Solar interface evaporator based on amphoteric polyelectrolyte photo-thermal hydrogel, preparation method and application

Abstract

The invention provides a solar interface evaporator based on amphoteric polyelectrolyte photo-thermal hydrogel, a preparation method and application, and belongs to the field of solar interface evaporation. The solar interface evaporator with a three-dimensional multi-surface evaporation structure is prepared by combining the polyelectrolyte resisting effect of the amphoteric polyelectrolyte photo-thermal hydrogel and the porous capillary effect of the sponge, and has the characteristics of high light absorptivity, good water absorption effect, excellent antibacterial property, mechanical property, salt resistance, evaporation property and the like; particularly, compared with a traditional hydrogel-based solar interface evaporator, the water delivery capacity and the salt resistance in high-concentration saline water are greatly improved through the application of the autonomously designed zwitterionic hydrogel, water molecules in the saline water are activated through the cooperation of salt-resistant ionized water, the evaporation enthalpy is reduced, and the evaporation efficiency is improved. And a great positive effect is achieved on improvement of the evaporation rate. The evaporator is easy to prepare and excellent in multi-dimensional performance, and a new way and thought are provided for application to seawater desalination and wastewater treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar interfacial evaporation, and relates to a solar interfacial evaporator based on amphoteric polyelectrolyte photo-thermal hydrogel, a preparation method thereof and an application thereof. Background Art

[0002] Water resources are the basic natural resources for human survival and strategic economic resources. Facing the intensification of the contradiction between the supply and demand of fresh water resources, the development and utilization of seawater, which accounts for 97% of the global water resources, has become the key to breaking the deadlock. Although the current mainstream seawater desalination technologies have been industrialized, their operation mostly depends on the technical characteristics of high-grade heat energy or stable electric energy supply, resulting in a high energy consumption intensity and a significant carbon footprint. Compared with conventional fossil energy, solar energy is one of the cleanest energy sources and is inexhaustible. Therefore, using solar energy for seawater desalination is an effective path for sustainable fresh water acquisition. The photo-thermal materials in traditional solar distillation devices are usually placed at the bottom of water or dispersed in water in the form of nanofluids. Not only a large amount of sunlight is reflected on the water surface, but the incident sunlight also has to pass through a relatively thick water layer to be absorbed by the photo-thermal materials. Eventually, the entire water body is heated by volume heating, resulting in large heat losses. A low evaporation rate (water production) per unit area requires a large floor area, so it cannot be widely used.

[0003] The proposed solar interfacial evaporation technology has improved the drawbacks of traditional solar distillation and become a milestone in the development of solar evaporation technology. This is mainly attributed to the fact that photothermal materials can localize the heat converted from solar energy at the evaporation interface for water evaporation, greatly reducing heat loss and thus enhancing the evaporation rate. Hydrogels have shown excellent performance in many types of solar interfacial evaporators because they can change the hydrogen bond state of water molecules and reduce the enthalpy of water evaporation by adjusting the interactions between water-polymer networks-hydrophilic functional groups. Nevertheless, the strong hydration of salt ions and the problem of salt crystallization during long-term evaporation remain one of the bottlenecks in the solar interfacial evaporation technology for treating saline feed solutions. The hydration of salt ions requires more energy for water evaporation, and salt crystallization seriously affects the absorption of sunlight by the evaporator and water transport, and restricts the outward diffusion of water vapor, resulting in a decrease in the evaporation rate and fresh water production. Drawing on the characteristics of biological ion channels that have both cation / anion selectivity and interaction selectivity, the charges carried on the polymer chains of polyelectrolyte hydrogels are similar to the functions of biological ion channels, and the binding of anionic / cationic salt ions can be effectively inhibited through ion selectivity. However, due to the polyelectrolyte effect, most hydrogel polymer chains adopt a folded conformation in salt water, making the water supply capacity mismatch with evaporation and also leading to a decrease in the evaporation rate. In addition, traditional hydrogel evaporators generally have poor mechanical properties, such as low mechanical strength (<120 kPa), which is also one of the factors limiting the structural design and practical application of hydrogel-based evaporators. How to design a hydrogel-based evaporator with excellent multi-dimensional properties and not affect or even improve the evaporation performance when treating salt water remains a challenge. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a solar interfacial evaporator based on amphoteric polyelectrolyte photothermal hydrogel to solve the problems of poor mechanical properties, poor water transport performance, and poor anti-salt performance of existing hydrogel-based evaporators in salt water. The present invention utilizes the anti-salt ion hydration effect of amphoteric polyelectrolyte photothermal hydrogel to activate water molecules in salt water, break the energy barrier required for evaporation, and reduce energy consumption; utilizes the anti-polyelectrolyte effect to make the polymer chains adopt a stretched conformation in salt water, enhancing the water transport performance. At the same time, the cationic and anionic groups on the polymer chains can respectively attract sodium ions and chloride ions in salt water, separating positive and negative salt ions and effectively preventing salt crystallization; utilizes the hierarchical porous structure of the sponge to provide channels for water transport and the diffusion and reflux of salt ions from the evaporation interface back to the feed liquid pool, further enhancing the water transport performance and anti-salt performance. At the same time, the soft sponge as the basic framework of the evaporator can greatly enhance its mechanical strength. In addition, the antibacterial property of the evaporator of the present invention can effectively resist biological contamination, thereby prolonging the service life of the evaporator and reducing the cleaning cost.

[0005] The first aspect of the present invention provides a solar interface evaporator based on an amphoteric polyelectrolyte photothermal water gel, comprising a porous sponge and an amphoteric polyelectrolyte photothermal water gel embedded in the internal pores of the porous sponge; the amphoteric polyelectrolyte photothermal water gel comprises a polymer network formed by a high molecular polymer and a photothermal conversion material dispersed in the polymer network; the high molecular polymer comprises polyvinyl alcohol, a cationic polymer, an anionic polymer and a crosslinking agent.

[0006] Preferably, the degree of crosslinking of the amphoteric polyelectrolyte photothermal water gel is 1% to 2%; in the amphoteric polyelectrolyte photothermal water gel, the mass fractions of polyvinyl alcohol, cationic polymer, anionic polymer, and photothermal conversion material are 3 to 7 wt%, 0.5 to 1.5 wt%, 0.5 to 1.5 wt%, and 3 to 8 wt%, respectively.

[0007] Preferably, the cationic polymer includes one or a combination of two or more of chitosan, chitosan quaternary ammonium salt, polyallylamine hydrochloride, polyethyleneimine or polydiallyl dimethyl ammonium chloride; the anionic polymer includes one or a combination of two or more of poly(p-styrene sulfonate), poly(p-styrene sulfonic acid), sodium hyaluronate or sodium dextran sulfate; the photothermal conversion material includes one or a combination of two or more of carbon nanotubes, graphene, carbonized biomass (such as carbonized wood chips), metal nanoparticles (such as gold and silver nanoparticles), titanium dioxide, polypyrrole or polydopamine; and the cross-linking agent is a mixture of a hydrochloric acid solution and a glutaraldehyde solution.

[0008] Preferably, the porous sponge includes polyvinyl alcohol sponge, melamine sponge, polyurethane sponge, cellulose sponge or polyester sponge; the porosity of the porous sponge is 80% to 99%, and the internal pore size distribution is 40 to 180 μm.

[0009] The second aspect of the present invention provides a method for preparing a solar interface evaporator based on an amphoteric polyelectrolyte photothermal water gel, comprising the following steps:

[0010] Step 1: adding polyvinyl alcohol powder and cationic polymer powder into an aqueous solution, heating and stirring to obtain a mixed solution A;

[0011] Step 2: adding anionic polymer powder and photothermal conversion material to the mixed solution A, and stirring thoroughly to obtain a mixed solution B;

[0012] Step 3: adding a crosslinking agent to the mixed solution B at a crosslinking degree of 1% to 2%, and preparing a hydrogel precursor solution after rapid stirring; in the hydrogel precursor solution, the mass fractions of polyvinyl alcohol, cationic polymer, anionic polymer, and photothermal conversion material are 3 to 7 wt%, 0.5 to 1.5 wt%, 0.5 to 1.5 wt%, and 3 to 8 wt%, respectively;

[0013] Step 4: Immerse the porous sponge completely into the hydrogel precursor solution. After the porous sponge is completely wetted, place it at room temperature to obtain a solar interface evaporator based on amphoteric polyelectrolyte photothermal hydrogel.

[0014] Preferably, the cationic polymer includes one or a combination of two or more of chitosan, polyallylamine hydrochloride, polyethyleneimine, or polydiallyldimethylammonium chloride; the anionic polymer includes one or a combination of two or more of sodium poly(styrenesulfonate), poly(styrenesulfonic acid), sodium hyaluronate, or sodium dextran sulfate; the photothermal conversion material includes one or a combination of two or more of carbon nanotubes, graphene, carbonized biomass (such as carbonized wood chips), metal nanoparticles (such as gold and silver nanoparticles), titanium dioxide, polypyrrole, or polydopamine.

[0015] Preferably, the crosslinking agent is a mixture of hydrochloric acid solution and glutaraldehyde solution; wherein, the mass fraction of the hydrochloric acid solution is 2-4 wt%, preferably 3 wt%; the mass fraction of the glutaraldehyde solution is 50 wt%; the volume ratio of the hydrochloric acid solution to the glutaraldehyde solution is 6:1-3:1, preferably 5:1.

[0016] Preferably, the crosslinking degree is calculated according to the following formula:

[0017]

[0018] Wherein, GA represents glutaraldehyde and PVA represents polyvinyl alcohol.

[0019] Preferably, in the hydrogel precursor solution, the mass fraction of polyvinyl alcohol is preferably 5 wt%; the mass fraction of the cationic polymer is preferably 1 wt%; the mass fraction of the anionic polymer is preferably 1 wt%; the mass fraction of the photothermal conversion material is preferably 5 wt%.

[0020] Preferably, the crosslinking degree of the hydrogel precursor solution is 1.5%.

[0021] Preferably, in Step 1, the temperature of heating and stirring is 80-95 °C, preferably 90 °C; the stirring speed is 50-150 rpm, preferably 100 rpm; the stirring time is 4-8 hours, preferably 6 hours;

[0022] In Step 2, the stirring speed is 100-300 rpm, preferably 200 rpm; the stirring time is 0.5-1.5 hours, preferably 1 hour;

[0023] In Step 3, the rotation speed of rapid stirring is 400-600 rpm, preferably 500 rpm; the stirring time is 3-8 minutes, preferably 5 minutes;

[0024] In Step 4, the immersion time is 20 to 40 minutes, preferably 30 minutes.

[0025] Preferably, the porous sponge includes a polyvinyl alcohol (PVA) sponge, a melamine sponge, a polyurethane sponge, a cellulose sponge, or a polyester sponge; the porosity of the porous sponge is 80% to 99%, and the internal pore size distribution is 40 to 180 μm.

[0026] The third aspect of the present invention provides an application of a solar interfacial evaporator based on an amphoteric polyelectrolyte photo-thermal hydrogel in the preparation of solar desalination materials.

[0027] Advantages of the present invention: By using the solar interfacial evaporator based on an amphoteric polyelectrolyte photo-thermal hydrogel provided by the present invention, the anti-polyelectrolyte effect and anti-salt ion hydration effect of the zwitterionic hydrogel are utilized to enhance the water transport capacity and anti-salt ability of the evaporator in saline water, and the water transport capacity and mechanical strength (>560 kPa) are enhanced by using a layered porous structure of polyvinyl alcohol sponge, thereby enhancing the evaporation performance of the evaporator in saline water. The evaporation rate can reach 3.35 kg / (m 2 ·h) continuously for 9 hours in a 10 wt% NaCl solution, and there is no obvious salt deposition and structural change on the surface of the evaporator. The evaporation rate can reach 2.94 kg / (m 2 ·h) in a 15 wt% NaCl solution, and the evaporation rate can reach 2.87 kg / (m 2 ·h) in a 20 wt% NaCl solution, and the antibacterial rate of the evaporator against Escherichia coli is as high as 100%. The above-mentioned evaporator provides a new approach and idea for the development of the next-generation solar interfacial evaporation system applied to seawater desalination and wastewater treatment. Description of the Drawings

[0028] Figure 1 It is an electron microscope image and an X-ray energy spectrometer elemental analysis chart of the solar interfacial evaporator prepared in Example 1 of the present invention under dry conditions.

[0029] Figure 2 It is the FTIR infrared absorption peaks of polyvinyl alcohol (PVA), chitosan (CS), sodium polystyrene sulfonate (PSS), and amphoteric polyelectrolyte photo-thermal hydrogel in Example 1 of the present invention.

[0030] Figure 3 It is the ultraviolet-visible-near-infrared light absorption spectrum chart of the solar interfacial evaporator (PCP evaporator) prepared in Example 1 of the present invention under dry conditions.

[0031] Figure 4 It is a process diagram of a water droplet with a diameter of 3 mm hitting the upper surface of the solar interfacial evaporator prepared in Example 1 of the present invention from a height of 5 cm.

[0032] Figure 5 For the evaporator (3×3×7 cm) prepared in Example 1 of the present invention under a light irradiance of 1 kW / m 2 The mass change diagram and evaporation rate diagram during evaporation in salt water with different salinities; among them, (a) is the mass change diagram during evaporation, and (b) is the evaporation rate diagram.

[0033] Figure 6 Schematic diagram of the evaporator (3×3×7 cm) prepared in Example 1 of the present invention returning to its original state after being mechanically compressed.

[0034] Figure 7 Changes in the continuous evaporation for 9 hours of Example 1 of the present invention and Comparative Example 1 in 20 wt% NaCl solution; among them, (a) is the change diagram of the evaporation upper surface of Example 1, and (b) is the change diagram of each evaporation surface of Comparative Example 1.

[0035] Figure 8 Comparison diagram before and after seawater desalination in the outdoor evaporation experiment of the evaporator prepared in Example 1 of the present invention, where (a) is the change in the ion concentrations of seawater and collected fresh water before and after seawater desalination, and (b) is the change in the turbidity of turbid seawater and collected fresh water before and after seawater desalination. Detailed implementation manners

[0036] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples cited are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0037] All reagents in the present invention are purchased from Shanghai Macklin Biochemical Co., Ltd.

[0038] Example 1

[0039] Weigh 5 g of PVA powder and 1 g of CS powder and add them to 92.5 g of acetic acid aqueous solution (2 wt%). Place the beaker in a water bath at 90 °C and stir at a speed of 100 rpm for 6 h; after cooling to room temperature, add 1 g of PSS powder and 0.5 g of carbon nanotubes (CNTs). After stirring at a speed of 200 rpm for 1 h, use a mixed solution of 3 wt% HCl solution and 50 wt% GA solution as a crosslinking agent and co-drop 810 μL of the crosslinking agent according to the volume ratio of the two of 5:1. Control the crosslinking degree to be 1.5%, and quickly stir at a speed of 500 rpm for 5 min to prepare a hydrogel precursor solution. Then, completely immerse the PVA sponge (3×3×9 cm, effective evaporation height of 7 cm) into the beaker for 30 min, and take it out and place it at room temperature for 8 h to prepare a solar interface evaporator based on amphoteric polyelectrolyte photo-thermal hydrogel.

[0040] Example 2

[0041] Weigh 3 g of PVA powder and 1.5 g of CS powder and add them to 93.5 g of acetic acid aqueous solution (2 wt%). Place the beaker in a water bath at 90 °C and stir at 100 rpm for 6 h. After cooling to room temperature, add 1.5 g of PSS powder and 0.5 g of carbon nanotubes (CNTs). Stir at 200 rpm for 1 h, then use a mixed solution of 3 wt% HCl solution and 50 wt% GA solution as a crosslinking agent and drop a total of 486 μL of the crosslinking agent according to the volume ratio of the two of 5:1. Control the crosslinking degree to be 1.5%, and quickly stir at 500 rpm for 5 min to prepare a hydrogel precursor solution. Then completely immerse the PVA sponge (3×3×9 cm, effective evaporation height is 7 cm) into the beaker for 30 min, and after taking it out, place it at room temperature for 8 h to prepare a solar interface evaporator based on zwitterionic polyelectrolyte photothermal hydrogel.

[0042] Example 3

[0043] Weigh 7 g of PVA powder and 1.5 g of CS powder and add them to 89.5 g of acetic acid aqueous solution (2 wt%). Place the beaker in a water bath at 90 °C and stir at 100 rpm for 6 h. After cooling to room temperature, add 1.5 g of PSS powder and 0.5 g of carbonized wild jujube wood chips. Stir at 200 rpm for 1 h, then use a mixed solution of 3 wt% HCl solution and 50 wt% GA solution as a crosslinking agent and drop a total of 1122 μL of the crosslinking agent according to the volume ratio of the two of 5:1. Control the crosslinking degree to be 1.5%, and quickly stir at 500 rpm for 5 min to prepare a hydrogel precursor solution. Then completely immerse the melamine sponge (3×3×9 cm, effective evaporation height is 7 cm) into the beaker for 30 min, and after taking it out, place it at room temperature for 8 h to prepare a solar interface evaporator based on zwitterionic polyelectrolyte photothermal hydrogel.

[0044] Example 4

[0045] Weigh 5 g of PVA powder and 1 g of CS powder and add them to 93 g of acetic acid aqueous solution (2 wt%). Place the beaker in a water bath at 90 °C and stir at 100 rpm for 6 h. After cooling to room temperature, add 0.5 g of PSS powder and 0.5 g of graphene. Stir at 200 rpm for 1 h, then use a mixed solution of 3 wt% HCl solution and 50 wt% GA solution as a crosslinking agent and drop a total of 536 μL of the crosslinking agent according to the volume ratio of the two of 5:1. Control the crosslinking degree to be 1%, and quickly stir at 500 rpm for 5 min to prepare a hydrogel precursor solution. Then completely immerse the polyurethane sponge (3×3×9 cm, effective evaporation height is 7 cm) into the beaker for 30 min, and after taking it out, place it at room temperature for 8 h to prepare a solar interface evaporator based on zwitterionic polyelectrolyte photothermal hydrogel.

[0046] Example 5

[0047] Weigh 5 g of PVA powder and 1 g of polyallylamine hydrochloride powder, add them to 92.5 g of deionized water. Place the beaker in a water bath at 90 °C and stir at a speed of 100 rpm for 6 h. After cooling to room temperature, add 1 g of sodium salt of dextran sulfate powder and 0.5 g of carbon nanotubes (CNTs). After stirring at 200 rpm for 1 h, use the mixed solution of 3 wt% HCl solution and 50 wt% GA solution as the cross-linking agent and drop a total of 810 μL of the cross-linking agent according to the volume ratio of the two of 5:1. Control the cross-linking degree to 1.5%, and quickly stir at a speed of 500 rpm for 5 min to prepare a hydrogel precursor solution. Then, completely immerse the melamine sponge (3×3×9 cm, effective evaporation height of 7 cm) into the beaker for 30 min, and after taking it out, place it at room temperature for 8 h to prepare a solar interface evaporator based on zwitterionic polyelectrolyte photothermal hydrogel.

[0048] Example 6

[0049] Weigh 5 g of PVA powder and 1 g of polyethyleneimine powder, add them to 92.5 g of deionized water. Place the beaker in a water bath at 90 °C and stir at a speed of 100 rpm for 6 h. After cooling to room temperature, add 1 g of poly(styrenesulfonic acid) powder and 0.5 g of carbon nanotubes (CNTs). After stirring at 200 rpm for 1 h, use the mixed solution of 3 wt% HCl solution and 50 wt% GA solution as the cross-linking agent and drop a total of 1084 μL of the cross-linking agent according to the volume ratio of the two of 5:1. Control the cross-linking degree to 2%, and quickly stir at a speed of 500 rpm for 5 min to prepare a hydrogel precursor solution. Then, completely immerse the polyurethane sponge (3×3×9 cm, effective evaporation height of 7 cm) into the beaker for 30 min, and after taking it out, place it at room temperature for 8 h to prepare a solar interface evaporator based on zwitterionic polyelectrolyte photothermal hydrogel.

[0050] Comparative Example 1

[0051] The difference between Comparative Example 1 and Example 1 is that the polymer in the hydrogel precursor solution of Comparative Example 1 is only PVA. The specific preparation steps are as follows: Weigh 5 g of PVA powder and add it to 94.5 g of deionized water. Stir the beaker in a water bath at 90 °C at a speed of 100 rpm for 6 h. After cooling to room temperature, add 0.5 g of CNTs and stir for 1 h at a speed of 200 rpm. Then, a mixed solution of 3 wt% HCl solution and 50 wt% GA solution is used as a crosslinking agent and a total of 810 μL of the crosslinking agent is co-dropped according to the volume ratio of the two of 5:1. Control the crosslinking degree to 1.5%. After rapidly stirring at a speed of 500 rpm for 5 min, a hydrogel precursor solution is prepared. Then, a PVA sponge (3×3×9 cm, effective evaporation height is 7 cm) is completely immersed in the beaker for 30 min, and after taking it out, it is placed at room temperature for 8 h to prepare a solar interface evaporator based on PVA hydrogel.

[0052] Comparative Example 2

[0053] The difference between Comparative Example 2 and Example 1 is that the crosslinking degree of the hydrogel precursor solution in Comparative Example 2 is 3%. The specific preparation steps are as follows: Weigh 5 g of PVA powder and 1 g of CS powder and add them to 92.5 g of acetic acid aqueous solution (2 wt%). Stir the beaker in a water bath at 90 °C at a speed of 100 rpm for 6 h. After cooling to room temperature, add 1 g of PSS powder and 0.5 g of carbon nanotubes (CNTs) and stir for 1 h at a speed of 200 rpm. Then, a mixed solution of 3 wt% HCl solution and 50 wt% GA solution is used as a crosslinking agent and a total of 1642 μL of the crosslinking agent is co-dropped according to the volume ratio of the two of 5:1. Control the crosslinking degree to 3%. After rapidly stirring at a speed of 500 rpm for 5 min, a hydrogel precursor solution is prepared. Then, a PVA sponge (3×3×9 cm, effective evaporation height is 7 cm) is completely immersed in the beaker for 30 min, and after taking it out, it is placed at room temperature for 8 h. Due to the too high crosslinking degree, the viscosity of the hydrogel precursor solution is too high, resulting in the failure to fill the photo-thermal hydrogel in the internal voids of the porous sponge, that is, the solar interface evaporator based on the amphoteric polyelectrolyte photo-thermal hydrogel is not successfully prepared.

[0054] The evaporator (solar interface evaporator) prepared in Example 1 and the evaporator (PVA evaporator) prepared in Comparative Example 1 were characterized and tested, and the results are as follows:

[0055] (1) Characterize the dried solar interface evaporator. The polyvinyl alcohol sponge filled with the amphoteric polyelectrolyte photo-thermal hydrogel (prepared into a solar interface evaporator, see Figure 1)Due to the addition of CNTs, it presents an overall black color, which lays the foundation for high light absorption rate and efficient photothermal conversion. The existence of the multi-layer structure will cause multiple refractions and scatterings of light, thereby increasing the optical path and further enhancing the light utilization rate. In addition to tightly adhering to the PVA sponge skeleton, the pores in the middle of the skeleton are also evenly filled with a large amount of amphoteric polyelectrolyte photothermal hydrogel, which increases the roughness while still retaining the porous structure. This high surface activity makes it easier for water molecules to adsorb on the material surface, thereby increasing the hydrophilicity, which also provides a strong guarantee for efficient solar interface evaporation and seawater desalination. In addition, the energy dispersive spectrometer (EDS) also proves the successful preparation of the amphoteric polyelectrolyte photothermal hydrogel and the uniform distribution of each component. At the position where the amphoteric polyelectrolyte photothermal hydrogel is filled in the middle of the polyvinyl alcohol sponge skeleton, C and O are the basic elements of all components, the existence of N element represents CS, and the existence of S element represents PSS. Figure 2 shows the Fourier transform infrared spectra (FTIR) of the amphoteric polyelectrolyte photothermal hydrogel (PCP) without CNTs, PVA, CS, and PSS. All samples show broad and strong absorption peaks in the range of 3000–3700 cm -1 , which are attributed to the stretching vibrations of -OH or -NH2. In the infrared spectrum of pure PVA, the peaks at 1087 cm -1 and 2931 cm -1 correspond to the stretching vibration of C-O and the symmetric -CH2 vibration, respectively. The characteristic absorption peak of C=O of CS appears at 1640 cm -1 , while the absorption peaks at 1260 cm -1 and 1607 cm -1 correspond to the stretching vibrations of C-H and N-H, respectively. With the gradual addition of PVA and CS, the stretching vibration peaks of -OH and -NH2 in the amphoteric polyelectrolyte photothermal hydrogel shift slightly towards lower wavenumbers, which is due to the formation of intermolecular and intramolecular hydrogen bonds. In addition, the absorption peaks at 1039 cm -1 and 1182 cm -1 originate from the symmetric stretching vibration and asymmetric stretching vibration of the S=O group of SO3 - , respectively. The characteristic absorption peak of C=C of PSS appears in the range of 1450–1600 cm -1 , and the vibration peak of the para-substituted benzene ring is located at 810–833 cm -1 . The stretching vibration peak of the C=N bond formed after the cross-linking of CS with glutaraldehyde (GA) appears in the range of 1630–1690 cm -1 ; while PVA and GA form a C-O-C-O polyether structure through an aldol reaction, and its coupled vibration peak appears at 1050–1200 cm -1The infrared spectrum of the amphoteric polyelectrolyte hydrogel showed the main characteristic peaks of PVA, CS and PSS, indicating that the hydrogel was successfully prepared.

[0056] (2) Figure 3 The absorbance test results of the solar interface evaporator (PCP evaporator) in the wavelength range from 280 to 2500nm under completely dry conditions are shown. Under the action of MWCNTs and the layered porous structure, the light absorption rate of the solar interface evaporator is calculated to be 95.9% based on the test results. It is worth noting that the light absorption rate of the evaporator will be higher in the actual evaporation process, that is, in the wet state.

[0057] (3) Figure 4 The high-speed camera captured the impact process of a 3mm diameter water droplet falling freely from a height of 5cm onto the upper surface of the solar interface evaporator. The experiment showed that the droplet was completely absorbed about 711ms after hitting the surface of the solar interface evaporator. This phenomenon proves that the material has excellent water absorption performance, which can effectively ensure the continuous water supply during the evaporation process; at 1kW / m 2 Under light irradiance, Figure 5 (a) shows the change in mass of the feed liquid during evaporation in different salinity feed liquids using a solar interface evaporator with an effective evaporation height of 7 cm. It is obvious that the mass of the 10wt% feed liquid decreases the fastest, that is, the evaporation rate is the largest. Figure 5 (b) shows the change of evaporation rate of the liquid in the process of evaporation in different salinity liquids by the solar interface evaporator with an effective evaporation height of 7 cm. The evaporation rate of 10wt% liquid is as high as 3.35kg / (m 2 ·h), the evaporation rate in 15wt% NaCl solution is as high as 2.94kg / (m 2 ·h), the evaporation rate in 20wt% NaCl solution can reach 2.87kg / (m 2 ·h); It is worth noting that the evaporation rate of the evaporator in salt water is slightly higher than that in pure water due to the anti-salt ion hydration of the amphoteric polyelectrolyte photothermal gel.

[0058] (4) Typical solar interface evaporator compression test process Figure 6 As shown, the 7 cm high solar interfacial evaporator has robust compression performance and withstands 80% compression strain without any structural damage. After the pressure is removed, the solar interfacial evaporator can restore its original shape, showing super strong mechanical stability.

[0059] (5)1kW / m 2Under light irradiance, the salt precipitation on the surface of the solar interface evaporator (PCP evaporator) prepared in Example 1 and the PVA evaporator prepared in Comparative Example 1 during the evaporation process of a 20 wt% feed solution for 9 h was compared to evaluate the durability and salt resistance of the evaporator. Figure 7 Figure (a) shows the surface changes of the solar interface evaporator. During the evaporation process lasting up to 9 h, not only was there no salt crystallization on the upper surface, but also the evaporation rate did not decrease significantly. Since the evaporation rate on the upper surface was faster than that on the side, there was naturally no salt crystallization on the side of the solar interface evaporator. From Figure 7 Figure (b), it can be seen that for the PVA evaporator, starting from 1 h, a small amount of salt crystals began to appear at the edges of the edges, and after 2 h, large areas of salt crystals began to appear on each evaporation surface. After 9 h, due to the accumulation of salt, the surface of the PVA evaporator had become hard.

[0060] (6) As can be seen from Figure 8 Figure (a), when using the solar interface evaporator based on amphoteric polyelectrolyte photothermal hydrogel prepared in Example 1 for seawater desalination using the turbid seawater in the Bohai Bay in the winter outdoor environment in Dalian, the ion concentration in the collected fresh water was reduced to below the drinking water standard stipulated by the World Health Organization, and the fresh water was significantly clearer and more transparent, as shown in Figure 8 Figure (b).

[0061] In summary, the solar interface evaporator based on amphoteric polyelectrolyte photothermal hydrogel prepared by the present invention can improve the performance of the solar interface evaporator in treating salt-containing feed solutions.

[0062] Although the above embodiments have detailed the technical solutions of the present invention, they are only some preferred embodiments of the present invention rather than all implementation manners. Based on this embodiment, without departing from the design spirit and principles of the present invention, other embodiments obtained through non-creative labor, as well as any modifications, equivalent replacements or improvements made thereto, all fall within the protection scope of the claims of the present invention.

Claims

1. A solar interface evaporator based on an amphoteric polyelectrolyte photo-thermal hydrogel, characterized in that, It includes a porous sponge and an amphoteric polyelectrolyte photothermal hydrogel embedded in the internal pores of the porous sponge; the amphoteric polyelectrolyte photothermal hydrogel includes a polymer network formed by a high molecular polymer and a photothermal conversion material dispersed in the polymer network; the high molecular polymer includes polyvinyl alcohol, a cationic polymer, anionic polymer, and a crosslinking agent.

2. The solar interface evaporator based on the amphoteric polyelectrolyte photo-thermal hydrogel according to claim 1, wherein, The crosslinking degree of the amphoteric polyelectrolyte photothermal hydrogel is 1% - 2%, and the mass fractions of polyvinyl alcohol, cationic polymer, anionic polymer, and photothermal conversion material in the amphoteric polyelectrolyte photothermal hydrogel are 3 - 7 wt%, 0.5 - 1.5 wt%, 0.5 - 1.5 wt%, and 3 - 8 wt% respectively.

3. The solar interface evaporator based on the amphoteric polyelectrolyte photo-thermal hydrogel according to claim 1, wherein, The cationic polymer includes one or a combination of two or more of chitosan, chitosan quaternary ammonium salt, polyallylamine hydrochloride, polyethyleneimine, or polydiallyldimethylammonium chloride; the anionic polymer includes one or a combination of two or more of sodium poly(styrenesulfonate), poly(styrenesulfonic acid), sodium hyaluronate, or sodium dextran sulfate; the photothermal conversion material includes one or a combination of two or more of carbon nanotubes, graphene, carbonized biomass, metal nanoparticles, titanium dioxide, polypyrrole, or polydopamine; the crosslinking agent is a mixture of hydrochloric acid solution and glutaraldehyde solution.

4. The solar interface evaporator based on the amphoteric polyelectrolyte photo-thermal hydrogel according to claim 1, wherein, The porous sponge includes polyvinyl alcohol sponge, melamine sponge, polyurethane sponge, cellulose sponge, or polyester sponge; the porosity of the porous sponge is 80% - 99%, and the internal pore size distribution is 40 - 180 μm.

5. A preparation method of a solar interface evaporator based on an amphoteric polyelectrolyte photo-thermal hydrogel, characterized in that, It includes: Step 1: Add polyvinyl alcohol powder and cationic polymer powder into an aqueous solution, heat and stir to obtain a mixed solution A; Step 2: Add anionic polymer powder and photothermal conversion material into the mixed solution A, and stir well to obtain a mixed solution B; Step 3: Add a crosslinking agent to the mixed solution B according to a crosslinking degree of 1% - 2%, and quickly stir to prepare a hydrogel precursor solution; in the hydrogel precursor solution, the mass fractions of polyvinyl alcohol, cationic polymer, anionic polymer, and photothermal conversion material are 3 - 7 wt%, 0.5 - 1.5 wt%, 0.5 - 1.5 wt%, and 3 - 8 wt% respectively; Step 4: Completely immerse the porous sponge into the hydrogel precursor solution, and after the porous sponge is completely wetted, place it at room temperature to obtain a solar interface evaporator based on the amphoteric polyelectrolyte photothermal hydrogel.

6. The preparation method according to claim 5, characterized in that, The cationic polymer includes one or a combination of two or more of chitosan, chitosan quaternary ammonium salt, polyallylamine hydrochloride, polyethyleneimine, or polydiallyldimethylammonium chloride; the anionic polymer includes one or a combination of two or more of sodium poly(styrenesulfonate), poly(styrenesulfonic acid), sodium hyaluronate, or sodium dextran sulfate; the photothermal conversion material includes one or a combination of two or more of carbon nanotubes, graphene, carbonized biomass, metal nanoparticles, titanium dioxide, polypyrrole, or polydopamine.

7. The preparation method according to claim 5, characterized in that, The crosslinking agent is a mixture of hydrochloric acid solution and glutaraldehyde solution; wherein, the mass fraction of the hydrochloric acid solution is 2-4 wt%, preferably 3 wt%; the mass fraction of the glutaraldehyde solution is 50 wt%; the volume ratio of the hydrochloric acid solution to the glutaraldehyde solution is 6:1-3:1, preferably 5:

1.

8. The preparation method according to claim 7, characterized in that, The degree of crosslinking is calculated according to the following formula: Wherein, GA represents glutaraldehyde and PVA represents polyvinyl alcohol.

9. The preparation method according to claim 5, characterized in that, In step 1, the temperature of heating and stirring is 80-95 °C, the stirring speed is 50-150 rpm, and the stirring time is 4-8 hours; in step 2, the stirring speed is 100-300 rpm, and the stirring time is 0.5-1.5 hours; in step 3, the rotation speed of rapid stirring is 400-600 rpm, and the stirring time is 3-8 minutes; in step 4, the immersion time is 20-40 minutes.

10. Application of the solar interface evaporator based on the zwitterionic polyelectrolyte photothermal hydrogel prepared by the preparation method according to any one of claims 5-9 in the preparation of solar desalination materials.

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