Three-dimensional modified polyvinyl alcohol hydrogel and preparation method and application thereof

Abstract

The present application relates to a kind of three-dimensional modified polyvinyl alcohol hydrogel and its preparation method and application, it is related to evaporation material technical field, it is to few layer FLG and alpha type Bi2O3 Doped in polyvinyl alcohol hydrogel, and Ppy vapor deposition is carried out on the surface of hydrogel, and three-dimensional modified polyvinyl alcohol hydrogel 3D-PVA@Bi2O3-FLG / Ppy PEMs is obtained.The evaporation rate of material prepared by the method reaches 4.03kg / (m 2 ·h) after final optimization, while in the evaporation experiment of simulating the north sea water polluted by methylene blue dye, it shows the stable evaporation rate of 3.06kg / (m 2 ·h), and the degradation effect of pollutant in evaporated water reaches 81% in light experiment, the material prepared by the method not only has high evaporation rate in seawater desalination application, but also shows great potential and application prospect in treating seawater polluted by organic dye.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of evaporative materials, in particular to a three-dimensional modified polyvinyl alcohol hydrogel and a preparation method and application thereof. BACKGROUND

[0002] Solar seawater desalination has the advantages of not consuming conventional energy, not producing secondary pollution, and low operation cost. As a high evaporation efficiency method of locally heating the gas-liquid interface, interfacial evaporation has become a research hotspot in the field of seawater desalination. Unlike the overall heating and bottom heating of traditional solar stills, the interfacial evaporation technology limits the photo-thermal material to the air-water interface, which not only reduces heat loss and improves the utilization rate of solar energy, but also increases the surface area of seawater evaporation. In the interfacial evaporation system of solar seawater desalination, photo-thermal conversion materials are the key to achieving high-efficiency photo-thermal conversion. The heat generated by the materials is used to drive the generation of steam. The stronger the light absorption capacity of the materials, the more basic energy for photo-thermal conversion.

[0003] Solar interfacial evaporation materials can be classified into two different categories, namely carbon-based materials and plasmonic-based absorbers. Common carbon-based photo-thermal materials include carbon black, graphite, graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, and activated carbon, etc. Although existing evaporation materials exhibit excellent freshwater production rate and photo-thermal conversion efficiency, for the multi-component seawater contaminated by various organic matters, organic pollutants will be adsorbed on the surface of the evaporation material during the evaporation process, affecting the freshwater production rate and photo-thermal conversion efficiency, which also brings new challenges to the solar-driven interfacial evaporator. Although some scholars have gradually applied photocatalytic materials to interfacial evaporation, the photocatalytic effect is sacrificed while the evaporation rate is maintained. The pollutants remaining in the evaporated water cannot be removed after the generation of steam, and there is a lack of interfacial evaporation materials that can simultaneously achieve high evaporation rate and effective degradation of organic pollutants.

[0004] Therefore, for a freshwater production device for organic solvent and dye water, it should include the following two parts. On the one hand, it has excellent interfacial evaporation, by which clean water can be produced from undrinkable water. On the other hand, it has excellent pollutant treatment capacity, by which the remaining pollutants (dyes and organic solvents) in the contaminated water can be removed. SUMMARY

[0005] The purpose of the present application is to provide a three-dimensional modified polyvinyl alcohol hydrogel with high evaporation rate and effective degradation of organic pollutants to solve the above problems.

[0006] The first aspect of the present application provides a preparation method of a three-dimensional modified polyvinyl alcohol hydrogel, which is to dope few-layer graphene (FLG) and alpha-type Bi2O3 in a polyvinyl alcohol hydrogel, and perform Ppy vapor deposition on the surface of the hydrogel to obtain a three-dimensional modified polyvinyl alcohol hydrogel 3D-PVA@Bi2O3-FLG / Ppy PEMs, comprising the following steps:

[0007] S1, preparing PVA@Bi2O3: taking a proper amount of polyvinyl alcohol to prepare a polyvinyl alcohol solution, weighing a proper amount of Bi2O3 and adding it into the polyvinyl alcohol solution, stirring to uniformly disperse the Bi2O3 in the polyvinyl alcohol solution, and obtaining a PVA@Bi2O3 solution;

[0008] S2, preparing 3D-PVA@Bi2O3-FLG PEMs: dissolving FLG in water, stirring uniformly, then adding the PVA@Bi2O3 solution obtained in S1, stirring, then adding a crosslinking agent and water, stirring again, then pouring into a mold, placing the mold in a frozen environment, taking it out after freezing, repeating freezing and thawing, soaking it in water after thawing, finally washing with pure water to remove the surface unreacted chemicals, and obtaining 3D-PVA@Bi2O3-FLG PEMs, wherein the crosslinking agent is obtained by stirring a glutaraldehyde solution, a methanol solution and an acetic acid solution, then adding sulfuric acid and diluting again;

[0009] S3, preparing 3D-PVA@Bi2O3-FLG / Ppy PEMs: performing a polypyrrole Ppy surface polymerization reaction on the 3D-PVA@Bi2O3-FLG PEMs obtained in S2 by using a chemical vapor deposition technology, washing the surface residues with water after the reaction is completed, and drying to obtain 3D-PVA@Bi2O3-FLG / Ppy PEMs.

[0010] By using the above technical solution, polyvinyl alcohol is used as a raw material, Bi2O3 with good photocatalytic effect is added as a photocatalyst, and graphene material with good light-heat conversion performance is added, and a three-dimensional modified polyvinyl alcohol carbon-based light-heat evaporation material with high evaporation rate and effective degradation of organic pollutants is prepared by in-situ polymerization, repeated freezing, film setting and chemical deposition, etc. Due to the doping of hydrophobic materials graphene and bismuth oxide, the network structure in the PVA hydrogel is crosslinked, which creates rich adsorption sites for organic pollutants and creates conditions for subsequent photocatalysis. In the evaporation process, the porous outer surface network structure is beneficial to the diffuse reflection of light, enhances the light absorption performance of the material and improves the energy utilization rate, and realizes the high evaporation performance of the material.

[0011] Preferably, the preparation method comprises the following steps:

[0012] S1, preparing PVA@Bi2O3: a certain amount of polyvinyl alcohol was dissolved in water under stirring to obtain a 0.1 g / mL polyvinyl alcohol solution, and a certain amount of Bi2O3 was weighed and added into the polyvinyl alcohol solution, the addition amount of Bi2O3 and the addition amount of polyvinyl alcohol being 1: (0.5-1.5), the Bi2O3 was uniformly dispersed in the polyvinyl alcohol solution under stirring to obtain a PVA@Bi2O3 solution;

[0013] S2, preparing 3D-PVA@Bi2O3-FLG PEMs: 0.04-0.1 g of FLG was dissolved in 4-10 mL of water under stirring for 1 h to obtain a uniform solution, then 6-12 mL of the PVA@Bi2O3 solution obtained in S1 was taken, the FLG uniform solution was added into the PVA@Bi2O3 solution, 0.6-1.2 mL of a crosslinking agent and 4.6-2.4 mL of water were added after stirring at room temperature for 1 h, the solution was stirred for 1 h again, then poured into a mold, the mold was placed in a frozen environment at -20℃-(-40℃) for 8-12 h, then taken out and thawed at room temperature for 2-4 h, and the freezing and thawing were repeated for 4-6 times, then the product was soaked in water for 24-48 h, the water was changed every 12 h during the soaking, and finally the product was washed with pure water to remove the unreacted chemicals on the surface to obtain 3D-PVA@Bi2O3-FLG PEMs; the crosslinking agent was prepared as follows: a glutaraldehyde solution, a methanol solution and an acetic acid solution were mixed according to a mass ratio of 2: (4-6) : (4-6), a sulfuric acid solution was added after stirring uniformly, the mass ratio of the sulfuric acid solution to the glutaraldehyde solution was (0.8-1.4) : 2, water 40-60 mL was added after the solution was completely reacted to yellow-brown to dilute and stir uniformly to obtain a light yellow crosslinking agent;

[0014] S3, preparing 3D-PVA@Bi2O3-FLG / Ppy PEMs: the 3D-PVA@Bi2O3-FLG PEMs obtained in S2 were subjected to a surface polymerization reaction of polypyrrole Ppy by using a chemical vapor deposition technology, the product was washed with water after the reaction to remove the residues on the surface, and then dried to obtain 3D-PVA@Bi2O3-FLG / Ppy PEMs.

[0015] Preferably, in the above preparation method technical solution, the step S1 is specifically as follows: S1, preparing PVA@Bi2O3: 1 g of polyvinyl alcohol was added into 10 mL of water, and the polyvinyl alcohol was dissolved completely under magnetic stirring at 90℃ for 2 h to obtain a 0.1 g / mL polyvinyl alcohol solution, and 1 g of Bi2O3 was weighed and added into the polyvinyl alcohol solution under continuous stirring to uniformly disperse the Bi2O3 in the polyvinyl alcohol solution to obtain a PVA@Bi2O3 solution; in the step S2, the inner cavity of the mold is a plurality of cylindrical chambers, and the height of the cylindrical chambers is 2 cm and the diameter is 0.6 cm.

[0016] Preferably, in the above technical scheme of the preparation method, the preparation method of the crosslinking agent in step S2 is: adding 2 mL of glutaraldehyde solution, 5 mL of methanol solution and 5 mL of acetic acid solution into a beaker, stirring uniformly, then slowly stirring while adding 1 mL of sulfuric acid solution, and then adding 50 mL of water into the beaker after the solution is completely reacted to yellow-brown, and stirring uniformly to obtain a light yellow crosslinking agent.

[0017] Preferably, in the above technical scheme of the preparation method, step S2 is specifically: S2, preparing 3D-PVA@Bi2O3-FLG PEMs: dissolving 0.05 g of FLG in 5 mL of water, stirring at room temperature for 1 h to obtain a uniform solution, adding the PVA@Bi2O3 solution obtained in S1, stirring at room temperature for 1 h, then adding 1 mL of the crosslinking agent and 2 mL of water, stirring again for 1 h, then pouring into a mold, placing the mold in a-20℃ freezing environment for 10 h, taking out and thawing at room temperature for 3 h, repeating the freezing and thawing for 5 times, immersing in deionized water for 24 h after thawing, replacing the water every 12 h, and finally washing in pure water for 5 min to remove the surface unreacted chemicals, to obtain 3D-PVA@Bi2O3-FLG PEMs.

[0018] Preferably, in the above technical scheme of the preparation method, step S3 is specifically: S3, preparing 3D-PVA@Bi2O3-FLG / Ppy PEMs: preparing a large beaker, placing the 3D-PVA@Bi2O3-FLG PEMs obtained in S2 in the beaker, and placing a culture dish in the beaker, dropping 70-100 μl of py into the culture dish, placing the beaker in a 50-70℃ vacuum drying oven for 1-2 h to complete the chemical vapor deposition of polypyrrole, and then washing the surface unreacted py in pure water and drying to obtain 3D-PVA@Bi2O3-FLG / Ppy PEMs.

[0019] Preferably, in the above technical scheme of the preparation method, step S3 is specifically: S3, preparing 3D-PVA@Bi2O3-FLG / Ppy PEMs: preparing a large beaker, placing the 3D-PVA@Bi2O3-FLG PEMs obtained in S2 in the beaker, and placing a culture dish in the beaker, dropping 80 μl of py into the culture dish, placing the beaker in a 60℃ vacuum drying oven for 1 h to complete the chemical vapor deposition of polypyrrole, and then placing in pure water for 5 min to remove the surface unreacted py, and drying to obtain 3D-PVA@Bi2O3-FLG / Ppy PEMs.

[0020] By adopting the technical solutions, the specific steps of the preparation method and the shape and structure of the mold are optimized to improve the evaporation rate of the three-dimensional modified polyvinyl alcohol hydrogel and the efficiency of degrading organic pollutants.

[0021] The second aspect of the present application provides a three-dimensional modified polyvinyl alcohol hydrogel prepared by any one of the preparation methods described above.

[0022] The third aspect of the present application provides the application of the three-dimensional modified polyvinyl alcohol hydrogel described above in seawater desalination and sewage treatment.

[0023] In the application technical solution described above, the three-dimensional modified polyvinyl alcohol hydrogel is placed in the water to be treated and is placed under sunlight, so that it floats on the water surface, the bottom end of the three-dimensional modified polyvinyl alcohol hydrogel is placed below the water surface, and the top end is located above the water surface and is used to receive heat of sunlight and evaporate water.

[0024] In summary, the present application includes at least one of the following beneficial technical effects:

[0025] 1. The 3D-PVA@Bi2O3-FLG / Ppy PEMs have obvious layered mesh structure inside, and due to the doping of hydrophobic materials graphene and bismuth oxide, the cross-linking of the network structure in the PVA hydrogel is facilitated, which also creates abundant adsorption sites for organic pollutants and creates conditions for subsequent photocatalysis. In the evaporation process, the porous outer surface mesh structure is beneficial to diffuse reflection of light, enhances the light absorption performance of the material and thus improves the energy utilization rate, and realizes high evaporation performance of the material.

[0026] 2. The 3D-PVA@Bi2O3-FLG / Ppy PEMs have superior light absorption and heat conversion capacity. Under one sunlight, the surface temperature rises rapidly from room temperature to 38-39℃ within 20 minutes, and after one hour of irradiation, the surface temperature of the material finally fluctuates at about 42℃. Under one standard sunlight, the surface temperature of the material is 315k (41.85℃) when the material reaches the best evaporation rate. Therefore, the 3D-PVA@Bi2O3-FLG / Ppy PEMs not only have excellent water absorption performance, but also have excellent light-heat conversion capacity, so that the 3D-PVA@Bi2O3-FLG / Ppy PEMs become an ideal choice for interfacial evaporation.

[0027] 3. In the wavelength region of 200-2500nm of the solar spectrum, the light absorption rate of the unmodified PVA is concentrated in about 5% at a wavelength of 400-1400nm and about 30% at a wavelength of 1400-2400nm, while the light-heat conversion material after modification has an absorption rate of about 70%-80% in almost the whole wavelength region, which indicates that the material has obvious light absorption advantage.

[0028] 4. The evaporation rate of pure water under standard sunlight for one hour is stable at 0.3 kg / m 2 ·h, which is about 4.6 times that of pure water. The evaporation rate of the optimized cylindrical model under the same conditions increased to 3.12 kg / m 2 ·h, which is about 4.6 times that of pure water. The evaporation rate of the optimized cylindrical model under the same conditions increased to 3.12 kg / m 2 ·h, which is about 4.6 times that of pure water. The evaporation rate of the optimized cylindrical model under the same conditions increased to 3.12 kg / m 2 ·h, which is about 4.6 times that of pure water. The evaporation rate of the optimized cylindrical model under the same conditions increased to 3.12 kg / m 2 ·h, which is about 4.6 times that of pure water. The evaporation rate of the optimized cylindrical model under the same conditions increased to 3.12 kg / m 2 ·h, which is about 4.6 times that of pure water. The evaporation rate of the optimized cylindrical model under the same conditions increased to 3.12 kg / m

[0029] 5. Under the condition of 8 ng / L of water body pollutant concentration, the photocatalytic experiment was carried out for 6 hours, and the methylene blue concentration of the evaporated water sample was detected at different time intervals. It can be observed that the photocatalytic effect is obvious in the first 4 hours, and the removal rate is about 15% per hour. The removal rate reached 81% at the sixth hour. It can be seen that the material has obvious effect in the field of photocatalytic degradation and excellent durability. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 (a) is a comparison chart of the evaporation rates of pure water and PVA@Bi2O3-FLG / Ppy evaporation materials with different shapes, (b) is the relative deformation of the model after COMSOL simulation optimization, (c) is the comparison chart of the evaporation rates of PVA@Bi2O3-FLG / Ppy 3D-PEMs under different concentrations of C 16 H 18 ClN3S under one hour of sunlight, (d) is a comparison chart of the removal rates of C 16 H 18 ClN3S under one hour of sunlight, (d) is a comparison chart of the removal rates of C

[0031] Figure 2are the comparison diagrams of various data of 3D-PVA@Bi2O3-FLG / Ppy PEMs before and after optimization in this application by COMSOL simulation and optimization, (a) and (a') are the surface irradiance before and after optimization, respectively, (b) and (b') are the isothermal surface before and after optimization, respectively, (c) and (c') are the water vapor transpiration velocity of the section before and after optimization, respectively, (d) and (d') are the relative humidity before and after optimization, respectively, (e) and (e') are the surface pressure before and after optimization, respectively, (f) and (f') are the total water vapor flux before and after optimization, respectively;

[0032] Figure 3 (a-c) are SEM images of PVA, (d-f) are SEM images of 3D-PVA@Bi2O3-FLG / Ppy PEMs, (g-h) are contact angle images of PVA, (i-j) are contact angle images of 3D-PVA@Bi2O3-FLG / Ppy PEMs;

[0033] Figure 4 (a-a') and (b-b') are infrared thermal imaging change diagrams of pure water and 3D-PVA@Bi2O3-FLG / Ppy PEMs under one sunlight for 1 hour, respectively, (c) is a corresponding temperature point line diagram, (d) is the temperature of the surface of 3D-PVA@Bi2O3-FLG / Ppy PEMs under COMSOL simulation and optimization;

[0034] Figure 5 (a) is the XRD diagram of PVA and 3D-PVA@Bi2O3-FLG / Ppy PEMs, (b) is the FT-IR spectrum diagram of 3D-PVA@Bi2O3-FLG / Ppy PEMs, (c) is the XPS energy spectrum diagram of PVA and 3D-PVA@Bi2O3-FLG / Ppy PEMs, (d) is the Bi 4f energy spectrum diagram, (e) is the O1s energy spectrum diagram, (f) is the N1s energy spectrum diagram, (g) is the UV-vis absorption spectrum diagram of PVA and 3D-PVA@Bi2O3-FLG / Ppy PEMs, (h) is the UV-vis reflection spectrum diagram of PVA and 3D-PVA@Bi2O3-FLG / Ppy PEMs;

[0035] Figure 6 is the comparison diagram of the evaporation rate of the four PVA hydrogels two-dimensional plane prepared in Example 4 and Comparative Examples 1-3 of this application. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments and drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art can make modifications or equivalent substitutions based on their understanding of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention, and all should be included in the protection scope of the present invention.

[0037] The reagents used in the following examples are as follows: polyvinyl alcohol 1799 (PVA, alcoholysis degree: 98-99% (mol / mol)), bismuth oxide (Bi2O3, ≥99.9%), methylene blue (C 16 H 18 ClN3S, ≥95%) and pyrrole (C4H5N, ≥99%, abbreviated as py) were provided by Shanghai Yien Chemical Technology Co., Ltd.; glutaraldehyde (C5H8O2, 25-28%) and acetic acid (CH3COOH, ≥99.5%) were provided by Xilong Science Co., Ltd.; methanol (CH4O, ≥99.9%) was provided by MacLean Chemical Reagent Co., Ltd.; sulfuric acid (H2SO4, 95-98%) was provided by Chengdu Kelong Chemical Co., Ltd.; few-layer graphene (Few layers graphene, physical method, thickness: 1.0-1.77 nm, sheet diameter: 10-50 μm, number of layers: 1-5, purity >90%, abbreviated as FLG) was provided by Suzhou Carbon Graphene Technology Co., Ltd. The selected seawater was obtained from the adjacent seawater of Beihai, Guangxi Zhuang Autonomous Region in August, with an average salinity of approximately 2.8 wt%; all chemicals were used as received without further purification, and deionized water was used in all experiments.

[0038] The information of instruments and equipment is as follows: field emission scanning electron microscope (FESEM, Hitachi Regulus8100, Japan), X-ray diffractometer (XRD, Bruker D8 Venture, Germany), X-ray photoelectron spectrometer (XPS, ThermoScientific K-Alpha, USA), ultraviolet / visible / near-infrared diffuse reflectance tester (UV-vis-NIR, PerkinElmer Lambda950, USA), Fourier transform infrared spectrometer (FTIR, Thermo Fisher Scientific NicoletiS5, USA), optical contact angle meter (JC2000C1), and infrared thermal imager (Hikmicro H10).

[0039] The 3D-PVA@Bi2O3-FLG / Ppy PEMs prepared in the present application are three-dimensional modified polyvinyl alcohol hydrogel materials, and the full English name is Three dimensions-polyvinyl alcohol Bi2O3 Few layers graphene Ppy Photothermal evaporation of materials.

[0040] Other specific conditions not specified are carried out according to conventional conditions or manufacturer's recommended conditions, and the reagents or instruments used without specifying the manufacturer are conventional products that can be purchased on the market.

[0041] I. Examples

[0042] Example 1

[0043] A preparation method of a three-dimensional modified polyvinyl alcohol hydrogel, comprising the following steps:

[0044] S1, preparing PVA@Bi2O3: 1g of polyvinyl alcohol is added to 10mL of water, and after being fully dissolved under magnetic stirring at 90℃ for 2h, 0.1g / mL of polyvinyl alcohol solution is obtained. 1g of Bi2O3 is weighed and added to the polyvinyl alcohol solution while stirring to make Bi2O3 uniformly dispersed in the polyvinyl alcohol solution, obtaining a PVA@Bi2O3 solution.

[0045] S2, preparing 3D-PVA@Bi2O3-FLG PEMs: 0.05g of FLG is dissolved in 5mL of water, and stirred at room temperature for 1h to obtain a uniform solution. The PVA@Bi2O3 solution obtained in S1 is added, and stirred at room temperature for 1h. Then 1mL of crosslinking agent and 2mL of water are added, and stirred again for 1h. Then pour into a mold, and freeze the mold in a-20℃ freezing environment for 10h. Then take out and thaw at room temperature for 3h, and repeat the freezing and thawing for 5 times. After thawing, immerse it in deionized water for 24h, and change the water every 12h. Finally, wash it in pure water for 5min to remove the surface unreacted chemicals, obtaining 3D-PVA@Bi2O3-FLG PEMs.

[0046] The configuration method of the crosslinking agent is as follows: add 2mL of glutaraldehyde solution, 5mL of methanol solution and 5mL of acetic acid solution into a beaker, and stir well. Then continue to slowly stir while adding 1mL of sulfuric acid solution. After the solution is completely reacted to yellow-brown, add 50mL of water into the beaker to dilute, and stir well to obtain a light yellow crosslinking agent.

[0047] The inner cavity of the mold is a plurality of cylindrical chambers, the height of the cylindrical chamber is 2 cm, the diameter is 0.6 cm, and the upper 0.5 cm area of the cylindrical chamber is a conical shape with the same bottom and height, and the diameter of the middle part of the cylindrical chamber is smaller than that of the two ends.

[0048] S3, preparation of 3D-PVA@Bi2O3-FLG / Ppy PEMs: prepare a large beaker, place the 3D-PVA@Bi2O3-FLG PEMs obtained in S2 in the beaker, and place a culture dish in the beaker, drop 80 μl of py into the culture dish, place the beaker in a 60℃ vacuum drying oven and dry for 1h, complete the chemical vapor deposition of polypyrrole, after the reaction is completed, place it in pure water for 5min to remove the surface unreacted py, and dry to obtain 3D-PVA@Bi2O3-FLG / Ppy PEMs.

[0049] Example 2

[0050] A method for preparing a three-dimensional modified polyvinyl alcohol hydrogel, comprising the following steps:

[0051] S1, preparation of PVA@Bi2O3: 1g of polyvinyl alcohol is added to 10mL of water, and after being fully dissolved under magnetic stirring at 90℃ for 2h, 0.1g / mL of polyvinyl alcohol solution is obtained, 0.5g of Bi2O3 is weighed and added to the polyvinyl alcohol solution while stirring to make Bi2O3 uniformly dispersed in the polyvinyl alcohol solution, and PVA@Bi2O3 solution is obtained.

[0052] S2, preparation of 3D-PVA@Bi2O3-FLG PEMs: 0.04g of FLG is dissolved in 4mL of water, and stirred at room temperature for 1h to obtain a uniform solution, then 6ml of PVA@Bi2O3 solution obtained in S1 is taken, the FLG uniform solution is added to the PVA@Bi2O3 solution, and stirred at room temperature for 1h, then 0.6mL of crosslinking agent and 1.6mL of water are added, and stirred again for 1h, then poured into a mold, the mold is placed in a-40℃ freezing environment for 8h, then taken out and thawed at room temperature for 2h, and then repeated freezing and thawing for 5 times, after thawing, it is soaked in deionized water for 24h, and the water is changed every 12h, finally washed with pure water for 5min to remove the surface unreacted chemicals, and 3D-PVA@Bi2O3-FLG PEMs are obtained.

[0053] The configuration method of the crosslinking agent is as follows: 2mL of glutaraldehyde solution, 4mL of methanol solution and 4mL of acetic acid solution are added to a beaker, stirred uniformly, then slowly stirred while adding 0.8mL of sulfuric acid solution, after the solution is completely reacted to yellow brown, 40mL of water is added to the beaker for dilution, and the crosslinking agent is obtained after stirring uniformly.

[0054] The inner cavity of the mold is a plurality of cylindrical chambers, the height of the cylindrical chamber is 2cm, the diameter is 0.6cm, and the 0.5cm area at the upper part of the cylindrical chamber is a conical shape with the same bottom and height.

[0055] S3, preparation of 3D-PVA@Bi2O3-FLG / Ppy PEMs: prepare a large beaker, place the 3D-PVA@Bi2O3-FLG PEMs obtained in S2 in the beaker, and put a petri dish in the beaker, drop 70μl of py into the petri dish, place the beaker in a 50℃ vacuum drying oven and dry for 2h, complete the chemical vapor deposition of polypyrrole, after the reaction is completed, place it in pure water for 5min to remove the surface unreacted py, and dry to obtain 3D-PVA@Bi2O3-FLG / Ppy PEMs.

[0056] Example 3

[0057] A method for preparing a three-dimensional modified polyvinyl alcohol hydrogel, comprising the following steps:

[0058] S1, preparation of PVA@Bi2O3: 1g of polyvinyl alcohol is added to 10mL of water, and after being fully dissolved under magnetic stirring at 90℃ for 2h, a 0.1g / mL polyvinyl alcohol solution is obtained, 1.5g of Bi2O3 is weighed and added to the polyvinyl alcohol solution while stirring to make the Bi2O3 uniformly dispersed in the polyvinyl alcohol solution, and a PVA@Bi2O3 solution is obtained.

[0059] S2, preparation of 3D-PVA@Bi2O3-FLG PEMs: 0.1g of FLG is dissolved in 10mL of water, and stirred at room temperature for 1h to obtain a uniform solution, then 12ml of PVA@Bi2O3 solution obtained in S1 is taken, the FLG uniform solution is added to the PVA@Bi2O3 solution, and stirred at room temperature for 1h, then 1.2mL of crosslinking agent and 2.4mL of water are added, stirred again for 1h, then poured into a mold, the mold is placed in a-30℃ freezing environment for 12h, then taken out and thawed at room temperature for 4h, then repeated freezing and thawing for 5 times, after thawing, it is soaked in deionized water for 48h, and the water is changed every 12h, finally washed with pure water for 5min to remove the surface unreacted chemicals, and 3D-PVA@Bi2O3-FLG PEMs are obtained.

[0060] The configuration method of the crosslinking agent is as follows: 2mL of glutaraldehyde solution, 6mL of methanol solution and 6mL of acetic acid solution are added to a beaker, stirred uniformly, then slowly stirred while adding 1.4mL of sulfuric acid solution, after the solution is completely reacted to yellow brown, 50mL of water is added to the beaker for dilution, stirred uniformly to obtain a light yellow crosslinking agent.

[0061] The inner cavity of the mold is a plurality of cylindrical chambers, the height of the cylindrical chamber is 2cm, the diameter is 0.6cm.

[0062] S3, preparation of 3D-PVA@Bi2O3-FLG / Ppy PEMs: prepare a large beaker, place the 3D-PVA@Bi2O3-FLG PEMs obtained in S2 in the beaker, and place a culture dish in the beaker, and drop 100 μl of py into the culture dish, place the beaker in a 70°C vacuum drying oven and dry for 1 h, complete the gas-phase chemical deposition of polypyrrole, after the reaction is completed, place it in pure water for 5 min to remove the surface undeposited py, and then dry to obtain 3D-PVA@Bi2O3-FLG / Ppy PEMs.

[0063] Example 4

[0064] The difference from Example 1 is that the inner cavity of the mold presents a flat shape.

[0065] Example 4

[0066] Comparative Example 1

[0067] The difference from Example 4 is that "0.05 g graphene (FLG)" in S2 is changed to "0.1 g carbon nanotubes (CNTs)", and the remaining steps are the same, and finally PVA-CNTs hydrogel is obtained.

[0068] Comparative Example 2

[0069] The difference from Example 4 is that "0.05 g graphene (FLG)" in S2 is changed to "0.025 g graphene oxide (rGO)", and the remaining steps are the same, and finally PVA-rGO hydrogel is obtained.

[0070] Comparative Example 3

[0071] The difference from Example 4 is that "0.05 g graphene (FLG)" in S2 is changed to "0.5 g titanium dioxide (TiO2)", and the remaining steps are the same, and finally PVA-TiO2 hydrogel is obtained.

[0072] Three, performance detection experiment

[0073] 1. Solar-driven interfacial evaporation performance test and photocatalytic ability test

[0074] 1.1 Solar-driven interfacial evaporation performance test

[0075] During the interfacial evaporation process, the device is mainly composed of three-dimensional modified polyvinyl alcohol carbon-based photothermal material and EVA foam cotton. A beaker is prepared, and the water to be treated is poured into the beaker. The three-dimensional modified polyvinyl alcohol hydrogel is placed in the water to be treated and placed under sunlight so that it floats on the water surface. The bottom end of the three-dimensional modified polyvinyl alcohol hydrogel is placed below the water surface, and the top end is located above the water surface and is used to receive sunlight for heating and evaporate water. Foam cotton is placed around the material for heat insulation and to give the photothermal material the ability to self-float. The interfacial evaporation experiment is carried out in a laboratory environment with a temperature of 25-30°C and a humidity of 40%.

[0076] A solar simulator (TRM-PD) was used to simulate sunlight, and a meteorological and ecological environment monitor (PC-WX4) was used to record the light intensity. During the evaporation process, a high-precision 1 / 10,000th electronic balance was used to record the mass change of the water during evaporation, and an infrared thermal imager was used to monitor the temperature change on the surface of the photothermal material during the interfacial evaporation process. Finally, the evaporation rate was calculated using formula (1).

[0077]

[0078] Where V is the evaporation rate (kg / m 2 ·h); △m is the change in water mass before and after evaporation (kg); s is the evaporation area (m 2 );t is the evaporation time (h).

[0079] The three-dimensional modified polyvinyl alcohol carbon-based photothermal materials in the experiment were 3D-PVA@Bi2O3-FLG / Ppy PEMs prepared in Examples 1-4. Figure 1 a summarizes the optimal evaporation rate under various shapes. As can be seen from the figure, the evaporation rate of pure water after one hour of exposure to standard sunlight is stable at 0.3 kg / m 2 h, the evaporation rate of the PVA@Bi2O3-FLG / Ppy two-dimensional planar material (Example 4) increased to 1.41 kg / m after one hour under the same conditions. 2 ·h, which is about 4.6 times that of pure water, indicating that the photothermal materials and photothermal coatings are effective.

[0080] The same material was further made into a three-dimensional column by freeze demolding (Example 3), in which the height and diameter of the rising cylinder were 2 cm and 0.6 cm respectively, taking into account the water absorption height and material stability of the material. The cylinders were evenly distributed from the center of the plane on a known plane size, ensuring that the columnar material received more sunlight without affecting the escape of water vapor. The final optimized columnar model under the same conditions increased the evaporation rate to 3.12 kg / m 2 h, which is 2.2 times higher than that of two-dimensional planar materials, and Figure 1As can be seen in a, the evaporation rate of the material rises obviously within 0-40 min, indicating that this shape and arrangement is conducive to the heat absorption and evaporation of the material.

[0081] Further changing the cylindrical upper part of 0.5 cm into a conical shape with the same base and height, the evaporation rate of the material rises by 0.1 kg / m 2 ·h again. 2 ·h.

[0082] Finally, the data of the improved three-dimensional material are introduced into the COMSOL software for simulation. Under the same conditions, the shape of the material is simulated and optimized. After 188 iterations, the final optimized shape is shown in 1b, in which the red to blue transition represents the relative change in shape. It can be observed that the change is mainly concentrated in the middle part of the cylinder, which is reduced in diameter and becomes a column with thick upper and lower parts and thin middle part, which is more conducive to heat entering and water vapor transmission. The specific data of the optimized shape are shown in Table 1. Figure 2 .

[0083] The theoretical evaporation rate of the finally optimized model reaches 4.12 kg / m 2 ·h. After the optimized model is exported, the actual evaporation experiment is carried out, and the evaporation rate reaches 4.03 kg / m 2 ·h, which is 97.82% of the simulation state, close to the theoretical data, and is 25.16% higher than the 3.22 kg / m 2 ·h before optimization, confirming the superiority of the shape of the material after simulation and optimization.

[0084] Figure 2 Table 1 Comparison of surface data of 3D-PVA@Bi2O3-FLG / Ppy PEMs before and after COMSOL simulation and optimization, (a) and (a') are the surface irradiance of the material. Under one sunlight, the irradiance of the model before optimization can only reach close to 1 W / m 2 (ie a standard solar intensity) on the conical part of the material, and the irradiance received by the middle part of the cylinder is 0.6-0.8 W / m 2 , while the irradiance of the entire surface of the optimized model maintains around 1 W / m 2 , which can be seen that the irregular change of the structure is conducive to the reception of sunlight by the internal cylinder, thereby improving the energy utilization rate. Figure 2 (b) and (b') are the isothermal surfaces of the material. The highest isothermal surface before optimization is concentrated in a small part of the material center, and the distance between the entire isothermal surface is small and conical covering the surface of the material. After optimization, the highest temperature is closer to the surface of the material, and the coverage area increases. The higher isothermal surface is closer to the surface of the model rather than being concentrated above the model before optimization. Figure 2(c) and (c') are the water vapor diffusion rates of the model cross section, the water vapor diffusion rate in the model before optimization is about 0.04 m / s, after optimization, the middle cylindrical height is reduced and the diameter of the middle cylinder is reduced, which is more conducive to water vapor diffusion, and the rate is also increased to about 0.1 m / s, thereby increasing the evaporation rate of the model. The relative humidity of the model under the evaporation state is Figure 2 (d) and (d') show that the relative humidity gradually decreases from the inside to the outside, which corresponds to the water vapor diffusion rate of the model cross section, and the relative humidity distribution after optimization is more uniform, indicating that the evaporation rate is faster. Figure 2 (e) and (e') are the relative pressure of the material surface, Figure 2 (f) and (f') are the total water vapor flux of the material surface, that is, the water evaporation rate, it can be seen that the water vapor flux of the optimized model is larger, which shows that the evaporation rate is higher, and the above model performance shows that the optimized model has higher evaporation rate and light-heat conversion efficiency.

[0085] According to the results, the 3D-PVA@Bi2O3-FLG / Ppy PEMs prepared in Examples 1-4 have good evaporation efficiency in solar-driven interfacial evaporation, and among Examples 1-4, Example 1 is the optimal example, so the 3D-PVA@Bi2O3-FLG / Ppy PEMs prepared in Example 1 are selected for subsequent characterization experiments and performance detection experiments.

[0086] 1.2 Photocatalytic capacity test

[0087] One of the advantages of the material of the present application is that it has high evaporation rate and photocatalytic degradation effect on the bottom evaporation water body, so when testing the photocatalytic effect, the evaporation device is closed to evaporate water vapor back to the water body, ensuring that the total amount of water body does not change, and the evaporation water sample is extracted at different time periods for detection of the concentration of organic pollutant methylene blue.

[0088] Methylene blue solution prepared with Beihai seawater is used as the water to be treated, simulating seawater polluted by organic dye wastewater, and the concentration of methylene blue solution in the evaporation water before and after evaporation is measured by ultraviolet spectrophotometer (Lambda 35, Perkin Elmer, America). The removal rate calculation formula is:

[0089]

[0090] Wherein C0 and C1 are the concentrations of methylene blue solution in the initial solution and the water after evaporation, respectively, and η is the removal rate.

[0091] Photocatalytic experiments were carried out on water bodies with different pollutant concentrations of 2 mg / L, 4 mg / L, 6 mg / L, 8 mg / L and 10 mg / L, and the pollutant concentration of the water body within 1 hour was recorded as Figure 1As shown in Figure c. At a concentration of 2 mg / L, the pollutant removal effect over time was not obvious, with a photocatalytic removal rate of approximately 7% after one hour. As the concentration of pollutants in the evaporated water increased, the removal rate within one hour increased from 7% at 2 mg / L to 10% at 8 mg / L. However, the catalytic effect decreased when it rose to 10 mg / L. This was attributed to the high concentration of organic pollutants, which hindered the photocatalytic groups from receiving light and the attachment and degradation of methylene blue.

[0092] The concentration with the best removal effect was further selected to conduct a photocatalytic experiment for 6 consecutive hours. Evaporated water samples were taken at different time periods to test the methylene blue concentration. It can be observed that the photocatalytic effect was obvious in the first 4 hours, with an hourly removal rate of about 15%. By the sixth hour, the removal rate reached 81%. It can be seen that the material prepared by this method has obvious effects in the field of photocatalytic degradation and excellent durability.

[0093] 1.3 Water content and reswelling test

[0094] Three groups of parallel samples were taken to test the water content and reswelling degree of PVA and 3D-PVA@Bi2O3-FLG / Ppy PEMs prepared in Example 1. The specific steps were as follows: the prepared evaporation material was soaked in water and weighed as M0, then placed in a freeze drying oven and dried to a constant mass. After complete drying, its weight was weighed as M0. f , substitute into the formula

[0095]

[0096] Calculate its moisture content W W . Further weight M F The material is placed in water and soaked until the weight is constant, and its weight is weighed as M b , substitute into the formula

[0097]

[0098] The reswelling degree is calculated as S.

[0099] The test results are as follows Figure 1 As shown in d, Figure 1 d shows that the water content of the unmodified PVA is about 85%, which is similar to the 3D-PVA@Bi2O3-FLG / Ppy PEMs with a water content of about 83%, indicating that the modification has little effect on the water absorption properties of PVA. The re-swelling degree of the two groups of materials was further tested, and their re-swelling rates were maintained at 60% to 63%, indicating the stability of the material structure and excellent durability.

[0100] 2. Structure and Performance Characterization

[0101] 2.1 SEM images

[0102] The morphology and structure of PVA and 3D-PVA@Bi2O3-FLG / Ppy PEMs prepared in Example 1 were detected by field emission scanning electron microscopy, and the results are shown in Figure 3 As can be seen from the SEM images, the surface of the unmodified PVA material shows a scale-like protrusion Figure 3 , a-c), compared with the obvious layered mesh structure of 3D-PVA@Bi2O3-FLG / Ppy PEMs under the same magnification Figure 3 , d-f), due to the doping of hydrophobic materials graphene and bismuth oxide, which is conducive to the crosslinking of the network structure in the PVA hydrogel, which also creates abundant adsorption sites for organic pollutants and creates conditions for subsequent photocatalysis. During the evaporation process, the porous outer surface mesh structure is conducive to the diffuse reflection of light, enhancing the light absorption performance of the material and thus improving the energy utilization rate, achieving high evaporation performance of the material.

[0103] 2.2 Water absorption performance

[0104] Because the efficient solar-driven interfacial evaporation performance not only has excellent light-heat conversion performance, but also must have strong water transport capacity, the water absorption and energy absorption of PVA and 3D-PVA@Bi2O3-FLG / Ppy PEMs prepared in Example 1 were tested by an optical contact angle measuring instrument, Figure 3 (g-h) and (i-j) are the water contact angle and water absorption performance of PVA and 3D-PVA@Bi2O3-FLG / Ppy PEMs, respectively. When the water droplets contact the material surface, they all show hydrophilicity and quickly spread on the material surface, and finally enter the hydrogel interior. In the same time (50 ms), the modified photo-thermal evaporation material shows stronger water absorption performance.

[0105] 2.3 Light-heat conversion performance

[0106] In addition to excellent water transport capacity, the material also needs to have efficient light-heat conversion performance to achieve solar steam generation. The light-heat conversion performance of 3D-PVA@Bi2O3-FLG / Ppy PEMs prepared in Example 1 was studied using an infrared thermal imager, Figure 4 is the change of the sample surface temperature with time under sunlight, and Figure 4(b), (b') and (c) can be seen, the surface temperature of 3D-PVA@Bi2O3-FLG / Ppy PEMs rapidly rises from room temperature to 38-39℃ within 20 min, and the temperature of the material surface fluctuates around 42℃ after one hour irradiation, while from the side thermal imaging figure it can be observed that the heating part always remains in the liquid surface part of the evaporating water body, the middle and lower parts of the water body are close to room temperature, which means that the evaporative material concentrates heat on the water surface, and further indicates that the material has good heat absorption and insulation performance.

[0107] In order to compare the photo-thermal conversion performance, the thermal response of pure water was investigated under the same conditions, and the results are shown in Figure 4 In (a) and (a'), the temperature of the pure water body rises to about 30℃ within 20 min, and the water temperature remains at about 32℃ after one hour irradiation, while from the side figure it can be seen that the temperature of the entire evaporating water body rises to 32℃, which greatly wastes heat. In addition, the image simulated by COMSOL shows that Figure 4 d), under one standard sunlight, the surface temperature of the material reaches 315k (41.85℃) when it reaches the best evaporation rate, which is similar to the best temperature captured by the thermal imager, which further verifies the photo-thermal conversion performance of the evaporative material. Therefore, 3D-PVA@Bi2O3-FLG / Ppy PEMs not only has excellent water absorption performance, but also has excellent photo-thermal conversion capacity, making 3D-PVA@Bi2O3-FLG / Ppy PEMs an ideal choice for interfacial evaporation.

[0108] 2.4 XRD and XPS spectrum

[0109] The crystal structure and element valence of the surface of the evaporative material were evaluated by X-ray diffraction and X-ray photoelectron spectroscopy. XRD studied the characteristics of the photocatalyst Bi2O3 in the 3D-PVA@Bi2O3-FLG / Ppy PEMs prepared in Example 1 Figure 5 a), from Bi2O3 PDF #76-1730, several obvious peaks appear at 27.3°, 33.2°, 37.6°, 46.3° and 52.3°, and corresponding characteristic peaks are generated at the corresponding positions in PVA@Bi2O3-FLG / Ppy, which indicates that Bi2O3 stable crystals are on the surface of the evaporative material. In addition, it is observed that the original PVA hydrogel produces two sharp peaks at 19.5° and 40.3°, which are also reflected in 3D-PVA@Bi2O3-FLG / Ppy PEMs, but the intensity is reduced, which indicates that the introduction of Bi2O3 will limit the interaction between PVA molecular chains to some extent, thereby affecting the crystallinity of PVA groups.

[0110] The infrared spectrum of the sample was measured by Fourier transform infrared spectrometer to analyze the functional groups and chemical composition of the surface of the modified material. The scanning wave number range was 400-4000 cm -1 ; It can be seen from the FT-IR spectrum of 3D-PVA@Bi2O3-FLG / Ppy PEMs ( Figure 5 b), sample at 3260 cm -1 and 2914cm -1 There is an obvious absorption band at 1087cm, which may be the stretching vibration of -OH. -1 The characteristic absorption peak at 412 cm further confirms the presence of alcohol (PVA). -1 and 1401cm -1 The absorption peak at is attributed to the bending vibration of Bi-O, indicating the existence of α-Bi2O3 and the integrity of its structure. This is consistent with the results of XRD. The XPS energy spectrum of PVA and 3D-PVA@Bi2O3-FLG / Ppy PEMs ( Figure 5 c) It can be seen that the Bi 4f and N1s peaks in the modified evaporated material are significantly enhanced, which is because the doping of Ppy and α-Bi2O3 in the modified material is rich in N and Bi elements.

[0111] Among them, the XPS spectrum of Bi element is as follows Figure 5 As shown in d, the Bi 4f peak in α-Bi2O3 is formed by the coupling of the orbital motion and spin motion of the electrons, which causes the orbital energy level to split and form 4f 5 / 2 and 4f 7 / 2 There are two peaks, and the corresponding binding energies are 175.10eV and 163.20eV respectively. The XPS spectrum of O 1s is shown in Figure 5 As shown in e, the two peaks corresponding to the binding energy at 530.68eV and 531.28eV can be attributed to the oxygen atoms in the Bi-O band and the surface hydroxyl groups (-OH); the XPS spectrum of N 1s is shown in Figure 5 As shown in Figure f, the peak at 397.60 eV can be attributed to NH in the photothermal coating Ppy. The above results all indicate the successful doping of the photocatalyst α-Bi2O3 and the effective deposition of the photothermal coating Ppy.

[0112] Having a broad spectral absorption band is also one of the performance criteria for measuring photothermal materials. In the 200-2500nm solar spectrum wavelength region, the absorption and reflection spectra of PVA and 3D-PVA@Bi2O3-FLG / Ppy PEMs were measured by using a UV-visible-near-infrared spectrometer. Figure 5The light absorption rate of the unmodified PVA is concentrated in the wavelength of 400-1400 nm, about 5%, and the wavelength of 1400-2400 nm, about 30%, while the light absorption rate of the modified photo-thermal material is almost 70%-80% in the whole wavelength range, indicating that the material has obvious light absorption advantage. Further from the light reflectivity spectrum, the light reflectivity of the two materials in the whole wavelength range corresponds to the light absorption rate, and the smaller light reflectivity can reduce the light loss, which proves that the modified material has obvious advantage in photo-thermal conversion performance.

[0113] 3. Performance comparison

[0114] In addition, the evaporation rate test of the 3D-PVA@Bi2O3-FLG / Ppy PEMs prepared in Example 4 of the present method and Comparative Examples 1-3 was carried out under the same conditions, and the evaporation rate results of the two-dimensional planar materials are shown in Figure 6 and compared with the evaporation rates of other reported materials (see references 1-16), it is found that the evaporation rate of PSF@PDA / TiO2-Ag / Ppy HFMs achieves excellent performance, with an evaporation rate of 4.03 kg / (m 2 ·h), which exceeds a large number of reported photo-thermal materials in this field (see Table 1).

[0115] Table 1 Comparison of evaporation rates of materials in Example 1 and existing reports

[0116]

[0117]

[0118] In summary, the 3D-PVA@Bi2O3-FLG / Ppy PEMs prepared by the present method have an evaporation rate of 1.41 kg / (m 2 ·h) when they are in planar shape, which is about 4.6 times that of pure water, and after optimization, the evaporation rate reaches 3.12 kg / (m 2 ·h) when they are in cylindrical shape, 3.22 kg / (m 2 ·h) when they are in conical shape, and finally, after optimization, the evaporation rate reaches a high evaporation rate of 4.03 kg / (m 2 ·h) under one sunlight, and in the evaporation experiment of simulated North Sea water contaminated by methylene blue dye, it shows an evaporation rate of 3.06 kg / (m 2• The stable evaporation rate of h) achieved 81% of the degradation effect on pollutants in the evaporative water body in the continuous 6-hour light experiment; it is proved that the 3D-PVA@Bi2O3-FLG / Ppy PEMs prepared by the method have not only high evaporation rate in seawater desalination application, but also great potential and application prospect in the treatment of seawater polluted by organic dye.

[0119] References 1-16 are as follows:

[0120] [1] Cao Y, Zhu X, Ni Z, et al. Construction of PVA hydrogel-based solar-driven interfacial distillation device and its performance research in selective adsorption of organic solvents and removal of Rh B [J]. Separation and Purification Technology, 2022, 295: 121274.

[0121] [2] Hu G, Cao Y, Huang M, et al. Salt-resistant carbon nanotubes / polyvinyl alcohol hybrid gels with tunable water transport for high-efficiency and long-term solar steam generation [J]. Energy Technology, 2020, 8(1): 1900721.

[0122] [3] Chen L, Wu Y, Xing W, et al. Mechanically robust composite hydrogels for high performance solar driven interface evaporation [J]. Chemical Engineering Science, 2023, 267: 118330.

[0123] [4] Chen Y, Qiu H, Li X, et al. Three-Level pore structure hydrogels for solar vapor generation [J]. Applied Surface Science, 2022, 582: 152483.

[0124] [5] Zhou X, Zhao F, Guo Y, et al. A hydrogel-based antifouling solar evaporator for highly efficient water desalination [J]. Energy & Environmental Science, 2018, 11(8): 1985-1992.

[0125] [6] Yang Z, Liu Y, Xue K, et al. PEI-GOs / PVA photothermal sponge with enhanced interfacial solar steam generation and seawater desalination [J]. Materials Today Communications, 2023, 35: 106195.

[0126] [7] Yu F, Ming X, Xu Y, et al. Quasimetallic molybdenum carbide-based flexible polyvinyl alcohol hydrogels for enhancing solar water evaporation [J]. Advanced Materials Interfaces, 2019, 6(24): 1901168.

[0127] [8] Mohapatra S. Multifunctional bio-based photothermal hydrogel for highly efficient seawater desalination and contaminant adsorption [J]. Journal of Environmental Chemical Engineering, 2022, 10(6): 108616.

[0128] [9] Sheng K, Tian M, Wang J, et al. Molecular architecting of photothermal hydrogels reinforced by polar-porous C2NxO1-x for efficient solar water purification [J]. Desalination, 2022, 541: 116060.

[0129]

[10] Liu J, Zhu J, Guo S, et al. In-situ constructing cellulose / PVA hydrogel with confinement capillarity for efficient solar interfacial evaporation [J]. Desalination, 2023, 565: 116855.

[0130]

[11] Zhao X, Chen Y, Yin Y, et al. Janus polypyrrole nanobelt@polyvinyl alcohol hydrogel evaporator for robust solar-thermal seawater desalination and sewage purification [J]. ACS Applied Materials&Interfaces, 2021, 13(39): 46717-46726.

[0131]

[12] Zhou X, Zhao F, Guo Y, et al. Architecting highly hydratable polymer networks to tune the water state for solar water purification [J]. Science Advances, 2019, 5(6): eaaw5484.

[0132]

[13] Hao L, Liu N, Bai H, et al. High-performance solar-driven interfacial evaporation through molecular design of antibacterial, biomass-derived hydrogels [J]. Journal of Colloid and Interface Science, 2022, 608: 840-852.

[0133]

[14] Li F, Li N, Wang S, et al. Self-repairing and damage-tolerant hydrogels for efficient solar-powered water purification and desalination [J]. Advanced Functional Materials, 2021, 31(40): 2104464.

[0134]

[15] Zhao L, Yang Z, Wang J, et al. Boosting solar-powered interfacial water evaporation by architecting 3D interconnected polymetric network in CNT cellular structure [J]. Chemical Engineering Journal, 2023, 451: 138676.

[0135]

[16] Zhou X, Guo Y, Zhao F, et al. Topology-controlled hydration of polymer network in hydrogels for solar-driven wastewater treatment [J]. Advanced Materials, 2020, 32(52): 2007012.

Claims

1. A method for preparing a three-dimensional modified polyvinyl alcohol hydrogel, characterized in that: The method involves doping 1-5 layers of few-layer graphene (FLG) and α-Bi2O3 into a polyvinyl alcohol hydrogel, and performing polypyrrole (Ppy) vapor deposition on the surface of the hydrogel to obtain a three-dimensional modified polyvinyl alcohol hydrogel 3D-PVA@Bi2O3-FLG / PpyPEMs, which includes the following steps: S1. Preparation of PVA@Bi2O3: Take an appropriate amount of polyvinyl alcohol to prepare a polyvinyl alcohol solution, weigh an appropriate amount of Bi2O3 and add it to the polyvinyl alcohol solution, and stir until the Bi2O3 is evenly dispersed in the polyvinyl alcohol solution to obtain a PVA@Bi2O3 solution; S2. Preparation of 3D-PVA@Bi2O3-FLG PEMs: FLG is dissolved in water, stirred evenly, and then added to the PVA@Bi2O3 solution obtained in S1. After stirring, a cross-linking agent and water are added, and the mixture is stirred again and poured into a mold. The mold is placed in a freezing environment and then taken out and thawed at room temperature. The freezing and thawing cycles are repeated. After thawing, the mold is immersed in water and finally rinsed with pure water to remove unreacted chemicals on the surface to obtain 3D-PVA@Bi2O3-FLG PEMs. The cross-linking agent is obtained by stirring a glutaraldehyde solution, a methanol solution, and an acetic acid solution, adding sulfuric acid to react, and then diluting the mixture. S3. Preparation of 3D-PVA@Bi2O3-FLG / Ppy PEMs: The 3D-PVA@Bi2O3-FLG PEMs obtained in S2 were subjected to Ppy surface polymerization reaction using chemical vapor deposition technology. After the reaction was completed, the surface residue was washed with water and then dried to obtain 3D-PVA@Bi2O3-FLG / Ppy PEMs.

2. The preparation method according to claim 1, wherein: The following steps are involved: S1. Preparation of PVA@Bi2O3: Dissolve an appropriate amount of polyvinyl alcohol in water under stirring to obtain a 0.1 g / mL polyvinyl alcohol solution. Weigh an appropriate amount of Bi2O3 and add it to the polyvinyl alcohol solution. The ratio of Bi2O3 to polyvinyl alcohol is 1:(0.5-1.5). Stir until Bi2O3 is evenly dispersed in the polyvinyl alcohol solution to obtain a PVA@Bi2O3 solution. S2. Preparation of 3D-PVA@Bi2O3-FLG PEMs: Dissolve 0.04-0.1g FLG in 4-10mL water and stir at room temperature for 1h to obtain a uniform solution. Then take 6-12mL of the PVA@Bi2O3 solution obtained by S1, add the FLG uniform solution to the PVA@Bi2O3 solution, stir at room temperature for 1h, add 0.6-1.2mL of cross-linking agent and 1.6-2.4mL of water, stir again for 1h and pour into a mold. Place the mold in a freezing environment of -20℃ to -40℃ and freeze for 8-12h, then take it out and thaw at room temperature for 2-4h, repeat freezing and thawing 4-6 times, soak it in water for 24-48h after thawing, change the water every 12h, and finally rinse with pure water to remove the unreacted chemicals on the surface to obtain 3D-PVA@Bi2O3-FLG PEMs; the crosslinking agent is prepared as follows: glutaraldehyde solution, methanol solution, and acetic acid solution are mixed in a mass ratio of 2:(4-6):(4-6), stirred evenly, and then sulfuric acid solution is added. The mass ratio of the sulfuric acid solution to the glutaraldehyde solution is (0.8-1.4):

2. After the solution is completely reacted to a yellowish brown color, 40-60 mL of water is added to dilute and stirred evenly to obtain a light yellow crosslinking agent; S3. Preparation of 3D-PVA@Bi2O3-FLG / Ppy PEMs: The 3D-PVA@Bi2O3-FLG PEMs obtained in S2 were subjected to surface polymerization of polypyrrole (Ppy) using chemical vapor deposition technology. After the reaction was completed, the surface residue was washed with water and then dried to obtain 3D-PVA@Bi2O3-FLG / Ppy PEMs.

3. The preparation method according to claim 2, wherein: S1. Preparation of PVA@Bi2O3: 1 g of polyvinyl alcohol was added to 10 mL of water and magnetically stirred at 90°C for 2 h to fully dissolve to obtain a 0.1 g / mL polyvinyl alcohol solution. 1 g of Bi2O3 was weighed and added to the polyvinyl alcohol solution with continuous stirring to uniformly disperse Bi2O3 in the polyvinyl alcohol solution to obtain a PVA@Bi2O3 solution. In step S2, the inner cavity of the mold is a plurality of cylindrical cavities, and the height of the cylindrical cavity is 2 cm and the diameter is 0.6 cm.

4. The preparation method according to claim 3, wherein: The cross-linking agent in S2 is prepared as follows: 2 mL of glutaraldehyde solution, 5 mL of methanol solution, and 5 mL of acetic acid solution are added to a beaker, and after being thoroughly stirred, 1 mL of sulfuric acid solution is added while continuing to slowly stir. After the solution is completely reacted and turns yellowish brown, 50 mL of water is added to the beaker to dilute it, and after stirring evenly, a light yellow cross-linking agent is obtained; In step S2, the 0.5 cm area on the upper part of the cylindrical chamber is a cone with the same bottom and height, and the diameter of the middle part of the cylindrical chamber is smaller than the diameters of the two ends.

5. The preparation method according to claim 4, characterized in that: S2. Preparation of 3D-PVA@Bi2O3-FLG PEMs: Dissolve 0.05 g FLG in 5 mL of water, stir at room temperature for 1 hour to obtain a uniform solution, add it to the PVA@Bi2O3 solution obtained in S1, stir at room temperature for 1 hour, then add 1 mL of cross-linker and 2 mL of water. Stir again for 1 hour and pour into a mold. Place the mold in a -20°C freezing environment and freeze it for 10 hours. Then take it out and thaw it at room temperature for 3 hours. Repeat the freezing and thawing process 5 times. After thawing, soak it in deionized water for 24 hours, changing the water every 12 hours. Finally, rinse it in pure water for 5 minutes to remove unreacted chemicals on the surface to obtain 3D-PVA@Bi2O3-FLG PEMs.

6. The preparation method according to claim 2, wherein: S3. Preparation of 3D-PVA@Bi2O3-FLG / Ppy PEMs: prepare a large beaker, place the 3D-PVA@Bi2O3-FLG PEMs obtained in S2 in the beaker, and place a culture dish in the beaker. Drop 70-100 μl of pyrrole (py) into the culture dish, place the beaker in a 50-70°C vacuum drying oven and dry it for 1-2 hours to complete the Ppy vapor phase chemical deposition. After the reaction is completed, rinse the undeposited py on the surface with pure water and dry it to obtain 3D-PVA@Bi2O3-FLG / Ppy PEMs.

7. The preparation method according to claim 6, characterized in that: S3. Preparation of 3D-PVA@Bi2O3-FLG / Ppy PEMs: prepare a large beaker, place the 3D-PVA@Bi2O3-FLG PEMs obtained in S2 in the beaker, and place a culture dish in the beaker. Drop 80μl of py into the culture dish, and place the beaker in a 60℃ vacuum drying oven to dry for 1 hour to complete polypyrrole vapor phase chemical deposition. After the reaction is completed, rinse in pure water for 5 minutes to remove the undeposited py on the surface and then dry to obtain 3D-PVA@Bi2O3-FLG / Ppy PEMs.

8. A three-dimensional modified polyvinyl alcohol hydrogel, characterized in that: The preparation method is described in any one of claims 1 to 7.

9. Use of the three-dimensional modified polyvinyl alcohol hydrogel according to claim 8 in seawater desalination and sewage treatment.

10. The use according to claim 9, characterized in that: The three-dimensional modified polyvinyl alcohol hydrogel is placed in water to be treated and placed under sunlight to float on the water surface. The bottom end of the three-dimensional modified polyvinyl alcohol hydrogel is placed below the water surface, and the top end is located above the water surface and is used to receive sunlight to be heated and evaporate water.

Images