A reversible photo-thermal evaporator based on biomass ash and biochar and a preparation method and application thereof

Abstract

The application discloses a reversible photothermal evaporator based on biomass ash and biochar as well as a preparation method and application thereof. The evaporator is prepared by dissolving polyvinyl alcohol and chitosan in an acetic acid aqueous solution, mixing biomass ash and biochar to obtain a spraying solution, and spraying the spraying solution on a filter membrane with a reversible polyhedral structure having edges and corners, and then spraying a glutaraldehyde solution to form a hydrogel layer. The photothermal evaporator can be used for seawater desalination and exhibits excellent seawater desalination performance. The core features are as follows. Firstly, the photothermal evaporator can provide an efficient resource utilization path for biomass thermal conversion byproducts. Secondly, the unique reversible structure can realize periodic switching of the working surface during operation, and relying on the self-cleaning mechanism of the alternating cycle, the photothermal evaporator can realize continuous and stable treatment of high-concentration brine, and effectively overcome the performance degradation problem caused by salt accumulation of a traditional solar interface evaporator.

Description

Technical Field

[0001] This invention relates to the field of photothermal evaporation materials technology, and more specifically, to a reversible photothermal evaporator based on biomass ash and biochar, its preparation method, and its application. Background Technology

[0002] With the dual pressures of intensifying global climate change and accelerated industrialization, the increasing scarcity of freshwater resources has become a serious problem facing society today. To address this challenge, various seawater desalination methods have been developed. Current methods are mainly divided into thermal methods (such as multi-stage flash evaporation) and membrane methods (such as reverse osmosis and electrodialysis). However, these methods typically require sophisticated high-pressure equipment and centralized infrastructure, as well as the consumption of large amounts of non-renewable fossil fuels, making them difficult to benefit vast underdeveloped regions, remote islands, and disaster-stricken areas worldwide. In contrast, solar-driven interfacial evaporation (SDIE) has been recognized as a sustainable solution for seawater desalination and wastewater purification. Its ability to directly utilize ubiquitous solar energy to convert seawater or polluted water sources into clean drinking water offers advantages in terms of cost, efficiency, and environmental friendliness.

[0003] In SDIE systems, photothermal materials that absorb solar energy and convert it into heat are key factors determining the overall efficiency, stability, and durability of the system. Carbon-based materials, due to their broad spectral absorption of sunlight and excellent physicochemical stability, are commonly used as substrates for preparing photothermal conversion materials. During biomass pyrolysis for gasification, heating, or oil production, solid byproducts such as biochar and biomass ash are simultaneously generated. Biochar is a common carbon-based material and can serve as an excellent precursor for preparing biomass-based photothermal conversion materials. However, these materials have low oxygen-containing functional group content and weak surface polarity, exhibiting hydrophobic characteristics, which limits their efficiency in seawater desalination. Therefore, improving seawater desalination efficiency by controlling the hydrophilicity of materials has become a key research issue in this field. Notably, biomass ash, another solid byproduct of biomass pyrolysis, is not only rich in hydrophilic inorganic mineral elements but also contains a large number of oxygen-containing functional groups, exhibiting excellent hydrophilicity. It can serve as a potential modifying component to alleviate the aforementioned hydrophobicity problem. Based on this, it is hoped that by precisely controlling the carbon-ash ratio, the photothermal conversion efficiency and hydrophilicity of the material can be synergistically optimized and dynamically balanced, providing technical support for its stable and efficient application in the field of seawater desalination.

[0004] A photothermal evaporator is formed by loading photothermal conversion materials onto a filter membrane. During solar-driven interfacial evaporation, salt crystals gradually deposit on the evaporator surface as water evaporates. On one hand, these salt crystals block incident light, reducing the evaporator's light absorption capacity and consequently lowering its photothermal conversion efficiency, while also increasing maintenance costs. On the other hand, the strong hydration of salt ions significantly reduces the freedom of movement of water molecules. Water evaporation requires additional heat to break the bonds between ions and water molecules, leading to an increase in enthalpy of evaporation and ultimately a decrease in overall evaporation conversion efficiency. Traditional photothermal evaporators often employ a planar filter membrane structure loaded with photothermal conversion materials. Therefore, regular cleaning or replacement of the filter membrane is necessary for desalination to ensure continuous and efficient operation, posing challenges to the evaporator's continuous and stable operation and practical maintenance. If the geometry of the filter membrane can be optimized, on the one hand, the shape design can induce the formation of a concentration gradient, thereby achieving precise guidance for the transport of salt ions, thus reducing salt saturation and enhancing system stability; on the other hand, by designing a reversible A / B side working mode, the cumbersome process of periodic disassembly and desalination can be eliminated. This will have important engineering significance for achieving continuous and efficient operation of the evaporator and improving the actual freshwater production efficiency. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the single-component utilization of biochar or biomass ash in existing solar-driven interfacial evaporation methods results in poor performance, requires regular desalination, and has high maintenance costs. In order to overcome the above-mentioned defects of the prior art, the present invention provides a photothermal evaporator based on biomass ash and biochar, its preparation method and application.

[0006] The first aspect of the present invention provides a method for preparing a photothermal evaporator based on biomass ash and biochar, comprising the following steps: S1. Prepare an aqueous acetic acid solution by dissolving polyvinyl alcohol and chitosan in the aqueous acetic acid solution to obtain a PVA-CS solution; S2. Mix biomass ash and biochar evenly, then add them to the PVA-CS solution and stir evenly to obtain the spraying solution. S3. Provide a filter membrane with an edge and corner reversible polyhedral structure. The reversible polyhedral structure is an N-fold rotationally symmetric and vertically mirror-symmetric structure, including a central through-hole and an annular wall. The surface projection of the annular wall is an annular structure with an N-sided polygonal through-hole at the center and an N-sided outer contour. The edge of the annular structure corresponds to the projection of the edge of the reversible polyhedral structure. The line connecting the apex of the annular structure and the apex of the polygonal through-hole corresponds to the projection of the corner of the reversible polyhedral structure. N=5, 6, 7, or 8. The side of the filter membrane facing upward before flipping is side A, and the side facing upward after flipping is side B. After flipping again, the side facing upward is side A again, and so on. S4. Spray the spraying solution onto surface A of the reversible polyhedral filter membrane, then spray glutaraldehyde and let it dry to form a hydrogel layer. S5. Flip the filter membrane with the flippable polyhedral structure, spray the coating solution onto surface B of the filter membrane with the flippable polyhedral structure, then spray glutaraldehyde and let it dry to form a hydrogel layer, thus obtaining a flippable photothermal evaporator based on biomass ash and biochar.

[0007] The above scheme combines the excellent light absorption performance of biochar with the reliable hydrophilicity of biomass ash, achieving a balance between "blackbody absorption" and "water transport" in the mixed material. Simultaneously, the two-dimensional planar filter membrane is constructed into a three-dimensional, periodically flippable polyhedral structure. The concentration gradient induced at its edges and corners precisely guides salt ion transport, thereby accurately locking salt crystallization at the preset deposition site. An A / B double-sided flippable structure and operating mechanism are introduced. When surface A has deposited a certain amount, the filter membrane can be flipped to utilize surface B for deposition, while the salt deposited on surface A is dissolved during the B-side deposition. Similarly, when surface B has deposited a certain amount, the filter membrane can be flipped to utilize the dissolved salt on surface A for deposition, while the salt deposited on surface B is dissolved and can be used for the next flip. This cyclical flipping and deposition eliminates the cumbersome process of periodically disassembling the filter membrane for desalination, enabling continuous and efficient operation of the evaporator.

[0008] In one possible implementation, in step S1, the volume ratio of acetic acid to water in the aqueous acetic acid solution is 0.1%-10%, the concentration of polyvinyl alcohol is 10-30 mg / mL, and the concentration of chitosan is 10-30 mg / mL.

[0009] In one possible implementation, the concentration of biomass ash added is 0.1-80 mg / mL, and the concentration of biochar added is 0.1-80 mg / mL.

[0010] In one possible implementation, the volume ratio of the added glutaraldehyde solution to the added spray solution in steps S4 and S5 is (0.04-0.8):1, and the amount of spray solution added is 400ml of spray solution per square meter of the filter membrane with the flip-up polyhedral structure.

[0011] In one possible implementation, the dissolution in step S1 involves stirring at 60-80°C for 0.5-3 hours.

[0012] In one possible implementation, the mixing in step S2 is carried out at 20-30°C for 8-12 hours.

[0013] In one possible implementation, the material of the reversible polyhedral filter membrane in step S4 is selected from at least one of polyvinylidene fluoride filter membrane, aqueous mixed cellulose ester filter membrane, polytetrafluoroethylene filter membrane, polyethersulfone microporous filter membrane, nylon filter membrane, and hydrophilic polycarbonate filter membrane.

[0014] In one possible implementation, the drying in step S4 is natural air drying, which takes 1-3 minutes.

[0015] A second aspect of the present invention is to provide a reversible photothermal evaporator based on biomass ash and biochar, which is prepared by the above-described preparation method.

[0016] A third aspect of the present invention is to provide an application of a reversible photothermal evaporator based on biomass ash and biochar in seawater desalination.

[0017] The beneficial effects of this invention are as follows: 1. By constructing a unique polyhedral solar thermal evaporator, the concentration gradient induced at its edges and corners is used to precisely guide the transport of salt ions, thereby accurately locking salt crystallization at a preset deposition site. Simultaneously, the introduction of an A / B double-sided reversible structure and operating mechanism allows the evaporator to periodically switch working surfaces during operation. This alternating cleaning mechanism enables continuous and stable treatment of high-concentration brine, overcoming the performance degradation problem caused by salt accumulation in traditional solar interface evaporators.

[0018] 2. The composite material formed by physically mixing biomass ash and biochar achieves complementary advantages. Biochar ensures high light absorption, while biomass ash provides numerous polar sites, endowing the material with excellent superhydrophilicity. Furthermore, this method offers a good synergistic resource utilization pathway for biomass ash and biochar, resulting in significant environmental benefits. Attached Figure Description

[0019] Figure 1 The image shows a physical diagram of the flippable polyhedral structure formed by folding and splicing filter membranes according to the present invention. The second row of structures is an axonometric view of the first row of structures, the third row is a structural diagram of the first row of structures after being flipped from the inside out, and the fourth row is an axonometric view of the third row of structures. Figure 2 The contact angle of the raw materials with different ratios of biomass ash and biomass carbon in Examples 1-5 is shown to reflect the changes in their hydrophilic properties. Figure 3 Comparison of the ultraviolet-visible-near-infrared absorption spectra of the raw materials with different ratios of biomass ash and biomass carbon in Examples 1-5 with AM 1.5 solar spectra; Figure 4The evaporation rates of the photothermal evaporators prepared by different ratios of biomass ash and biomass carbon in Examples 1-5; Figure 5 (a) Evaporation rate of CPM-3 in 3.5% simulated seawater for 40 hours, physical images and infrared photographs, and (b) Evaporation of CPM-3 in simulated seawater for 7 days. Detailed Implementation

[0020] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the claims of the present invention.

[0021] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In some instances, terms having a conventional meaning are defined herein for clarification or ease of reference, and such definitions should not be construed as indicating a significant difference from conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and employed by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents, and instruments shall be performed according to the manufacturer's instructions and parameters.

[0023] This invention provides a photothermal evaporator based on biomass materials, its preparation method, and its application. The preparation method is as follows, including the following steps: S1. Prepare an aqueous acetic acid solution by adding polyvinyl alcohol and chitosan to the aqueous acetic acid solution and stirring at 60-80℃ for 0.5-3 h to dissolve the polyvinyl alcohol and chitosan, thereby obtaining a PVA-CS solution. S2. Mix biomass ash and biochar evenly, then add them to PVA-CS solution and stir at 20-30℃ for 8-12 hours until evenly mixed to obtain the spraying solution. S3. Provide a filter membrane with an edge and corner reversible polyhedral structure. The reversible polyhedral structure is an N-fold rotationally symmetric and vertically mirror-symmetric structure, including a central through-hole and an annular wall. The surface projection of the annular wall is an annular structure with an N-sided polygonal through-hole at the center and an N-sided outer contour. The edge of the annular structure corresponds to the projection of the edge of the reversible polyhedral structure. The line connecting the apex of the annular structure and the apex of the polygonal through-hole corresponds to the projection of the corner of the reversible polyhedral structure. N=5, 6, 7, or 8. The side of the filter membrane facing upward before flipping is side A, and the side facing upward after flipping is side B. After flipping again, the side facing upward is side A again, and so on. S4. Spray the spraying solution onto surface A of the reversible polyhedral filter membrane, then spray glutaraldehyde and let it dry to form a hydrogel layer. S5. Flip the filter membrane with the flippable polyhedral structure, spray the coating solution onto surface B of the filter membrane with the flippable polyhedral structure, then spray glutaraldehyde and let it dry to form a hydrogel layer, thus obtaining a flippable photothermal evaporator based on biomass ash and biochar.

[0024] In this process, the volume ratio of acetic acid to water in the acetic acid aqueous solution is 0.1-10%. Using the acetic acid aqueous solution as the matrix, the added concentration of polyvinyl alcohol is 10-30 mg / mL, the added concentration of chitosan is 10-30 mg / mL, the added concentration of biomass ash is 0.001-80 mg / mL, and the added concentration of biochar is 0.001-80 mg / mL. In steps S4 and S5, the volume ratio of the added glutaraldehyde solution to the added spraying solution is (0.04-0.8):1. The amount of spraying solution added is 400 ml per square meter of the reversible polyhedral filter membrane.

[0025] The material of the reversible polyhedral filter membrane is selected from at least one of polyvinylidene fluoride filter membrane, aqueous mixed cellulose ester filter membrane (MCE), polytetrafluoroethylene filter membrane (PTFE), polyethersulfone microporous filter membrane (PES), nylon filter membrane, and hydrophilic polycarbonate filter membrane.

[0026] Preferred, see Figure 1 The reversible polyhedral structure is composed of N identical star-shaped corners folded from filter membranes, and each star-shaped corner is a structure that is mirror-symmetrical from left to right and from top to bottom. Each star-shaped corner includes an edge and a corner, and the surface projection of each corner is distributed on the mirror-symmetrical plane of the star-shaped corner. Figure 1 The first row shows a reversible polyhedral structure made of folded and spliced ​​filter membranes, with 5-fold symmetry, 6-fold symmetry, 7-fold symmetry and 8-fold symmetry structures from left to right; the second row shows the axonometric views of the reversible polyhedral structures in the first row. Figure 1The third row consists of polyhedral structures obtained by flipping the 5-fold, 6-fold, 7-fold, and 8-fold symmetrical structures of the first row from the inside out. The geometric characteristics of this structure also satisfy the description of a reversible polyhedral structure with rotational symmetry and vertical mirror symmetry, so it is also applicable to the preferred concept of the filter membrane geometry design of the present invention. Figure 1 The fourth row is an isometric view of the flip-up polyhedral structure in the third row. Preferably, the filter membrane is... Figure 1 The rightmost one in the first row is a reversible polyhedral structure with eight rotational symmetries and vertical mirror symmetries, formed by folding and splicing polyvinylidene fluoride filter membranes. Of course, the above-mentioned reversible polyhedral structure can also be applied to the concept of this invention simply by flipping the filter membrane vertically. Figure 1 The actual images in the invention are all obtained by folding and splicing flat filter membranes. In fact, filter membranes with the flippable polyhedral structure described in this invention can also be prepared by using other methods such as 3D printing.

[0027] In the obtained photothermal evaporator based on biomass materials, the bottom layer is a filter membrane substrate, the middle layer contains biomass ash and biochar, and then hydrogel encapsulates the entire middle layer to form a final integrated hydrogel layer with a thickness of 100-200 μm.

[0028] The above preparation method yields a photothermal evaporator based on biomass materials, which can be applied in seawater desalination. In the seawater desalination process, a reversible polyhedron structure with eight-fold rotational symmetry and vertical mirror symmetry, formed by folding and splicing polyvinylidene fluoride filter membranes, is preferred. This reversible polyhedron structure can be flipped every 10 hours to facilitate salt deposition and dissolution.

[0029] The technical effects of the present invention will be further described below through specific embodiments.

[0030] Example 1 Preparation of spraying solution: 0.1 ml of acetic acid was added to 10 ml of water and stirred until homogeneous to obtain an acetic acid aqueous solution. Then, 0.2 g of polyvinyl alcohol (PVA) and 0.2 g of chitosan (CS) were dissolved in the above acetic acid aqueous solution. The mixture was heated and stirred at 60°C for 2 hours to obtain a pale yellow PVA-CS solution. Next, 0.8 g of biochar was added to the PVA-CS solution and stirred overnight to obtain spraying solution M-1.

[0031] The filter membrane used in this embodiment is a reversible polyhedron structure with an octagonal star shape, formed by folding and splicing polyvinylidene fluoride filter membranes. It features eightfold rotational symmetry and vertical mirror symmetry, and includes a central through-hole and annular walls. The projection of the annular walls is an annular structure with an octagonal central through-hole and an octagonal outer contour. The edges of the annular structure correspond to the projections of the edges of the reversible polyhedron structure, and the line connecting the apex of the annular structure to the apex of the polygonal through-hole corresponds to the projections of the corners of the reversible polyhedron structure. Figure 1 The structure shown is on the far right of the first row. The reversible polyhedral filter membrane has side A facing upwards before flipping, side B facing upwards after flipping, and so on, with each side having an area of ​​625 mm². 2 Half of the spraying solution M-1 was evenly sprayed onto surface A of the PVDF polyvinylidene fluoride filter membrane with the above-mentioned reversible polyhedral structure using a spray gun. Then, 0.1 ml of glutaraldehyde solution was sprayed on top, and the membrane was allowed to air dry for 3 minutes to form a thin layer of hydrogel on surface A. The reversible polyhedral filter membrane was then flipped to obtain surface B. The other half of the spraying solution M-1 was sprayed onto surface B of the reversible polyhedral filter membrane. Then, 0.1 ml of glutaraldehyde solution was sprayed on top, and the membrane was allowed to air dry for 3 minutes to form a hydrogel layer. This yielded a reversible photothermal evaporator based on biomass ash and biochar, ultimately forming the reversible evaporator CPM-1.

[0032] Example 2 The difference between this embodiment and Embodiment 1 is that 0.26 g of biomass ash and 0.52 g of biochar were added to the PVA-CS solution and stirred overnight to obtain the spraying solution M-2. This ultimately forms the tilting evaporator CPM-2.

[0033] Example 3 The difference between this embodiment and Embodiment 1 is that 0.4 g of biomass ash and 0.4 g of biochar are added to the PVA-CS solution and stirred overnight to obtain the spraying solution M-3. This ultimately forms the tilting evaporator CPM-3.

[0034] Example 4 The difference between this embodiment and Embodiment 1 is that 0.52 g of biomass ash and 0.26 g of biochar were added to the PVA-CS solution and stirred overnight to obtain the spraying solution M-4. This ultimately forms the tilting evaporator CPM-4.

[0035] Example 5 The difference between this embodiment and Embodiment 1 is that 0.8g of biomass ash is added to the PVA-CS solution and stirred overnight to obtain the spraying solution M-5. This ultimately forms the tilting evaporator CPM-5.

[0036] When the rotary evaporators CPM-1 to CPM-5 obtained in Examples 1-5 were tested, the operating temperature was 1 kW•m. -2 Under simulated sunlight (xenon lamp light source), the evaporator is placed on an analytical balance connected to a computer to record mass changes in real time and evaluate the evaporation performance of the evaporator.

[0037] Table 1 below shows the elemental percentage distribution of M-1 and M-5. M-1 is mainly composed of biochar with a high C content (96.50%). Trace amounts of elements such as Na, Mg, Al, and Si indicate that the original minerals of the biomass are uniformly embedded in the carbon matrix. M-5 is biomass ash with a Si content of 93.36%. Through high-temperature oxidation, the organic carbon components are removed, leaving inorganic residues mainly composed of silicon dioxide.

[0038] Table 1. Elemental percentage distribution of M-1 and M-5 The performance characteristics are as follows: First, the dynamic wetting process of biomass ash and biochar raw materials with different proportions in Examples 1-5 was analyzed using a contact angle meter. Based on the time scale, it was found that the wettability of different materials varied. The results are as follows: Figure 2 As shown. For pure biochar M-1, the droplet spreads and then completely retracts after impact, maintaining a spherical profile throughout the contact period, exhibiting a hydrophobic surface. For pure biomass ash M-5, after impact at t = 0s, the spreading front reaches its maximum visible range at t = 0.08s, after which the liquid rapidly disappears and is absorbed into the biomass ash. At t≈0.12s, the droplet almost completely disappears, exhibiting excellent hydrophilicity. As the amount of hydrophilic biomass ash incorporated into M-2, M-3, and M-4 gradually increases, the wetting and spreading rate of the water droplets gradually accelerates, ultimately exhibiting progressively superior hydrophilicity.

[0039] Then, the ultraviolet-visible-near-infrared absorption spectra of the biomass ash and biomass carbon raw materials in Examples 1-5 were analyzed and compared with the AM 1.5 solar spectrum. Figure 3 As shown. Figure 3 The absorptivity of biomass ash and biochar materials with different proportions in the ultraviolet-visible-near-infrared region (200-2500 nm) is shown. The black dashed line in the figure represents the standard solar spectral irradiance, with its peak power located in the visible light band, which is key to evaluating the solar thermal conversion efficiency. M-1 and M-5 both show relatively low absorptivity. M-2, M-3, and M-4 maintain high absorptivity across the entire measurement wavelength range, at 94.6%, 97.8%, and 92.2%, respectively, with M-3 showing the best performance.

[0040] The test results of the evaporation rate of the rotary evaporator obtained in Examples 1-5 are as follows: Figure 4 As shown. Figure 4 The data show the steady-state evaporation rates of five biomass ash and biochar composite evaporators (CPM-1 to CPM-5) under solar irradiation. All samples exhibited efficient interfacial solar vapor generation performance, with CPM-3 showing the highest evaporation rate.

[0041] Finally, long-term operating data of the CPM-3 evaporator in 3.5% simulated seawater are presented to comprehensively evaluate its salt tolerance and system stability, as detailed below. Figure 5 As shown. Figure 5 (a) Presents the evaporation rate of CPM-3 tested continuously for 40 hours in 3.5% simulated seawater, along with physical images and infrared photographs. Figure 5 (b) Evaporation of CPM-3 in simulated seawater over 7 consecutive days is presented. (a) The evaporation rate of CPM-3 under 40h continuous illumination remained at a high level and exhibited obvious periodic fluctuations. Before each manual flipping operation, the evaporation rate decreased slightly, possibly due to the inhibition of light absorption and water transport by interfacial salt accumulation. After flipping at 10h, 20h, and 30h (flipping here refers to flipping the flippable polyhedron structure from the inside out), the evaporation rate instantly recovered or even increased, indicating that the interfacial performance was effectively reset. Physical photographs show that as evaporation proceeds, white salt crystals begin to accumulate on the photothermal interface at time points such as 10h and 20h. Salt coverage reduces local light absorption and may block capillary channels, thereby reducing evaporation performance. However, infrared photographs show that the evaporation interface still maintains a high and uniform temperature distribution during salt accumulation. This indicates that the high light absorption characteristics and excellent thermal localization ability of CPM-3 effectively resist the interference of salt scale on the temperature field, ensuring that the thermal driving force does not significantly decrease. Simultaneously, the manual flipping operation places the salt accumulation sideways underwater. Relying on the capillary channels and water flow diffusion within the hydrophilic porous structure, it promotes the rapid dissolution and migration of high-concentration brine into the bulk water. This physical intervention, combined with the material's inherent wettability, is key to maintaining its high stability for 40 hours.

[0042] Figure 5 (b) It is shown that during a continuous 7-day 8-hour daily light cycle, the evaporation rate of CPM-3 did not exhibit a significant structural decrease. This demonstrates the excellent durability of the material structure.

[0043] In summary, this invention proposes a reversible solar evaporator based on biomass ash and biochar and its preparation method. A reversible evaporator based on biomass ash and biochar with a hydrogel thin layer loaded is prepared by spraying. It achieves ideal water transport capacity with less energy input, effectively reduces the enthalpy of water evaporation, and achieves fixed-point salting of the solar evaporator under good evaporation effect. Effective desalination and continuous evaporation can be achieved by simply flipping the device.

[0044] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for the preparation of a reversible photo-thermal evaporator based on biomass ash and biochar, characterized by, Includes the following steps: S1. Prepare an aqueous acetic acid solution by dissolving polyvinyl alcohol and chitosan in the aqueous acetic acid solution to obtain a PVA-CS solution; S2. Mix biomass ash and biochar evenly, then add them to the PVA-CS solution and stir evenly to obtain the spraying solution. S3. Provide a filter membrane with an edge and corner reversible polyhedral structure. The reversible polyhedral structure is an N-fold rotationally symmetric and vertically mirror-symmetric structure, including a central through-hole and an annular wall. The surface projection of the annular wall is an annular structure with an N-sided polygonal through-hole at the center and an N-sided outer contour. The edge of the annular structure corresponds to the projection of the edge of the reversible polyhedral structure. The line connecting the apex of the annular structure and the apex of the polygonal through-hole corresponds to the projection of the corner of the reversible polyhedral structure. N=5, 6, 7, or 8. The side of the filter membrane facing upward before flipping is side A, and the side facing upward after flipping is side B. After flipping again, the side facing upward is side A again, and so on. S4. Spray the spraying solution onto surface A of the reversible polyhedral filter membrane, then spray glutaraldehyde and let it dry to form a hydrogel layer. S5. Flip the filter membrane with the flippable polyhedral structure, spray the coating solution onto surface B of the filter membrane with the flippable polyhedral structure, then spray glutaraldehyde solution and let it dry to form a hydrogel layer, thus obtaining a flippable photothermal evaporator based on biomass ash and biochar.

2. The production method according to claim 1, characterized by, In step S1, the volume ratio of acetic acid to water in the acetic acid aqueous solution is 0.1%-10%, the concentration of polyvinyl alcohol is 10-30 mg / mL, and the concentration of chitosan is 10-30 mg / mL.

3. The preparation method according to claim 1, characterized in that, In step S2, the concentration of biomass ash added is 0.1-80 mg / mL, and the concentration of biochar added is 0.1-80 mg / mL.

4. The method of claim 1, wherein, In steps S4 and S5, the volume ratio of the added glutaraldehyde solution to the added spraying solution is (0.04-0.8):1, and the amount of spraying solution added is 400ml per square meter of the filter membrane with the flip-up polyhedral structure.

5. The preparation method according to claim 1, characterized in that, The dissolution in step S1 involves stirring at 60-80℃ for 0.5-3 hours.

6. The method of claim 1, wherein, The mixing in step S2 is carried out at 20-30℃ for 8-12 hours.

7. The preparation method according to claim 1, characterized in that, The material of the reversible polyhedral filter membrane in step S4 is selected from at least one of polyvinylidene fluoride filter membrane, aqueous mixed cellulose ester filter membrane, polytetrafluoroethylene filter membrane, polyethersulfone microporous filter membrane, nylon filter membrane, and hydrophilic polycarbonate filter membrane.

8. The method of claim 1, wherein, The drying process in step S4 is natural air drying, which takes 1-3 minutes.

9. A reversible photo-thermal evaporator based on biomass ash and biochar, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The application of the reversible photothermal evaporator based on biomass ash and biochar as described in claim 9 in seawater desalination.

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