Photothermal conversion materials, devices, and methods capable of improving saline-alkali soil and simultaneously producing salt and purifying water

Abstract

This invention discloses a photothermal conversion material, device, and method capable of improving saline-alkali soil and simultaneously producing salt and purifying water, belonging to the fields of saline-alkali soil improvement and seawater desalination. The preparation method includes dropwise addition of a polyethyleneimine electrolyte solution to an alkaline graphene oxide solution, followed by uniform deposition onto one side of a clean hydrophilic substrate. Heat treatment is then used to fully bond a black light-absorbing agent with the hydrophilic substrate. Finally, octyltrimethoxysilane solution is deposited onto the same side of the hydrophilic photothermal conversion material via vapor deposition. After washing and drying, a bifacial heterogeneous photothermal conversion material is obtained. The material of this invention exhibits bifacial heterogeneity; its hydrophobic upper surface ensures stable and efficient photothermal conversion, while its hydrophilic lower surface continuously extracts salt ions from the saline-alkali soil. It is inexpensive, easy to cut, and suitable for various salinity levels and application scenarios, making it widely applicable for soil improvement at different salinity and alkalinity levels.

Description

Technical Field

[0001] This invention belongs to the field of saline-alkali soil improvement and seawater desalination, and specifically relates to a two-sided heterogeneous photothermal conversion material, device and method that can cyclically leach saline-alkali soil, extract salt crystals and generate water of crystallization. Background Technology

[0002] Soil salinization is widespread in arid and coastal cities, threatening food production and severely impacting the sustainable development of human society. Solar thermal conversion technology, with its clean and environmentally friendly characteristics, has attracted significant attention in recent years. This technology utilizes only sustainable sunlight as a driving force and a photothermal converter as a carrier to achieve highly efficient water evaporation. In recent years, various methods have been developed to improve the efficiency of photothermal converters, such as enhancing light absorption, increasing photothermal conversion efficiency, strengthening thermal insulation properties, and optimizing water supply. After more than a decade of development, photothermal conversion efficiency has been significantly improved. However, applying it to real-world scenarios remains extremely challenging.

[0003] Seawater desalination, as a major application area of ​​current photothermal conversion technology, has received widespread attention from the academic community. The biggest challenge facing the application of photothermal technology in seawater desalination is the problem of salt crystallization and contamination on materials. Once salt contamination occurs, the light absorption efficiency of the photothermal converter decreases, ultimately leading to a decline in conversion efficiency and even irreversible structural damage. This significantly reduces the water production performance of the photothermal converter and drastically shortens its lifespan. Therefore, there is an urgent need to develop an efficient and feasible strategy to enhance the salt contamination resistance of light absorbers.

[0004] Existing research has shown that the migration, enrichment, and deposition of salt ions in photothermal converters can be altered by controlling the wetting properties of materials. One effective strategy to improve the salt resistance of materials is to enhance their hydrophilicity. For example, by grafting hydrophilic additives (such as polyethyleneimine), photothermal converters can be endowed with superhydrophilic properties (water contact angle ~0°), enhancing the diffusion and dilution of concentrated salt ions, thereby hindering the salt crystallization process and ultimately improving the material's salt resistance. Another strategy proven to improve the salt contamination resistance of materials is the complete opposite of the first: preparing photothermal evaporators with superhydrophobic surfaces. For example, by depositing superhydrophobic polymers (polydimethylsiloxane) onto the surface of the photothermal evaporator, the hydrophobic properties of the evaporator can be modified to superhydrophobic (water contact angle ~150°), thereby hindering the upward migration of brine and ultimately achieving salt resistance. Although these two methods have made some progress in the field of seawater desalination, there are still few cases of their application in improving saline-alkali soils. Exploring the application of photothermal technology in improving saline-alkali soil can not only expand the application scenarios of photothermal technology, but also provide new ideas for the improvement of saline-alkali soil.

[0005] Patent CN 109603596 A discloses a "metal-organic framework material photothermal seawater desalination membrane." In this invention, the photothermal converter consists of three layers: a photothermal conversion layer, a salt-barrier layer, and a buoyancy layer. It exhibits excellent photothermal conversion rate and seawater desalination performance, and the material demonstrates good stability. However, the thickness of the photothermal converter described in the invention is too small, making it difficult to prevent heat loss through conduction at the interface. This results in low photothermal conversion efficiency, and the metal-organic framework preparation process is complex and costly.

[0006] Patent CN 107739066 A discloses a method for preparing graphene photothermal conversion materials for seawater desalination and water purification. This invention involves preparing a slurry from graphene powder, a polymer with a chain-like molecular structure, and a solvent, followed by drying and high-temperature heat treatment to obtain a photothermal conversion material with good mechanical strength. After high-temperature carbonization, this material exhibits excellent photothermal conversion performance, and the porous structure of the polymer foam provides excellent water absorption. Applying this photothermal method to seawater desalination results in excellent photothermal water distillation efficiency. This photothermal conversion material is suitable for rapid seawater distillation and desalination. However, the synthesis process of this photothermal conversion material requires a large energy input, which does not meet the basic requirements of sustainable development, and it does not consider the desalination treatment of high-concentration brine. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies, explore new applications of existing photothermal technology, and provide a photothermal conversion material, device, and method that can improve saline-alkali soil and simultaneously produce salt-purified water. This two-dimensional photothermal conversion material balances high photothermal conversion efficiency with the ability to confine salt crystallization sites. On one hand, the hydrophilic bottom surface continuously absorbs saline-alkali soil leachate through a siphon effect, providing sufficient source water for photothermal conversion and ensuring high pure water production efficiency. On the other hand, the superhydrophobic upper surface effectively hinders the upward migration of salt crystals, not only effectively suppressing the formation of salt contamination but also confining the formation sites of salt crystals, thus achieving salt crystal recovery. This photothermal converter uses inexpensive two-dimensional materials as a substrate, greatly reducing the amount of light absorber used and lowering the construction cost of the photothermal converter. Simultaneously, the preparation process is simple and rapid.

[0008] The specific technical solution adopted in this invention is as follows:

[0009] In a first aspect, the present invention provides a method for preparing a photothermal conversion material that can improve saline-alkali soil and simultaneously produce salt for water purification, as detailed below:

[0010] S1: Polyethyleneimine electrolyte solution is added dropwise to alkaline graphene oxide solution and allowed to react fully to obtain a black light absorber;

[0011] S2: The black light absorber is uniformly deposited on one side surface of a clean hydrophilic substrate. The black light absorber is fully bonded to the hydrophilic substrate through heat treatment. After washing and drying, a hydrophilic photothermal conversion material is obtained.

[0012] S3: Octyltrimethoxysilane solution is deposited on the same side surface of the hydrophilic photothermal conversion material by vapor deposition, and after washing and drying, a two-sided heterogeneous photothermal conversion material is obtained.

[0013] Preferably, the pH value of the graphene oxide solution is 9-12, and the pH value is preferably 11.

[0014] Preferably, the mixing concentration ratio of the graphene oxide solution and the polyethyleneimine electrolyte solution is 3:1 to 3:12; the concentration of the graphene oxide solution is preferably 3 mg / mL, and the concentration of the polyethyleneimine electrolyte solution is preferably 9 mg / mL.

[0015] Preferably, the hydrophilic substrate is a hydrophilic fiber filter membrane or hydrophilic fiber filter paper, and the heat treatment refers to heat treatment in an oven at 60-100°C for 1-12 hours.

[0016] Preferably, the octyltrimethoxysilane solution refers to octyltrimethoxysilane with a volume of 100-1000 μL, which is dispersed in the vacuum chamber in the gas phase to construct the hydrophobic surface layer of the photothermal evaporator (i.e., a two-sided heterogeneous photothermal conversion material). The volume of octyltrimethoxysilane is preferably 600 μL.

[0017] In a second aspect, the present invention provides a bifacial heterogeneous photothermal conversion material obtained by any of the preparation methods described in the first aspect.

[0018] Thirdly, the present invention provides a photothermal conversion device that can improve saline-alkali soil and simultaneously produce salt and purify water, including a soil washing unit, a washing water storage unit and a photothermal conversion unit disposed in the inner cavity of the device shell; the inner top of the device shell is an upwardly convex conical structure;

[0019] The rinsing water storage unit is a pool structure located at the bottom of the inner cavity. A soil rinsing unit is provided circumferentially in the inner cavity above the rinsing water storage unit. The main body of the soil rinsing unit is used to hold the saline-alkali soil to be treated. A perforated partition is fixed at the bottom cross section, and the rinsing water can fall into the rinsing water storage unit through the partition. The photothermal conversion unit is a topless cylindrical structure with a hollow interior. The top is covered with two heterogeneous photothermal conversion materials as described in the second aspect. The hydrophilic substrate of the two heterogeneous photothermal conversion materials is located below and extends circumferentially below the water level of the rinsing water storage unit through a hydrophilic medium.

[0020] Preferably, the top of the device housing is made of a transparent material that allows sunlight to pass through.

[0021] Preferably, the two-sided heterogeneous photothermal conversion material has a concave funnel-shaped layered structure, and the hydrophilic medium is one or more of non-woven fabric, polymer filter membrane, fiber filter paper, graphene membrane, and biochar membrane.

[0022] Fourthly, the present invention provides a method for improving saline-alkali soil and simultaneously producing salt and purifying water using any of the photothermal conversion devices described in the third aspect, as follows:

[0023] The top of the photothermal conversion unit is exposed to sunlight, while the soil washing unit is filled with saline-alkali soil to be treated. Water is then added to the saline-alkali soil for soil washing. The washed liquid falls from the bottom perforated partition into the washing water storage unit. The hydrophilic medium absorbs the saline-alkali water washing liquid in the washing water storage unit and transfers it to two heterogeneous photothermal conversion materials. Through the asymmetric wetting properties of the two heterogeneous photothermal conversion materials, the hydrophilic substrate at the bottom continuously absorbs the saline-alkali water washing liquid from the hydrophilic medium, while the hydrophobic layer at the top restricts the salt crystallization sites, thus separating the clean water from the salt. Specifically:

[0024] As the photothermal reaction of the two heterogeneous photothermal conversion materials with the saline-alkali water rinsing solution continues, water molecules in the saline-alkali water rinsing solution continuously undergo phase transitions and escape. When they come into contact with the top of the device shell, they condense and flow back to the soil rinsing unit along the inner wall under the action of gravity, realizing continuous rinsing of saline-alkali soil. As the water evaporates, the concentration of saline-alkali water at the hydrophilic base of the two heterogeneous photothermal conversion materials continues to increase, and the salt concentration reaches its highest point at the bottom tip. The salt eventually nucleates and crystallizes and is deposited and falls off under the action of gravity, collected in the cylindrical shell of the photothermal conversion unit.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1) The photothermal conversion rate of the bifacial heterogeneous photothermal conversion material prepared by the present invention under illumination conditions is 2.81 times that of pure water and 1.28 times that of the control group.

[0027] 2) Due to the high light absorption efficiency, good thermal insulation, excellent photothermal conversion performance, and unique salt confinement effect of the two-dimensional heterogeneous photothermal conversion material prepared by this invention, the practical application potential of this two-dimensional heterogeneous photothermal conversion material is significant, with a photothermal evaporation rate reaching 1.692 kg m³. -2 h -1 .

[0028] 3) The bifacial heterogeneous photothermal conversion material prepared by the present invention uses a two-dimensional filter membrane or filter paper as a framework, which can greatly save the amount of light absorber and reduce the production cost of the photothermal conversion material. In addition, the synthesis and preparation method of the bifacial heterogeneous photothermal conversion material is simple, the conditions are mild, it is convenient to use, and the performance is excellent.

[0029] 4) The photothermal conversion device of the present invention is easy to manufacture into a small portable device, and can also be enlarged for industrial applications. It can continuously generate clean water, purify saline water, and repair saline-alkali soil by relying solely on the input of sunlight.

[0030] 5) The bi-sided heterogeneous photothermal conversion material prepared by the present invention uses filter membrane or filter paper as a substrate, can be recycled, has strong plasticity, and can be adapted to various scenarios. It can not only achieve efficient evaporation of pure water, but also continuously and efficiently extract salt and water from saline water.

[0031] 6) The bifacial heterogeneous photothermal conversion material prepared in this invention selects carbonaceous material graphene oxide as the photothermal conversion body and combines it with a polymer to achieve a high proportion of solar light absorption. At the same time, the hydrophilic two-dimensional filter membrane / filter paper with rich pore structure is used as the substrate to ensure sufficient water supply. Meanwhile, the photothermal evaporator is surrounded by thermally insulating air, which can greatly reduce heat loss and allow more energy to be used for water evaporation. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the two-sided heterogeneous photothermal conversion material in this invention, a scanning electron microscope micrograph at magnification, and an elemental analysis diagram.

[0033] Figure 2 This is a graph showing the photothermal conversion rate of the two heterogeneous photothermal conversion materials in this invention at different folding angles;

[0034] Figure 3 This is a diagram illustrating the purification effect of the two-sided heterogeneous photothermal conversion material on saline-alkali water in this invention.

[0035] Figure 4 This is a schematic diagram of the photothermal conversion device in this invention;

[0036] Figure 5 This is a schematic diagram of the principle of the photothermal conversion unit;

[0037] The attached diagram is labeled as follows: 1 Soil washing unit, 2 Wash water storage unit, 3 Photothermal conversion unit, 4 Two-sided heterogeneous photothermal conversion material. Detailed Implementation

[0038] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly, provided that there is no mutual conflict.

[0039] This invention provides a photothermal conversion material that can improve saline-alkali soil and simultaneously produce salt and purify water. This material can repair saline-alkali soil, desalinate saline-alkali water, and extract pure water. Specifically, this photothermal conversion material has two heterogeneous sides. Its hydrophobic upper surface ensures stable and efficient photothermal conversion, while its hydrophilic lower surface can continuously extract salt ions from saline-alkali soil. It is inexpensive, easy to cut, and suitable for various salinity and application scenarios, with a wide range of applications, and can be used for soil improvement of different salinity and alkalinity.

[0040] The preparation method of the photothermal conversion material of this invention mainly includes the preparation of graphene oxide, the preparation of hydrophilic complex, the pretreatment of a two-dimensional substrate, the surface loading of the hydrophilic complex, and the vapor deposition of a hydrophobic polymer, as detailed below:

[0041] S1: The pH of the graphene oxide solution was adjusted to 9–12 using 0.1M and 0.05M sodium hydroxide solutions to obtain solution A. In practical applications, a pH of 11 is preferred. Polyethyleneimine was selected to prepare the polymer electrolyte solution, resulting in solution B. The molecular weight of the polymer electrolyte material is 1000–10000, with a preferred molecular weight of 10000.

[0042] Graphene oxide solution can be purchased directly, or it can be prepared using the following method:

[0043] S11: Add graphite sheets to a solution containing 120 mL of concentrated H2SO4, 24.99 g of K2S2O8 and 24.99 g of P2O5 at 80 °C, and keep it for 4.5 h to allow it to react fully, to obtain mixture A.

[0044] S12: Wash the mixture A with deionized water until the pH of the washing solution is neutral, and then dry it at 60°C to obtain pre-oxidized graphite.

[0045] S13: Add 30g of pre-oxidized graphite powder and 15g of sodium nitrate to 690mL of concentrated sulfuric acid at 0℃ to obtain a mixed cold solution. Then slowly add 90g of potassium permanganate to the mixed cold solution while it is being vigorously stirred. During this process, the solution temperature must be kept below 4℃ to obtain mixture B.

[0046] S14: Slowly pour 1380 mL of deionized water and 25 mL of 30% hydrogen peroxide solution into mixture B, and allow it to react fully at 35°C for 2 hours to obtain a bright yellow mixture C.

[0047] S15: Rinse mixture C with hydrochloric acid solution (10%, 10.8L) to remove residual sulfate ions, then centrifuge at 8000 rpm to obtain concentrated graphene oxide. Redisperse the concentrated graphene oxide in deionized water and sonicate for 30 minutes to exfoliate it again. Repeat the above centrifugation and exfoliation operation several times (preferably three times) to obtain mixture D.

[0048] S16: Dialyze the mixture D, then soak it in deionized water to remove acid and other ions to obtain a graphene oxide solution (preferably with a concentration of 3 mg / mL).

[0049] S2: With a concentration ratio of solution A to solution B of 3:1 to 3:12 (preferably 3:9), solution B is added dropwise to solution A, and the mixture is subjected to ultrasound to allow it to react fully, resulting in a black light absorber, namely a charged graphene oxide composite solution.

[0050] S3: The two-dimensional filter membrane / paper is washed sequentially with deionized water and anhydrous ethanol, repeated several times, and then dried in an oven at 60°C to obtain a clean and dry two-dimensional substrate. A black light-absorbing agent (i.e., a graphene oxide-polymer solution) is added dropwise to the clean and dry two-dimensional substrate, allowing the black light-absorbing agent to be uniformly deposited on one side of the two-dimensional hydrophilic substrate. Subsequently, heat treatment is performed to fully bond the graphene oxide composite with the substrate. After washing and drying, the hydrophilic photothermal conversion material is obtained. Here, heat treatment refers to heat treatment in an oven at 60–100°C (preferably 60–80°C) for 1–12 hours.

[0051] After cleaning and drying, an octyltrimethoxysilane solution is deposited onto the same side surface of the hydrophilic photothermal conversion material via vapor deposition. After cleaning and drying, a two-sided heterogeneous photothermal conversion material is obtained. Here, vapor deposition refers to treatment in a vacuum drying oven at 50–100°C (preferably 70°C) for 1–12 hours. The octyltrimethoxysilane solution refers to a volume of 100–1000 μL, which is evaporated and diffused in a vacuum atmosphere to construct the hydrophobic surface layer of the photothermal evaporator. The preferred volume of the octyltrimethoxysilane is 600 μL.

[0052] like Figure 1 The diagram shows the microstructure of the two-dimensional photothermal conversion material of this invention. As can be seen, the composite material formed by graphene oxide and the polymer electrolyte is deposited on a two-dimensional substrate. The graphene oxide and the polymer electrolyte are bonded together by forces such as electrostatic interactions, while the charged graphene oxide composite is bonded to the two-dimensional substrate by van der Waals forces.

[0053] Based on its unique multidimensional structure, the designed light absorber possesses a multilayered structure, giving it excellent potential for photothermal fractionation and extraction of salt and water. On the upper surface, the loaded light absorber enables the photothermal converter to exhibit outstanding solar absorptivity (94.0%) across the solar spectrum. Simultaneously, the deposition of hydrophobic additives on the upper surface protects it from salt contamination, ensuring efficient and stable photothermal desalination performance, with salt crystallization sites confined to the bottom layer of the photothermal evaporator. In the lower layer, the two-dimensional substrate exhibits superhydrophilic properties. On one hand, it can rapidly replenish water vapor lost through photothermal evaporation, ensuring a stable photothermal evaporation efficiency. On the other hand, the siphon effect of the photothermal evaporator allows for directional transport of saline-alkali water, fixing the salt crystallization sites. Thus, the upper layer continuously generates clean water vapor, which is condensed and refluxed through the conical top, achieving multiple cycles of saline-alkali soil leaching. Meanwhile, the lower layer continuously accumulates salt crystals, which eventually deposit at the bottom of the photothermal conversion unit, achieving salt resource recovery.

[0054] Based on the aforementioned heterogeneous photothermal conversion materials, this invention also provides a photothermal conversion device capable of improving saline-alkali soil and simultaneously producing salt and purifying water, such as... Figure 4 As shown, the device mainly comprises a soil leaching unit 1, a leaching water storage unit 2, and a photothermal conversion unit 3. These three units are all housed within the device's casing, forming a multifunctional unit (salt-alkali soil leaching, saline-alkali soil extract storage, clean water regeneration, and salt crystallization recovery). The inner top of the device casing has an upward-convex conical structure, which allows evaporated water to condense at the top and slide down the inner wall. Furthermore, the top of the device casing should be made of a transparent material that allows sunlight to pass through, facilitating the photothermal reaction between the two heterogeneous photothermal conversion materials to achieve brine separation.

[0055] The leachate storage unit 2 is located at the bottom of the inner cavity and has a pool structure. The soil rinsing unit 1 is arranged circumferentially inside the device shell and is located above the leachate storage unit 2. The main body inside the soil rinsing unit 1 is used to hold the saline-alkali soil to be treated, and a perforated partition is fixed to the bottom cross-section. In actual use, the leachate in the soil rinsing unit 1 can continuously flow into the leachate storage unit 2 through the holes in the partition for temporary storage and collection.

[0056] The photothermal conversion unit 3 is a topless cylindrical structure with a hollow interior. The top is covered with the aforementioned two heterogeneous photothermal conversion materials 4. The hydrophilic substrate of the two heterogeneous photothermal conversion materials 4 is located at the bottom and extends circumferentially below the water level of the rinse water storage unit 2 through a hydrophilic medium.

[0057] In practical applications, the two-sided heterogeneous photothermal conversion material 4 has a concave funnel-shaped layered structure, and its size can be flexibly adjusted and cut according to actual needs, adapting to different application scenarios. The hydrophilic medium is a hydrophilic two-dimensional material, including but not limited to non-woven fabrics, polymer filter membranes, fiber filter paper, graphene membranes, and biochar membranes.

[0058] The aforementioned photothermal conversion device can be used to improve saline-alkali soil and simultaneously produce salt for water purification. The specific method is as follows:

[0059] The soil washing unit 1 is filled with saline-alkali soil to be treated, and then water is added to the saline-alkali soil to provide initial photothermal conversion raw water for the initial soil washing. After the soil washing liquid migrates to the washing water storage unit 2, the photothermal conversion unit 3 is placed in the photothermal conversion zone, and then the device is placed under a light source for salt-water separation extraction. The liquid after soil washing falls into the washing water storage unit 2 from the bottom perforated partition. The hydrophilic medium absorbs the saline-alkali water washing liquid in the washing water storage unit 2 to the two heterogeneous photothermal conversion materials 4. The two heterogeneous photothermal conversion materials 4, through their asymmetric wetting properties on both sides, allow the hydrophilic base at the bottom to continuously absorb the saline-alkali water washing liquid from the hydrophilic medium, while the hydrophobic layer at the top restricts the salt crystallization sites, thus separating the clean water from the salt, as detailed below:

[0060] like Figure 5 As shown, with the continuous photothermal reaction of the two heterogeneous photothermal conversion materials 4 with the saline-alkali water rinsing solution, water molecules in the saline-alkali water rinsing solution continuously undergo phase transitions and escape. When they come into contact with the top of the device shell, they condense and flow back to the soil rinsing unit 1 along the inner wall under the action of gravity, realizing continuous rinsing of saline-alkali soil multiple times. As the water evaporates, the concentration of saline-alkali water at the hydrophilic substrate of the two heterogeneous photothermal conversion materials 4 continues to increase, reaching the highest salt concentration at the bottom tip. The salt eventually nucleates and crystallizes and deposits under the action of gravity, collecting in the cylindrical shell of the photothermal conversion unit 3.

[0061] Specifically, when light shines on the two heterogeneous photothermal conversion materials 4, the light absorber on the upper layer of the photothermal converter absorbs the light, and most of the light energy is absorbed by the graphene oxide-polyethyleneimine covering the surface of the two-dimensional substrate. A small portion of the light can penetrate into the interior of the two heterogeneous photothermal conversion materials 4, and is absorbed after multiple scatterings. The light absorber generates heat after absorbing the light energy, and the heat is confined to the material surface by the surrounding thermally insulating air, greatly reducing heat loss. Salt-containing water (saline-alkali soil leaching solution) is directionally pumped to the irradiated area by the hydrophilic bottom surface of the photothermal converter through a siphon force. The water molecules, existing in the form of a thin film, rapidly absorb heat and form steam, which evaporates from the pores of the photothermal converter and comes into contact with the bottomless inverted cone at the top of the device shell, condenses, and forms pure droplets. Under the action of gravity, these droplets flow to the saline-alkali soil to leach it.

[0062] In other words, the water absorbed by the bottom layer is transferred to the photothermal conversion zone of the photoabsorber via two heterogeneous photothermal converters. There, it absorbs the heat energy converted by the photoabsorbent on the top surface of the converter, resulting in heat exchange and the generation of steam. This steam evaporates from the pores of the photothermal evaporator and condenses into droplets upon encountering the room-temperature conical top of the device casing, yielding clear, transparent clean water. This clean water flows down the conical top through the sidewalls to the bottom saline-alkali soil, where it is repeatedly leached, thus improving the saline-alkali soil.

[0063] Example 1

[0064] This embodiment evaluates the photothermal conversion efficiency of a two-sided heterogeneous photothermal conversion material, as detailed below:

[0065] 1) A certain volume of water is added to the water storage device, and two heterogeneous photothermal conversion materials are placed on it. The changes in water quality and the temperature and humidity of the environment are recorded by an automatic balance and a thermometer and hygrometer. This is the device for evaluating the photothermal conversion efficiency.

[0066] The specific process is as follows:

[0067] ① Under conditions of no light, observe the change in water mass for 1 hour and calculate the rate of change of water mass per unit time vi, which is the background value of water evaporation under natural conditions.

[0068] ② The light intensity was calibrated to 1 sun using an optical power meter. Then, the light spot was irradiated onto the surface of the two-dimensional photothermal conversion material. The average temperature change of the photothermal conversion material before and after 1 hour of irradiation was recorded. The mass change of water was recorded using a real-time recording balance. The rate of change of water mass per unit time vii was calculated.

[0069] ③The rate of water evaporation under this light intensity is obtained by subtracting the rate vi of the blank experimental group from the rate vii measured in ②.

[0070] The results are as follows Figure 2 The figure shows the dark evaporation efficiency of pure water (H2O) under dark conditions, and the photothermal conversion rates of H2O, a flat two-dimensional photothermal conversion material, and a folded two-dimensional photothermal conversion material under illumination. As can be seen from the figure, compared to pure water and the flat two-dimensional photothermal conversion material, the photothermal conversion rate of the folded two-dimensional photothermal conversion material reaches 1.692 kgm³. -2 h -1 .

[0071] Example 2

[0072] This embodiment evaluates the stability and water production efficiency of the two-sided heterogeneous photothermal conversion material, as detailed below:

[0073] 1) The stability of the photothermal conversion body was evaluated by conducting long-term photothermal evaporation performance tests using the folded bifacial heterogeneous photothermal conversion body described in Example 1. The specific process is as follows:

[0074] ① Weigh a certain amount of original saline-alkali soil, measure the soil water holding capacity of the original saline-alkali soil, use water that reaches the soil water holding capacity to perform one leaching of the soil, and collect the leaching water of the saline-alkali soil.

[0075] ② Add the leaching water from the saline-alkali soil to the water storage unit of the photothermal conversion device, connect it to a balance and computer for real-time quality recording, and simultaneously record the ambient temperature and humidity;

[0076] ③ The light intensity of the calibrated light source is set to 1 sun. Then, the photothermal conversion device is adjusted so that the light spot fully illuminates the surface of the two-dimensional photothermal conversion material. The mass change of water is recorded using a real-time recording balance, and the rate of change of water mass per unit time is calculated.

[0077] Table 1 shows the change in the rate of pure water production over time after a 12-hour photothermal conversion experiment.

[0078] Table 1. Changes in purified water from solar thermal generation over time.

[0079] Time (h) <![CDATA[Water production rate (kg m -2 h -1 )]]> 1 1.619 2 1.484 3 1.453 4 1.484 5 1.438 6 1.402 7 1.369 8 1.313 9 1.351 10 1.322 11 1.352 12 1.359

[0080] Example 3

[0081] This embodiment evaluates the desalination efficiency of saline-alkali soil using a two-sided heterogeneous photothermal conversion material, as detailed below:

[0082] The purified water obtained from the photothermal evaporation experiment using the folded bifacial heterogeneous photothermal converter in Example 1 was used to repeatedly wash the saline-alkali soil to evaluate the remediation effect. The specific process is as follows:

[0083] ① Weigh 40g of original saline-alkali soil, measure the soil water holding capacity of the original saline-alkali soil, perform one leaching, collect the leaching water of the saline-alkali soil, dilute it to the measurement range of the conductivity meter, and then perform conductivity test.

[0084] ② The original soil was leached 7 times in a cycle, and the measured electrical conductivity was recorded. The salinity was obtained according to the correspondence between electrical conductivity and salinity.

[0085] The final result is shown in Table 2, which illustrates the change in salinity with the number of leaching cycles. Figure 3 .

[0086] Table 2. Changes in salinity of saline-alkali soil extract with leaching frequency.

[0087] frequency <![CDATA[Salinity (mg L -1 )]]> 1 7445.1 2 5270.5 3 6337.2 4 4924.4 5 2798.8 6 1897.7 7 1785.8

[0088] The results of the examples show that the bifacial heterogeneous photothermal conversion material synthesized using graphene oxide, polymer electrolyte, and octyltrimethoxysilane possesses excellent light absorption and good insulation properties, enabling efficient conversion of sunlight into heat. The unique bifacial heterogeneity and device of the photothermal converter allow water to exist on its surface in the form of a thin film. The strong siphon effect and abundant pore structure of the lower surface continuously and efficiently achieve phase change in the saline-alkali soil leachate, forming pure water vapor. This vapor is then condensed and refluxed to complete multiple cycles of soil leaching. The excellent hydrophobic effect of the upper surface enhances the material's salt resistance, achieving the improvement of saline-alkali soil and efficient extraction of salt-water separation from the soil leachate. Specifically, in this example, over time, the photothermal evaporation device ultimately reduced the salinity in the saline-alkali soil leachate from 7445.1 mg / L. -1 Reduced to 1785.8 mg / L -1 This reduced the risk by 76.01%. This example demonstrates the saline-alkali soil remediation capability and the potential for efficient extraction of salt-water from saline-alkali water using the developed bifacial heterogeneous photothermal evaporator and device.

[0089] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A method for improving saline-alkali soil and simultaneously producing salt for water purification using a photothermal conversion device, characterized in that, The photothermal conversion device includes a soil washing unit (1), a washing water storage unit (2), and a photothermal conversion unit (3) disposed in the inner cavity of the device shell; the inner top of the device shell is a cone-shaped structure with an upward protrusion; the washing water storage unit (2) is a pool structure located at the bottom of the inner cavity, and the inner cavity above the washing water storage unit (2) is provided with the soil washing unit (1) along the circumference; the main body inside the soil washing unit (1) is used to hold the saline-alkali soil to be treated, and the bottom cross section is fixed with a perforated partition, through which the washing water can fall into the washing water storage unit (2); the photothermal conversion unit (3) is a cylindrical structure without a top, hollow inside, and the top is covered with two heterogeneous photothermal conversion materials (4); the hydrophilic base of the two heterogeneous photothermal conversion materials (4) is located at the bottom, and extends into the water level of the washing water storage unit (2) in the circumference through a hydrophilic medium; The two-sided heterogeneous photothermal conversion material (4) has a concave funnel-shaped layered structure; The specific preparation method of the two-sided heterogeneous photothermal conversion material (4) is as follows: S1: Polyethyleneimine electrolyte solution is added dropwise to alkaline graphene oxide solution and allowed to react fully to obtain a black light absorber; S2: The black light absorber is uniformly deposited on one side surface of a clean hydrophilic substrate. The black light absorber is fully bonded to the hydrophilic substrate through heat treatment. After washing and drying, a hydrophilic photothermal conversion material is obtained. S3: Octyltrimethoxysilane solution is deposited on the same side surface of the hydrophilic photothermal conversion material by vapor deposition, and after washing and drying, a two-sided heterogeneous photothermal conversion material is obtained. The specific method for improving saline-alkali soil and simultaneously producing salt for water purification is as follows: The top of the photothermal conversion unit (3) is irradiated with sunlight, while the soil washing unit (1) is filled with saline-alkali soil to be treated. Water is then added to the saline-alkali soil for soil washing. The liquid after soil washing falls from the bottom perforated partition into the washing water storage unit (2). The hydrophilic medium absorbs the saline-alkali water washing liquid in the washing water storage unit (2) to the two heterogeneous photothermal conversion materials (4). The two heterogeneous photothermal conversion materials (4) have asymmetrical wetting properties on both sides. The hydrophilic base at the bottom can continuously absorb the saline-alkali water washing liquid from the hydrophilic medium, and the hydrophobic layer at the top restricts the crystallization sites of the salt, making the clean The separation of water and salt is as follows: As the photothermal reaction of the two heterogeneous photothermal conversion materials (4) on the salt and alkali water rinsing liquid continues, the water molecules in the salt and alkali water rinsing liquid continuously undergo phase change and escape. When they touch the top of the device shell, they condense and flow back to the soil rinsing unit (1) along the inner wall under the action of gravity, thus realizing the continuous rinsing of the saline-alkali soil. As the water evaporates, the salt and alkali water concentration at the hydrophilic base of the two heterogeneous photothermal conversion materials (4) continues to increase. The salt concentration reaches its highest point at the bottom tip. The salt eventually nucleates and crystallizes and is deposited and falls off under the action of gravity, and is collected in the cylindrical shell of the photothermal conversion unit (3).

2. The method for improving saline-alkali soil and simultaneously producing salt for water purification according to claim 1, characterized in that, The pH value of the graphene oxide solution is 9-12.

3. The method for improving saline-alkali soil and simultaneously producing salt for water purification according to claim 2, characterized in that, The pH value of the graphene oxide solution is 11.

4. The method for improving saline-alkali soil and simultaneously producing salt for water purification according to claim 1, characterized in that, The mixing concentration ratio of the graphene oxide solution and the polyethyleneimine electrolyte solution is 3:1 to 3:

12.

5. The method for improving saline-alkali soil and simultaneously producing salt for water purification according to claim 4, characterized in that, The concentration of the graphene oxide solution is 3 mg / mL, and the concentration of the polyethyleneimine electrolyte solution is 9 mg / mL.

6. The method for improving saline-alkali soil and simultaneously producing salt for water purification according to claim 1, characterized in that, The hydrophilic substrate is a hydrophilic fiber filter membrane or hydrophilic fiber filter paper, and the heat treatment refers to heat treatment in an oven at 60~100 ℃ for 1~12 hours.

7. The method for improving saline-alkali soil and simultaneously producing salt for water purification according to claim 1, characterized in that, The octyltrimethoxysilane solution is a 100-1000 μL volume octyltrimethoxysilane solution that is diffused into a vacuum atmosphere after being evaporated into a gas.

8. The method for improving saline-alkali soil and simultaneously producing salt for water purification according to claim 7, characterized in that, The volume of the octyltrimethoxysilane is 600 μL.

9. The method for improving saline-alkali soil and simultaneously producing salt for water purification according to claim 1, characterized in that, The top of the device housing is made of a transparent material that allows sunlight to pass through.

10. The method for improving saline-alkali soil and simultaneously producing salt for water purification according to claim 1, characterized in that, The hydrophilic medium is one or more of the following: nonwoven fabric, polymer filter membrane, fiber filter paper, graphene membrane, and biochar membrane.

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