Self-floating double-layer solar evaporator with Janus characteristics and preparation method and application thereof

Abstract

The application provides a self-floating double-layer solar evaporator with Janus characteristics and a preparation method and application thereof, and belongs to the technical field of solar evaporator preparation. The preparation method is as follows: gourd sponge is calcined and ground into carbonized gourd sponge powder, which is dispersed into a polyvinyl alcohol / sodium alginate solution to obtain a dispersion liquid containing the carbonized gourd sponge; the gourd sponge is used as a support, and the polyvinyl alcohol / sodium alginate solution and the dispersion liquid containing the carbonized gourd sponge are sequentially poured, and a double-layer gel containing vertical pores is formed by stepwise freezing; the double-layer gel is thawed and crosslinked through a calcium chloride solution, washed, and freeze-dried to obtain a double-layer aerogel; the photo-thermal surface of the aerogel is sprayed with a silane coupling agent / ethanol solution to complete hydrophobic modification, and the self-floating double-layer solar evaporator with Janus characteristics is obtained. The solar evaporator prepared by the application has a high evaporation rate and has a wide application prospect in the fields of seawater desalination and wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of solar evaporator manufacturing technology, specifically to a self-floating double-layer solar evaporator with Janus characteristics, its manufacturing method, and its application. Background Technology

[0002] Freshwater is the cornerstone of human survival and development, crucial for maintaining human health, supporting social production, and ensuring livelihoods. However, the distribution of water resources on Earth is extremely uneven. Seawater accounts for as much as 97.5%, but its high salinity makes it unusable directly. Of the remaining 2.5% of freshwater, approximately 87% is frozen in polar and mountainous regions as glaciers and ice sheets, making it difficult to access directly. This means that readily available freshwater resources, such as rivers, lakes, and groundwater, account for only 0.325% of the Earth's total water volume, and these limited resources face the challenge of uneven distribution. To address the freshwater shortage, many seawater desalination and wastewater treatment processes have been developed, utilizing different methods to desalinate seawater and desalinate wastewater to obtain freshwater. However, traditional seawater desalination and wastewater treatment processes require large amounts of non-renewable energy input, which is not only extremely costly but also highly polluting. Solar energy, as a natural, renewable, and clean energy source, can be applied to photocatalysis and solar thermal conversion. The conversion of solar energy to thermal energy has the highest conversion efficiency among various solar energy collection technologies. Solar-driven water evaporation, which generates steam by converting solar energy into heat, is considered one of the most efficient and simple technologies for seawater desalination and wastewater purification.

[0003] High-performance solar-driven interfacial evaporators are crucial for efficiently absorbing sunlight and converting it into heat energy to drive water evaporation. As the core component of solar-driven interfacial evaporators, which handles both light absorption and thermal dynamics, the design and fabrication of solar photothermal conversion materials have been a key research focus. In recent years, various types of solar photothermal conversion materials, such as nano-metal particles, carbon-based materials, semiconductors, and polymers, have been extensively studied. Among them, carbon-based materials have shown broad application prospects due to their excellent thermal stability, wide-bandgap solar absorptivity, and high-efficiency solar-to-thermal energy conversion performance. Furthermore, to prevent heat loss to the water body, an insulating water transport layer is typically placed between the photothermal conversion material and the water body, ensuring continuous water supply while effectively improving energy utilization efficiency. Compared to chaotic water supply channels, vertical channels can significantly shorten the water transport path and accelerate the supply speed of water to the evaporation surface. Aerogel composites, with their good hydrophilicity, low enthalpy of vaporization, and high evaporation rate, are ideal interfacial evaporation materials. However, challenges remain in how to improve the dispersibility of photothermal conversion materials in gels and their interaction with the matrix, thereby ensuring the stability and durability of the evaporator; and how to optimize water transport paths and enhance salt resistance to further increase the evaporation rate and expand applications in complex seawater and polluted wastewater environments. Summary of the Invention

[0004] The purpose of this invention is to propose a self-floating double-layer solar evaporator with Janus characteristics, its preparation method and application. The prepared solar evaporator has excellent evaporation performance.

[0005] The technical solution of this invention is implemented as follows:

[0006] This invention provides a method for preparing a self-floating double-layer solar evaporator with Janus characteristics, comprising the following steps:

[0007] S1. Add polyvinyl alcohol to deionized water, stir at 80-90℃ for 2-3 hours, and cool to room temperature to obtain a polyvinyl alcohol aqueous solution;

[0008] S2. Add sodium alginate to deionized water, stir at 50-60℃ for 0.5-1h, and cool to room temperature to obtain an aqueous solution of sodium alginate;

[0009] S3. Mix the polyvinyl alcohol aqueous solution and the sodium alginate aqueous solution, and stir at 300-600 rpm for 0.5-1h to obtain a polyvinyl alcohol / sodium alginate mixed solution;

[0010] S4. Calcine the loofah sponge at 390-410℃ for 5-10 minutes, grind it and pass it through a 200-mesh sieve to obtain carbonized loofah sponge powder. Then add the carbonized loofah sponge powder to a polyvinyl alcohol / sodium alginate mixed solution and stir for 1-2 hours to obtain a carbonized loofah sponge / polyvinyl alcohol / sodium alginate dispersion.

[0011] S5. Lay the loofah sponge in the mold as a support, pour in a polyvinyl alcohol / sodium alginate mixed solution level with the loofah sponge, place it on a freezing table at a temperature of -10℃ to -20℃, freeze for 1-2 hours to build vertical channels as the water transport layer of the evaporator, then pour in carbonized loofah sponge / polyvinyl alcohol / sodium alginate dispersion and freeze for 1-2 hours as the photothermal layer to form a double-layer structure gel.

[0012] S6. Immerse the frozen-formed bilayer gel block in calcium chloride solution for 6-12 hours, remove the gel block, wash with water, freeze-dry to obtain a bilayer aerogel.

[0013] S7. Spray 5-15 mL of silane coupling agent / ethanol solution at a distance of 5-10 cm from the upper surface of the aerogel photothermal layer to achieve hydrophobic modification of the upper surface of the aerogel, thereby obtaining a self-floating double-layer solar evaporator with Janus characteristics.

[0014] As a further improvement of the present invention, the degree of polymerization of polyvinyl alcohol in step S1 is 1700-1800, and the concentration of the polyvinyl alcohol aqueous solution is 8-12 wt%.

[0015] As a further improvement of the present invention, the concentration of the sodium alginate aqueous solution in step S2 is 1-4 wt%.

[0016] As a further improvement of the present invention, the mixing mass ratio of the polyvinyl alcohol aqueous solution and the sodium alginate aqueous solution in step S3 is (1-4):1.

[0017] As a further improvement of the present invention, in the carbonized loofah / polyvinyl alcohol / sodium alginate dispersion in step S4, the concentration of carbonized loofah is 2-5 wt%.

[0018] As a further improvement of the present invention, the shape and size of the mold in step S5 are matched with the shape and size of the loofah sponge, so that the loofah sponge can be tightly filled in the mold, and there is no obvious gap between the inner surface of the mold and the outer surface of the loofah sponge. The thickness of the loofah sponge is 4-6 mm, the amount of polyvinyl alcohol / sodium alginate mixed solution injected needs to completely fill and just cover the loofah sponge, and the height of the added carbonized loofah sponge / polyvinyl alcohol / sodium alginate dispersion is 4-6 mm.

[0019] As a further improvement of the present invention, the concentration of the CaCl2 solution in step S6 is 2-5 wt%.

[0020] As a further improvement of the present invention, the concentration of the silane coupling agent / ethanol solution in step S7 is 1-3 wt%, and the silane coupling agent is selected from one of methyltrimethoxysilane, hexadecyltrimethoxysilane, vinyltrimethoxysilane, trimethylchlorosilane, octyltriethoxysilane, perfluorodecyltriethoxysilane, dimethyldimethoxysilane, and anilinemethyltrimethoxysilane.

[0021] This invention further protects a self-floating double-layer solar evaporator with Janus characteristics prepared by the above-described method.

[0022] This invention further protects the application of a self-floating double-layer solar evaporator with Janus characteristics prepared by the above-described method in seawater desalination and wastewater purification. Under 1 solar radiation intensity, the evaporator achieves a pure water evaporation rate exceeding 2.7 kg m³. -2 h -1 The evaporation rate in a 3.5 wt% NaCl solution exceeds 2.6 kg m³. -2 h -1 The evaporation rate in a 10 wt% NaCl solution exceeds 2.5 kg m³. -2 h-1 The evaporation rate in a 20 wt% NaCl solution exceeds 2.2 kg m -2 h -1 .

[0023] The present invention has the following beneficial effects:

[0024] 1. This invention uses natural and renewable loofah sponges as a supporting framework, which not only strengthens the overall mechanical structure of the evaporator but, more importantly, enables it to float on water. The loofah sponges are carbonized to obtain light-absorbing carbon materials, achieving photothermal conversion of solar energy into thermal energy. The loofah sponges are composite-modified using biocompatible polymers such as sodium alginate and polyvinyl alcohol as the main matrix. The raw materials are widely available, extremely low in cost, and environmentally friendly. This provides a material basis for large-scale, sustainable solar-driven seawater desalination and wastewater treatment.

[0025] 2. This invention constructs a bilayer structure with Janus properties, exhibiting hydrophobic upper and lower surfaces, and combines this with the natural three-dimensional channels in loofah sponge and vertical pores constructed by freezing polyvinyl alcohol / sodium alginate, achieving synergistic management of moisture, light, heat, and salinity. This structure can float on water, localizing heat at the evaporation interface, accelerating the water transport path, thereby effectively reducing bulk heat loss and significantly improving the solar evaporation rate and efficiency.

[0026] 3. The "stepwise freezing-simultaneous crosslinking" preparation process used in this invention is simple to operate and has low energy consumption. This process first uses stepwise freezing to initially shape a bottom hydrophobic layer with vertical channels, then further freezes to form a top photothermal layer. Next, calcium ions are used to simultaneously crosslink sodium alginate and form a synergistic network with polyvinyl alcohol. Finally, freeze-drying yields a bilayer aerogel. This method ensures a tight bond between the two layers through chemical crosslinking and physical entanglement, resulting in good interfacial stability and preventing interlayer separation during use.

[0027] 4. The evaporator prepared by this invention integrates multiple functions such as self-floating, high-efficiency photothermal conversion, rapid water transport, salt crystallization resistance and mechanical durability. While achieving high-efficiency solar seawater desalination, it also shows broad application potential in treating complex water bodies such as polluted wastewater. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1This is a schematic diagram of the process of the solar evaporator prepared in Embodiment 1 of the present invention.

[0030] Figure 2 This is a digital photograph of the solar evaporator prepared in Example 1 of the present invention floating on the water surface.

[0031] Figure 3 This is a SEM image of the internal vertical channels of the solar evaporator prepared in Example 1 of the present invention.

[0032] Figure 4 The contact angle is the surface of the photothermal layer of the solar evaporator prepared in Example 1 of the present invention.

[0033] Figure 5 This is a SEM image of the disordered porous structure inside the solar evaporator prepared in Comparative Example 1 of the present invention.

[0034] Figure 6 This is a digital photograph of the solar evaporator prepared in Comparative Example 2 of the present invention in water.

[0035] Figure 7 The contact angle of the photothermal layer surface of the solar evaporator prepared in Comparative Example 3 of the present invention is shown.

[0036] Figure 8 This is a diagram of the experimental setup for interfacial evaporation using a xenon lamp to simulate sunlight in Test Example 1 of the present invention.

[0037] Figure 9 Na in seawater and collected condensate in Test Example 2 of this invention + K + Mg 2+ Ca 2+ Ion concentration.

[0038] Figure 10 These are digital photographs and ultraviolet spectra of the dye wastewater before and after purification in Test Example 3 of this invention. Detailed Implementation

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0040] This embodiment provides a method for preparing a self-floating double-layer solar evaporator with Janus characteristics. The preparation process is as follows: Figure 1 As shown, it includes the following steps:

[0041] S1. Add 1g of polyvinyl alcohol (degree of polymerization 1750) to 9g of deionized water, stir at 90℃ for 2h, cool to room temperature, and obtain a 10wt% polyvinyl alcohol aqueous solution.

[0042] S2. Add 2g of sodium alginate to 98g of deionized water, stir at 60℃ for 1h, cool to room temperature, and obtain a sodium alginate aqueous solution with a concentration of 2wt%.

[0043] S3. Mix 10g of a 10wt% polyvinyl alcohol aqueous solution and 10g of a 2wt% sodium alginate aqueous solution, and stir at 300rpm for 1h to obtain a polyvinyl alcohol / sodium alginate mixed solution.

[0044] S4. Calcine the loofah sponge at 400℃ for 5 minutes, grind it and pass it through a 200-mesh sieve to obtain carbonized loofah sponge powder. Add 1g of carbonized loofah sponge powder to 24g of polyvinyl alcohol / sodium alginate (PVA / SA) mixed solution and stir for 1 hour to obtain a 4wt% carbonized loofah sponge polyvinyl alcohol / sodium alginate dispersion (C-PVA / SA).

[0045] S5. Lay a 5mm thick loofah sponge in a mold. The shape and size of the mold match the shape and size of the loofah sponge so that the loofah sponge can be tightly filled in the mold and there is no obvious gap between the inner surface of the mold and the outer surface of the loofah sponge. Pour in a polyvinyl alcohol / sodium alginate mixed solution level with the loofah sponge, place it on a freezing table at -20℃, and freeze for 2 hours to build vertical channels as the water transport layer of the evaporator. Then pour in a 5mm high carbonized loofah sponge polyvinyl alcohol / sodium alginate dispersion (C-PVA / SA), freeze for 2 hours to form a photothermal layer, and form a double-layer structure gel.

[0046] S6. Immerse the frozen-formed bilayer gel in a 2wt% calcium chloride solution for 6 hours, remove the gel block, wash with water, freeze-dry, and obtain a bilayer aerogel.

[0047] S7. At a distance of 10 cm from the surface of the aerogel photothermal layer, a 2 wt% vinyltrimethoxysilane / ethanol solution is sprayed to achieve hydrophobic modification until the cumulative amount of the sprayed solution reaches 10 mL, thus obtaining a self-floating double-layer solar evaporator with Janus characteristics.

[0048] Digital photographs show that the manufactured solar evaporator can float on the surface of the evaporating water without the addition of external force. Figure 2 ). Scanning electron microscopy revealed that vertical channels were successfully constructed inside the solar evaporator. Figure 3The contact angle test results show that the surface of the solar evaporator's photothermal layer has hydrophobic properties. Figure 4 This proves that the hydrophobic modification was successful.

[0049] Comparative Example 1: The only difference between this comparative example and Example 1 is that the vertical channels were not constructed on a freezing stage at -20°C during the preparation process. The specific preparation process is as follows:

[0050] S1. Add 1g of polyvinyl alcohol (degree of polymerization 1750) to 9g of deionized water, stir at 90℃ for 2h, cool to room temperature, and obtain a 10wt% polyvinyl alcohol aqueous solution.

[0051] S2. Add 2g of sodium alginate to 98g of deionized water, stir at 60℃ for 1h, cool to room temperature, and obtain an aqueous solution of sodium alginate with a concentration of 2wt%.

[0052] S3. Mix 10g of a 10wt% polyvinyl alcohol aqueous solution and 10g of a 2wt% sodium alginate aqueous solution, and stir at 300rpm for 1h to obtain a polyvinyl alcohol / sodium alginate mixed solution.

[0053] S4. Calcine the loofah sponge at 400℃ for 5 minutes, grind it and pass it through a 200-mesh sieve to obtain carbonized loofah sponge powder. Add 1g of carbonized loofah sponge powder to 24g of polyvinyl alcohol / sodium alginate mixed solution and stir for 1 hour to obtain a carbonized loofah sponge polyvinyl alcohol / sodium alginate dispersion with a concentration of 4wt%.

[0054] S5. Lay a 5mm thick loofah sponge in a mold. The shape and size of the mold match the shape and size of the loofah sponge so that the loofah sponge can be tightly filled in the mold and there is no obvious gap between the inner surface of the mold and the outer surface of the loofah sponge. Pour in a polyvinyl alcohol / sodium alginate mixed solution level with the loofah sponge, place it in a refrigerator at -20℃ and freeze for 2 hours to build the water transport layer of the evaporator. Then pour in a 5mm high carbonized loofah sponge polyvinyl alcohol / sodium alginate dispersion and freeze for 2 hours to form a photothermal layer, forming a double-layer structure gel.

[0055] S6. Immerse the frozen-formed bilayer gel in a 2wt% calcium chloride solution for 6 hours, remove the gel block, wash with water, freeze-dry, and obtain a bilayer aerogel.

[0056] S7. At a distance of 10 cm from the surface of the aerogel photothermal layer, a 2 wt% vinyltrimethoxysilane / ethanol solution is sprayed to achieve hydrophobic modification until the cumulative amount of the sprayed solution reaches 10 mL, thus obtaining a self-floating double-layer solar evaporator with Janus characteristics.

[0057] Its internal scanning electron microscope image is as follows Figure 5 As shown, compared with Example 1, the interior has a disordered channel structure.

[0058] Comparative Example 2: The only difference between this comparative example and Example 1 is that no loofah sponge was added as a support during the preparation process. The specific preparation process is as follows:

[0059] S1. Add 1g of polyvinyl alcohol (degree of polymerization 1750) to 9g of deionized water, stir at 90℃ for 2h, cool to room temperature, and obtain a 10wt% polyvinyl alcohol aqueous solution.

[0060] S2. Add 2g of sodium alginate to 98g of deionized water, stir at 60℃ for 1h, cool to room temperature, and obtain a sodium alginate aqueous solution with a concentration of 2wt%.

[0061] S3. Mix 10g of a 10wt% polyvinyl alcohol aqueous solution and 10g of a 2wt% sodium alginate aqueous solution, and stir at 300rpm for 1h to obtain a polyvinyl alcohol / sodium alginate mixed solution.

[0062] S4. Calcine the loofah sponge at 400℃ for 5 minutes, grind it and pass it through a 200-mesh sieve to obtain carbonized loofah sponge powder. Add 1g of carbonized loofah sponge powder to 24g of polyvinyl alcohol / sodium alginate mixed solution and stir for 1 hour to obtain a carbonized loofah sponge polyvinyl alcohol / sodium alginate dispersion with a concentration of 4wt%.

[0063] S5. Pour a 5mm high polyvinyl alcohol / sodium alginate mixed solution into the mold, place it on a freezing table at -20℃, freeze for 2 hours to build vertical channels as the water transport layer of the evaporator, then pour in a 5mm high carbonized loofah polyvinyl alcohol / sodium alginate dispersion, freeze for 2 hours as the photothermal layer, and form a double-layer structure gel.

[0064] S6. Immerse the frozen-formed bilayer gel in a 2wt% calcium chloride solution for 6 hours, remove the gel block, wash with water, freeze-dry, and obtain a bilayer aerogel.

[0065] S7. At a distance of 10 cm from the surface of the aerogel photothermal layer, a 2 wt% vinyltrimethoxysilane / ethanol solution is sprayed to achieve hydrophobic modification until the cumulative amount of the sprayed solution reaches 10 mL, thus obtaining a self-floating double-layer solar evaporator with Janus characteristics.

[0066] Digital photos of the evaporator in water, such as Figure 6 As shown, compared to Example 1, it cannot float on the water surface because no loofah is added as support.

[0067] Comparative Example 3: The difference between this comparative example and Example 1 is that no hydrophobic modification was performed. The specific steps are as follows:

[0068] S1. Add 1g of polyvinyl alcohol (degree of polymerization 1750) to 9g of deionized water, stir at 90℃ for 2h, cool to room temperature, and obtain a 10wt% polyvinyl alcohol aqueous solution.

[0069] S2. Add 2g of sodium alginate to 98g of deionized water, stir at 60℃ for 1h, cool to room temperature, and obtain a sodium alginate aqueous solution with a concentration of 2wt%.

[0070] S3. Mix 10g of a 10wt% polyvinyl alcohol aqueous solution and 10g of a 2wt% sodium alginate aqueous solution, and stir at 300rpm for 1h to obtain a polyvinyl alcohol / sodium alginate mixed solution.

[0071] S4. Calcine the loofah sponge at 400℃ for 5 minutes, grind it and pass it through a 200-mesh sieve to obtain carbonized loofah sponge powder. Add 1g of carbonized loofah sponge powder to 24g of polyvinyl alcohol / sodium alginate mixed solution and stir for 1 hour to obtain a carbonized loofah sponge polyvinyl alcohol / sodium alginate dispersion with a concentration of 4wt%.

[0072] S5. Lay a 5mm thick loofah sponge in a mold. The shape and size of the mold match the shape and size of the loofah sponge so that the loofah sponge can be tightly filled in the mold and there is no obvious gap between the inner surface of the mold and the outer surface of the loofah sponge. Pour in a polyvinyl alcohol / sodium alginate mixed solution that is level with the loofah sponge, place it on a freezing table at -20℃, and freeze for 2 hours to build vertical channels as the water transport layer of the evaporator. Then pour in a 5mm high carbonized loofah sponge polyvinyl alcohol / sodium alginate dispersion and freeze for 2 hours to form a photothermal layer, thus forming a double-layer structure gel.

[0073] S6. Immerse the frozen-formed bilayer aerogel in a 2wt% calcium chloride solution for 6 hours, remove the gel block, wash with water, freeze-dry, and obtain a bilayer aerogel.

[0074] The aerogel produced has a photothermal layer contact angle as shown in the figure. Figure 7 As shown, it exhibits hydrophilicity.

[0075] Example 2

[0076] This embodiment provides a method for preparing a self-floating double-layer solar evaporator with Janus characteristics, including the following steps:

[0077] S1. Add 1g of polyvinyl alcohol (degree of polymerization 1700) to 11.5g of deionized water, stir at 90℃ for 2h, cool to room temperature, and obtain a polyethylene aqueous solution with a concentration of 8wt%.

[0078] S2. Add 1g of sodium alginate to 99g of deionized water, stir at 60℃ for 1h, and cool to room temperature to obtain an aqueous solution of sodium alginate with a concentration of 1wt%.

[0079] S3. Mix 10g of 8wt% polyvinyl alcohol aqueous solution and 10g of 1wt% sodium alginate aqueous solution, and stir at 300rpm for 1h to obtain a polyvinyl alcohol / sodium alginate mixed solution.

[0080] S4. Calcine the loofah sponge at 400℃ for 5 minutes, grind it and pass it through a 200-mesh sieve to obtain carbonized loofah sponge powder. Add 1g of carbonized loofah sponge powder to 49g of polyvinyl alcohol / sodium alginate mixed solution and stir for 1 hour to obtain a 2wt% carbonized loofah sponge polyvinyl alcohol / sodium alginate dispersion.

[0081] S5. A 5mm thick loofah sponge is laid in a mold as a support. The shape and size of the mold match the shape and size of the loofah sponge so that the loofah sponge can be tightly filled in the mold and there is no obvious gap between the inner surface of the mold and the outer surface of the loofah sponge. A polyvinyl alcohol / sodium alginate mixed solution level with the loofah sponge is poured in and placed on a freezing table at -20℃. After freezing for 2 hours, vertical channels are constructed as the water transport layer of the evaporator. Then, a 5mm high carbonized loofah sponge polyvinyl alcohol / sodium alginate dispersion is poured in and frozen for 2 hours as the photothermal layer to form a double-layer structure gel.

[0082] S6. Immerse the frozen gel block in a 2wt% calcium chloride solution for 6 hours, remove the gel block, wash with water, freeze dry, and obtain a bilayer aerogel.

[0083] S7. At a distance of 10 cm from the surface of the aerogel photothermal layer, a 2 wt% vinyltrimethoxysilane / ethanol solution is sprayed to achieve hydrophobic modification until the cumulative amount of the sprayed solution reaches 5 mL, thus obtaining a self-floating double-layer solar evaporator with Janus characteristics.

[0084] Example 3

[0085] This embodiment provides a method for preparing a self-floating double-layer solar evaporator with Janus characteristics, including the following steps:

[0086] S1. Add 1.2g of polyvinyl alcohol (degree of polymerization 1800) to 8.8g of deionized water, stir at 90℃ for 2h, cool to room temperature, and obtain a polyvinyl alcohol aqueous solution with a concentration of 12wt%.

[0087] S2. Add 1g of sodium alginate to 24g of deionized water, stir at 60℃ for 1h, cool to room temperature, and obtain an aqueous solution of sodium alginate with a concentration of 4wt%.

[0088] S3. Mix 10g of 12wt% polyvinyl alcohol aqueous solution and 5g of 4wt% sodium alginate aqueous solution, and stir at 300rpm for 1h to obtain a polyvinyl alcohol / sodium alginate mixed solution.

[0089] S4. Calcine the loofah sponge at 400℃ for 10 min, grind it and pass it through a 200-mesh sieve to obtain carbonized loofah sponge powder. Disperse 1g of carbonized loofah sponge powder into 19g of polyvinyl alcohol / sodium alginate mixed solution and stir for 1h to obtain a carbonized loofah sponge polyvinyl alcohol / sodium alginate dispersion with a concentration of 5wt%.

[0090] S5. A 5mm thick loofah sponge is laid in a mold as a support. The shape and size of the mold match the shape and size of the loofah sponge so that the loofah sponge can be tightly filled in the mold and there is no obvious gap between the inner surface of the mold and the outer surface of the loofah sponge. A polyvinyl alcohol / sodium alginate mixed solution level with the loofah sponge is poured in and placed on a freezing table at -20℃. After freezing for 2 hours, vertical channels are constructed as the water transport layer of the evaporator. Then, a 5mm high carbonized loofah sponge polyvinyl alcohol / sodium alginate dispersion is poured in and frozen for 2 hours as the photothermal layer to form a double-layer structure gel.

[0091] S6. Immerse the frozen gel block in a 5 wt% calcium chloride solution for 6 hours, remove the gel block, wash with water, freeze dry, and obtain a bilayer aerogel.

[0092] S7. At a distance of 10 cm from the surface of the aerogel photothermal layer, a 2 wt% vinyltrimethoxysilane / ethanol solution is sprayed to achieve hydrophobic modification until the cumulative amount of the sprayed solution reaches 10 mL, thus obtaining a self-floating double-layer solar evaporator with Janus characteristics.

[0093] Example 4

[0094] This embodiment provides a method for preparing a self-floating double-layer solar evaporator with Janus characteristics, including the following steps:

[0095] S1. Add 1g of polyvinyl alcohol (degree of polymerization 1800) to 9g of deionized water, stir at 90℃ for 2h, cool to room temperature, and obtain a polyvinyl alcohol aqueous solution with a concentration of 10wt%.

[0096] S2. Add 1g of sodium alginate to 24g of deionized water, stir at 60℃ for 1h, cool to room temperature, and obtain a sodium alginate aqueous solution with a concentration of 4wt%.

[0097] S3. Mix 9g of 10wt% polyvinyl alcohol aqueous solution and 3g of 4wt% sodium alginate aqueous solution, and stir at 300rpm for 1h to obtain a polyvinyl alcohol / sodium alginate mixed solution.

[0098] S4. Calcine the loofah sponge at 400℃ for 5 minutes, grind it and pass it through a 200-mesh sieve to obtain carbonized loofah sponge powder. Disperse 1.2g of carbonized loofah sponge powder into 38.8g of polyvinyl alcohol / sodium alginate mixed solution and stir for 1 hour to obtain a carbonized loofah sponge polyvinyl alcohol / sodium alginate dispersion with a concentration of 3wt%.

[0099] S5. A 6mm thick loofah sponge is laid in a mold as a support. The shape and size of the mold match the shape and size of the loofah sponge so that the loofah sponge can be tightly filled in the mold and there is no obvious gap between the inner surface of the mold and the outer surface of the loofah sponge. A polyvinyl alcohol / sodium alginate mixed solution level with the loofah sponge is poured in and placed on a freezing table at -20℃ for 2 hours to build vertical channels as the water transport layer of the evaporator. Then, a 6mm high carbonized loofah sponge polyvinyl alcohol / sodium alginate dispersion is poured in and frozen for 2 hours to form a photothermal layer, thus forming a double-layer structure gel.

[0100] S6. Immerse the frozen gel block in a 4 wt% calcium chloride solution for 6 hours, remove the gel block, wash with water, freeze dry, and obtain a bilayer aerogel.

[0101] S7. At a distance of 5 cm from the surface of the aerogel photothermal layer, a 2 wt% vinyltrimethoxysilane / ethanol solution is sprayed to achieve hydrophobic modification until the cumulative amount of the sprayed solution reaches 5 mL, thus obtaining a self-floating double-layer solar evaporator with Janus characteristics.

[0102] Test Example 1: Solar Interface Evaporation Test

[0103] The evaporation effect of a solar evaporator was investigated through an evaporation experiment. The specific steps are as follows: Figure 8As shown, the prepared solar evaporator was placed in a beaker filled with pure water, with the photothermal layer facing upwards. The diameter of the solar evaporator was approximately equal to the inner diameter of the beaker. A xenon lamp (CEL-S500-T5, Beijing Zhongjiao Jinyuan Technology Co., Ltd.) equipped with an AM1.5G filter was used as the light source to continuously illuminate the solar evaporator from above, and a light power meter (CEL-NP2000-2, Beijing Zhongjiao Jinyuan Technology Co., Ltd.) was used to assist in adjusting the light power density. The beaker was placed on an analytical balance (ME104E / 02, Mettler Toledo Instruments Ltd.) and its position was adjusted so that the solar evaporator was completely covered by the xenon lamp spot centered on the light source. The test lasted for 60 minutes, and the mass change of the entire device was recorded every 5 minutes using the balance, and the evaporation rate of the solar evaporator was calculated. During the water evaporation measurement, the laboratory temperature was maintained at 22±2℃ and the ambient humidity was 45%. Since the average concentration of seawater is 3.5 wt%, three different concentrations of NaCl solutions (3.5, 10, and 20 wt%) were prepared to simulate seawater and two types of high-salinity wastewater, respectively. The target solutions were used instead of the pure aqueous solutions in the evaporation tests of the 3.5 wt% NaCl, 10 wt% NaCl, and 20 wt% NaCl solutions. The results are shown in Table 1 below.

[0104] Table 1

[0105] <![CDATA[Evaporation rate (kg m -2 h -1 ).]]> pure water 3.5wt% NaCl 10wt% NaCl 20wt% NaCl Example 1 2.937 2.886 2.664 2.33 Example 2 2.879 2.821 2.586 2.294 Example 3 2.922 2.872 2.659 2.306 Example 4 2.763 2.698 2.503 2.242 Comparative Example 1 1.723 1.653 1.425 1.322 Comparative Example 2 0.636 0.55 0.401 0.435 Comparative Example 3 2.153 1.523 1.326 1.184

[0106] As shown in Table 1, the solar evaporator prepared in the embodiments of the present invention has a high evaporation rate in different water environments, and is significantly better than the solar evaporators prepared in Comparative Examples 1-3.

[0107] The only difference between Comparative Example 1 and Example 1 is that the vertical channels were not constructed on a freezing platform at -20°C during the preparation process. Due to the lack of vertical channels, the prepared solar evaporator lacked directional water transport capability and an effective salt repulsion path. Compared to the Example, in water evaporation tests, the disordered water transport channels prolonged the water transport path, thus reducing the evaporation rate. In simulated seawater, it could not efficiently transport water while simultaneously and rapidly returning the precipitated salt to the bulk solution, thus easily leading to channel blockage and performance degradation in high-salinity water.

[0108] The only difference between Comparative Example 2 and Example 1 is that no loofah sponge was added as a support during the preparation process. Because no loofah was introduced as a supporting framework, its overall density was too high to float on the water surface. This structural defect caused it to gradually sink during testing, forcing the absorbed solar heat to disperse throughout the water body, failing to achieve effective heat localization at the gas-liquid interface. Therefore, the interfacial evaporation mechanism that should have been achieved completely failed, and its working mode degenerated into inefficient bulk heating. In this mode, a large amount of heat energy was used to heat the water in the non-evaporation areas, resulting in significant heat loss and ultimately causing its evaporation rate to be much lower than that of the example with self-floating and interfacial evaporation capabilities. This result conversely confirms the crucial role of the loofah support layer in achieving self-floating, constructing interfacial evaporation, and improving energy efficiency.

[0109] The only difference between Comparative Example 3 and Example 1 is that no hydrophobic modification was performed. Because no hydrophobic modification was performed, its photothermal layer surface exhibits completely hydrophilic properties. In simulated seawater evaporation experiments, this hydrophilic surface causes water to continuously spread and remain on the evaporator's upper surface. This results in the absorbed solar heat not only being used to drive the evaporation of interfacial water but also being largely dissipated in heating the surface water film and the underlying bulk seawater, causing severe heat loss. Simultaneously, continuous evaporation causes salt to rapidly crystallize and precipitate in the heated surface water film, adhering firmly and accumulating, quickly clogging the internal water channels and hindering water supply. Ultimately, this manifests as a significant decrease in the evaporation rate over time, making stable and efficient continuous evaporation impossible.

[0110] Test Example 2: Actual Solar-Driven Seawater Desalination Test

[0111] The actual seawater desalination effect of Example 1 was verified through a continuous evaporation experiment. The specific steps are as follows: The actual solar-driven seawater desalination test was conducted from 9:00 AM to 5:00 PM, verifying the evaporator's performance throughout the day by performing 8 hours of evaporation. Environmental changes and water loss were recorded every hour. Seawater was taken from the nearshore area of ​​the East China Sea. The ion concentration of the collected condensate was determined using an inductively coupled plasma atomic emission spectrometer (ICP-5000). The results showed that after 8 hours of continuous evaporation testing, the solar evaporator prepared in Example 1 showed no significant salt precipitation. The concentration of ions (Na+, Na+, Na+, Na+) in the solution before and after evaporation was significantly reduced. + K + Mg 2+ Ca 2+ Further quantitative analysis of the concentration revealed that the ion concentration was far below the World Health Organization's recommended ion concentration for drinking water. Figure 9 This demonstrates the feasibility and durability of the self-floating double-layer solar evaporator with Janus characteristics prepared in this invention in practical solar-driven seawater desalination applications.

[0112] Test Example 3: Dye Wastewater Purification Experiment

[0113] The dye wastewater purification capacity of the solar evaporator prepared in Example 1 was verified using an evaporation experiment. The specific steps are as follows: Rhodamine B, tartrazine, Congo red, and methylene blue solutions with a concentration of 20 mg / L were prepared using deionized water as simulated wastewater. During the evaporation test, the target solutions were used instead of the pure aqueous solution in Example 1. The initial color of each dye wastewater and the collected condensate was photographed under natural light using a digital camera, and the characteristic absorption peak positions and intensities were observed using a UV-Vis spectrophotometer. The results showed that... Figure 10 As shown, four simulated dye wastewaters [Congo Red (Congo Red) Figure 10 a) Methylene blue ( Figure 10 b), Rhodamine B ( Figure 10 c), lemon yellow ( Figure 10 [d] All samples exhibited their own typical and vibrant colors. After purification by the solar evaporator prepared in Example 1, all collected condensate samples were colorless and transparent under natural light, forming a stark contrast with the color of the original wastewater. This visually demonstrates that the dye molecules were effectively trapped on the other side of the evaporator and failed to pass through with the water vapor. The disappearance of the characteristic peaks of the pollutants in the ultraviolet-visible absorption spectrum also confirms this.

[0114] 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 within the protection scope of the present invention.

Claims

1. A method for preparing a self-floating double-layer solar evaporator with Janus properties, characterized in that, The method comprises the following steps: S1. Add polyvinyl alcohol into deionized water, stir at a temperature of 80-90℃ for 2-3h, cool to room temperature to obtain a polyvinyl alcohol aqueous solution; S2. Add sodium alginate into deionized water, stir at a temperature of 50-60℃ for 0.5-1h, cool to room temperature to obtain a sodium alginate aqueous solution; S3. Mix the polyvinyl alcohol aqueous solution and the sodium alginate aqueous solution, stir at a speed of 300-600 rpm for 0.5-1h to obtain a polyvinyl alcohol / sodium alginate mixed solution; S4. Calcine loofah at a temperature of 390-410℃ for 5-10min, grind and sieve through a 200-mesh sieve to obtain carbonized loofah powder, then add the carbonized loofah powder into the polyvinyl alcohol / sodium alginate mixed solution, stir for 1-2h to obtain a carbonized loofah / polyvinyl alcohol / sodium alginate dispersion; S5. Lay loofah in a mold as support, pour the polyvinyl alcohol / sodium alginate mixed solution to the level of the loofah, place on a freezing table at a temperature of -10℃ to -20℃, freeze for 1-2h to build a vertical channel as a water delivery layer of an evaporator, then pour the carbonized loofah / polyvinyl alcohol / sodium alginate dispersion and freeze for 1-2h as a photothermal layer to form a double-layer structure gel; S6. Soak the double-layer structure gel block formed by freezing into a CaCl2 solution and react for 6-12h, take out the gel block, wash with water, freeze-dry to obtain a double-layer structure aerogel; S7. Spray 5-15 mL of a silane coupling agent / ethanol solution at a position 5-10 cm away from the upper surface of the photothermal layer of the aerogel to realize hydrophobic modification of the upper surface of the aerogel to obtain a self-floating double-layer solar evaporator with Janus characteristics.

2. The method of claim 1, wherein the self-floating dual-layer solar evaporator with Janus properties is prepared by the steps of: The polyvinyl alcohol in step S1 has a degree of polymerization of 1700-1800, and the polyvinyl alcohol aqueous solution has a concentration of 8-12 wt%.

3. The method of claim 1, wherein the self-floating dual-layer solar evaporator with Janus properties is prepared by the steps of: In step S2, the sodium alginate aqueous solution has a concentration of 1-4 wt%.

4. The method of claim 1, wherein the self-floating dual-layer solar evaporator with Janus properties is prepared by the steps of: In step S3, the mixing mass ratio of the polyvinyl alcohol aqueous solution to the sodium alginate aqueous solution is (1-4):

1.

5. The method of claim 1, wherein the self-floating dual-layer solar evaporator with Janus properties is prepared by the steps of: In step S4, in the carbonized loofah / polyvinyl alcohol / sodium alginate dispersion, the concentration of the carbonized loofah is 2-5 wt%.

6. The method of claim 1, wherein the self-floating dual-layer solar evaporator with Janus properties is prepared by the steps of: In step S5, the shape and size of the mold match those of the loofah, so that the loofah can be tightly packed in the mold, and there is no obvious gap between the inner surface of the mold and the outer surface of the loofah. The thickness of the loofah is 4-6 mm, the polyvinyl alcohol / sodium alginate mixed solution is poured to completely fill and just cover the loofah, and the height of the added carbonized loofah / polyvinyl alcohol / sodium alginate dispersion is 4-6 mm.

7. The method of claim 1, wherein the self-floating dual-layer solar evaporator with Janus properties is prepared by the steps of: In step S6, the concentration of the CaCl2 solution is 2-5 wt%.

8. The method of claim 1, wherein the self-floating dual-layer solar evaporator with Janus properties is prepared by the steps of: In step S7, the concentration of the silane coupling agent / ethanol solution is 1-3 wt%, and the silane coupling agent is selected from one of methyltrimethoxysilane, hexadecyltrimethoxysilane, vinyltrimethoxysilane, trimethylchlorosilane, octyltriethoxysilane, perfluorodecyltriethoxysilane, dimethyldimethoxysilane, and anilinomethyltrimethoxysilane.

9. A self-floating double-layer solar evaporator with Janus characteristics prepared by the preparation method of any one of claims 1-8.

10. Use of a self-floating double-layer solar evaporator with Janus properties prepared according to the method of any one of claims 1-8 in seawater desalination and wastewater purification, which has a pure water evaporation rate of more than 2.7 kg m -2 h -1 in 3.5 wt% NaCl solution, more than 2.6 kg m -2 h -1 in 10 wt% NaCl solution, more than 2.5 kg m -2 h -1 in 20 wt% NaCl solution, more than 2.2 kg m -2 h -1 .

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