Two-dimensional covalent organic framework humidity sensor and preparation method and application thereof

Abstract

The invention provides a two-dimensional covalent organic framework humidity sensor and a preparation method and application thereof, and belongs to the technical field of humidity sensors. The method comprises the following steps: injecting an Sc (OTf) 3 aqueous solution into a culture dish to form a gas-liquid interface, respectively dissolving a first monomer and a second monomer into a solvent, mixing to form a mixed solution, spreading the mixed solution on the liquid surface, and performing catalytic reaction by using Sc (OTf) 3 to obtain the 2D-COF film, and transferring the obtained 2D COF film to a substrate, and depositing a gold interdigital electrode on the surface of the film through a mask plate to form a top contact structure, thereby obtaining the two-dimensional covalent organic framework humidity sensor. Through the confinement effect of the gas-liquid interface, the continuous and flat crystal film with nano-scale thickness and atomic-scale surface roughness and with certain mechanical strength can be prepared. Due to the characteristics of the thin film, the thin film can have good electrode contact characteristics and current transmission lines, and is good in performance in an electrical test.

Description

Technical Field

[0001] This invention belongs to the field of humidity sensor technology, specifically relating to a two-dimensional covalent organic framework humidity sensor, its preparation method, and its application. Background Technology

[0002] Covalent organic frameworks (COFs) are a class of novel porous materials with precise pore structures and designable surface chemistry. Their excellent thermal stability and chemical tunability make them ideal candidates for humidity sensing. Traditional humidity detection technologies mainly rely on optical sensing mechanisms, such as solvation colorimetric effects or fluorescence quenching effects based on COFs. Although the response is intuitive and fast, it is easily affected by ambient light and difficult to achieve accurate quantification (J. Am. Chem. Soc. 2020, 142, 783-791 Humidity Sensing through Reversible Isomerization of a Covalent Organic Framework; ACS Appl. Mater. Interfaces 2021, 13, 33449-33463 Highly Crystalline Covalent Organic Frameworks Act as a Dual-Functional Fluorescent-Sensing Platform for Myricetin and Water, and Adsorbents for Myricetin). In contrast, resistive sensing technology has advantages such as signal stability and ease of quantization, while the unique π-conjugated structure of COFs materials provides the foundation for their electrical sensing performance.

[0003] Currently, commercial humidity sensors mainly use metal oxides or polymer materials as sensing elements. Although the technology is mature, problems such as slow response speed and limited detection range still exist. In the COF material system, powdered COFs are severely restricted in their device application due to problems such as high interparticle contact resistance and poor processing performance. Two-dimensional COF thin films effectively solve this problem through continuous crystal structure (Materials Letters 328 (2022) 133123 Fabrication asensor based on sulfonate-based COF for humidity sensing). Among them, imine-bonded 2D COF thin films prepared by interfacial polymerization (such as COF-366) have become a research hotspot due to their large size, high crystallinity and good conductivity. The electrical performance of these films can be further improved by introducing conjugated ligands (such as porphyrin, thiophene, triazine, etc.), and their carrier mobility has approached the level of polycrystalline silicon.

[0004] However, existing humidity sensors based on 2D COF thin films still have significant shortcomings: First, the detection range is typically limited to 30-80% RH, making it difficult to meet the needs of monitoring extreme environments; second, the sensitivity is generally 1-2 orders of magnitude lower than that of commercial polymer sensors; furthermore, most devices exhibit poor long-term stability. These problems mainly stem from insufficient precision in thin film structure control and uneven distribution of functional groups. Therefore, developing novel COF thin film sensors with wide detection range, high sensitivity, and excellent stability has become a key research focus. Summary of the Invention

[0005] The purpose of this invention is to provide a two-dimensional covalent organic framework (2D COF) humidity sensor, its preparation method, and its application. By selecting strongly polar and electron-withdrawing monomers, an ultra-thin 2D COF film is produced using an aqueous interfacial polymerization method, and the 2D COF humidity sensor is integrated onto a flexible substrate to achieve ultra-high sensitivity, fast response / recovery time, and low hysteresis effect. Ultimately, it can be applied to wearable health monitoring systems, such as real-time respiratory monitoring and abnormal breathing pattern detection (e.g., asthma, sleep apnea).

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention first provides a two-dimensional covalent organic framework humidity sensor, which includes, from bottom to top: a substrate, a 2D COF thin film disposed on the substrate, and gold interdigitated electrodes disposed on the 2D COF thin film;

[0008] The 2D COF film is synthesized through a gas-liquid interface.

[0009] Preferably, the substrate is a PET substrate.

[0010] This invention also provides a method for fabricating a two-dimensional covalent organic framework humidity sensor, comprising:

[0011] Step 1: Inject Sc(OTf)3 aqueous solution into a petri dish to form a gas-liquid interface. Dissolve the first monomer and the second monomer in the solvent respectively, mix them to form a mixed solution, and then spread it on the liquid surface. Utilize Sc(OTf)3 to catalyze the reaction to obtain a 2D-COF film. The first monomer is TPB or TPT, and the second monomer is DHTA or THTA.

[0012] Step 2: Transfer the 2D COF thin film prepared in Step 1 onto the substrate, and deposit gold (Au) interdigitated electrodes on the surface of the thin film through a mask to form a top contact structure, thereby obtaining a two-dimensional covalent organic framework humidity sensor.

[0013] Preferably, the molar ratio of the first monomer to the second monomer is 2:(2-3).

[0014] Preferably, the concentration of Sc(OTf)3 is 1 mM.

[0015] Preferably, the reaction temperature in step one is room temperature, and the reaction time is 24-72 hours.

[0016] Preferably, in step two, the substrate thickness is 500 μm, the 2D COF film thickness is 2-3 nm, the gold (Au) interdigitated electrode thickness is 60 nm, and the channel length is 500 μm.

[0017] The present invention also provides the application of the above-mentioned two-dimensional covalent organic framework humidity sensor in wearable health monitoring systems.

[0018] Beneficial effects of the present invention

[0019] 1) This invention uses TPB or TPT as the first monomer and studies the effect of the material band structure on the humidity sensing performance of COF by changing the central core (triazine / benzene). Using DHTA or THTA as the linker, the pore size and hydrophilicity of COF are precisely controlled by changing the symmetry and hydroxyl density of the linker, thereby optimizing the water adsorption capacity.

[0020] 2) This invention utilizes the confinement effect of the gas-liquid interface to prepare continuous, smooth, and mechanically strong crystalline thin films with nanometer-scale thickness (2-3 nm) and atomic-level surface roughness (<0.5 nm). The characteristics of these films enable them to possess excellent electrode contact properties and current transmission lines, resulting in good performance in electrical testing.

[0021] 3) Ultra-high sensitivity: The sensitivity reaches 66124% (%)RH at a relative humidity of 98%. -1 This is one of the highest values ​​reported among similar sensors to date.

[0022] Ultra-fast response / recovery time: 0.12s (response) / 0.40s (recovery), far exceeding traditional polymer and nanomaterial-based sensors.

[0023] Extremely low hysteresis: only ~1.0% RH, indicating that the adsorption-desorption process is highly reversible and the test results are accurate in real time.

[0024] Wide temperature range stability: Maintains stable performance within the range of 25–75℃, suitable for complex environmental temperature changes.

[0025] Excellent selectivity: It shows no response to common gases in air and respiration, such as carbon dioxide, oxygen, nitrogen, and argon, as well as low-polarity organic molecules like methanol, ethanol, and ether. It can eliminate interference from other gases during respiratory monitoring and adapt to complex environments.

[0026] Wafer-level fabrication: Large-area controllable fabrication of ultrathin, ultrasmooth COF films is achieved through interfacial polymerization. It exhibits excellent processability and perfectly adapts to the integration requirements of devices of different sizes.

[0027] 4) The two-dimensional covalent organic framework humidity sensor of the present invention can be applied in wearable health monitoring systems, specifically: volunteers wear masks equipped with two-dimensional ordered crystalline polymer film humidity sensors, and real-time current monitoring is performed under different exercise states such as walking and running, as well as different pathological conditions, to accurately track respiratory frequency and respiratory intensity in real time during different intensities of exercise.

[0028] 1. Exercise-induced respiratory monitoring (dynamic physiological state)

[0029] Breathing pattern differentiation:

[0030] Mouth breathing: faster response (0.23s response / 0.34s recovery) and carries more water vapor than nasal breathing, resulting in a larger current response value, making it suitable for high-intensity exercise monitoring.

[0031] Nasal breathing: The response is slower (0.51s response / 0.67s recovery), but it precisely matches the resting breathing rate of healthy adults (e.g., 3.41s / breath during walking, approximately 18 breaths / minute).

[0032] Exercise intensity correlation: The respiratory rate increased significantly during running (1.64 seconds / breath, approximately 37 breaths / minute when running with nasal breathing), and the sensor simultaneously captured changes in oral and nasal breathing signals, confirming its dynamic monitoring capability.

[0033] 2. Sleep apnea monitoring (pathological state identification)

[0034] Normal breathing: regular, smooth electrical signal curve.

[0035] Apnea: Characteristic plateau signal (ΔI / I0≤27), lasting ≥10s, consistent with clinical definition.

[0036] Asthma attack: Rapid respiratory signals with an interval of 0.37 seconds (162 breaths / minute ≈ 3Hz), close to the physiological limit, can identify acute bronchospasm. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of a two-dimensional covalent organic framework humidity sensor according to the present invention; in the figure, 1 is the substrate, 2 is the 2D COF thin film, and 3 is the gold interdigitated electrode.

[0038] Figure 2 This is a reaction flow diagram of the 2D COF thin film of the present invention;

[0039] Figure 3 This invention relates to a 2D COF membrane humidity sensing performance testing device; a humidity environment is provided by the evaporation method of saturated salt solution, and the electrical signal is read through a source meter.

[0040] Figure 4 This invention is a 2D COF TPT-THTA Microscopic photographs;

[0041] Figure 5 This invention is a 2D COF TPT-THTA X-ray photoelectron spectroscopy and infrared spectroscopy;

[0042] Figure 6 The current response curve of the 2D COF film humidity sensor of the present invention is shown.

[0043] Figure 7 The response curve of the 2D COF film humidity sensor of this invention;

[0044] Figure 8 This invention is a 2D COF TPT-THTA Sensitivity curve of membrane humidity sensor;

[0045] Figure 9 The above is the response / recovery time curve of the 2D COF film humidity sensor of the present invention;

[0046] Figure 10 This is the cyclic stability curve of the 2D COF film humidity sensor of the present invention;

[0047] Figure 11 This invention is a 2D COF TPT-THTA The membrane's hysteresis, operating temperature, selectivity, and flexible sensing curves;

[0048] Figure 12 This invention is a 2D COF TPT-THTA Application curves for membrane respiration monitoring;

[0049] Figure 13 This invention is a 2D COF TPT-THTA Disease and sleep disorder monitoring curves. Detailed Implementation

[0050] This invention first provides a two-dimensional covalent organic framework humidity sensor, such as... Figure 1 As shown, the sensor comprises, from bottom to top: a substrate 1, a 2D COF thin film 2 disposed on the substrate, and a gold interdigitated electrode 3 disposed on the 2D COF thin film;

[0051] The 2D COF film is synthesized through a gas-liquid interface.

[0052] According to the present invention, the substrate is preferably a PET substrate.

[0053] This invention first provides a method for fabricating a two-dimensional covalent organic framework humidity sensor, comprising:

[0054] Step 1: A Sc(OTf)3 aqueous solution is injected into a petri dish to form a gas-liquid interface. The first and second monomers are dissolved in the solvent and mixed to form a mixed solution, which is then spread on the liquid surface. The reaction is catalyzed by Sc(OTf)3. The preferred reaction temperature is room temperature, and the preferred reaction time is 24-72 hours. The monomer molecules pre-assemble at the interface, followed by a condensation reaction to grow a continuous film. Finally, the film is purified by washing with water / acetone to obtain a 2D COF film. The reaction process is as follows: Figure 2 As shown, the first monomer is 1,3,5-tris(4-aminophenyl)benzene (TPB) or 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TPT), and the second monomer is 2,5-dihydroxyterephthalaldehyde (DHTA) or 2,4,6-tricarboxymethylpyrogallol (THTA); the structure is as follows:

[0055]

[0056] According to the present invention, the molar ratio of the first monomer and the second monomer is 2:(2-3); the concentration of Sc(OTf)3 is 1 mM.

[0057] Step 2: Transfer the 2D COF film prepared in Step 1 onto a substrate, and deposit gold (Au) interdigitated electrodes on the film surface using a mask to form a top contact structure, thus obtaining a two-dimensional covalent organic framework humidity sensor. The substrate is preferably a 2cm × 2cm PET (polyethylene terephthalate) flexible substrate.

[0058] According to the present invention, the substrate thickness is preferably 500 μm, the 2D COF film thickness is preferably 2-3 nm, the gold (Au) interdigitated electrode thickness is preferably 60 μm, and the channel length is 500 μm.

[0059] The present invention also provides the application of the above-mentioned two-dimensional covalent organic framework humidity sensor in wearable health monitoring systems.

[0060] The present invention will be further described in detail below with reference to specific embodiments. All raw materials involved in the embodiments are commercially available.

[0061] Example 1 2D COF TPT-THTA Thin film preparation

[0062] A static gas-liquid interface was formed by injecting 20 mL of scandium trifluoromethanesulfonate [Sc(OTf)3] aqueous solution (1 mM) into a petri dish. 1.4 mg of monomers TPT and 0.8 mg of THTA were dissolved separately in 2 mL of chloroform (both at 2 mM). After removing undissolved monomers, 25 μL of each solution was mixed and spread onto the gas / water interface. Using scandium trifluoromethanesulfonate as a catalyst, the reaction was carried out at room temperature for 3 days to obtain 2DCOF. TPT-THTA Thin film. The film was then repeatedly washed with deionized water and acetone to remove unreacted monomers and catalyst.

[0063] Figure 4 This invention is a 2D COF TPT-THTA The images are microscopic images; Figure a) is an optical microscope image, showing that the film is continuous, smooth, and covers a large area; Figure b) is an atomic force microscope image, showing that the film is thin: 2.3 nm, and the surface roughness is at the atomic level <0.5 nm; Figure c) is a scanning electron microscope image, showing that the film is self-sustaining and can be transferred to different substrates without damage; Figure d) is a transmission electron microscope image, showing that the lattice fringes indicate crystallinity and a regular structure.

[0064] Figure 5 This invention is a 2D COF TPT-THTA X-ray photoelectron spectroscopy and infrared spectrum; in the figure, a) X-ray photoelectron spectroscopy, b) infrared spectrum. Verify the formation of imine bonds (-C=N-), the occurrence of condensation reaction, and explain the chemical composition of COF.

[0065] Example 2 2D COF TPT-DHTA Thin film preparation

[0066] A 20 mL aqueous solution of scandium trifluoromethanesulfonate (1 mM) was injected into a petri dish to form an air-water interface. 1.4 mg of monomer TPT (2 mM) and 1 mg of DHTA (3 mM) were each dissolved in 2 mL of chloroform, then mixed to obtain a mixed solution. After removing undissolved monomers, 50 μL of the mixed solution was spread onto the interface. The reaction was carried out at room temperature for 3 days to obtain 2D COF. TPT-DHTA The membrane was purified by washing with water / acetone.

[0067] Example 3 2D COF TPB-THTA Thin film preparation

[0068] The experimental conditions and procedures were the same as in Example 1, except that 1.4 mg TPB and 0.8 mg THTA monomer (both in 2 mM chloroform solution) were reacted for 3 days under Sc(OTf)3 catalysis to obtain 2D COF. TPB-THTA film.

[0069] Example 4 2D COF TPB-DHTA Thin film preparation

[0070] The experimental conditions and procedures were the same as in Example 1, except that a chloroform solution of 1.4 mg TPB (2 mM) and 1 mg DHTA (3 mM) was spread at the interface of a 1 mM Sc(OTf)3 aqueous solution, and reacted at room temperature for 3 days to obtain 2D COF. TPB-DHTA film.

[0071] Example 5: Fabrication of a two-dimensional covalent organic framework humidity sensor

[0072] Substrate preparation: Before transfer, the device is cleaned and hydrophilized. First, the substrate is ultrasonically cleaned with isopropanol and dried. Then, the substrate is placed in the reaction chamber of a plasma cleaner, and after being evacuated to 0.1-10 Pa, 10-100 sccm of high-purity oxygen is introduced to maintain a working pressure of 10-100 Pa. Next, a 50-500W radio frequency or microwave power supply is turned on to excite the plasma and treat it for 30 seconds to 10 minutes to allow active oxygen species to react with the material surface to generate hydrophilic groups (-OH, -COOH), finally obtaining a superhydrophilic surface (contact angle <10°).

[0073] Masking: The 2D-COF films prepared in Examples 1-4 were transferred onto the substrate, and a patterned mask with a thickness of 0.1 mm was applied to the surface of the 2D COF film on the PET substrate. The film transfer was performed using in-situ horizontal transfer technology at the solution interface to attach the 2D COF film to the device surface.

[0074] Electrode fabrication: A gold (Au) interdigitated electrode with a thickness of 60 nm was deposited by thermal evaporation.

[0075] The four humidity sensors prepared in Example 5 above were tested using the following methods:

[0076] Test environment setup: Place the device in a sealed test chamber, connect a Keithley 2612A source meter for electrical testing, and apply a 3V bias voltage and test current.

[0077] Humidity control: Using saturated aqueous solutions of N2 and different salts (LiCl, CuCl, MgCl2, K2CO3, NaBr, NaCl, KCl, Cu2SO4), the relative humidity was precisely controlled at 25℃ (2%, 11%, 22%, 33%, 43%, 57%, 75%, 85%, 98%), and each was left to stand for three minutes in each suitable environment.

[0078] Figure 6 This is the current response curve of the 2D COF film humidity sensor of the present invention; in the figure, a) is the 2D COF... TPT-THTA b) is 2DCOF TPT-DHTA c) is a 2D COFTPB-THTA ,d) is 2D COF TPB-DHTA As can be seen, the current response ranges from the pA level at low humidity to the μA level at high humidity, and a larger current response value makes the instrument's detection more accurate.

[0079] Figure 7 This is the response curve of the 2D COF film humidity sensor of the present invention; in the figure, a) is the 2D COF... TPT-THTA b) is 2DCOF TPT-DHTA c) is a 2D COF TPB-THTA ,d) is 2D COF TPB-DHTA Among them, 2DCOF TPT-THTA Its sensitivity is highest at 98% RH, reaching 43,000, thanks to the electron-rich structure of the triazine unit in its molecular structure and the abundance of hydrophilic hydroxyl sites on its surface.

[0080] Figure 8 This invention is a 2D COF TPT-THTA The membrane humidity sensor's response curve; in the figure, S1 and S2 are the slopes of the response-relative humidity curves in the low humidity region (2-33% RH) and the high humidity region (33-98% RH), respectively, which represent the sensitivity. In the low humidity region, the sensitivity S1 = 2405%·(%)RH -1 In high humidity areas, the sensitivity S2 reaches as high as 66124% (%) RH. -1 Sensitivity (S) calculation method: = ΔResponse / ΔRH (ΔResponse is the change in response, ΔRH is the change in relative humidity, ΔResponse = (I...) / ΔRH) RH -I0) / I0=ΔI / I0, where I RH These are the current values ​​measured at the corresponding relative humidity. I0 is the current value at the initial (2% RH) humidity, and ΔI is the current change at different humidity levels relative to the initial humidity of 2%.

[0081] Figure 9 This is the response / recovery time curve of the 2D COF film humidity sensor of the present invention; in the figure, a) is the 2D COF... TPT-THTA b) is a 2D COF TPT-DHTA c) is a 2D COF TPB-THTA ,d) is 2D COF TPB-DHTA As can be seen, all membranes exhibit fast response / recovery times. Among them, the 2D COF... TPT-THTA The response / recovery time is 0.12 / 0.40s, thanks to its nanoscale ultrathin and flat membrane structure, which enables rapid adsorption and desorption, as well as good electrode contact.

[0082] Figure 10This is the cyclic stability curve of the 2D COF film humidity sensor of the present invention; in the figure, a) is the 2D COF... TPT-THTA b) is a 2D COF TPT-DHTA c) is a 2D COF TPB-THTA ,d) is 2D COF TPB-DHTA As can be seen, all membranes maintained the same initial response after 100 cycles of testing, without significant attenuation, demonstrating their good stability.

[0083] Figure 11 This invention is a 2D COF TPT-THTA The membrane exhibits hysteresis, operating temperature, selectivity, and flexibility sensing curves. Figure a) shows the hysteresis curve, indicating a maximum hysteresis error of only 1% RH within the 2-98% RH range. b) shows the operating temperature curve, demonstrating good linearity within the 25-75℃ range. c) shows the selectivity curve, indicating no response to common gases in the atmosphere and respiration, as well as low-polarity volatile organic molecules, demonstrating good selectivity. d) shows the flexibility curve, indicating good linearity under bending conditions from 0-300°, exhibiting good flexibility. These advantages enable it to adapt to complex external environments and better suit its application in wearable respiratory monitoring devices.

[0084] By having volunteers wear masks equipped with 2D COF humidity sensors and monitor their breathing rate and intensity in real time under different conditions such as walking and running, it is possible to achieve accurate real-time monitoring of breathing rate and intensity under different exercise intensities. Figure 12 The present invention is 2DCOF TPT-THTA Application curves of membrane respiration monitoring; in the figure, a) is 2D COF TPT-THTA The response and recovery time curves of the humidity sensor for nasal and oral breathing (nasal breathing: 0.51s response / 0.67s recovery; oral breathing: (0.23s response / 0.34s recovery)), b) is the 2D COF TPT-THTA The humidity sensor displays real-time monitoring curves of nasal and oral respiration under different exercise intensities during walking and running. Regarding respiration intensity, mouth breathing carries more water vapor than nasal breathing, resulting in a higher current response value. In terms of frequency, breathing speed increases during running, leading to shorter respiration intervals compared to walking (nasal breathing: 3.41 s / breath, approximately 18 breaths / minute during walking; 1.64 s / breath, approximately 37 breaths / minute during running; mouth breathing: 3.20 s / breath, approximately 19 breaths / minute during walking; 1.44 s / breath, approximately 42 breaths / minute during running).

[0085] Figure 13 This invention is a 2D COF TPT-THTAMonitoring curves for diseases and sleep disorders; in the figure, the respiratory interval is 3.48s in a healthy state, and 0.37s in an asthmatic state with rapid and short breathing. During sleep, if no signal is detected for more than 10 seconds, it indicates the presence of apnea and a sudden drop in respiratory intensity during a state of asphyxia.

Claims

1. A two-dimensional covalent organic framework humidity sensor, characterized in that, The sensor comprises, from bottom to top, a substrate, a 2D COF film arranged on the substrate, and a gold interdigital electrode arranged on the 2D COF film. The 2D COF film is obtained by gas-liquid interface synthesis.

2. The two-dimensional covalent organic framework humidity sensor of claim 1, wherein, The substrate is a PET substrate.

3. The method of claim 1, wherein the method further comprises: The application further discloses a preparation method of the two-dimensional covalent organic framework humidity sensor. Step one: injecting Sc(OTf)3 aqueous solution into a culture dish to form a gas-liquid interface, dissolving a first monomer and a second monomer in a solvent respectively, mixing to form a mixed solution, spreading on the liquid surface, and using Sc(OTf)3 to catalyze the reaction to obtain a 2D-COF film; the first monomer is TPB or TPT, and the second monomer is DHTA or THTA; Step two: transferring the 2D COF film obtained in step one to a substrate, depositing a gold interdigital electrode on the surface of the film through a mask plate to form a top contact structure, and obtaining the two-dimensional covalent organic framework humidity sensor.

4. The method of claim 3, wherein the method further comprises: The molar ratio of the first monomer to the second monomer is 2:(2-3).

5. The method of claim 3, wherein the method further comprises: The concentration of Sc(OTf)3 is 1 mM.

6. The method of claim 3, wherein the method further comprises: The reaction temperature in step one is room temperature, and the reaction time is 24-72 h.

7. The method of claim 3, wherein the method further comprises: In step two, the thickness of the substrate is 500 μm, the thickness of the 2D COF film is 2-3 nm, the thickness of the gold (Au) interdigital electrode is 60 nm, and the channel length is 500 μm.

8. Application of the two-dimensional covalent organic framework humidity sensor in a wearable health monitoring system.

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