A solar interface water evaporator with a double-layer multi-level pore structure and a construction method thereof

Abstract

The application provides a solar interface water evaporator with a double-layer multi-stage pore structure and a construction method thereof, and belongs to the technical field of solar energy application, and aims to solve the technical problem that the salt resistance and evaporation efficiency of a solar evaporator are difficult to be considered simultaneously.The preparation method comprises the following steps: dispersing and dissolving a photothermal material and a polymer in an organic solvent to prepare a mixed solution; introducing the mixed solution into a mold and adding a pore-forming agent to uniformly mix to form a first layer structure; pouring the mixed solution into the mold again to form a second layer structure above the first layer structure; and immersing the bottom of the mold into a refrigerant to perform orientation pre-freezing, freeze-drying and pore-forming agent removal to obtain the solar evaporator.The solar evaporator prepared by the application exhibits high and stable evaporation performance in NaCl solutions with different concentrations, high salt resistance, good self-cleaning capacity and the like, and the double-layer multi-stage pore composite foam has wide application prospects in sewage treatment and seawater desalination.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar energy application, and in particular relates to a solar interface water evaporator with a double-layer multi-level pore structure and a construction method thereof. Background Art

[0002] Freshwater is an indispensable resource on Earth, crucial for maintaining ecological balance, promoting economic development, and fostering social progress. However, the increasing severity of drought and desertification worldwide has exacerbated freshwater shortages, making addressing this issue urgent. Seawater desalination technology is widely considered a potential solution. Traditional desalination technologies include multi-stage flash evaporation, multi-effect distillation, electrodialysis, and reverse osmosis. However, these technologies still suffer from certain challenges, such as high energy consumption, complex operation, and high equipment costs. In recent years, interfacial water evaporators (IWEs) fabricated from photothermal materials have been recognized as one of the most promising technologies for alleviating clean water shortages due to their unique porous structure and efficient use of solar energy, resulting in energy savings and low costs. However, despite the numerous advantages of solar-driven IWE, IWEs also face challenges, such as stability under diverse environmental conditions, particularly in harsh environments such as high-salinity waters or extreme climates. Furthermore, the manufacturing and maintenance costs of IWEs are a significant concern, especially for large-scale applications. Therefore, although this technology has great potential, further research and technical improvements are still needed in practical applications to overcome existing limitations and realize its maximum benefits in solving the problem of freshwater shortage.

[0003] Based on this, the present invention proposes a new method for preparing a high-efficiency solar interfacial water evaporator with a double-layer, multi-level pore structure. The resulting evaporator exhibits high salt tolerance, excellent evaporation performance, and good desalination and self-cleaning capabilities. This method utilizes polyacrylonitrile (PAN), which exhibits excellent hydrophilicity, and thermoplastic polyurethane (TPU), which exhibits excellent mechanical properties, as the three-dimensional framework of the solar evaporator. Using CNTs as the photothermal conversion material, the present invention combines a salt template method with an oriented freezing technique to prepare a TPU / PAN / CNTs (TPCD) composite foam with a double-layer, multi-level pore structure. TPCD's unique double-layer, multi-level pore structure—a lower honeycomb pore structure and an upper vertical, ordered channel structure—enables the evaporator to achieve efficient solar water evaporation and desalination performance. This is primarily due to the lower honeycomb structure acting as a reservoir, providing sufficient water for seawater evaporation. The upper vertical, ordered channel structure, on the one hand, shortens the downward migration path of salt ions, allowing them to circulate efficiently within the evaporator, avoiding the formation of localized high concentrations of salt ions and thus suppressing salt crystallization on the evaporation surface, resulting in excellent salt tolerance. Furthermore, the uniformly distributed vertical ordered channels have a low degree of curvature. Compared with pore structures with higher curvature and uneven distribution and varying pore sizes, the viscous forces between them and evaporating water molecules are significantly reduced, promoting water vapor diffusion and improving evaporation efficiency. Thanks to these structural advantages, TPCD foam achieves efficient and stable evaporation performance in NaCl solutions of varying concentrations. This double-layer, multi-level porous composite foam has broad application prospects in wastewater treatment and seawater desalination.

[0004] The use of three-dimensional porous composite foams in seawater desalination has garnered widespread research attention. Currently, most solar evaporators suffer from slow evaporation rates and poor salt tolerance, resulting in low reuse rates. Therefore, developing a salt-tolerant and reusable solar evaporator remains a challenging task.

[0005] In 2022, Zhang et al. designed an expandable double-layer bacterial cellulose (BC) biofoam evaporator, in which the CuS / BC composite material was used as the light-to-heat conversion layer and the regenerated BC biofoam was used as the water transport and insulation layer. The evaporation rate was as high as 1.44 kg m -2 h -1 , the evaporation efficiency reaches 83.5%. In addition, the double-layer BC bio-foam has self-floating properties and can float stably for more than 6 weeks. It has excellent self-cleaning ability and can dissolve 2g of salt in 4.8cm within 120 minutes. 2 Clean the inside of the circle.

[0006] In 2021, Huang et al. prepared a salt-resistant solar evaporator by depositing carbon black on a super-hydrophilic polystyrene / lignocellulose (PS / LF) skeleton. The evaporator has an optimized porous structure and can achieve continuous desalination in a high-concentration salt water environment (15% NaCl). -2 Under solar irradiation, the evaporation rate is stable at 1.90 kg m -2 h -1 , the evaporation efficiency is as high as 85.5%. The evaporator has a high porosity and a small pore channel curvature, which makes it have good salt resistance.

[0007] In 2023, Wang et al. designed a novel biomimetic solar evaporation system with microchannels and macrochannels of different wettability. Inspired by the function of poplar trees, the system transports salt water through microchannels to the evaporator surface through capillary forces. The remaining water after evaporation flows back into the water through the macrochannels before the salt crystallizes, giving the evaporation system excellent desalination performance. For high-concentration salt water, the biomimetic evaporator can achieve an evaporation rate of 1.123 kg m -2 h -1 Furthermore, the long-term desalination performance of the evaporation system was well achieved, with a metal ion purification rate of up to 99.9%. By optimizing the design of microchannels and macrochannels, saturated brine desalination with a high evaporation rate was achieved, demonstrating the effectiveness and stability of the biomimetic evaporation system in the desalination of extremely high-concentration brine.

[0008] In 2022, Zhou et al. reported a rechargeable PPC-PAM hydrogel, in which pre-cross-linked PVA, glutaraldehyde (GA) and polydopamine (PDA) were added to PAM to form a skeleton, which greatly improved the mechanical properties of the hydrogel. During the freeze-drying process, a large number of interconnected pores were present in the polymerized hydrogel, which ensured a sustainable supply of water and strong light absorption for solar steam power generation. Even after storage for 150 days, the PPC-PAM hydrogel can still return to its original shape after swelling in water. Under the irradiation of one sun intensity, the evaporation rate of PPC-PAM was stabilized at 3.03 kg m within 152 hours. -2 h -1 . However, its salt tolerance is poor.

[0009] In 2022, Guo et al. proposed a vertically porous molybdenum disulfide / hectorite double-layer aerogel structure for efficient solar water evaporation. Its top molybdenum disulfide layer acts as an efficient solar absorber with excellent light absorption and photothermal conversion performance. Its bottom layer’s vertical water transport path and natural strong hydrophilicity ensure a stable water supply to the evaporation layer and prevent the accumulation of salt at the evaporation interface. The results show that the constructed super-hydrophilic molybdenum disulfide / hectorite double-layer aerogel has excellent self-driven desalination performance and can achieve self-cleaning within 30 minutes under extreme conditions simulating salt crystallization. In addition, under a light intensity of 1kW m -2 Under the conditions of -2 h -1 The evaporation efficiency is 85.99%. MoS2 / hectorite double-layer aerogel has the advantages of low cost, simple preparation, high strength and good salt resistance.

[0010] The current state of research at home and abroad indicates that three-dimensional porous composite foams have attracted widespread attention as solar evaporators, with promising applications in wastewater treatment and seawater desalination. However, the solar interfacial evaporators currently prepared still have some challenges. For example, while the preparation of evaporators with both microchannels and macrochannels improves salt tolerance, the preparation process is complex. Some evaporators have achieved excellent salt tolerance through structural and material optimization, but this sometimes comes at the expense of evaporation efficiency. Therefore, the preparation of solar evaporators with both good water evaporation performance and good salt tolerance remains a challenge. Summary of the Invention

[0011] To address the technical challenges of solar evaporators, which struggle to balance salt tolerance and evaporation efficiency, this paper proposes a solar interfacial water evaporator with a double-layer, multi-level pore structure and its construction method. The resulting solar evaporator exhibits efficient and stable evaporation performance in NaCl solutions of varying concentrations, high salt tolerance, and excellent self-cleaning capabilities. This double-layer, multi-level pore composite foam has broad application prospects in wastewater treatment and seawater desalination. This preparation method offers advantages such as simplicity, ease of operation, controllable pore and cell morphology, and the ability to form evaporators with complex shapes.

[0012] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0013] A method for constructing a solar interface water evaporator with a double-layer multi-level pore structure, characterized in that:

[0014] (1) dispersing and dissolving the photothermal material and the high molecular polymer in an organic solvent to prepare a mixed solution;

[0015] (2) introducing the mixed solution into a mold and adding a porogen and mixing evenly to form a first layer structure;

[0016] (3) pouring the mixed solution into the mold again to form a second layer structure on top of the first layer structure;

[0017] (4) immersing the bottom of the mold in a freezing liquid to perform orientation pre-freezing, and then freeze-drying to obtain a solar water evaporator precursor;

[0018] (5) The porogen in the solar water evaporator precursor was removed to obtain a TPU / PAN / CNTs solar water evaporator with a double-layer multi-level pore structure.

[0019] The photothermal materials are graphene, carbon black, carbon nanotubes (CNTs), titanium oxide (TiO2), zinc oxide (ZnO), two-dimensional transition metal carbides and nitrides (Mxenes), etc. The addition amount of the photothermal materials is 9-21wt% of the high molecular polymer.

[0020] The high molecular polymer includes polyacrylonitrile (PAN) and polyurethane TPU, polypyrrole (PPy) and TPU, polyaniline (PANI) and TPU, etc., the mass ratio of the two is 1:1-1:5, and the mass volume ratio of the high molecular polymer to the organic solvent is 0.06-0.12 g / mL.

[0021] The organic solvent is N,N-dimethylacetamide.

[0022] The porogen is NaCl particles, sugar particles, paraffin, etc., and the mass volume ratio of the porogen to the mixed solution in the first layer structure is 0.3-0.5 g / mL.

[0023] The volume ratio of the mixed solution used in the first layer structure to the mixed solution used in the second layer structure is (2-3):(2-3).

[0024] The freezing liquid used in the orientation pre-freezing is liquid nitrogen, and the pre-freezing time is 5-10 minutes.

[0025] The freeze-drying method comprises immersing the mold in a low-temperature ethanol bath having a temperature of 0 to -120° C. for 48 to 72 hours.

[0026] The method for removing the porogen in step (5) is: immersing the solar water evaporator precursor in a solution capable of dissolving the porogen; the solution is water or ethanol or toluene, and the corresponding solution is selected according to the type of the porogen.

[0027] Beneficial effects of the present invention:

[0028] (1) This invention uses polyacrylonitrile (PAN) with excellent hydrophilicity and thermoplastic polyurethane (TPU) with excellent mechanical properties as the three-dimensional framework of the solar evaporator, and CNTs as the photothermal conversion material. A TPU / PAN / CNTs (TPCD) composite foam with a double-layered multi-level pore structure is prepared using a salt template method and oriented freezing technology. TPCD's unique double-layered multi-level pore structure, i.e., a lower honeycomb pore structure and an upper vertical ordered channel structure, enables the evaporator to achieve efficient solar water evaporation and desalination performance.

[0029] (2) The honeycomb structure of the lower layer of the present invention acts as a water storage tank to provide sufficient water for seawater evaporation. The vertical ordered channel structure of the upper layer, on the one hand, shortens the path of salt ions migrating downward, allowing salt ions to circulate well inside the evaporator, avoiding the local generation of high concentrations of salt ions, thereby inhibiting the generation of salt crystals on the evaporation surface, making it have excellent high salt resistance. On the other hand, the uniformly distributed vertical ordered channels have a lower curvature. Compared with the pore structure with higher curvature and uneven distribution and different pore sizes, the viscous force between them and the evaporating water molecules is significantly reduced, promoting water vapor diffusion and improving evaporation efficiency. Thanks to the above structural advantages, TPCD foam achieves efficient and stable evaporation performance in NaCl solutions of different concentrations.

[0030] (3) The three-dimensional foam evaporator constructed by the present invention has an upper layer with a vertical ordered channel structure and a lower layer with a honeycomb structure, which provides a new method and new idea for improving the evaporation performance and salt resistance of the solar evaporator. The double-layer multi-level porous composite foam has broad application prospects in sewage treatment and seawater desalination. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 Schematic diagram of the preparation steps of the TPU / PAN / CNTs double-layer multi-level pore solar water evaporator of the present invention.

[0033] Figure 2 (a) Homemade solar water evaporation test system, (b) Schematic diagram of solar interface water evaporation simulation.

[0034] Figure 3 Solar water evaporator for water transport structure of bionic trees.

[0035] Figure 4SEM images of TPCD interface solar water evaporator; (a, a1, a2): Example 8; (b, b1, b2): Example 1; (c, c1, c2): Example 9; (d, d1, d2): Example 10.

[0036] Figure 5 The wetting performance (a), climbing effect (b) and water absorption rate (c) of the evaporator of TPD (Comparative Example 1) and TPCD (Example 5) are shown.

[0037] Figure 6 Mechanical properties of the TPCD evaporator (Example 5); (a) load-bearing capacity, (b) compressive stress-strain curves parallel and (c) perpendicular to the directional freezing direction.

[0038] Figure 7 Thermal conductivity (a) and light absorption properties of TPD (Comparative Example 1), TPC (Comparative Example 2), and TPCD (Example 5); (b: reflectivity, c: transmittance, d: absorptivity).

[0039] Figure 8 The evaporation performance of the evaporator of Examples 1 to 7; (a) Schematic diagram of the evaporation process of the TPCD-T evaporator, (b) Schematic diagram of the evaporation process of the TPCD-L evaporator, (c) Effect of CNTs content on the evaporation performance of the TPCD-T evaporator, (d) Effect of CNTs content on the evaporation performance of the TPCD-L evaporator.

[0040] Figure 9 The salt tolerance of the TPCD evaporator (Example 5); (a) evaporation performance of TPCD-T at different brine concentrations, (b) evaporation performance of TPCD-L at different brine concentrations, (c) cyclic evaporation performance of TPCD-T in simulated seawater (3.5 wt%), (d) cyclic evaporation performance of TPCD-L in simulated seawater (3.5 wt%), (e) accumulation of evaporated surface salt after continuous evaporation of TPCD-T in simulated seawater (3.5 wt%) for 12 h.

[0041] Figure 10 The seawater evaporation performance of the TPCD-T evaporator (Example 6) under outdoor real environment; (a) temperature, light intensity and evaporation rate change over time, (b) ion concentration change before and after seawater desalination. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0043] Example 1

[0044] A double-layer multi-level hole solar water evaporator with high efficiency of solar water evaporation and good salt tolerance adopts PAN and TPU as the base materials of the evaporator and CNTs as the photothermal material of the evaporator. Figure 1 As shown, the preparation method comprises the following steps:

[0045] (1) Weigh 0.36 g of CNTs, pour into 50 mL of N,N-dimethylacetamide (DMAC) solution, and ultrasonicate at 25 °C for 8 h to obtain a uniformly dispersed CNT suspension solution;

[0046] (2) 2 g of PAN and 2 g of TPU were dissolved in the suspension solution obtained in step (1), and treated with a constant temperature magnetic stirrer for 8 h to completely dissolve them to obtain a well-dispersed and uniform TPU / PAN / CNTs mixed solution, which was then allowed to stand at room temperature for use;

[0047] (3) First, 25 mL of the TPU / PAN / CNTs mixed solution obtained in step (2) was poured into a homemade cylindrical solution casting mold consisting of a polytetrafluoroethylene cylinder and a brass bottom. Subsequently, 10 g of NaCl particles were poured into the mixed solution and mechanically stirred to form a first layer structure. Then, 25 mL of the PAN / TPU / CNTs mixed solution was slowly poured onto the upper layer of the first layer structure. Finally, the bottom of the container was immersed in liquid nitrogen for orientation pre-freezing for 10 min.

[0048] (4) The pre-frozen PAN / TPU / CNTs / NaCl double-layer structure complex obtained in step (3) was first extracted and frozen in an ethanol bath at -75°C for 48 h, then taken out and soaked in deionized water for 48 h to remove NaCl particles, and finally freeze-dried for 72 h. A TPU / PAN / CNTs solar water evaporator (hereinafter referred to as "TPCD") with a double-layer multi-level porous structure was successfully prepared.

[0049] Example 2-10 A solar evaporator was prepared according to the preparation steps in Example 1, with only some process parameters adjusted. The specific process parameters are shown in Table 1:

[0050] Table 1 List of process parameters in Examples 1-10

[0051]

[0052] Comparative Example 1

[0053] (1) 2 g of PAN and 2 g of TPU were dissolved in 50 mL of DMAC solution and treated with a constant temperature magnetic stirrer for 12 h to completely dissolve them to obtain a well-dispersed and uniform TPU / PAN mixed solution, which was then allowed to stand at room temperature for use.

[0054] (2) First, 25 mL of the TPU / PAN mixed solution obtained in step (1) was poured into a homemade cylindrical solution casting mold consisting of a polytetrafluoroethylene cylinder and a brass bottom. Subsequently, 10 g of NaCl particles were poured into the mixed solution and mechanically stirred to form a first layer structure. Then, 25 mL of the PAN / TPU mixed solution was slowly poured onto the upper layer of the first layer structure. Finally, the bottom of the container was immersed in liquid nitrogen for orientation pre-freezing for 10 minutes.

[0055] (3) The pre-frozen PAN / TPU / NaCl double-layer structure complex obtained in step (2) was first extracted and frozen in an ethanol bath at -75°C for 72 hours, then taken out and soaked in deionized water for 48 hours to remove NaCl particles, and finally freeze-dried for 72 hours to successfully prepare a TPU / PAN solar water evaporator (hereinafter referred to as TPD) with a double-layer structure.

[0056] Comparative Example 2

[0057] (1) Weigh 0.36 g of CNTs, pour into 50 mL of N,N-dimethylacetamide (DMAC) solution, and ultrasonicate at 25 °C for 8 h to obtain a uniformly dispersed CNT suspension solution;

[0058] (2) 2 g of PAN and 2 g of TPU were dissolved in the suspension solution obtained in step (1), and treated with a constant temperature magnetic stirrer for 8 h to completely dissolve them to obtain a well-dispersed and uniform TPU / PAN / CNTs mixed solution, which was then allowed to stand at room temperature for use;

[0059] (3) Pour 50 mL of the TPU / PAN / CNTs mixed solution obtained in step (2) into a homemade cylindrical solution casting mold consisting of a polytetrafluoroethylene cylinder and a brass bottom, and then immerse the bottom of the container in liquid nitrogen for orientation pre-freezing for 10 minutes.

[0060] (4) The pre-frozen PAN / TPU / CNTs complex obtained in step (3) was placed in an ethanol bath at -75°C for extraction for 72 hours, and then freeze-dried for 72 hours to prepare a TPU / PAN / CNTs solar water evaporator (hereinafter referred to as "TPC") with a vertical tubular pore structure.

[0061] In order to better illustrate the present invention, the properties of the interface solar water evaporators of Examples 1-10 of the present invention and Comparative Examples 1 and 2 are introduced in conjunction with the accompanying drawings.

[0062] Homemade solar water evaporation test system, including solar simulator and information acquisition system ( Figure 2 (a)). The solar simulator used a xenon lamp (CEL-HXF300) equipped with an AM 1.5G filter, and the light intensity was measured using an optical power meter (CEL-NP2000-2A, China). The change in water mass over time during evaporation was measured using an analytical balance (GT204, Shanghai Youke Instrument Co., Ltd.) with an accuracy of 0.1 mg, and simultaneously communicated with a computer in real time to evaluate the evaporation rate and evaporation efficiency. The water temperature and the evaporation surface temperature of the evaporator were measured and recorded using a thermocouple power meter (HT-9815) and an infrared (IR) camera (FLIRA615, USA). In this experiment, a glass beaker was used as a water container, and the dust-free paper was folded into two parts, one part was placed on the polyethylene (PE) foam used as insulation and support material, and the other part was immersed in water. The effective evaporation area was 5 cm 2 The evaporator is placed on the dust-free paper ( Figure 2 (b)). Adjust the position of the light source so that the simulated sunlight can shine vertically on the evaporation surface of the evaporator.

[0063] Inspired by the water transport of trees, this invention uses oriented freezing and particle leaching technology to construct a solar interfacial water evaporator with PAN and TPU as the base materials and CNTs as the photothermal conversion material. The lower layer of the water evaporator is a porous honeycomb structure that mimics the roots of trees, which is used to collect and store water. The upper layer is a vertical ordered channel structure that mimics the diameter of the tree stem, which is conducive to rapid water transport. The CNTs photothermal conversion material mimics the leaves of trees, which is conducive to absorbing sunlight ( Figure 3 ).

[0064] Figure 4 The cross-sectional SEM images of the TPCD interface solar water evaporator (Example 1, Example 8, Example 9, Example 10). Figure 4 It can be seen that all samples have formed a double-layer multi-level pore structure, with the upper layer being a vertical ordered channel structure and the lower layer being a porous honeycomb structure. Many micropores exist on the surface of the tubular and honeycomb macropores, forming a multi-level pore structure. With the increase of PAN / TPU content (3g, 4g, 5g, and 6g in Examples 8, 1, 9, and 10, respectively), the pore size of the upper ordered channel decreases. This is mainly due to the increase in PAN / TPU content, the increase in the concentration of the cast mixed solution, and the decrease in the solvent content in the same volume of solution. The pore structure of the ordered channel is mainly formed by the freezing crystallization of the solvent at low temperatures, thus resulting in a decrease in the pore size. In addition, the size of the lower honeycomb pores does not change significantly. This is mainly because the honeycomb pores are mainly formed by the leaching of NaCl particles and are controlled by the size of the NaCl particles.

[0065] Figure 5 The wetting performance, climbing effect and water absorption rate of the evaporator TPD (Comparative Example 1) and TPCD (Example 5) are given, which have an important influence on the evaporation performance of the evaporator. Figure 5 (a) It can be seen that the TPD double-layer porous evaporator has good hydrophilicity. The water contact angles of the upper and lower layers of the evaporator decrease to 0° within 6.5s and 4.8s respectively. In addition, the water contact angles of the upper and lower layers of the TPCD double-layer porous evaporator decrease to 0° within 1.6s and 0.54s respectively, indicating that the introduction of CNFs improves the hydrophilicity of the evaporator. Figure 5 (b) It can be seen that when the TPCD evaporator is placed in water, water is transported to its surface within 50 seconds, showing a good climbing rod effect, indicating that it has a fast water transport capability. Figure 5 (c) As can be seen, the mass of dry TPCD is 1.3571 g, and after water absorption equilibrium, its mass is 5.4107 g, and the water absorption rate of TPCD is 298.6%. These results show that the TPCD evaporator has good hydrophilic properties and water transmission and storage capabilities, providing good conditions for efficient solar water evaporation.

[0066] Figure 6 The mechanical properties of the TPCD (Example 5) evaporator are given. It can be seen that in the parallel directional freezing direction, the evaporator has good compressive resistance. When it bears 100g, 200g and 500g weights, no deformation is found ( Figure 6 a). In the parallel directional freezing direction, during the compression process, the maximum deformation of the evaporator is 13%, and its deformation does not recover, indicating that the evaporator in this direction has poor rebound ability and good compressive resistance ( Figure 6 b) In the perpendicular freezing direction, at 20% strain, the evaporator exhibited excellent elasticity during compression, retaining 91.9% of its initial compressive strength after 10 compression cycles. These results demonstrate that the TPCD evaporator exhibits anisotropic mechanical properties, exhibiting excellent compressive resistance in the parallel freezing direction and excellent elasticity in the perpendicular freezing direction.

[0067] The thermal conductivity of the evaporator is an important factor affecting its evaporation performance. Figure 7 (a) shows the thermal conductivity of TPD (Comparative Example 1), TPC (Comparative Example 2) and TPCD (Example 5). The thermal conductivity of pure water is 0.6 Wm -1 K -1 In comparison, the import coefficients of TPD, TPC, and TPCD are 0.054 W m -1 K -1 , 0.08 and 0.075Wm -1 K -1, are far lower than the thermal conductivity of pure water. Therefore, during the evaporator's operation, the heat from sunlight will be concentrated primarily on the evaporation surface, with minimal heat loss. Compared to TPC without NaCl particles, TPCD with NaCl particles has a lower thermal conductivity, providing a better advantage in the water evaporation process.

[0068] The light-to-heat conversion performance of the evaporator is another important factor affecting its evaporation performance, which mainly depends on the light absorption properties of the material. Figure 7 (b, c, d) show the reflectivity, transmittance, and absorptivity of the upper layer (TPCD-T) and lower layer (TPCD-L) of TPD (Comparative Example 1) and TPCD (Example 5) to sunlight. As can be seen from the figure, compared with the 84.1% reflectivity of the TPD evaporator without CNFs, the upper and lower layers of the TPCD evaporator have higher absorptivity, lower reflectivity, and lower transmittance. The light absorption capacity of TPCD-T and TPCD-L in the ultraviolet and near-infrared regions is significantly enhanced, absorbing 97.7% and 97.5% of the incident light, respectively, with reflectivity as low as 2.23% and 2.35%. Therefore, the addition of CNFs now enhances the light absorption capacity of the evaporator TPCD, thereby significantly enhancing the water evaporation performance.

[0069] Figure 8 Schematic diagrams of the evaporation process of the evaporator in Examples 1-7 and the effect of CNTs content on the evaporation performance of the evaporator are given. Figure 8 (a, b) are schematic diagrams of the evaporation process when the upper layer of the evaporator is used as the evaporation surface (TPCD-T) and the lower layer of the evaporator is used as the evaporation surface (TPCD-L). Figure 8 (c, d) It can be seen that the evaporation rate and evaporation efficiency of TPCD-T and TPCD-L evaporators both show a trend of increasing first and then decreasing with the increase of CNTs content. This is mainly because CNTs are photothermal conversion materials. When their content increases, the solar light absorption rate and photothermal conversion performance of the TPCD evaporator are improved, so the evaporation rate and evaporation efficiency are also improved accordingly. However, as the CNTs content increases further, the photothermal conversion efficiency is reduced due to their easy agglomeration. When the CNTs content is 17%, the evaporation rate and evaporation efficiency of TPCD-T and TPCD-L reach the optimal value, which are 2.66 kg m -2 h -1 and 2.42 kg m -2 h -1 , 108.2% and 117.1%, therefore, the CNTs content is preferably 17%.

[0070] During the desalination process, salt deposition is the main problem that prevents the evaporator from maintaining high evaporation efficiency for a long time. The salt accumulated inside the evaporator will block the water supply channel, thereby blocking the steam diffusion channel and reducing the evaporation rate. The accumulation of salt on the evaporation surface will severely limit the solar absorption rate and reduce the evaporation rate. Therefore, how to solve the problem of salt deposition in the evaporator and improve the salt resistance of the evaporator remains a huge challenge. Figure 9 The salt tolerance of the TPCD evaporator (Example 5) is given. Figure 9 (a, b) It can be seen that in different simulated brine concentrations of 0, 3.5, 5, 10, 20, and 25 wt.%, the evaporation rate and evaporation efficiency of TPCD-T and TPCD-L slightly decrease with the increase of simulated brine concentration. When the salinity of the simulated brine increases from 0% to 25%, the evaporation rates of TPCD-T and TPCD-L increase from 2.66 and 2.27 kg m, respectively. -2 h -1 reduced to 2.06 and 1.78 kg m -2 h -1 However, the evaporation performance of the evaporator in 3.5wt.% simulated seawater did not change significantly compared with that in pure water, which shows that TPCD has excellent salt tolerance and broad application prospects in seawater desalination. Figure 9 (c, d) It can be seen that with the increase in the number of seawater evaporation cycles, the evaporation rate and evaporation efficiency of the TPCD-T and TPCD-L evaporators do not change significantly. After 12 evaporation cycles, they still maintain a high evaporation rate and evaporation efficiency of 2.61 kg m -2 h -1 and 2.54 kg m -2 h -1 , 120.1% and 115.9%. At the same time, after 12 hours of continuous evaporation, no salt accumulation was observed on the evaporation surface of TPCD-T ( Figure 9 (e)). The above results show that TPCD has excellent salt tolerance.

[0071] In order to evaluate the practical performance of the TPCD-T evaporator, an outdoor experiment under natural conditions was conducted on the evaporator of Example 5. Figure 10 (a) It can be seen that the evaporation performance of the TPCD-T evaporator is positively correlated with the light intensity and ambient temperature. The higher the light intensity and ambient temperature, the better the evaporation performance of the evaporator. Around 13:00 noon, the light intensity reached a maximum of 1021W / m 2 The outdoor temperature reached a maximum of 30.7°C, and the evaporation rate reached 3.08 kg m -2 h -1 In addition, the average solar radiation intensity and ambient temperature are 740W / m 2Under outdoor conditions of 22.7℃ and 14.7℃, TPCD-T can generate 22.87kg m -2 of fresh water. Figure 10 (b) shows the water purification capacity of the TPCD-T evaporator, that is, the K before and after seawater evaporation and desalination is measured. + 、Na + , Ca 2+ and Mg 2+ The concentration of plasma changes. + The concentration ranged from 1.08×10 4 mg L -1 Reduced to 2.2548 mg L -1 , the removal rate is 99.9%. In addition, K + Mg 2+ and Ca 2+ The ion concentrations were reduced to 1.167 mg L -1 , 0.0159mg L -1 and 0.2408 mgL -1 , in line with the World Health Organization's standard requirements for ion concentration in drinking water.

[0072] Example 11

[0073] A double-layer multi-stage porous solar water evaporator with high efficiency and good salt tolerance uses PPy and TPU as the base materials of the evaporator and carbon black as the photothermal material of the evaporator. The preparation method includes the following steps:

[0074] (1) Weigh 2 g of carbon black, add 50 mL of N,N-dimethylacetamide (DMAC) solution, and ultrasonicate at 25°C for 8 h to obtain a uniformly dispersed carbon black suspension solution;

[0075] (2) 2 g of PPy and 10 g of TPU were dissolved in the suspension solution obtained in step (1), and treated with a constant temperature magnetic stirrer for 8 h to completely dissolve them to obtain a well-dispersed and uniform TPU / PPy / carbon black mixed solution, which was then allowed to stand at room temperature for use;

[0076] (3) First, 30 mL of the TPU / PPy / carbon black mixed solution obtained in step (2) was poured into a homemade cylindrical solution casting mold consisting of a polytetrafluoroethylene cylinder and a brass bottom. Then, 15 g of sugar particles were poured into the mixed solution and mechanically stirred to form a first layer structure. Then, 25 mL of the TPU / PPy / carbon black mixed solution was slowly poured onto the upper layer of the first layer structure. Finally, the bottom of the container was immersed in liquid nitrogen for orientation pre-freezing for 5 minutes.

[0077] (4) The pre-frozen TPU / PPy / carbon black double-layer structure complex obtained in step (3) was first placed in an ethanol bath at -75°C for extraction and freezing for 60 hours, then taken out and soaked in deionized water for 60 hours to remove sugar particles, and finally freeze-dried for 72 hours to successfully prepare a TPU / PPy / carbon black solar water evaporator with a double-layer multi-level porous structure.

[0078] Example 12

[0079] A double-layer multi-stage pore solar water evaporator with high efficiency and good salt tolerance uses PANI and TPU as substrate materials and graphene as the photothermal material of the evaporator. The preparation method includes the following steps:

[0080] (1) Weigh 1.68 g of graphene, pour into 50 mL of N,N-dimethylacetamide (DMAC) solution, and ultrasonicate at 25 °C for 8 h to obtain a uniformly dispersed graphene suspension solution;

[0081] (2) 2 g of PANI and 6 g of TPU were dissolved in the suspension solution obtained in step (1), and treated with a constant temperature magnetic stirrer for 8 h to completely dissolve them to obtain a well-dispersed and uniform TPU / PANI / graphene mixed solution, which was then allowed to stand at room temperature for use;

[0082] (3) First, 20 mL of the TPU / PANI / graphene mixed solution obtained in step (2) was poured into a homemade cylindrical solution casting mold consisting of a polytetrafluoroethylene cylinder and a brass bottom. Subsequently, 6 g of paraffin was poured into the mixed solution and mechanically stirred to form a first layer structure. Then, 25 mL of the TPU / PANI / graphene mixed solution was slowly poured onto the upper layer of the first layer structure. Finally, the bottom of the container was immersed in liquid nitrogen for orientation pre-freezing for 8 minutes.

[0083] (4) First, the pre-frozen TPU / PANI / graphene double-layer structure complex obtained in step (3) was placed in an ethanol bath at -75°C for extraction and freezing for 48 hours, then taken out and soaked in toluene for 48 hours to remove the paraffin, and finally freeze-dried for 72 hours to successfully prepare a TPU / PANI / graphene solar water evaporator with a double-layer multi-level pore structure.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for constructing a solar interfacial water evaporator with a double-layer multi-level pore structure, characterized in that: (1) Dispersing and dissolving the photothermal material and the high molecular polymer in an organic solvent to prepare a mixed solution; (2) introducing the mixed solution into the mold and adding the porogen to mix evenly to form the first layer structure; (3) Pour the mixed solution into the mold again to form a second layer structure on top of the first layer structure; (4) Immersing the bottom of the mold in a freezing liquid to perform orientation pre-freezing, followed by freeze drying to obtain a solar water evaporator precursor; (5) Removing the porogen from the solar water evaporator precursor to obtain a solar water evaporator with a double-layer multi-level pore structure; The high molecular polymer includes two high molecular polymers, one of which is any one of polyacrylonitrile, polypyrrole or polyaniline, and the other is polyurethane, the mass ratio of the two is (1:1)-(1:5), and the mass volume ratio of the high molecular polymer to the organic solvent is 0.06-0.12 g / mL.

2. The method for constructing a solar interface water evaporator with a double-layer multi-level pore structure according to claim 1, characterized in that: The photothermal material is any one or more of graphene, carbon black, carbon nanotubes, titanium oxide, zinc oxide, two-dimensional transition metal carbides and nitrides, and the addition amount of the photothermal material is 9-21wt% of the high molecular polymer.

3. The method for constructing a solar interface water evaporator with a double-layer multi-level pore structure according to claim 1, characterized in that: The organic solvent is N, N-dimethylacetamide.

4. The method for constructing a solar interface water evaporator with a double-layer multi-level pore structure according to claim 1, characterized in that: The porogen is any one or more of NaCl particles, sugar particles and paraffin wax, and the mass volume ratio of the porogen to the mixed solution in the first layer structure is 0.3-0.5 g / mL.

5. The method for constructing a solar interface water evaporator with a double-layer multi-level pore structure according to claim 1, characterized in that: The volume ratio of the mixed solution used in the first layer structure to the mixed solution used in the second layer structure is (2-3): (2-3).

6. The method for constructing a solar interface water evaporator with a double-layer multi-level pore structure according to claim 1, characterized in that: The freezing liquid used in the orientation pre-freezing is liquid nitrogen, and the pre-freezing time is 5-10 minutes.

7. The method for constructing a solar interface water evaporator with a double-layer multi-level pore structure according to claim 1, characterized in that: The freeze-drying method comprises immersing the mold in a low-temperature ethanol bath at a temperature of 0 to -120° C. for 48 to 72 hours.

8. The method for constructing a solar interface water evaporator with a double-layer multi-level pore structure according to claim 1, characterized in that: The method for removing the porogen in step (5) is: immersing the solar water evaporator precursor in a solution capable of dissolving the porogen; the solution is any one of water, ethanol or toluene.

9. A solar interfacial water evaporator having a double-layer multi-level pore structure prepared by the construction method according to any one of claims 1 to 8.

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