elimination of dirt and dust from the moisture flow, sorbent-mediated water production via sorption-desorption cycles, and subsequent water collection, with potential purification if necessary. Notably, the characteristics of the atmospheric water harvesting sorbent exert a substantial influence on both the overall water yield and the energy consumption associated with the process (FIG. 1 A).

[0065] Considerable efforts have been made to investigate cutting-edge atmospheric water harvesting sorbents exhibiting high water uptake, rapid sorption-desorption kinetics, and energyefficient water release. Polymeric hydrogels may be a useful class of candidates, due to their remarkable water retention capacity and the ability to modulate desorption temperatures through distinct polymer-water interactions. Thermoresponsive hydrogels represent a subclass of hydrogels that undergo phase transitions in response to temperature fluctuations. Hydrogels exhibiting lower critical solution temperatures (LCST), such as poly(N-isopropylacrylamide) (PNIAPM), are useful as atmospheric water harvesting sorbents, as their characteristic hydrophilic-to-hydrophobic transition at temperatures exceeding the LCST facilitates water release at the molecular level (FIG. 8).

[0066] The hygroscopic performance of thermoresponsive hydrogel sorbents may be increased, particularly under low RH conditions, via the integration of hygroscopic salts such as lithium chloride (LiCl) and calcium chloride (CaCh) into the hydrogel matrix, to develop composite sorbents with improved moisture absorption capabilities. Without wishing to be bound by any theory, it is hypothesized that salts can liquefy the adsorbed vapor through deliquescence, while the hydrogel network serves as a molecular reservoir for storing liquid water. However, suchcomposite sorbents may risk salt leakage at elevated RH due to uncontrolled deliquescence and insufficient salt confinement, and may suffer from poor swelling capacity caused by the salting-out effect with high salt content, which can deteriorate sorbent performance and narrow the range of applicable scenarios.

[0067] Moreover, higher temperatures may allow for more complete water desorption, as aggregated salt hydrates necessitate considerable activation energy for decomposition. Alternatively, the swelling capacity can be preserved under controlled water capture if hygroscopic ions are immobilized within a confined domain. The potential reduction in energy consumption during desorption may be attained without the formation of aggregated crystal hydrates, given the limited mobility of ions. Methods and materials described below and herein can allow for the confined hydration in thermoresponsive hydrogels for energy-efficient atmospheric water harvesting (FIG. IB). The confined hygroscopic sites attached to the polymer chain can largely be immobilize salt ions, for example enabling confined water networking and hydrogel swelling within the molecular mesh rather than uncontrolled salt liquefaction. Upon mild heating, the disintegration of the water molecule network and subsequent water escape can be facilitated by the conformational change of the thermoresponsive gel matrix.

[0068] Described below and herein are molecularly confined hydration in thermoresponsive hydrogels. The molecularly defined hydration in thermoresponsive hydrogels may be accomplished, in some examples, through a bifunctional polymeric network composed of hygroscopic zwitterionic moieties and thermoresponsive moieties. The ion immobilization within the zwitterionic segment can yield confined hygroscopic sites, facilitating stable and advantageous water absorption across a range of RH levels. Concurrently, the incorporation of a thermoresponsive segment can enable the release of water at comparatively low temperatures, underscoring the synergistic contribution of both the confined sites and the thermoresponsive network. Additionally, the microgel configuration endows the sorbent with rapid sorptiondesorption kinetics. Results described below demonstrate that thermoresponsive zwitterionic microgel can achieve a water uptake of 1 g g'1at 60% RH within 100 minutes and allow the release of approximately 80% of the captured water within 20 minutes at temperatures as low as 40 °C. Further disclosed below, by incorporating photothermal absorbers, solar-driven atmospheric water harvesting can attain similar water release performance under one sun illumination. With a comprehensively favorable performance, the methods and materials described herein present an effective and energy-efficient solution for the design of next-generation atmospheric water harvesting sorbents, which holds potential to alleviate the global water crisis at the materials level.EXAMPLE 2: METHODS AND MATERIALS

[0069] All chemicals were used without further purification. N-isopropyl acrylamide (NIP AM, >99%), [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (DMAPS, 95%), N,N'-m ethylenebisacrylamide (BIS, 99%), ammonium persulfate (APS, >98%), sorbitane monooleate (Span 80), cyclohexane (>99.9%), acetone (>99.9%), N,N,N',N'-Tetramethyl ethylenediamine (TEMED), hydrochloric acid (HC1), poly(sodium 4-styrenesulfonate), lithium chloride and pyrrole were purchased from Sigma- Aldrich.

[0070] Fabrication of thermoresponsive zwitterionic microgels (TZMGs) : Solution A was prepared by dissolving NIP AM, DMAPS, BIS (0.3 M), and APS (0.4 M) in water, with NIP AM fixed at 10 wt.% and NIPAM:DMAPS molar ratios varying between 1 :0.1 and 1 : 1. Span 80 (0.025 vol%) was added to cyclohexane to produce solution B. Solution A was purged with nitrogen for 15 min, combined with solution B (1 :4 v / v ratio), and stirred, with TEMED (0.02 vol%) added after 30 and 60 min. After 24 h, the product was washed with cyclohexane, acetone, and water, then freeze-dried for 72 h. The resulting thermoresponsive zwitterionic microgel powder was immersed in 4 M LiCl for 24 h, washed, and freeze-dried again for 72 h.

[0071] Fabrication of water-dispersed polypyrrole (Ppy:PSSf. To 0.1 M HC1, 0.27 g / mL polystyrene-sulfonate and 1.5 M ammonium persulfate were dissolved under N2, and 20 g pyrrole was added. The reaction proceeded at 20 °C for 4 h, and the pH was adjusted to 7.0. The polypyrrole-polystyrene sulfonate solution was dialyzed, freeze-dried, and redispersed in DI water to obtain a 0.1 g / mL Ppy solution.

[0072] Fabrication of Photothermo-responsive zwitterionic microgels (PZMGs): Solution A was prepared similarly to thermoresponsive zwitterionic microgels above, with the addition of 0.1 g / mL Ppy:PSS (2, 5, 10, 15 vol%). The PZMG synthesis procedure was identical to that of thermoresponsive zwitterionic microgels above, yielding ion-loaded PZMG powder after freeze- drying.

[0073] Sample morphologies were observed using scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) (Hitachi S5500). Fourier transform infrared (FTIR) spectra were collected using a Thermo Mattson Infinity Gold FTIR Spectrometer with a liquid nitrogen-cooled narrow band mercury cadmium telluride detector and a Ge crystal attenuated total reflectance (ATR) cell. X-ray diffraction (XRD) profiles were acquired with a Rigaku Miniflex 600 diffractometer. Thermogravimetric analysis was performed using a PerkinElmer TGA 4000 with an airflow rate of 25 mL min1and a heating rate of 10 °C min1. Sorption-desorption performance was assessed using a Surface Measurement Systems dynamicvapor sorption (DVS) Adventure instrument, with samples preheated at 90 °C, 0% relative humidity (RH) for 60 min, and stabilized at 25 °C for 30 min. Evaporation and phase transition behaviours were evaluated using a TA Instruments differential scanning calorimetry (DSC) 250 with a fixed scan rate of 2 °C min-1. Ion concentrations were determined via ICP-MS (Agilent 7500ce). A dry, sealed cabinet containing desiccants was employed to prevent moisture sorption during sample transfer for characterization and performance measurements.EXAMPLE 3: CHARACTERIZATION AND PROPERTIES OF HYDROGELS

[0074] The thermoresponsive zwitterionic microgel (TZMG) were synthesized from a bifunctional copolymer, created through in-situ free-radical polymerization of [2- (methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (DMAPS) and N- Isopropylacrylamide (NIP AM) monomers, followed by LiCl loading. The resulting ion-loaded P(NIPAM-co-DMAPS) network may comprise at least two functional segments: a hygroscopic moiety, achieved through salt-immobilized PDMAPS with confined hygroscopic sites, and a thermoresponsive moiety, derived from PNIPAM (FIG. 2A). Fourier transform infrared (FTIR) spectroscopy was performed to analyze its chemical composition (FIG. 2B). For DMAPS, it may be understood that peaks at approximately 1036 cm1and 1178 cm1may signify symmetric and asymmetric stretching vibrations of S=O, respectively. The peak at roughly 1546 cm1may correspond to amide II in PNIPAM. The P(NIPAM-co-DMAPS) spectrum features a combination of these monomers' characteristic peaks, confirming successful copolymerization. Moreover, X- ray diffraction (XRD) patterns of hydrogels, with a varying range of NIPAM:DMAPS copolymerization mole ratios from 1 :0.1 to 1 : 1.0 after ion loading, exhibited no distinct LiCl peaks. Without being bound by any theory, these results may indicate that the majority of salt ions may be present as ion pairs with zwitterions, rather than forming aggregated crystalline LiCl (FIG. 2C). To assess the salt-responsive property's influence on hydrogel swelling ability, the hydrogels can be immersed in LiCl solution. A 4 M LiCl solution was selected for PDMAPS swelling (FIG. 9A). FIG. 2D illustrates the swelling ratio increase from ~0.5 g g1for PNIPAM to -12 g g1for DMAPS. Electrostatic interactions may cause self-association between zwitterionic groups of -N (CHs)2and -SO3 , which can be disrupted by Li+ / CF ion pairing with zwitterions — a saltingin effect. Polymers like PNIPAM experience a salting-out effect, characterized by decreased hydrability in the presence of salt. Among the copolymer samples, the 1 : 1.0 copolymer hydrogel exhibited the highest swelling ability and potential water harvesting capacity, this phenomenon may result from the competition between two salt-responsive properties. The phase transition behavior of the copolymer hydrogel can be evaluated by monitoring the heat flow during temperature increase using differential scanning calorimetry (DSC). This phase transition can becharacterized by an endothermic peak in the DSC curve, representing the energy needed to disrupt polymer-solvent interactions and form a distinct polymer-rich phase. The phase transition temperature shifted from about 34 °C for the 1 :0.1 copolymer to about 39 °C for the 1 : 1.0 copolymer as the hydrophilicity enhanced with more zwitterions incorporated (FIG. 2E). Although the transition degree notably decreases with greater DMAPS incorporation, it still facilitated water release, as demonstrated in subsequent water desorption tests below.EXAMPLE 4: COMPARISON OF SALT AND HYDROGEL-MEDIATED SORBENTS FOR ATMOSPHERIC WATER HARVESTING

[0075] A qualitative comparison of different materials for atmospheric water harvesting may be described herein in terms of water uptake, kinetics, desorption efficiency and cyclability (FIG. 1C and Table 1). Desorption may be a key process for sorbents to release the absorbed water by heating. Sorbents with high desorption efficiency can release most of water under relatively low temperature, which can largely reduce the energy consumption for water production. As demonstrated herein, the reported lowest temperature that can realize the desorption of 80% water uptake can represent or correspond to the desorption efficiency of the sorbent. Hygroscopic salts show high vapor sorption capacity, but they deliquesce easily, which will result in sluggish kinetics due to the passivation layer formation. Salt-based hydrogels generally refer to a class of materials with hydroscopic salt embedded into a polymer matrix. Although the kinetics can be improved by storing the salt solution within the gel network, salt confinement may not be sufficient such that aggregated salt hydrates can still be formed during water sorption process. Since hydrates have high activation energy of decomposition, high desorption temperature may be required to release that part of water, and thus results in lowered desorption efficiency. Besides, polymers suffering from salting-out effect, like PNIPAM, typically have poor swelling ability, which may risk salt leakage under high RH, resulting in deteriorated cyclability. The hydrogel described herein may comprise zwitterionic moieties (PDMAPS) and thermoresponsive moieties (PNIPAM). The strong immobilization of salt ions within PDMAPS may help construct a confined water network without the formation of salt hydrates, while the conformational change within PNIPAM may also facilitate water release during desorption. Their synergistic contributions endow the hydrogel system described herein with high desorption efficiency. In addition, the diffusion length can largely be shortened by the microgel configuration, which can further enhance the kinetics of the system described herein.Table 1. Evaluation matrices of the cross-comparisons in terms of water uptake, kinetics, and desorption efficiency.Score Water uptake at 60% RH (g g'1)1 <0.62 0.6-0.83 0.8-1.04 1.0-1.25 >1.2Time to reach 80% water uptake at 60% ScoreRH (min)1 >2002 150-2003 100-1504 50-1005 <50Reported lowest temperature to desorb Score80% water uptake (°C)1 >952 95-803 80-654 65-505 <50EXAMPLE 5: PREPARATION AND ATMOSPHERIC WATER HARVESTING PERFORMANCE OF THERMORESPONSIVE ZWITTERIONIC MICROGELS

[0076] Thermoresponsive zwitterionic microgels (TZMGs) were synthesized via an inverse miniemulsion polymerization method (FIG. 3 A). Water-soluble monomers and crosslinkers undergo polymerization within surfactant-stabilized water-in-oil microdroplets, forming microgels. Upon completion of the ion impregnation process, the resultant thermoresponsive zwitterionic microgels were obtained. Scanning electron microscopy (SEM) imaging reveals the as-prepared thermoresponsive zwitterionic microgels possess dimensions of approximately 50-100 pm, with uniformly distributed salt ions. The atmospheric water harvesting properties of a series of thermoresponsive zwitterionic microgels with varying copolymerization ratios were systematically examined. For conciseness, a thermoresponsive zwitterionic microgel with a NIPAM:DMAPS mole ratio of 1 :0.1 may be denoted as TZMG-0.1, and analogous nomenclature may be used for others. Water vapor sorption isotherms were measured using a dynamic vapor sorption (DVS) system. Typically, the hygroscopic salt-driven moisture harvesting process exhibits a unique isotherm shape with three distinct phases: salt chemisorption, salt hydrate deliquescence, and subsequent salt solution absorption, wherein water uptake experiences a sudden increase at the deliquescence RH, as indicated by a slope change in isotherm. FIG. 3B displays no abrupt inflection step in the isotherm, suggesting that the water capture mechanism may be governed by confined hygroscopic sites rather than hygroscopic salt. The upward curve, alongside elevated RH, stems from hydrogel swelling caused by the increased water molecule mobility at high water activity. Concurrently, TZMG-1.0 demonstrated the highest water uptake under various RH conditions due to the increased copolymerization of hygroscopic moi eties. The water vapor sorption-desorption kinetics of thermoresponsive zwitterionic microgels were evaluated through a static test. Thermoresponsive zwitterionic microgels with different copolymerization ratios exhibited similar sorption kinetics at 60% RH, achieving equilibrium (weight change rate - O g g'1min'1) within approximately 100 minutes (FIGS. 10A and 10B). Furthermore, the optimized thermoresponsive zwitterionic microgel exhibits a water uptake of 0.23 g g'1at 15% RH and 0.48 g g'1at 30% RH, verifying its applicability in low RH regions (FIG. 3C). The sorption time required to attain 80% of saturated water uptake at 15, 30, and 60% RH was 50, 45, and 30 minutes, respectively. Such rapid kinetics, resulting from the short diffusion distance of microgels, potentially enhance overall productivity through multiple cycling operations.

[0077] The captured water in TZMG-1.0 can be released by approximately 90% within 15 minutes through mild heating at 60 °C. Furthermore, TZMG-1.0 can discharge over 80% of absorbed water within around 20 minutes at a relatively low temperature of 40 °C (FIG. 3D andFIG. 11). The exceptional water release property may be attained by incorporating thermoresponsive moieties into the copolymer network, whose conformational changes facilitate the escape of the confined water network, which may be supported by both hydrophilic polymer chains and pendant hygroscopic groups. In comparison to conventional PNIPAM-LiCl-based sorbents, which predominantly rely on salt for moisture harvesting, TZMG-1.0 demonstrates its advantage in efficient water release at substantially lower temperatures. In the case of PNIPAM- LiCl, elevated thermal energy may be requisite for decomposing salt hydrates, contributing to the desorption process (FIG. 12).

[0078] Conversely, the confined hygroscopicity and hydration of TZMG-1.0 enable efficient water release, underscoring the effectiveness of the proposed design. To gain a deeper understanding of the desorption process, the heat flow profiles of thermoresponsive zwitterionic microgels, PNIPAM-LiCl, and PDMAPS-LiCl were assessed using DSC. In contrast to PNIPAM- LiCl, thermoresponsive zwitterionic microgels and PDMAPS-LiCl exhibit a single primary evaporation peak, corroborating that the hygroscopicity source may be dominated by the hydration of confined hygroscopic ion pairs rather than the deliquescence process of free crystalline LiCl (FIG. 3E, FIG. 14A, and FIG. 14B). Moreover, the temperature at which major evaporation occurs increases from 32 °C for PNIPAM-LiCl to 34 °C for TZMG-0.1 and 39 °C for TZMG-1.0. This noticeable shift suggests that the incorporation of zwitterionic segments elevates the phase transition temperature, aligning with the previous experimental observations in FIG. 2E. Additionally, TZMG-1.0 can ideally and stably operate 12 cycles per day with 100-minute harvesting and 20-minute releasing at 60% RH (FIG. 3F). Given the broad operative RH range with competitive water uptake, rapid kinetics (FIG. 14A and FIG. 14B), and superior desorption behavior (FIG. 3G and Table 1), the thermoresponsive zwitterionic microgel is useful as an efficient atmospheric water harvesting sorbent, exhibiting outstanding comprehensive performance.EXAMPLE 6: PREPARATION AND ATMOSPHERIC WATER HARVESTING PERFORMANCE OF PZMGS

[0079] By incorporating photothermal absorbers, such as polypyrrole (Ppy), thermoresponsive zwitterionic microgel (TZMG) may be endowed with solar-driven water release capabilities. As the inverse miniemulsion polymerization method necessitates a homogeneous aqueous phase to generate stabilized emulsions, polypyrrole doped with polystyrene sulfonate (Ppy:PSS) may be employed to form a water-processable solution (FIG. 5A). Following a similar synthetic route to thermoresponsive zwitterionic microgels with water-dispersed Ppy incorporated as above, photothermal -responsive zwitterionic microgels (PZMGs) were obtained. The as-prepared PZMGsexhibited a similar morphology to therm oresponsive zwitterionic microgel (FIG. 4). PZMG-1, including a Ppy:PSS solution, demonstrated good solar absorption (-97%) over an extensive wavelength range from 250 to 2500 nm (FIG. 5B). The photothermal properties of PZMG-1 were assessed by monitoring the surface temperature under varying solar intensities (FIG. 5C). It was observed that the Ppy:PSS nanoparticles may attain heat confinement and efficient heating of the molecular mesh, allowing the surface of the molecular mesh to reach equilibrium temperatures of approximately 50, 60, and 70 °C within 10 minutes under 0.5, 1, and 1.5 sun illumination (FIG. 5C). The photothermal ability, combined with the relatively low regeneration temperature of the system, may enable solar-driven water release. The sorption- sol ar desorption properties of PZMG- 1 were evaluated (FIG. 5D). Under conditions of 30% and 60% RH sorption and 1 sun illumination desorption, PZMG-1 exhibited similar kinetics and almost identical water uptake (~0.5 and 1 g g’1, respectively) as TZMG-1.0, likely due to the minimal amount of added Ppy. It was observed that water can be released within 20 minutes under 1 sun, indicating the feasibility of water release driven by natural sunlight.

[0080] The water extraction test was performed using a homemade solar-driven atmospheric water harvesting system to verify the viability of atmospheric water extraction (FIG. 6A). The atmospheric water harvesting system was fabricated from a transparent glass dome for light penetration and vapor condensation, a water collection base, and a sealing ring. A PZMG layer (-2 mm) was packed in a petri dish surrounded by thermal insulation foam. The samples underwent moisture sorption in the homemade moisture generation chamber at -30% RH for 90 min and -60% RH for 120 min (FIG. 7), respectively, and water release was evaluated under simulated solar light with 1 sun intensity for 30 min. As seen in FIG. 6B, the PZMG layer was capable of absorbing -0.4 g g'1and -1.0 g g'1water at 30% and 60% RH, respectively, and release at least some of the water under sunlight. Additionally, to evaluate the cycle ability of the hydrogel matrix, batch cycling was performed. PZMG was capable of operating at 60% RH over 10 cycles with an average water uptake of about 0.99 g g’1, a water release of about 0.92 g g’1, and water collection of about 0.70 g g'1per cycle (FIG. 6C). It was observed that the hydrogel matrix had an average water collection of about 0.27 g g'1per cycle at 30% RH (FIG. 15). Moreover, the concentrations of various metal ions in the collected water were below the WHO standard (FIG. 6D). The results validate the freshwater delivery capability of PZMG. Without being bound by ay theory, it is believed that the yield and production efficiency can be further enhanced for example, more effective active or passive cooling approaches can be adapted to increase the temperature difference between sorbents and the condensation surface, such as cooling fans or radiative coolingsurfaces. Other methods known by those skilled in the arts may be employed to further improve the yield and production efficiency of the hydrogel matrices.

[0081] By implementing molecularly confined hydration in thermoresponsive hydrogels, sorbent design for atmospheric water harvesting (AWH) may be achieved. The underlying design rationale enables the manipulation of hygroscopicity and hydration through the synergistic interplay between confined ions and a thermoresponsive network. By utilizing a bifunctional polymeric network, which incorporates hygroscopic zwitterionic moieties alongside thermoresponsive constituents, stable water uptake, efficient water release at a remarkably low temperature of 40 °C, and rapid sorption-desorption kinetics may be achieved as demonstrated above. Furthermore, the incorporation of photothermal absorbers enables solar-driven atmospheric water harvesting, demonstrating comparable water release performance under natural sunlight. These examples may provide an effective design of energy -efficient and high-performance atmospheric water harvesting sorbents, which can contribute to addressing the global freshwater crisis at the materials level.REFERENCES

[0082] Aleid, S. et al. Salting-in Effect of Zwitterionic Polymer Hydrogel Facilitates Atmospheric Water Harvesting. ACS Materials Letters 4, 511 -520 (2022).

[0083] Capek, I. On inverse miniemulsion polymerization of conventional water-soluble monomers. Advances in Colloid and Interface Science 156, 35-61 (2010).

[0084] Chang, X. et al. Marine biomass-derived, hygroscopic and temperature-responsive hydrogel beads for atmospheric water harvesting and solar-powered irrigation. Journal of Materials Chemistry A 10, 18170-18184 (2022).

[0085] Deng, F., Wang, C., Xiang, C. & Wang, R. Bioinspired topological design of super hygroscopic complex for cost-effective atmospheric water harvesting. Nano Energy 90, 106642 (2021).

[0086] Deng, F., Xiang, C., Wang, C. & Wang, R. Sorption-tree with scalable hygroscopic adsorbent-leaves for water harvesting. Journal of Materials Chemistry A 10, 6576-6586 (2022).

[0087] Ejeian, M. & Wang, R.Z. Adsorption-based atmospheric water harvesting. Joule 5, 1678- 1703 (2021).

[0088] Entezari, A., Ejeian, M. & Wang, R. Super Atmospheric Water Harvesting Hydrogel with Alginate Chains Modified with Binary Salts. ACS Materials Letters 2, 471-477 (2020).

[0089] Fathieh, F. et al. Practical water production from desert air. Science Advances 4, eaat3198.

[0090] Feil, H., Bae, Y.H., Feijen, J. & Kim, S.W. Effect of comonomer hydrophilicity and ionization on the lower critical solution temperature of N-isopropyl acrylamide copolymers. Macromolecules 26, 2496-2500 (1993).

[0091] Guan, W ., Lei, C., Guo, Y., Shi, W. & Yu, G. Hygroscopic-Microgels-Enabled Rapid Water Extraction from Arid Air. Advanced Materials n / a, 2207786 (2022).

[0092] Guo, Y. et al. Hydrogels and Hydrogel-Derived Materials for Energy and Water Sustainability. Chemical Reviews 120, 7642-7707 (2020).

[0093] Guo, Y. et al. Scalable super hygroscopic polymer films for sustainable moisture harvesting in arid environments. Nature Communications 13, 2761 (2022).

[0094] Haechler, I. et al. Exploiting radiative cooling for uninterrupted 24-hour water harvesting from the atmosphere. Science Advances 7, eabf3978.

[0095] Hanikel, N., Prevot, M.S. & Yaghi, O.M. MOF water harvesters. Nature Nanotechnology 15, 348-355 (2020).

[0096] Heskins, M. & Guillet, J.E. Solution Properties of Poly(N-isopropylacrylamide). Journal of Macromolecular Science: Part A - Chemistry 2, 1441-1455 (1968).

[0097] Hua, M. et al. Strong tough hydrogels via the synergy of freeze-casting and salting out. Nature 590, 594-599 (2021).

[0098] Kallenberger, P.A. & Froba, M. Water harvesting from air with a hygroscopic salt in a hydrogel-derived matrix. Communications Chemistry 1, 28 (2018).

[0099] Kang, B., Tang, H., Zhao, Z. & Song, S. Hofmeister Series: Insights of Ion Specificity from Amphiphilic Assembly and Interface Property. ACS Omega 5, 6229-6239 (2020).

[0100] Kietzke, T. et al. Novel approaches to polymer blends based on polymer nanoparticles. Nature Materials 2, 408-412 (2003).

[0101] LaPotin, A., Kim, H., Rao, S.R. & Wang, E.N. Adsorption-Based Atmospheric Water Harvesting: Impact of Material and Component Properties on System -Lev el Performance. Accounts of Chemical Research 52, 1588-1597 (2019).

[0102] LaPotin, A. et al. Dual-Stage Atmospheric Water Harvesting Device for Scalable Solar- Driven Water Production. Joule 5, 166-182 (2021).

[0103] Lei, C. et al. Polyzwitterionic Hydrogels for Efficient Atmospheric Water Harvesting.Angewandte Chemie International Edition 61, e202200271 (2022).

[0104] Lei, Z. & Wu, P. A highly transparent and ultra-stretchable conductor with stable conductivity during large deformation. Nature Communications 10, 3429 (2019).

[0105] Li, R. et al. Hybrid Hydrogel with High Water Vapor Harvesting Capacity for Deployable Solar-Driven Atmospheric Water Generator. Environmental Science & Technology 52, 11367-11377 (2018).

[0106] Li, R., Shi, Y., Wu, M., Hong, S. & Wang, P. Improving atmospheric water production yield: Enabling multiple water harvesting cycles with nano sorbent. Nano Energy 67, 104255 (2020).

[0107] Li, R., Shi, Y., Wu, M., Hong, S. & Wang, P. Photovoltaic panel cooling by atmospheric water sorption-evaporation cycle. Nature Sustainability 3, 636-643 (2020).

[0108] Lord, J. et al. Global potential for harvesting drinking water from air using solar energy. Nature 598, 611-617 (2021).

[0109] Lu, H. et al. Tailoring the Desorption Behavior of Hygroscopic Gels for Atmospheric Water Harvesting in Arid Climates. Advanced Materials 34, 2205344 (2022).

[0110] Lu, H. et al. Materials Engineering for Atmospheric Water Harvesting: Progress and Perspectives. Advanced Materials 34, 2110079 (2022).[OHl] Markham, G., Obey, T.M. & Vincent, B. The preparation and properties of dispersions of electrically-conducting polypyrrole particles. Colloids and Surfaces 51, 239-253 (1990).

[0112] Matsumoto, K., Sakikawa, N. & Miyata, T. Thermo-responsive gels that absorb moisture and ooze water. Nature Communications 9, 2315 (2018).

[0113] Mekonnen, M.M. & Hoekstra, A. Y. Four billion people facing severe water scarcity. Science Advances 2, el 500323.

[0114] Mittal, H., Al Alili, A. & Alhassan, S.M. Adsorption isotherm and kinetics of water vapors on novel superporous hydrogel composites. Microporous and Mesoporous Materials 299, 110106 (2020).

[0115] Oki, T. & Kanae, S. Global Hydrological Cycles and World Water Resources. Science 313, 1068-1072 (2006).

[0116] Progress on Drinking Water, Sanitation and Hygiene: 2017 Update and SDG Baselines (World Health Organization and the United Nations Children’s Fund, 2017).

[0117] Roy, D., Brooks, W.L.A. & Sumerlin, B.S. New directions in thermoresponsive polymers. Chemical Society Reviews 42, 7214-7243 (2013).

[0118] Schild, H.G. Poly(N-isopropylacrylamide): experiment, theory and application. Progress in Polymer Science 17, 163-249 (1992).

[0119] Shechter, I., Ramon, O., Portnaya, I., Paz, Y. & Livney, Y.D. Microcalorimetric Study of the Effects of a Chaotropic Salt, KSCN, on the Lower Critical Solution Temperature (LCST) of Aqueous Poly(N-isopropylacrylamide) (PNIPA) Solutions. Macromolecules 43, 480-487 (2010).

[0120] Shi, W ., Guan, W ., Lei, C. & Yu, G. Sorbents for Atmospheric Water Harvesting: from Design Principles to Applications. Angewandte Chemie International Edition n / a (2022).

[0121] Shi, Y., Ma, C., Peng, L. & Yu, G. Conductive “Smart” Hybrid Hydrogels with PNIPAM and Nanostructured Conductive Polymers. Advanced Functional Materials 25, 1219-1225 (2015).

[0122] Song, Y. et al. High-yield solar-driven atmospheric water harvesting of metal-organic- framework-derived nanoporous carbon with fast-diffusion water channels. Nature Nanotechnology 17, 857-863 (2022).

[0123] Stuart, M.A.C. et al. Emerging applications of stimuli -responsive polymer materials. Nature Materials 9, 101-113 (2010).

[0124] Wang, J. et al. High-yield and scalable water harvesting of honeycomb hygroscopic polymer driven by natural sunlight. Cell Reports Physical Science 3, 100954 (2022).

[0125] Wu, M. et al. Metal- and halide-free, solid-state polymeric water vapor sorbents for efficient water- sorption- driven cooling and atmospheric water harvesting. Materials Horizons 8, 1518-1527 (2021).

[0126] Xu, J. et al. Efficient Solar-Driven Water Harvesting from Arid Air with Metal-Organic Frameworks Modified by Hygroscopic Salt. Angewandte Chemie International Edition 59, 5202- 5210 (2020).

[0127] Xu, J. et al. Ultrahigh solar-driven atmospheric water production enabled by scalable rapid-cycling water harvester with vertically aligned nanocomposite sorbent. Energy & Environmental Science 14, 5979-5994 (2021).

[0128] Yang, K. et al. Hollow spherical SiO2 micro-container encapsulation of LiCl for high- performance simultaneous heat reallocation and seawater desalination. Journal of Materials Chemistry A 8, 1887-1895 (2020).

[0129] Yilmaz, G. et al. Autonomous atmospheric water seeping MOF matrix. Science Advances 6, eabc8605.

[0130] Zhang, Y., Furyk, S., Bergbreiter, D.E. & Cremer, P.S. Specific Ion Effects on the Water Solubility of Macromolecules: PNIPAM and the Hofmeister Series. Journal of the American Chemical Society 127, 14505-14510 (2005).

[0131] Zhao, F. et al. Super Moi sture-Ab sorb ent Gels for All-Weather Atmospheric Water Harvesting. Advanced Materials 31, 1806446 (2019).

[0132] Zhou, X., Lu, H., Zhao, F. & Yu, G. Atmospheric Water Harvesting: A Review of Material and Structural Designs. ACS Materials Letters 2, 671-684 (2020).STATEMENTS REGARDING INCORPORATION BY REFERENCE AND VARIATIONS

[0133] All references throughout this application, for example patent documents, including issued or granted patents or equivalents and patent application publications, and non-patent literature documents or other source material are hereby incorporated by reference herein in their entireties, as though individually incorporated by reference.

[0134] All patents and publications mentioned in the specification are indicative of the levels of skill of those skilled in the art to which the invention pertains. References cited herein are incorporated by reference herein in their entirety to indicate the state of the art, in some cases as of their filing date, and it is intended that this information can be employed herein, if needed, to exclude (for example, to disclaim) specific embodiments that are in the prior art.

[0135] When a group of substituents is disclosed herein, it is understood that all individual members of those groups and all subgroups and classes that can be formed using the substituents are disclosed separately. When a Markush group or other grouping is used herein, all individual members of the group and all combinations and subcombinations possible of the group are intended to be individually included in the disclosure. As used herein, “and / or” means that one, all, or any combination of items in a list separated by “and / or” are included in the list; for example, “1, 2 and / or 3” is equivalent to “1, 2, 3, 1 and 2, 1 and 3, 2 and 3, or 1, 2, and 3”.

[0136] Every formulation or combination of components described or exemplified can be used to practice the invention, unless otherwise stated. Specific names of materials are intended to be exemplary, as it is known that one of ordinary skill in the art can name the same materialdifferently. It will be appreciated that methods, device elements, starting materials, and synthetic methods other than those specifically exemplified can be employed in the practice of the invention without resort to undue experimentation. All art-known functional equivalents, of any such methods, device elements, starting materials, and synthetic methods are intended to be included in this invention. Whenever a range is given in the specification, for example, a temperature range, a time range, or a composition range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure.

[0137] As used herein, “comprising” is synonymous with “including,” “containing,” or “characterized by,” and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, “consisting of’ excludes any element, step, or ingredient not specified in the claim element. As used herein, “consisting essentially of’ does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. Any recitation herein of the term “comprising”, particularly in a description of components of a composition, in a description of a method, or in a description of elements of a device, is understood to encompass those compositions, methods, or devices consisting essentially of and consisting of the recited components or elements, optionally in addition to other components or elements. The invention illustratively described herein suitably may be practiced in the absence of any element, elements, limitation, or limitations which is not specifically disclosed herein.

[0138] The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A water harvesting material, the water harvesting material comprising: a thermoresponsive gel network, wherein the thermoresponsive gel network comprises a thermoresponsive polymer and a crosslinking agent; and a hygroscopic material dispersed throughout the thermoresponsive gel network.

2. The water harvesting material of claim 1, wherein the thermoresponsive gel network comprises a matrix of crosslinked microgel structures.

3. The water harvesting material of claim 2, wherein the crosslinked microgel structures have a cross-sectional dimension of from about 50 nm to about 500 pm.

4. The water harvesting material of claim 1, wherein the thermoresponsive polymer comprises hydroxypropyl cellulose (HPC), poly(N-isopropylacrylamide) (PNIPAM), poly(N,N-diethylacrylamide) (PDEAM), poly(N-vinylcaprolactam) (PVCL), poly(N- isopropylmethacrylamide) (PNIPMAM), poly(N,N-dimethylacrylamide) (PDMA), or any combination of these.

5. The water harvesting material of claim 1, wherein the hygroscopic material comprises a hygroscopic salt, lithium chloride, magnesium chloride, calcium chloride, or any combination of these.

6. The water harvesting material of claim 1, wherein the hygroscopic material comprises a charged polymer network loaded with salt ions.

7. The water harvesting material of claim 1, wherein the crosslinking agent comprises glutaraldehyde, epichlorohydrin, diepoxy compounds, polyisocyanates, divinyl sulfone, formaldehyde, or any combination of these.

8. A method of making a water harvesting material, the method comprising: adding, to a solution of a thermoresponsive polymer, a solution of a hygroscopic material to generate a mixture; mixing the mixture of the thermoresponsive polymer and hygroscopic material at an elevated temperature for a period of time sufficient to ensure adequate mixing of solutions; adding, to the mixture of the thermoresponsive polymer and hygroscopic material, a crosslinking agent;adjusting a pH of the mixture of the thermoresponsive polymer, hygroscopic material, and crosslinking agent; and collecting the water harvesting material from the mixture, wherein the water harvesting material is a microgel structure comprising the thermoresponsive polymer.

9. The method of claim 8, wherein the microgel structure have a cross- sectional dimension of from about 50 nm to about 500 pm.

10. The method of claim 8, wherein the thermoresponsive polymer comprises hydroxypropyl cellulose (HPC), poly(N-isopropylacrylamide) (PNIPAM), poly(N,N- di ethyl acrylamide) (PDEAM), poly(N-vinylcaprolactam) (PVCL), poly(N- isopropylmethacrylamide) (PNIPMAM), poly(N,N-dimethylacrylamide) (PDMA), or any combination of these.

11. The method of claim 8, wherein the hygroscopic material comprises a hygroscopic salt, lithium chloride, magnesium chloride, calcium chloride, or any combination of these.

12. The method of claim 8, wherein the crosslinking agent comprises glutaraldehyde, epichlorohydrin, diepoxy compounds, polyisocyanates, divinyl sulfone, formaldehyde, or any combination of these.

13. The method of any one of claims 8-12, wherein the water harvesting material comprises the water harvesting material of any one of claims 1-7.

14. A water harvesting material, the water harvesting material comprising: a copolymer comprising a first monomer and a second monomer wherein the first monomer is a thermoresponsive monomer and the second monomer is an ionic monomer loaded with salt ions; a photothermal agent; and a crosslinking agent, wherein the copolymer and the photothermal agent are arranged in a form of a bifunctional polymeric network or matrix of crosslinked microgel structures.

15. The water harvesting material of claim 14, wherein the thermoresponsive monomer comprises N-isopropylacrylamide, N,N-diethylacrylamide, N-isopropylmethacrylamide, N- vinyl caprolactam, or any combination of these.

16. The water harvesting material of claim 14, wherein the crosslinking agent comprises N,N'-methylenebis(acrylamide) (BIS), ethylene glycol dimethacrylate (EGDMA), divinylbenzene (DVB), trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate (PETA), polyethylene glycol) diacrylate (PEGDA), glycidyl methacrylate (GMA), or any combination of these.

17. The water harvesting material of claim 14, wherein the ionic monomer comprises a cationic vinyl monomer, an anionic vinyl monomer, a zwitterionic vinyl monomer, or any combination of these.

18. The water harvesting material of claim 17, wherein the cationic vinyl monomer comprises 2-(methacryloyloxy)ethyltrimethylammonium chloride (METAC), [2- (methacryloyloxy)ethyl]trimethylammonium methosulfate (METAMS), vinylbenzyl trimethylammonium chloride (VBTAC), or any combination of these.

19. The water harvesting material of claim 17, wherein the anionic vinyl monomer comprises acrylic acid (AA), methacrylic acid (MAA), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), or any combination of these.

20. The water harvesting material of claim 17, wherein the zwitterionic vinyl monomer comprises 2-methacryloyloxyethyl phosphorylcholine (MPC), sulfobetaine methacrylate (SBMA), carboxybetaine methacrylate (CBMA), N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N- dimethylammonium betaine (SPE), or any combination of these.

21. The water harvesting material of claim 14, wherein the photothermal agent comprises carbon black, active carbon, polypyrrole: poly (styrene sulfonate), polyaniline: poly (styrene sulfonate), poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), or any combination of these.

22. The water harvesting material of claim 16, further comprising a catalyst wherein the catalyst comprises ammonium persulfate (APS), potassium persulfate (KPS), sodium persulfate (NaPS), azo-bis-isobutyronitrile (AIBN), benzoyl peroxide (BPO), 2,2'-azobis(2- methylpropionitrile) (AIBN), 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50), 2,2'- azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044), or any combination of these.

23. A method of making a water harvesting material, the method comprising: mixing a thermoresponsive polymer, an ionic monomer loaded with salt ions, and a photothermal agent in water to generate a first mixture;mixing a surfactant and a solvent to generate a second mixture; combining the first mixture and second mixture with a tertiary amine to generate a third mixture; freeze-drying the third mixture for a first time to generate a freeze-dried powder of the water harvesting material; submerging the freeze-dried powder in a solution comprising a hygroscopic material; and freeze-drying for a second time to generate the water harvesting material, wherein the water harvesting material is a microgel structure comprising the thermoresponsive polymer.

24. The method of claim 23, wherein combining the first mixture and second mixture with a tertiary amine is performed via dropwise addition.

25. The method of claim 24, wherein the tertiary amine comprises tetraethylenediamine, N,N,N’,N’ -tetramethylhexanediamine (TMHDA), or N,N,N’,N’- tetram ethyl -1,3 -butadi amine .

26. The method of claim 23, wherein the water harvesting material comprises microgel structures.

27. The method of claim 23, wherein the microgel structures have a cross- sectional dimension of from about 50 nm to about 500 pm.

28. The method of claim 23, wherein the thermoresponsive polymer comprises N-isopropyl acrylamide, N,N-di ethyl acrylamide, N-isopropylmethacrylamide, N-vinylcaprolactam, or any combination of these.

29. The method of claim 23, wherein the ionic monomer loaded with salt ions comprises a cationic vinyl monomer, an anionic vinyl monomer, a zwitterionic vinyl monomer, or any combination of these.

30. The method of claim 29, wherein the cationic vinyl monomer comprises 2- (methacryloyloxy)ethyltrimethylammonium chloride (METAC), [2- (methacryloyloxy)ethyl]trimethylammonium methosulfate (METAMS), vinylbenzyl trimethylammonium chloride (VBTAC), or any combination of these.

31. The method of claim 29, wherein the anionic vinyl monomer comprises acrylic acid (AA), methacrylic acid (MAA), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), or any combination of these.

32. The method of claim 29, wherein the zwitterionic vinyl monomer comprises 2-methacryloyloxyethyl phosphorylcholine (MPC), sulfobetaine methacrylate (SBMA), carboxybetaine methacrylate (CBMA), N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N- dimethylammonium betaine (SPE), or any combination of these.

33. The method of claim 23, wherein the photothermal agent comprises carbon black, active carbon, polypyrrole:poly(styrene sulfonate), polyaniline: poly (styrene sulfonate), poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), or any combination of these.

34. The method of claim 23, further comprising adding a crosslinking agent to the second mixture prior to combining the first mixture with the second mixture.

35. The method of claim 34, wherein the crosslinking agent comprises N,N'- methylenebis(acrylamide) (BIS), ethylene glycol dimethacrylate (EGDMA), divinylbenzene (DVB), trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate (PETA), poly(ethylene glycol) diacrylate (PEGDA), glycidyl methacrylate (GMA), or any combination of these.

36. The method of any one of claims 23-34, wherein the water harvesting material is the water harvesting material of any one of claims 14-22.

37. A method of harvesting water, the method comprising: providing the water harvesting material of any one of claims 1-7 or 14-22; exposing the water harvesting material to water for a duration of time sufficient to cause the water harvesting material to absorb water; heating the water harvesting material to desorb water; and collecting the desorbed water.

38. The method of claim 37, further comprising: treating the desorbed water to generate clean or drinkable water.

39. The method of claim 37, further comprising repeating one or more times: exposing the water harvesting material to water to re-hydrate the water harvesting material; heating the water harvesting material to desorb water; andcollecting the desorbed water.

40. The method of claim 37, wherein exposing the water harvesting material to water comprises exposing the water harvesting material to air or a gas having a relative humidity of from 10% to 100%.

41. The method of claim 37, wherein the heating of the water harvesting material comprises exposing the water harvesting material to light for increasing a temperature of the water harvesting material.

42. The method of claim 41, wherein the light has a wavelength in a range of from about 400 nm to about 1750 nm.

Images