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

Abstract

The invention relates to three-dimensional modified polyvinyl alcohol hydrogel as well as a preparation method and application thereof, and relates to the technical field of evaporation materials, few layers of FLG and alpha type Bi2O3 are doped in polyvinyl alcohol hydrogel, and Ppy vapor deposition is performed on the surface of the hydrogel to obtain the three-dimensional modified polyvinyl alcohol hydrogel 3D-PVA coated Bi2O3-FLG / Ppy PEMs. After the material prepared by the method is finally optimized, the evaporation rate reaches 4.03 kg / (m < 2 >. H), meanwhile, the stable evaporation rate of 3.06 kg / (m < 2 >. H) is shown in an evaporation experiment for simulating northern sea water polluted by methylene blue dye, and the degradation effect on pollutants in evaporated water reaches 81% in an illumination 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 treatment of seawater polluted by organic dye.

Description

Technical Field

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

[0002] Solar desalination has the advantages of not consuming conventional energy, not generating secondary pollution, and having low operating costs. Interfacial evaporation, as a high evaporation efficiency method of local heating of the gas-liquid interface, has become a research hotspot in the field of desalination. Unlike the overall heating and bottom heating of traditional solar distiller, interfacial evaporation technology limits the photothermal material to the air-water interface, which can not only reduce heat loss and improve the utilization rate of solar energy, but also increase the surface area of ​​seawater evaporation. In the interfacial evaporation system of solar desalination, photothermal conversion materials are the key to achieving efficient photothermal conversion. The heat generated by them is used to drive the generation of steam. The stronger the light absorption capacity of the material, the more basic energy for photothermal conversion.

[0003] There are two different categories of solar interfacial evaporation materials, namely carbon-based materials and plasma-based absorbers. Common carbon-based photothermal materials include carbon black, graphite, graphene, graphene oxide, reduced graphene oxide, carbon nanotubes and activated carbon. Although existing evaporation materials show excellent freshwater production rate and photothermal conversion efficiency, for multi-component seawater currently polluted by various organic substances, organic pollutants will be adsorbed on the surface of the evaporation material during the evaporation process, affecting its freshwater production rate and photothermal conversion efficiency, which also brings new challenges to solar-driven interfacial evaporators. Although some scholars have gradually applied photocatalytic materials to interfacial evaporation, the evaporation rate is sacrificed while having a photocatalytic effect. The pollutants remaining in the evaporated water body cannot be removed after the steam is generated. There is a lack of interfacial evaporation materials that have both high evaporation rate and effective degradation of organic pollutants.

[0004] Therefore, the fresh water production device for organic solvent and dye water should include the following two parts: on the one hand, it should have excellent interfacial evaporation, through which clean water can be produced from undrinkable water; on the other hand, it should have excellent pollutant treatment ability, through which residual pollutants (dyes and organic solvents) in polluted water can be removed. Summary of the invention

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

[0006] The first aspect of the present invention provides a method for preparing a three-dimensional modified polyvinyl alcohol hydrogel, which comprises: 2 O 3Ppy was doped into polyvinyl alcohol hydrogel and Ppy was vapor deposited on the surface of the hydrogel to obtain a three-dimensional modified polyvinyl alcohol hydrogel 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs, including the following steps:

[0007] S1. Preparation of PVA@Bi 2 O 3 : Take an appropriate amount of polyvinyl alcohol to prepare polyvinyl alcohol solution, weigh an appropriate amount of Bi 2 O 3 Add to the polyvinyl alcohol solution and stir until Bi 2 O 3 Evenly dispersed in polyvinyl alcohol solution, PVA@Bi 2 O 3 Solution;

[0008] S2. Preparation of 3D-PVA@Bi 2 O 3 -FLG PEMs: Dissolve FLG in water, stir evenly and add PVA@Bi obtained by S1 2 O 3 The solution was stirred, and then a cross-linking agent and water were added. After stirring again, the solution was poured into a mold. The mold was placed in a freezing environment and then taken out and thawed at room temperature. The mold was then frozen and thawed repeatedly. After thawing, the mold was immersed in water and finally rinsed with pure water to remove the unreacted chemicals on the surface to obtain 3D-PVA@Bi 2 O 3 -FLG PEMs, the crosslinking agent is obtained by stirring glutaraldehyde solution, methanol solution and acetic acid solution, adding sulfuric acid to react and then diluting;

[0009] S3. Preparation of 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs: 3D-PVA@Bi obtained from S2 2 O 3 -FLG PEMs use chemical vapor deposition technology to carry out surface polymerization of polypyrrole Ppy. After the reaction is completed, the surface residue is cleaned with water and then dried to obtain 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs.

[0010] By adopting the above technical solution, polyvinyl alcohol is used as raw material, and Bi with good photocatalytic effect is added. 2 O 3As a photocatalyst, and adding graphene materials with good photothermal conversion performance, a three-dimensional modified polyvinyl alcohol carbon-based photothermal evaporation material with high evaporation rate and effective degradation of organic pollutants was prepared through in-situ polymerization, repeated thawing and freezing, film setting and chemical deposition methods. Due to the doping of hydrophobic materials graphene and bismuth oxide, it is beneficial to the cross-linking 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 network structure is conducive to the diffuse reflection of light, enhancing the light absorption performance of the material, thereby improving the energy utilization rate and achieving high evaporation performance of the material.

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

[0012] S1. Preparation of PVA@Bi 2 O 3 : Take an appropriate amount of polyvinyl alcohol and dissolve it in water under stirring to obtain a 0.1g / mL polyvinyl alcohol solution. 2 O 3 Added to polyvinyl alcohol solution, Bi 2 O 3 The amount of added Bi is 1:(0.5-1.5) with polyvinyl alcohol. Stir until Bi 2 O 3 Evenly dispersed in polyvinyl alcohol solution, PVA@Bi 2 O 3 Solution;

[0013] S2. Preparation of 3D-PVA@Bi 2 O 3 -FLG PEMs: Dissolve 0.04-0.1g FLG in 4-10mL water, stir at room temperature for 1h to obtain a uniform solution, then take 6-12mL S1 of the obtained PVA@Bi 2 O 3 Solution, add FLG uniform solution to PVA@Bi 2 O 3 The solution was stirred at room temperature for 1 hour, and then 0.6-1.2 mL of cross-linking agent and 4.6-2.4 mL of water were added. After stirring for another 1 hour, the solution was poured into a mold. The mold was placed in a -20°C-(-40°C) freezing environment for 8-12 hours, and then taken out to thaw at room temperature for 2-4 hours. The freezing and thawing were repeated 4-6 times. After thawing, the mold was immersed in water for 24-48 hours, and the water was changed every 12 hours. Finally, the mold was rinsed with pure water to remove the unreacted chemicals on the surface to obtain 3D-PVA@Bi 2 O 3-FLG PEMs; the cross-linking 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), and sulfuric acid solution is added after stirring evenly, and the mass ratio of the sulfuric acid solution to the glutaraldehyde solution is (0.8-1.4):2, and after the solution is completely reacted to yellow-brown, 40-60 mL of water is added to dilute and stir evenly to obtain a light yellow cross-linking agent;

[0014] S3. Preparation of 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs: 3D-PVA@Bi obtained from S2 2 O 3 -FLG PEMs use chemical vapor deposition technology to carry out surface polymerization of polypyrrole Ppy. After the reaction is completed, the surface residue is cleaned with water and then dried to obtain 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs.

[0015] Preferably, in the above-mentioned preparation method technical solution, the step S1 is specifically as follows: S1, preparing PVA@Bi 2 O 3 : Add 1g of polyvinyl alcohol to 10mL of water and stir magnetically at 90℃ for 2h to fully dissolve to obtain a 0.1g / mL polyvinyl alcohol solution. 2 O 3 Add to the polyvinyl alcohol solution and stir continuously to make Bi 2 O 3 Evenly dispersed in polyvinyl alcohol solution, PVA@Bi 2 O 3 Solution; preferably in step S2, the inner cavity of the mold is a plurality of cylindrical chambers, and the height of the cylindrical chamber is 2 cm and the diameter is 0.6 cm.

[0016] Preferably, in the technical scheme of the above-mentioned preparation method, the configuration method of the cross-linking agent in step S2 is: add 2 mL of glutaraldehyde solution, 5 mL of methanol solution and 5 mL of acetic acid solution to a beaker, stir thoroughly, continue to stir slowly and add 1 mL of sulfuric acid solution at the same time, and after the solution is completely reacted to yellowish brown, add 50 mL of water to the beaker to dilute it, and stir evenly to obtain a light yellow cross-linking agent; preferably 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 diameter at both ends.

[0017] Preferably, in the above-mentioned preparation method technical solution, the step S2 is specifically as follows: S2, preparing 3D-PVA@Bi 2 O 3-FLGPEMs: 0.05 g FLG was dissolved in 5 mL water and stirred at room temperature for 1 h to obtain a uniform solution. PVA@Bi obtained by S1 was added 2 O 3 The solution was stirred at room temperature for 1 hour, and then 1 mL of cross-linking agent and 2 mL of water were added. After stirring again for 1 hour, the solution was poured into a mold. The mold was placed in a -20 °C freezing environment for 10 hours, and then taken out and thawed at room temperature for 3 hours. The freezing and thawing were repeated 5 times. After thawing, the mold was immersed in deionized water for 24 hours, and the water was changed every 12 hours. Finally, it was rinsed in pure water for 5 minutes to remove the unreacted chemicals on the surface to obtain 3D-PVA@Bi 2 O 3 -FLG PEMs.

[0018] Preferably, in the above-mentioned preparation method technical solution, the step S3 is specifically as follows: S3, preparing 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs: Prepare a large beaker and place the 3D-PVA@Bi obtained in S2 2 O 3 -FLG PEMs are placed in a beaker, and a petri dish is placed in the beaker. 70-100 μl of py is dropped into the petri dish. The beaker is placed in a 50-70 ° C vacuum drying oven and dried for 1-2 hours to complete the polypyrrole vapor phase chemical deposition. After the reaction is completed, the undeposited py on the surface is rinsed with pure water and then dried to obtain 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs.

[0019] Preferably, in the above-mentioned preparation method technical solution, the step S3 is specifically as follows: S3, preparing 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs: Prepare a large beaker and place the 3D-PVA@Bi obtained in S2 2 O 3 -FLG PEMs were placed in a beaker, and a petri dish was placed in the beaker. 80 μl of py was dropped into the petri dish. The beaker was placed in a 60°C vacuum drying oven and dried for 1 hour to complete the polypyrrole vapor phase chemical deposition. After the reaction was completed, it was placed in pure water for 5 minutes to remove the undeposited py on the surface and then dried to obtain 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs.

[0020] By adopting the above technical scheme, 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 invention provides a three-dimensional modified polyvinyl alcohol hydrogel prepared by any of the preparation methods described above.

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

[0023] In the above-mentioned application technology scheme, 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 to be heated and evaporate water.

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

[0025] 1. 3D-PVA@Bi of the present invention 2 O 3 -FLG / Ppy PEMs have an obvious layered mesh structure inside. Due to the doping of hydrophobic materials graphene and bismuth oxide, it is conducive to the cross-linking 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, thereby improving energy utilization and achieving high evaporation performance of the material.

[0026] 2.3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs have excellent light absorption and heat conversion capabilities. Under one sun, the surface temperature rises rapidly from room temperature to 38-39°C within 20 minutes, and after one hour of irradiation, the surface temperature of the material finally fluctuates around 42°C. Under a standard sun, the surface temperature of the material is 315k (41.85°C) when it reaches the optimal evaporation rate. Therefore, 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs not only have excellent water absorption properties, but also have outstanding photothermal conversion capabilities, making 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs are ideal for interfacial evaporation.

[0027] 3. In the 200-2500nm solar spectrum wavelength region, the light absorption rate of the unmodified PVA is concentrated at about 5% in the wavelength range of 400-1400nm and about 30% in the wavelength range of 1400-2400nm, while the light absorption rate of the modified photothermal material is concentrated at 70% to 80% in almost the entire band, indicating that the material has obvious light absorption advantages.

[0028] 4. Under the conditions of room temperature of 25-30℃ and humidity of 40%wt, the evaporation rate of pure water after one hour of exposure to standard sunlight is stable at 0.3kg / m 2 ·h, by PVA@Bi 2 O 3 -The evaporation rate of FLG / Ppy two-dimensional planar material increased to 1.41kg / m after one hour under the same conditions. 2 h, which is about 4.6 times that of pure water, indicating that the photothermal material and photothermal coating have significant effects. The evaporation rate of the optimized columnar model has increased to 3.12 kg / m under the same conditions. 2 h, which is 2.2 times higher than that of the two-dimensional plane material. After further changing the upper 0.5 cm of the cylinder to a cone with the same bottom and height, the evaporation rate of the material increased by another 0.1 kg / m 2 The final optimized shape is a column with thick top and bottom and thin middle, and the evaporation rate reaches 4.03kg / m 2 h, and 3.22 kg / m 2 h increased by 25.16%.

[0029] 5. Under the condition that the concentration of evaporated water pollutants is 8ng / L, the photocatalytic experiment is carried out for 6 consecutive hours. The evaporated water samples are taken at different time periods to detect the concentration of methylene blue. It can be observed that the photocatalytic effect is obvious in the first 4 hours, and the removal rate is about 15% per hour. By the sixth hour, the removal rate reaches 81%. It can be seen that the material has obvious effect in the field of photocatalytic degradation and excellent durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 (a) Pure water and PVA@Bi with different shapes 2 O 3 -FLG / Ppy evaporation material evaporation rate comparison chart, (b) is the relative deformation of the model after COMSOL simulation optimization, (c) is the different concentrations of C 16 H 18 C1N 3 S3D-PVA@Bi under one sun 2 O 3 - Evaporation rate of FLG / Ppy PEMs and 8m / LC 16 H 18 C1N 3 The comparison of S removal rate within six hours, (d) is PVA and 3D-PVA@Bi 2 O 3 - Comparison of water content and re-swelling test results of FLG / Ppy;

[0031] Figure 2 This is the 3D-PVA@Bi before and after COMSOL simulation optimization in this application 2 O 3 -Comparison of various data of FLG / Ppy PEMs, (a) and (a′) are the surface irradiance before and after optimization, (b) and (b′) are the isothermal surfaces before and after optimization, (c) and (c′) are the water vapor escape velocity of the section before and after optimization, (d) and (d′) are the relative humidity before and after optimization, (e) and (e′) are the surface pressure before and after optimization, (f) and (f′) are the total water vapor flux before and after optimization;

[0032] Figure 3 (ac) are SEM images of PVA, (df) are SEM images of 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs SEM images, (gh) is the contact angle image of PVA, (ij) is the contact angle image of 3D-PVA@Bi 2 O 3 -Contact angle images of FLG / Ppy PEMs;

[0033] Figure 4 (aa′) and (bb′) are pure water and 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs infrared thermal imaging changes within 1 hour under one sun, (c) is the corresponding temperature point line diagram, (d) is the 3D-PVA@Bi under COMSOL simulation 2 O 3 - Temperature of the FLG / Ppy PEMs surface;

[0034] Figure 5 (a) PVA and 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs XRD patterns, (b) 3D-PVA@Bi 2 O 3 - FT-IR spectra of FLG / Ppy PEMs, (c) PVA and 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs XPS spectrum, (d) Bi 4f spectrum, (e) O1s spectrum, (f) N1s spectrum, (g) PVA and 3D-PVA@Bi 2 O 3 -UV-vis absorption spectra of FLG / Ppy PEMs, (h)PVA and 3D-PVA@Bi2 O 3 -UV-vis reflectance spectrum of FLG / Ppy PEMs;

[0035] Figure 6 It is a comparison chart of the evaporation rates of four two-dimensional planes of PVA hydrogels prepared in Example 4 of the present application and Comparative Examples 1-3. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with 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 the understanding of the technical scheme of the present invention without departing from the spirit and scope of the technical scheme 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 (Bi 2 O 3 , ≥99.9%), methylene blue (C 16 H 18 C1N 3 S, ≥95%), pyrrole (C 4 H 5 N, ≥99%, abbreviated as py) was provided by Shanghai Yien Chemical Technology Co., Ltd.; glutaraldehyde (C 5 H 8 O 2 , 25-28%) and acetic acid (CH 3 COOH, ≥99.5%) was provided by Xilong Scientific Co., Ltd.; methanol (CH 4 O, ≥99.9%) was provided by MacLean Chemical Reagent Co., Ltd.; sulfuric acid (H 2 SO 4 , 95-98%) was provided by Chengdu Cologne Chemicals Co., Ltd.; Few layers graphene (physical method, thickness: 1.0-1.77nm, sheet diameter: 10-50μm, number of layers: 1-5, purity>90%, abbreviated as FLG) was provided by Suzhou Carbonfeng Graphene Technology Co., Ltd.; the selected seawater was taken from the seawater near the Beihai Sea in Guangxi Zhuang Autonomous Region in August, with an average salinity of about 2.8wt%; 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, PerkinElmerLambda950, USA), Fourier transform infrared spectrometer (FTIR, Thermo Fisher Scientific NicoletiS5, USA), optical contact angle meter (JC2000C1), infrared thermal imager (Hikmicro H10).

[0039] 3D-PVA@Bi prepared in this application 2 O 3 -FLG / Ppy PEMs, the Chinese name is three-dimensional modified polyvinyl alcohol hydrogel material, and the English full name is Three dimensions-polyvinyl alcohol Bi 2 O 3 Few layers graphenePpy Photothermal evaporation of materials.

[0040] For other specific conditions not specified, the experiments were carried out according to conventional conditions or those recommended by the manufacturer. Reagents or instruments used without indicating the manufacturer were conventional products that can be purchased commercially.

[0041] 1. Implementation

[0042] Example 1

[0043] A method for preparing a three-dimensional modified polyvinyl alcohol hydrogel comprises the following steps:

[0044] S1. Preparation of PVA@Bi 2 O 3 : Add 1g of polyvinyl alcohol to 10mL of water and stir magnetically at 90℃ for 2h to fully dissolve to obtain a 0.1g / mL polyvinyl alcohol solution. 2 O 3 Add to the polyvinyl alcohol solution and stir continuously to make Bi 2 O 3 Evenly dispersed in polyvinyl alcohol solution, PVA@Bi 2 O 3 Solution.

[0045] S2. Preparation of 3D-PVA@Bi 2O 3 -FLG PEMs: 0.05 g FLG was dissolved in 5 mL water and stirred at room temperature for 1 h to obtain a uniform solution. PVA@Bi obtained by S1 was added 2 O 3 The solution was stirred at room temperature for 1 hour, and then 1 mL of cross-linking agent and 2 mL of water were added. After stirring again for 1 hour, the solution was poured into a mold. The mold was placed in a -20 °C freezing environment for 10 hours, and then taken out and thawed at room temperature for 3 hours. The freezing and thawing were repeated 5 times. After thawing, the mold was immersed in deionized water for 24 hours, and the water was changed every 12 hours. Finally, it was rinsed in pure water for 5 minutes to remove the unreacted chemicals on the surface to obtain 3D-PVA@Bi 2 O 3 -FLG PEMs.

[0046] The preparation method of the cross-linking agent is as follows: add 2 mL of glutaraldehyde solution, 5 mL of methanol solution and 5 mL of acetic acid solution to a beaker, stir thoroughly, continue to stir slowly and add 1 mL of sulfuric acid solution at the same time, after the solution is completely reacted to yellow-brown, add 50 mL of water to the beaker to dilute, stir evenly to obtain a light yellow cross-linking agent.

[0047] The inner cavity of the mold is a plurality of cylindrical chambers, each of which is 2 cm high and 0.6 cm in diameter. 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 in the middle of the cylindrical chamber is smaller than the diameter at both ends.

[0048] S3. Preparation of 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs: Prepare a large beaker and place the 3D-PVA@Bi obtained in S2 2 O 3 -FLGPEMs were placed in a beaker, and a petri dish was placed in the beaker. 80 μl of py was dropped into the petri dish. The beaker was placed in a 60°C vacuum drying oven and dried for 1 hour to complete the polypyrrole vapor phase chemical deposition. After the reaction was completed, it was placed in pure water for 5 minutes to remove the undeposited py on the surface and then dried to obtain 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs.

[0049] Example 2

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

[0051] S1. Preparation of PVA@Bi 2 O 3 : Add 1g of polyvinyl alcohol to 10mL of water and stir magnetically at 90℃ for 2h to fully dissolve to obtain a 0.1g / mL polyvinyl alcohol solution.2 O 3 Add to the polyvinyl alcohol solution and stir continuously to make Bi 2 O 3 Evenly dispersed in polyvinyl alcohol solution, PVA@Bi 2 O 3 Solution.

[0052] S2. Preparation of 3D-PVA@Bi 2 O 3 -FLG PEMs: 0.04 g FLG was dissolved in 4 mL water and stirred at room temperature for 1 h to obtain a uniform solution. Then 6 mL of S1 was used to obtain PVA@Bi 2 O 3 Solution, add FLG uniform solution to PVA@Bi 2 O 3 The solution was stirred at room temperature for 1 hour, and then 0.6 mL of cross-linking agent and 1.6 mL of water were added. After stirring for another 1 hour, the solution was poured into a mold. The mold was placed in a -40 °C freezing environment and frozen for 8 hours. After that, the mold was taken out and thawed at room temperature for 2 hours. The freezing and thawing were repeated 5 times. After thawing, the mold was immersed in deionized water for 24 hours, and the water was changed every 12 hours. Finally, it was rinsed in pure water for 5 minutes to remove the unreacted chemicals on the surface to obtain 3D-PVA@Bi 2 O 3 -FLG PEMs.

[0053] The preparation method of the cross-linking agent is as follows: add 2 mL of glutaraldehyde solution, 4 mL of methanol solution and 4 mL of acetic acid solution to a beaker, stir thoroughly, continue to stir slowly and add 0.8 mL of sulfuric acid solution at the same time, after the solution is completely reacted to yellow-brown, add 40 mL of water to the beaker to dilute, stir evenly to obtain a light yellow cross-linking agent.

[0054] The inner cavity of the mold is a plurality of cylindrical chambers, each of which is 2 cm high and 0.6 cm in diameter, and a 0.5 cm area at the top of the cylindrical chamber is a cone with the same bottom and height.

[0055] S3. Preparation of 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs: Prepare a large beaker and place the 3D-PVA@Bi obtained in S2 2 O 3 -FLGPEMs were placed in a beaker, and a petri dish was placed in the beaker. 70 μl of py was dropped into the petri dish. The beaker was placed in a 50°C vacuum drying oven and dried for 2 h to complete the polypyrrole vapor phase chemical deposition. After the reaction was completed, it was placed in pure water for 5 min to remove the undeposited py on the surface and then dried to obtain 3D-PVA@Bi 2 O 3-FLG / Ppy PEMs.

[0056] Example 3

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

[0058] S1. Preparation of PVA@Bi 2 O 3 : Add 1g of polyvinyl alcohol to 10mL of water and stir magnetically at 90℃ for 2h to fully dissolve to obtain a 0.1g / mL polyvinyl alcohol solution. 2 O 3 Add to the polyvinyl alcohol solution and stir continuously to make Bi 2 O 3 Evenly dispersed in polyvinyl alcohol solution, PVA@Bi 2 O 3 Solution.

[0059] S2. Preparation of 3D-PVA@Bi 2 O 3 -FLG PEMs: 0.1 g FLG was dissolved in 10 mL water and stirred at room temperature for 1 h to obtain a uniform solution. Then 12 ml of S1 was taken to obtain PVA@Bi 2 O 3 Solution, add FLG uniform solution to PVA@Bi 2 O 3 The solution was stirred at room temperature for 1 hour, and then 1.2 mL of cross-linking agent and 2.4 mL of water were added. After stirring for another 1 hour, the solution was poured into a mold. The mold was placed in a -30 °C freezing environment and frozen for 12 hours. After that, the mold was taken out and thawed at room temperature for 4 hours. The freezing and thawing were repeated 5 times. After the thawing was completed, the mold was immersed in deionized water for 48 hours, during which the water was changed every 12 hours. Finally, it was rinsed in pure water for 5 minutes to remove the unreacted chemicals on the surface to obtain 3D-PVA@Bi 2 O 3 -FLG PEMs.

[0060] The preparation method of the cross-linking agent is as follows: add 2 mL of glutaraldehyde solution, 6 mL of methanol solution and 6 mL of acetic acid solution to a beaker, stir thoroughly, continue to stir slowly and add 1.4 mL of sulfuric acid solution at the same time, after the solution is completely reacted to yellow-brown, add 50 mL of water to the beaker to dilute, stir evenly to obtain a light yellow cross-linking agent.

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

[0062] S3. Preparation of 3D-PVA@Bi 2 O 3-FLG / Ppy PEMs: Prepare a large beaker and place the 3D-PVA@Bi obtained in S2 2 O 3 -FLGPEMs were placed in a beaker, and a petri dish was placed in the beaker. 100 μl of py was dropped into the petri dish. The beaker was placed in a 70°C vacuum drying oven and dried for 1 hour to complete the polypyrrole vapor phase chemical deposition. After the reaction was completed, it was placed in pure water for 5 minutes to remove the undeposited py on the surface and then dried to obtain 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs.

[0063] Example 4

[0064] The difference from Example 1 is that the inner cavity of the mold is planar.

[0065] 2. Comparison

[0066] Comparative Example 1

[0067] The difference from Example 4 is that the "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 the "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 the “0.05 g graphene (FLG)” in S2 is changed to “0.5 g titanium dioxide (TiO 2 )”, and the rest of the steps are the same, and finally PVA-TiO 2 Hydrogel.

[0072] 3. Performance Testing Experiment

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

[0074] 1.1 Solar-driven interface 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 to make it 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 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 at a temperature of 25-30°C and a humidity of 40%.

[0076] A solar simulator (TRM-PD) was used to simulate the solar light source, and a meteorological ecological environment monitor (PC-WX4) that matched the solar simulator was used to record the light intensity. During the evaporation process, a high-precision 1 / 10,000 electronic balance was used to record the mass change of the water evaporation process, and an infrared thermal imager was used to monitor the temperature change of the photothermal material surface during the interface 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 used in the experiment are 3D-PVA@Bi prepared in Examples 1-4. 2 O 3 -FLG / Ppy PEMs, Figure 1 a summarizes the best evaporation rates under various shapes. It can be seen from the figure that the evaporation rate of pure water after one hour of standard sunlight is stable at 0.3kg / m 2 ·h, by PVA@Bi 2 O 3 -FLG / Ppy two-dimensional planar material (Example 4) under the same conditions after one hour the evaporation rate rose to 1.41kg / m 2 ·h, which is about 4.6 times that of pure water, indicating that the photothermal materials and photothermal coatings have significant effects.

[0080] The same material was further made into a three-dimensional column by freezing demoulding (Example 3), wherein the height and diameter of the rising cylinder were 2 cm and 0.6 cm respectively, taking into account the material water absorption height and material stability. The cylinders were evenly distributed from the center of the plane in a known plane size, ensuring that the columnar material received more sunlight without affecting the escape of water vapor. The evaporation rate of the optimized columnar model under the same conditions rose to 3.12 kg / m2 h, which is 2.2 times higher than that of two-dimensional planar materials, and Figure 1 It can be seen from a that the evaporation rate of the material increases significantly within 0-40 min, indicating that this shape and arrangement are conducive to the heat absorption and evaporation of the material.

[0081] After further changing the upper 0.5 cm of the cylinder to a cone with the same bottom and height, the evaporation rate of the material increased by another 0.1 kg / m 2 , is 3.22kg / m 2 ·h.

[0082] Finally, the data of the improved three-dimensional material was imported into COMSOL software for simulation. Under the same conditions, the shape of the material was simulated and optimized. After 188 iterations, the final optimized shape is shown in 1b, where the transition from red to blue represents the relative change in shape. It can be observed that the change is mainly concentrated in the middle part of the cylinder, and its diameter is reduced to become a columnar shape with thick top and bottom and thin middle, which is more conducive to heat entry and water vapor transmission. The specific optimized data are shown in Figure 2 .

[0083] The theoretical evaporation rate of the model after final theoretical optimization reached 4.12kg / m 2 h, and then the optimized model was exported to conduct actual evaporation experiments, and the evaporation rate reached 4.03 kg / m 2 h, is 97.82% of the simulation state, close to the theoretical data, and 3.22kg / m 2 h increased by 25.16%, confirming the superiority of the material shape after simulation optimization.

[0084] Figure 2 3D-PVA@Bi before and after optimization for COMSOL software simulation 2 O 3 -Comparison of various data on the surface of FLG / Ppy PEMs. (a) and (a′) are the surface irradiance of the material. Under one sun, the model before optimization can only reach nearly 1W / m in the upper part of the material cone. 2 (i.e. a standard sunlight intensity), the radiation intensity received by the middle of the cylinder is 0.6~0.8W / m 2 , and the irradiation intensity of the entire model surface after optimization is maintained at 1W / m 2 It can be seen that the irregular changes in its structure are beneficial for the internal cylinder to receive sunlight, thereby improving energy utilization. Figure 2(b) and (b′) are the isothermal surfaces of the material. The highest isothermal surface before optimization is concentrated in a small area in the center of the material, and the entire isothermal surface has a small spacing and covers the material surface in a cone shape. After optimization, the highest temperature is closer to the material surface and the coverage area is increased. The higher isothermal surface is closer to the model surface instead of being concentrated above the model before optimization. Figure 2 (c) and (c′) are the water vapor escape speeds of the model section. The water vapor escape speed of the model before optimization is about 0.04 m / s. After optimization, the height of the middle cylinder is reduced and the diameter of the middle part of the cylinder is reduced, which is more conducive to the escape of water vapor. The speed is also increased to about 0.1 m / s, thereby increasing the evaporation rate of the model. The relative humidity of the model under evaporation state is Figure 2 As shown in (d) and (d′), the relative humidity gradually decreases from the inside to the outside, which corresponds to the water vapor escape rate of the model section. The optimized relative humidity distribution is more uniform, indicating a faster evaporation rate. Figure 2 (e) and (e′) are the relative pressures on the material surface, Figure 2 (f) and (f′) are the total water vapor flux on the material surface, that is, the water evaporation rate. It can be seen that the water vapor flux at the periphery of the optimized model is larger, which is manifested as a higher evaporation rate. The performance of the above models all indicate that the simulated optimized model has a higher evaporation rate and photothermal conversion efficiency.

[0085] According to the results, the 3D-PVA@Bi prepared in Examples 1-4 2 O 3 -FLG / Ppy PEMs have good evaporation efficiency in solar-driven interface evaporation, and among Examples 1-4, Example 1 is the best example, so the subsequent characterization experiments and performance testing experiments all use the 3D-PVA@Bi prepared in Example 1. 2 O 3 -FLG / Ppy PEMs are performed.

[0086] 1.2 Photocatalytic ability test

[0087] One of the advantages of the material of the present invention is that it has a high evaporation rate and a photocatalytic degradation effect on the bottom evaporating water body. When testing the photocatalytic effect, the evaporation device is closed to return the evaporated water vapor to the water body to ensure that the total amount of water body remains unchanged. Samples of the evaporated water body are extracted in different time periods to detect the concentration of methylene blue, an organic pollutant.

[0088] The methylene blue solution prepared from North Sea seawater was used as the water to be treated to simulate the seawater polluted by organic dye wastewater. The concentration of methylene blue solution in the evaporating water before and after evaporation was measured using an ultraviolet spectrophotometer (Lambda 35, Perkin Elmer, America). The removal rate calculation formula is:

[0089]

[0090] Among them C 0 and C 1 are the concentrations of methylene blue solution in the initial solution and in water after evaporation, respectively, and η is the removal rate.

[0091] Photocatalytic experiments were carried out on water bodies with different pollutant concentrations of 2mg / L, 4mg / L, 6mg / L, 8mg / L, and 10mg / L, and the concentration of water pollutants within 1 hour was recorded. Figure 1 c. At a concentration of 2 mg / L, the pollutant reduction effect over time was not obvious, and the photocatalytic removal rate after 1 hour was about 7%. 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, but when it increased to 10 mg / L, the catalytic effect decreased. This was attributed to the excessive 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 for a 6-hour continuous photocatalytic experiment. 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%. This shows 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 re-swelling test

[0094] Three groups of parallel samples were taken to test PVA and 3D-PVA@Bi prepared in Example 1. 2 O 3 -FLG / Ppy PEMs were tested for water content and re-swelling degree. The specific steps were as follows: the prepared evaporation material was soaked in water and weighed as M 0 Then put it into a freeze drying oven and dry it until the mass is constant. After it is completely dried, its weight is M f , substitute into the formula

[0095]

[0096] Calculate its moisture content as 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 re-swelling degree is calculated as S.

[0099] The test results are as follows Figure 1As shown in d, Figure 1 d shows that the water content of unmodified PVA is about 85%, which is different from the 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs are similar, indicating that the modification has little effect on the water absorption properties of PVA. The re-swelling rates of the two groups of materials were 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] Field emission scanning electron microscopy was used to study the PVA and 3D-PVA@Bi prepared in Example 1. 2 O 3 -FLG / Ppy PEMs morphology and structure were tested, and the results were as follows Figure 3 As shown in the SEM image, it can be seen that the surface of the unmodified PVA material exhibits scaly protrusions ( Figure 3 , ac), compared with 3D-PVA@Bi at the same magnification 2 O 3 -FLG / Ppy PEMs have a distinct layered mesh structure ( Figure 3 , df), due to the doping of hydrophobic materials graphene and bismuth oxide, it is conducive to the cross-linking of the network structure in 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 network structure is conducive to the diffuse reflection of light, enhancing the light absorption performance of the material, thereby improving the energy utilization rate and achieving high evaporation performance of the material.

[0103] 2.2 Water absorption performance

[0104] Since the efficient solar-driven interfacial evaporation performance must have strong water transport capacity in addition to excellent light-to-heat conversion performance, the PVA and 3D-PVA@Bi prepared in Example 1 were measured by optical contact angle measurement. 2 O 3 -FLG / Ppy PEMs are tested for water absorption and energy absorption, Figure 3 (gh) and (ij) are PVA and 3D-PVA@Bi, respectively. 2 O 3 -The water contact angle and water absorption performance of FLG / PpyPEMs show that when water droplets come into contact with the surface of the material, they become hydrophilic and quickly diffuse on the surface of the material and eventually enter the interior of the hydrogel. In the same time (50ms), the modified photothermal evaporation material exhibits stronger water absorption performance.

[0105] 2.3 Photothermal conversion performance

[0106] In addition to excellent water transport capacity, the material also needs to have efficient light-to-heat conversion performance to achieve solar steam generation. The 3D-PVA@Bi prepared in Example 1 was studied using an infrared thermal imager. 2 O 3 -Light-to-heat conversion performance of FLG / Ppy PEMs, Figure 4 is the change of sample surface temperature over time under sunlight, Figure 4 (b), (b′) and (c) show that 3D-PVA@Bi 2 O 3 -The surface temperature of FLG / Ppy PEMs rose rapidly from room temperature to 38-39°C within 20 minutes, and after one hour of irradiation, the temperature of the material surface finally fluctuated around 42°C. At the same time, from the thermal imaging image on the side, it can be observed that the heated part always remains on the liquid surface of the evaporating water body, and the middle and lower parts of the water body are close to room temperature. This shows that the evaporating material concentrates the heat on the water surface, which further shows that the material has good heat absorption and thermal insulation properties.

[0107] In order to compare their photothermal conversion performance, the thermal response of pure water was investigated under the same conditions. Figure 4 In (a) and (a′), the temperature of the pure water body rises to about 30°C within 20 minutes, and after one hour of irradiation, the water temperature remains at around 32°C. At the same time, it can be seen from the side view that the temperature of the entire evaporating water body rises to 32°C, which greatly wastes heat. In addition, it can be seen from the images simulated by COMSOL that ( Figure 4 d), under a standard sunlight, the surface temperature of the material when it reaches the optimal evaporation rate is 315K (41.85℃), which is similar to the optimal temperature captured by the thermal imager, which further verifies the photothermal conversion performance of the evaporation material. 2 O 3 -FLG / Ppy PEMs not only have excellent water absorption properties, but also have outstanding photothermal conversion capabilities, making 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs are ideal for interfacial evaporation.

[0108] 2.4 XRD and XPS spectra overview

[0109] The crystal structure and element valence state of the surface of the evaporated material were evaluated by X-ray diffraction and X-ray photoelectron spectroscopy. XRD studied the 3D-PVA@Bi prepared in Example 1. 2 O 3-Bi photocatalyst in FLG / Ppy PEMs 2 O 3 Features( Figure 5 a), by Bi 2 O 3 PDF#76-1730 shows that several obvious peaks appear at 27.3°, 33.2°, 37.6°, 46.3° and 52.3°. 2 O 3 -FLG / Ppy produced corresponding characteristic peaks, indicating that Bi 2 O 3 Stable crystallization occurs on the surface of the evaporated material. In addition, two sharp peaks are observed at 19.5° and 40.3° for the original PVA hydrogel, corresponding to the 3D-PVA@Bi 2 O 3 -FLG / Ppy PEMs, but with a lower intensity, indicating that Bi 2 O 3 The introduction of will limit the interaction between PVA molecular chains to a certain extent, thereby affecting the group crystallization degree of PVA.

[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 400-4000cm -1 ; 3D-PVA@Bi 2 O 3 -The FT-IR spectrum of FLG / Ppy PEMs shows that ( Figure 5 b), sample at 3260cm -1 and 2914cm -1 There is an obvious absorption band at 1087cm -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 that α-Bi 2 O 3 The existence of PVA and 3D-PVA@Bi 2 O 3 -Overall XPS spectrum of 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 Ppy and α-Bi 2 O 3The doping 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, α-Bi 2 O 3 The Bi 4f peak in the 4f region is due to 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 175.10 eV and 163.20 eV respectively. The XPS spectrum of O 1s is shown in Figure 5 e, the two peaks corresponding to the binding energies at 530.68 eV and 531.28 eV 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 f, the peak at 397.60 eV can be attributed to NH in the photothermal coating Ppy. The above results all indicate that the photocatalyst α-Bi 2 O 3 Successful doping and effective deposition of the photothermal layer Ppy.

[0112] Having a wide spectral absorption band is also one of the performance criteria for measuring photothermal materials. In the 200-2500nm solar spectrum wavelength region, the UV-visible-near infrared spectrometer was used to measure the absorption of PVA and 3D-PVA@Bi 2 O 3 -Absorption and reflection spectra of FLG / Ppy PEMs, such as Figure 5 g and 5f. The light absorption rate of the unmodified PVA is concentrated at about 5% in the wavelength range of 400-1400nm and about 30% in the wavelength range of 1400-2400nm, respectively, while the absorption rate of the modified photothermal material is concentrated at 70% to 80% in almost the entire wavelength band, indicating that the material has obvious light absorption advantages. It can be further seen from the light reflectivity spectrum that the light reflectivity and absorption rate of the two materials in the entire wavelength band correspond to each other, and the smaller light reflectivity can reduce light loss, which proves that the modified material has obvious advantages in light-thermal conversion performance.

[0113] 3. Performance comparison

[0114] In addition, the 3D-PVA@Bi prepared in Example 4 of this method 2 O 3 -FLG / Ppy PEMs and Comparative Examples 1-3 were tested for evaporation rate under the same conditions. The evaporation rate results of the two-dimensional planar materials are as follows: Figure 6 As shown in Figure 2, and compared with the evaporation rates of other materials reported (see references 1-16), it is found that PSF@PDA / TiO 2-Ag / Ppy HFMs achieved excellent evaporation rate of 4.03kg / (m 2 The evaporation rate of ·h) exceeds that of a large number of photothermal materials reported 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@Bi 2 O 3 When the FLG / Ppy PEMs are in a planar shape, the evaporation rate is 1.41 kg / (m 2 ·h), which is about 4.6 times that of pure water. After optimization, when it is cylindrical, its evaporation rate reaches 3.12kg / (m 2 ·h), after optimization, when it is cylindrical and cone-shaped, its evaporation rate reaches 3.22kg / (m 2 ·h), and finally optimized to a cylindrical cone with a thin center and thick ends, the evaporation rate reached 4.03kg / (m 2 h), and in the evaporation experiment simulating the North Sea water polluted by methylene blue dye, it showed a high evaporation rate of 3.06 kg / (m 2 h), and the degradation effect of pollutants in the evaporated water reached 81% in a continuous 6-hour illumination experiment; this proves that the 3D-PVA@Bi prepared by this method 2 O 3 -FLG / Ppy PEMs not only have a high evaporation rate in seawater desalination applications, but also show great potential and application prospects in treating seawater contaminated by organic dyes.

[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 inselective adsorption of organic solvents and removal of Rh B[J].Separationand Purification Technology,2022,295:121274.

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

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

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

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

[0125] [6]Yang Z,Liu Y,Xue K,et al.PEI-GOs / PVA photothermal sponge withenhanced 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-basedflexible 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 forhighly efficient seawater desalination and contaminant adsorption[J].Journalof Environmental Chemical Engineering,2022,10(6):108616.

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

[0129]

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

[0130]

[11] Zhao X,Chen Y,Yin Y,et al.Janus polypyrrole nanobelt@polyvinylalcohol hydrogel evaporator for robust solar-thermal seawater desalinationand 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 polymernetworks to tune the water state for solar water purification[J].ScienceAdvances,2019,5(6):eaaw5484.

[0132]

[13] Hao L,Liu N,Bai H,et al.High-performance solar-driven interfacialevaporation through molecular design of antibacterial,biomass-derivedhydrogels[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-toleranthydrogels 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 interfacialwater evaporation by architecting 3D interconnected polymetric network in CNTcellular structure[J].Chemical Engineering Journal,2023,451:138676.

[0135]

[16] Zhou X,Guo Y,Zhao F,et al.Topology-controlled hydration ofpolymer 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 is to dope a few layers of FLG and α-Bi2O3 into 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, including 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, stir to make Bi2O3 evenly dispersed in the polyvinyl alcohol solution, and obtain a PVA@Bi2O3 solution; S2, preparation of 3D-PVA@Bi2O3-FLG PEMs: dissolving FLG in water, stirring evenly and adding it to the PVA@Bi2O3 solution obtained in S1, stirring and adding a cross-linking agent and water, stirring again and pouring it into a mold, freezing the mold in a freezing environment, taking it out and thawing it at room temperature, repeating freezing and thawing, soaking it in water after thawing, and finally rinsing it with pure water to remove the unreacted chemical substances on the surface, thereby obtaining 3D-PVA@Bi2O3-FLG PEMs, wherein 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 it; 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.

2. The preparation method according to claim 1, characterized in that: The following steps are involved: S1. Preparation of PVA@Bi2O3: dissolving an appropriate amount of polyvinyl alcohol in water under stirring to obtain a 0.1 g / mL polyvinyl alcohol solution, weighing an appropriate amount of Bi2O3 and adding it to the polyvinyl alcohol solution, the added amount of Bi2O3 and the added amount of polyvinyl alcohol being 1:(0.5-1.5), stirring to uniformly disperse Bi2O3 in the polyvinyl alcohol solution, and obtaining a PVA@Bi2O3 solution; S2. Preparation of 3D-PVA@Bi2O3-FLG PEMs: Dissolve 0.04-0.1g FLG in 4-10mL water, 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 -20℃-(-40℃) freezing environment and freeze for 8-12h, then take 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 cross-linking 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), and sulfuric acid solution is added after stirring evenly, and the mass ratio of the sulfuric acid solution to the glutaraldehyde solution is (0.8-1.4):2, and after the solution is completely reacted to yellow-brown, 40-60 mL of water is added to dilute and stir evenly to obtain a light yellow cross-linking 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, characterized in that: 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 and stirred continuously to uniformly disperse Bi2O3 in the polyvinyl alcohol solution to obtain a PVA@Bi2O3 solution. Preferably, in step S2, the inner cavity of the mold is a plurality of cylindrical chambers, and the height of the cylindrical chamber is 2 cm and the diameter is 0.6 cm.

4. The preparation method according to claim 3, characterized in that: 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 fully stirred, 1 mL of sulfuric acid solution is added while continuing to slowly stir, and after the solution is completely reacted to a yellowish brown color, 50 mL of water is added to the beaker to dilute it, and after being stirred evenly, a light yellow cross-linking agent is obtained; Preferably, in step S2, the 0.5 cm area at the top of the cylindrical chamber is a cone with the same bottom and height, and the diameter of the middle of the cylindrical chamber is smaller than the diameters at both 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 water, stir at room temperature for 1 h to obtain a uniform solution, add it to the PVA@Bi2O3 solution obtained in S1, stir at room temperature for 1 h, then add 1 mL of cross-linking agent and 2 mL of water, stir again for 1 h and pour into a mold, place the mold in a -20°C freezing environment and freeze it for 10 h, then take it out and thaw it at room temperature for 3 h, repeat freezing and thawing 5 times, soak it in deionized water for 24 h after thawing, change the water every 12 hours, and finally rinse it in pure water for 5 min to remove the unreacted chemicals on the surface to obtain 3D-PVA@Bi2O3-FLG PEMs.

6. The preparation method according to claim 2, 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 put a culture dish in the beaker. Drop 70-100μl of py into the culture dish, and place the beaker in a 50-70℃ vacuum drying oven for 1-2h to complete polypyrrole 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 for 1h to complete the polypyrrole vapor phase chemical deposition. After the reaction is completed, rinse in pure water for 5min 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 of the three-dimensional modified polyvinyl alcohol hydrogel is placed below the water surface, and the top is located above the water surface and is used to receive sunlight to be heated and evaporate water.

Images