Light and heat evaporation material for saline loess site remediation and preparation method and application thereof

Abstract

The application relates to the technical field of environmental engineering, in particular to a light-heat evaporation material for saline loess site remediation and a preparation method and application thereof. The preparation method comprises the following steps: dispersing modified zeolite on the surface of polypropylene non-woven fabric, spraying pyrrole aqueous solution and ferric chloride aqueous solution in sequence, continuously spraying the modified zeolite for multiple times and spraying the pyrrole aqueous solution and the ferric chloride aqueous solution, and in-situ polymerization to form a cross-linked coating; preparing a spore suspension by using beef extract, protein peptone, manganese sulfate titanium white powder solution, nickel chloride hexahydrate solution, yeast extract, ammonium chloride solution and sodium chloride solution; immersing the polypropylene non-woven fabric with the cross-linked coating formed on the surface into the spore suspension and a sodium alginate-graphene oxide mixed solution in sequence; spraying calcium chloride solution; and after rinsing with deionized water and drying, the light-heat evaporation material is obtained. The material has excellent light-heat conversion capacity, light absorption rate and high water evaporation rate, and can significantly reduce the salt content of saline loess in a short time.

Description

Technical Field

[0001] This invention relates to the field of environmental engineering technology, specifically to a photothermal evaporation material for the remediation of saline loess sites, its preparation method, and its application. Background Technology

[0002] Saline loess sites are widely distributed in arid and semi-arid regions of northern my country. These sites are characterized by rapid accumulation of soil salts, intense evaporation, and difficulty in vegetation restoration, making them one of the core obstacles restricting regional agricultural development and ecological restoration. Under the combined effects of shallow groundwater burial and strong evaporation, salts migrate to the surface via capillary water and accumulate in large quantities, leading to soil structure damage, porosity degradation, and decreased permeability, severely inhibiting plant root development and water and nutrient absorption efficiency.

[0003] Currently, commonly used saline soil remediation technologies mainly fall into three categories: First, physical methods, such as freshwater flushing and desalination projects, but these methods generally rely on large amounts of water resources and are difficult to apply to areas with scarce water resources; second, chemical modification methods, such as applying soil conditioners like lime and gypsum to change the composition and structure of salts, but long-term use may lead to environmental risks such as soil acid-base imbalance and heavy metal accumulation; and third, phytoremediation methods, which rely on salt-tolerant plants to absorb and transport salts, but this method is slow to take effect, has high requirements for vegetation selection, and is difficult to cope with sites under high salt stress.

[0004] In addition, although some new evaporation-driven desalination technologies have emerged in recent years, they still suffer from problems such as high energy consumption, complex processes, high costs, and poor environmental adaptability, which limit their practical application and promotion in the vast saline loess areas.

[0005] Therefore, there is an urgent need to develop a new remediation technology that can achieve in-situ desalination of soil without the need for additional water or chemicals, and that can utilize natural energy. This technology should also be characterized by its simple structure, convenient operation, low cost, and strong sustainability, so as to achieve efficient, green, and large-scale remediation of saline loess sites. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a photothermal evaporation material for the remediation of saline loess sites, its preparation method, and its application. The present invention is highly efficient, green, and low-cost. The material possesses excellent photothermal conversion capabilities, and can rapidly evaporate capillary water and migrate salts to the material surface for crystallization and separation under sunlight, thereby achieving in-situ removal of soil salts.

[0007] In the preparation method of the photothermal evaporation material for saline loess site remediation of the present invention, modified zeolite is attached to the surface of polypropylene nonwoven fabric, and pyrrole aqueous solution and ferric chloride aqueous solution are sprayed in sequence. The modified zeolite is continuously coated and sprayed with pyrrole aqueous solution and ferric chloride aqueous solution multiple times, and in-situ polymerization is carried out to form a cross-linked coating. The prepared polypropylene nonwoven fabric was sequentially immersed in spore suspension and sodium alginate-graphene oxide mixed solution. After immersion, it was sprayed with calcium chloride solution and rinsed with deionized water to remove residual monomers, intermediate products and iron salt byproducts. After drying, the resulting photothermal evaporation material had a black surface and high light absorption performance. It has excellent photothermal conversion ability, light absorption rate and high water evaporation rate. Combined with the remediation system of buried water source and capillary water conveyance structure, it can significantly reduce the salinity of loess in a short time. It also has the advantages of low carbon, environmental protection and reusability. The photothermal evaporation material of this invention can effectively reduce the salinity of loess and form a green, efficient and low energy consumption in-situ remediation technology for saline loess. It is particularly suitable for the treatment of large areas of saline loess sites in arid and semi-arid regions.

[0008] The present invention provides a method for preparing a photothermal evaporation material for the remediation of saline loess sites, which specifically includes the following steps:

[0009] (1) The polypropylene nonwoven fabric was cleaned with dilute acid solution and dilute alkali solution in turn. Then, the modified zeolite was uniformly dispersed on the two surfaces of the polypropylene nonwoven fabric. Then, under the dark, pyrrole aqueous solution and ferric chloride aqueous solution were sprayed on the two surfaces in turn. Then, the above steps of dispersing the modified zeolite, spraying pyrrole aqueous solution and ferric chloride aqueous solution were repeated many times. The ambient temperature was maintained at 20-25℃. The two surfaces of the polypropylene nonwoven fabric were polymerized in situ to form a cross-linked coating.

[0010] (2) The polypropylene nonwoven fabric with a cross-linked coating on its surface is soaked in a spore suspension and a sodium alginate-graphene oxide mixed solution in sequence. After soaking, the polypropylene nonwoven fabric is taken out and calcium chloride solution is sprayed on both surfaces. Then it is rinsed with deionized water and finally dried to obtain a photothermal evaporation material for saline loess site remediation.

[0011] Furthermore, in step (1), the polypropylene nonwoven fabric is cleaned with dilute acid solution and dilute alkali solution in turn to improve the interfacial wettability and cleanliness of the material.

[0012] Furthermore, in step (1), the dilute acid solution and the dilute alkaline solution are 0.1M nitric acid solution and 0.1M sodium hydroxide solution, respectively.

[0013] Furthermore, the polypropylene nonwoven fabric mentioned in step (1) has a thickness of 0.7mm-1.5mm, a pore mesh number of 20-40 mesh, a corresponding equivalent pore size of approximately 250-500μm, and a porosity of 70-85%.

[0014] Further, the modified zeolite in step (1) is prepared by the following method: 10-15 mesh natural zeolite is placed in a 1.0M sodium hydroxide solution and magnetically stirred at 200-300 r / min for 6-10 h. After the reaction, the mixed slurry is allowed to settle or separated by filtration or centrifugation. The solid phase is collected and then repeatedly washed with deionized water. Each time, sufficient deionized water is added and shaken or stirred before filtration until the pH of the washing liquid is close to neutral and there is no obvious alkaline taste. The washed zeolite is placed in an oven at 60-105℃ and dried for 6-12 h to constant weight. After drying, it is cooled to room temperature and stored in a sealed bag or desiccator to obtain the modified zeolite.

[0015] Furthermore, in step (1), the mass of modified zeolite added per surface area of ​​the polypropylene nonwoven fabric in a single step is 0.5-1.0 g / cm³. 2 .

[0016] Furthermore, in step (1), the concentration of the pyrrole aqueous solution is 1 mol / L, and the concentration of the ferric chloride aqueous solution is 1-2 mol / L.

[0017] Furthermore, the pyrrole aqueous solution described in step (1) is prepared freshly and used immediately by pyrrole with a purity >99% and deionized water under light-protected conditions. The solution preparation temperature is maintained at 20-25℃, and the resistivity of the deionized water is >18.2 MΩ•cm. During the solution preparation process, ultrasonic stirring is performed at a frequency of 20-40 kHz for 5 minutes to ensure uniform dissolution. The pH of the ultrasonically obtained mixed solution is adjusted to 6.5-7.5 using 0.1 M sodium hydroxide solution and nitric acid solution. In addition, the prepared solution must be used within 10-15 minutes.

[0018] Furthermore, in step (1), the steps of dispersing modified zeolite in the tidal flat, spraying pyrrole aqueous solution and ferric chloride aqueous solution are repeated 3-5 times.

[0019] Furthermore, the mass fraction of the calcium chloride solution in step (2) is 1.0-3.0%.

[0020] Furthermore, in step (2), deionized water is used to rinse to remove residual monomers, intermediate products and iron salt byproducts.

[0021] Furthermore, in step (2), the soaking time in the spore suspension or sodium alginate-graphene oxide mixed solution is 4-10 min each time.

[0022] Furthermore, in step (2), drying refers to drying at 40-65℃ for 6-10 hours.

[0023] Furthermore, in step (2), the amount of calcium chloride solution sprayed on each surface is 0.5-2.0 mL / cm². 2 .

[0024] Further, the spore suspension in step (2) is prepared as follows: *Pasteurella multocida* is stored in cryovials. *Pasteurella multocida* is added to compound solution one to obtain compound solution A. The mass fraction of *Pasteurella multocida* in compound solution one is 0.05-0.2%. Compound solution A is cultured in a constant temperature incubator at 25-35℃ and a rotation speed of 180-300 r / min for 20-30 h. The cultured compound solution A is then inoculated into compound solution two at a volume ratio of 1-2%, and cultured for 64-96 h to obtain a suspension. Finally, the suspension is sterilized in a water bath at 80℃ for 15-30 min. The suspension is then centrifuged at a rotation speed of 6000-8000 r / min for 10 min. The precipitate is diluted with physiological saline to a spore concentration of 2.0 × 10⁻⁶. 10 -3.0×10 10 CFU / mL was used to obtain spore suspensions. In compound solution one, the solutes were beef extract, peptone, manganese titanium dioxide, and nickel chloride hexahydrate, and the solvent was deionized water. The concentrations of beef extract, peptone, manganese titanium dioxide, and nickel chloride hexahydrate in compound solution one were 4-10 g / L, 5-8 g / L, 10-15 mg / L, and 20-25 mg / L. In compound solution two, the solutes were yeast extract, ammonium chloride, manganese titanium dioxide, and nickel chloride hexahydrate, and the solvent was deionized water. The concentrations of yeast extract, ammonium chloride, manganese titanium dioxide, and nickel chloride hexahydrate in compound solution two were 5-10 g / L, 10-20 g / L, 10-15 mg / L, and 20-30 mg / L.

[0025] Furthermore, in the method for preparing spore suspension, the physiological saline is a sodium chloride solution with a mass fraction of 0.6-1.0%.

[0026] Furthermore, the sodium alginate-graphene oxide mixed solution described in step (2) is prepared by the following method: sodium alginate is dissolved in deionized water and magnetically stirred at 500-800 r / min for 30-50 min until fully dissolved. Then, graphene oxide powder is added and magnetically stirred at 1500-2800 r / min for 40-60 min to obtain the sodium alginate-graphene oxide mixed solution.

[0027] Furthermore, in the preparation method of the sodium alginate-graphene oxide mixed solution in step (2), the sodium alginate accounts for 1-5% of the mass fraction of the mixed solution, and the graphene oxide accounts for 5-10% of the mass fraction of the mixed solution.

[0028] The present invention also provides a photothermal evaporation material for saline loess site remediation prepared according to the above preparation method and its application in saline loess site remediation.

[0029] Furthermore, the surface of the photothermal evaporation material is black, and it has high light absorption performance, with an absorbance of up to 96.0% in the 200-2500nm spectral range and a dry tensile strength of not less than 1.8MPa.

[0030] The application of the aforementioned photothermal evaporation material in the remediation of saline loess sites involves first burying cotton ropes in the saline loess to form capillary water replenishment channels, then suspending the photothermal evaporation material above the surface of the saline loess, and finally carrying out site remediation under solar radiation.

[0031] Furthermore, in the aforementioned application, the material evaporates for 8 hours a day for 10 consecutive days under solar radiation; after the salt crystal coverage on the surface of the photothermal evaporation material reaches 80%, the material is replaced and the salt is collected.

[0032] Furthermore, in the application, within a 10-day treatment cycle, the photothermal evaporation material for saline loess site remediation reduces the salt concentration in the 3-4 cm soil layer by no less than 90%.

[0033] Furthermore, in the application, the cotton rope is a gel cotton rope or a regular cotton rope, and the saline loess is cylindrical saline loess.

[0034] Furthermore, in the aforementioned application, the number of cotton ropes is not less than the ratio of the diameter to the height of the cylindrical saline loess, and the length of the cotton ropes is not less than 10 times the ratio of the height to the diameter of the cylindrical saline loess, in cm.

[0035] Furthermore, in the aforementioned application, the diameter of the gel cotton rope depends on the number of gel coagulation times and the time. Specifically, one coagulation time means that the cotton rope is shaken in a container containing sodium alginate-graphene oxide composite solution for 3-6 hours and then placed in a 1-3% calcium chloride solution for 6-24 hours.

[0036] Furthermore, in the aforementioned application, the position of the photothermal material suspended above the ground surface should be greater than the ratio of the height to the diameter of the cylindrical saline loess, in cm.

[0037] This invention utilizes a photothermal evaporation material formed through in-situ polymerization and cross-linking. This material possesses excellent photothermal conversion capabilities, light absorption rate, and high water evaporation rate. When combined with a repair system using gel cotton rope and a gel cotton rope capillary water transport structure, it can significantly reduce the salinity of saline loess in a short period of time. It also has advantages such as low carbon footprint, environmental friendliness, and reusability. This invention provides a green, efficient, and low-energy-consumption in-situ remediation technology for saline loess, which is particularly suitable for the treatment of large-area saline loess sites in arid and semi-arid regions.

[0038] This invention addresses and strengthens saline loess based on the following mechanism: the prepared photothermal evaporation material possesses high light absorption and heat conversion efficiency, enabling efficient conversion of solar energy into thermal energy, driving rapid evaporation of surface moisture and forming a strong interfacial water vapor gradient; continuous water rise is achieved through gel cotton ropes and loess capillary channels, simultaneously carrying dissolved salts upwards along the water flow path; since evaporation occurs at the material interface, salts concentrate and crystallize upon reaching the surface of the evaporator (i.e., the photothermal evaporation material), fixing themselves to the material surface rather than seeping back into the soil; this avoids the risk of salt re-contact with the soil and roots, significantly mitigating the salt damage effect while improving soil permeability and plant growth potential; the material is lightweight and flexible, with minimal thermal expansion, allowing it to stably adhere to uneven surfaces, ensuring long-term continuous operation of the remediation system.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) In the preparation method of the present invention, modified zeolite is attached to the surface of polypropylene nonwoven fabric to increase adsorption sites. At the same time, modified zeolite, Bacillus pasteurellii, graphene oxide, sodium alginate and calcium chloride solution are used to form a composite reinforced cross-linked structure. The resulting photothermal evaporation material has excellent photothermal conversion ability, light absorption rate and high water evaporation rate. Combined with the repair system with buried water source and capillary water transport structure, it can significantly reduce the salt content of loess in a short time. It also has the advantages of low carbon, environmental protection and reusability. Through the crystallization of the material interface of the evaporator (i.e. photothermal evaporation material), the problem of salt returning to the soil is avoided, and the precise control of "surface salt accumulation and root zone desalination" is achieved, which improves the repair efficiency and stability.

[0041] (2) Unlike the traditional freshwater flushing method, the present invention adopts interfacial capillary water transport + solar-driven photothermal evaporation, which does not require an external water supply system and is particularly suitable for saline loess areas with scarce water resources.

[0042] (3) No chemical conditioning agents are required, the soil chemical composition is not changed, and no new pollution sources are introduced. The material can be recycled after use, which is in line with the sustainable development direction of ecological restoration.

[0043] (4) Evaporation rate as high as 4.43 kg / m 2•h, and the material has a dry tensile strength of 1.85MPa and a wet elongation of 59.8%, and can be used multiple times without being easily damaged, making it economical and durable;

[0044] (5) The restored saline loess can effectively support plant growth, and the seed germination rate and biomass are significantly improved, indicating that it not only removes salt but also improves the soil ecological function.

[0045] (6) The materials used in this invention are modified zeolite, Bacillus pasteurellus, graphene oxide, sodium alginate and calcium chloride as the main raw materials. The polymerization conditions are mild, the preparation cycle is short, and it is easy to promote to the engineering site for rapid deployment and maintenance. Attached Figure Description

[0046] Figure 1 The results are the average light absorption test results of the nonwoven fabric used in the examples and the photothermal evaporation material for saline loess site remediation prepared in Example 1.

[0047] Figure 2 The tensile strength test results are for the nonwoven fabric used in the examples and the photothermal evaporation material for saline loess site remediation prepared in Example 1.

[0048] Figure 3 The evaporation rate test results are for the nonwoven fabric used in the examples and the photothermal evaporation material for saline loess site remediation prepared in Example 1.

[0049] Figure 4 Test curves of salt loss in loess after the photothermal evaporation materials prepared in Examples 1-3 were used to repair saline loess.

[0050] Figure 5 The surface temperature test curves of the photothermal evaporation materials for saline loess remediation prepared in Examples 1-3 are shown.

[0051] Figure 6 pH and EC test curves of loess after the photothermal evaporation material prepared in Example 1 was used to repair saline loess. Detailed Implementation

[0052] To better understand the content of this invention, it will be further described below with reference to specific embodiments and accompanying drawings. The following embodiments are based on the technology of this invention and provide detailed implementation methods and operating steps, but the scope of protection of this invention is not limited to the following embodiments.

[0053] In the following examples, the nonwoven fabric was made of polypropylene and purchased from Chengdu Shuanglong Nonwoven Fabric Factory in Xindu District; the cotton rope was a highly absorbent pure cotton rope with a multi-strand twisted structure and purchased from Wenzhou Jihe Rope & Tape Co., Ltd.; *Pasteurella multocida* was purchased from the China Microbiological Culture Collection Center, with accession number CGMCC1.3687; and chemical reagents such as pyrrole, sodium hydroxide, nitric acid, ferric chloride solution, sodium alginate, calcium chloride, beef extract, peptone, manganese sulfate titanium dioxide, nickel chloride hexahydrate, yeast extract, ammonium chloride, and sodium chloride were purchased from Shaanxi Guoyao Group Co., Ltd.; and natural zeolite and graphene oxide were purchased from Henan Lize Environmental Protection Technology Co., Ltd.

[0054] The embodiment provides a photothermal evaporation material for the remediation of saline loess sites, the raw materials of which include: polypropylene nonwoven fabric, deionized water, modified zeolite, pyrrole aqueous solution, sodium hydroxide solution, nitric acid solution, ferric chloride aqueous solution, Bacillus pasteurellii, beef extract, peptone, manganese sulfate titanium dioxide solution, nickel chloride hexahydrate solution, yeast extract, ammonium chloride solution, sodium chloride solution, sodium alginate, graphene oxide, and calcium chloride.

[0055] Example 1:

[0056] In this embodiment, the polypropylene nonwoven fabric has a thickness of 1.0 mm, a pore size of 20 mesh, a corresponding equivalent pore size of approximately 250 μm, and a porosity of 80%; the sodium hydroxide solution has a concentration of 0.1 M; the nitric acid solution has a concentration of 0.1 M; the ferric chloride aqueous solution has a concentration of 1 mol / L; and the calcium chloride solution is a 2% (w / w) calcium chloride aqueous solution prepared from analytical grade calcium chloride.

[0057] The modified zeolite was prepared by the following method: 10-mesh natural zeolite was reacted with a 1.0M sodium hydroxide solution at 200 r / min with magnetic stirring for 6 h. After the reaction, the mixed slurry was allowed to settle or separated into solid and liquid phases by filtration or centrifugation. The solid phase was collected and then repeatedly washed with deionized water. Each time, sufficient deionized water was added and the mixture was shaken or stirred before filtration until the pH of the washing liquid was close to neutral and there was no obvious alkaline taste, in order to remove residual NaOH and dissolved impurity ions. The washed zeolite was placed in a 60℃ oven and dried for 12 h to constant weight. After drying, it was cooled to room temperature and stored in a sealed bag or desiccator to obtain the modified zeolite.

[0058] The concentration of the pyrrole aqueous solution is 1 mol / L. It is prepared freshly by mixing pyrrole with a purity >99% and deionized water under light-protected conditions. The solution is prepared at 20°C, and the resistivity of the deionized water is >18.2 MΩ•cm. The pyrrole aqueous solution is prepared by ultrasonic stirring at a frequency of 20 kHz for 5 minutes to ensure uniform dissolution. Finally, the pH of the pyrrole aqueous solution is adjusted to 6.5 with 0.1 M sodium hydroxide solution and 0.1 M nitric acid solution. In addition, the prepared solution must be used within 10 minutes.

[0059] The spore suspension was prepared as follows: *Bacillus pasteurellii* was stored in cryovials. The solutes in composite solution one were beef extract, peptone, manganese titanium dioxide, and nickel chloride hexahydrate. The solvent was deionized water. The concentrations of beef extract, peptone, manganese titanium dioxide, and nickel chloride hexahydrate in composite solution one were 6 g / L, 5 g / L, 10 mg / L, and 20 mg / L. *Bacillus pasteurellii* was added to composite solution one to obtain composite solution A. The mass fraction of *Bacillus pasteurellii* in composite solution one was 0.1%. Composite solution A was incubated in a constant temperature incubator at 25°C and 180 r / min for 24 h. The solutes in compound solution two were yeast extract, ammonium chloride, manganese sulfate titanium dioxide, and nickel chloride hexahydrate, and the solvent was deionized water. The concentrations of yeast extract, ammonium chloride, manganese sulfate titanium dioxide, and nickel chloride hexahydrate in compound solution two were 7 g / L, 10 g / L, 10 mg / L, and 25 mg / L, respectively. Compound solution A, after 24 hours of cultivation, was inoculated into compound solution two at a volume ratio of 1.5% (i.e., the volume fraction of compound solution A after 24 hours of cultivation was 1.5% of the volume fraction of compound solution two). The mixture was then incubated for 80 hours to obtain a suspension. Finally, the suspension was sterilized in an 80°C water bath for 20 minutes. The suspension was then centrifuged at 7000 rpm for 10 minutes, and the precipitate was diluted with physiological saline (0.6% sodium chloride solution) to a spore concentration of 2.3 × 10⁻⁶. 10 CFU / mL was used to obtain a spore suspension.

[0060] The sodium alginate-graphene oxide mixed solution was prepared as follows: Sodium alginate was dissolved in deionized water and magnetically stirred at 500 rpm for 30 min until fully dissolved. Then, graphene oxide powder was added, and the mixture was magnetically stirred at 1500 rpm for 40 min to obtain the mixed solution. The sodium alginate accounted for 2% of the mass fraction of the mixed solution, and the graphene oxide accounted for 7% of the mass fraction.

[0061] A method for preparing a photothermal evaporation material for saline loess site remediation specifically includes the following steps:

[0062] (1) The polypropylene nonwoven fabric was cleaned successively with 0.1M nitric acid solution and 0.1M sodium hydroxide solution to improve the interfacial wettability and cleanliness of the material; then, modified zeolite was uniformly dispersed on two opposite surfaces of the polypropylene nonwoven fabric, with a single addition mass of 0.5 g / cm³ on each surface. 2 Then, under light-protected conditions, spray 1 mol / L pyrrole aqueous solution and 1 mol / L ferric chloride aqueous solution onto the two surfaces in sequence. Then repeat the above steps of dispersing modified zeolite on the tidal flat, spraying pyrrole aqueous solution and ferric chloride aqueous solution three times, maintaining the ambient temperature at 20°C, and in situ polymerize to form cross-linked coatings on the two surfaces of the polypropylene nonwoven fabric.

[0063] (2) The polypropylene nonwoven fabric with a cross-linked coating on its surface was sequentially immersed in a spore suspension and a sodium alginate-graphene oxide mixed solution. The immersion time in the spore suspension or sodium alginate-graphene oxide mixed solution was 5 min each time. After immersion, the polypropylene nonwoven fabric was removed and two surfaces were sprayed with a 2.0% calcium chloride solution. The spraying amount for each surface was 1 mL / cm. 2 Afterwards, the material is rinsed with deionized water to remove residual monomers, intermediate products, and iron salt byproducts. Finally, the resulting polypropylene nonwoven fabric is dried at 50°C for 6 hours to obtain the photothermal evaporation material.

[0064] The surface of the resulting photothermal evaporation material is black.

[0065] Example 2:

[0066] In this embodiment, the polypropylene nonwoven fabric has a thickness of 0.7 mm, a pore size of 20 mesh, a corresponding equivalent pore size of approximately 250 μm, and a porosity of 80%; the sodium hydroxide solution has a concentration of 0.1 M; the nitric acid solution has a concentration of 0.1 M; the ferric chloride aqueous solution has a concentration of 1.5 mol / L; and the calcium chloride solution is a 1% (w / w) calcium chloride aqueous solution prepared from analytical grade calcium chloride.

[0067] The modified zeolite was prepared by the following method: 12-mesh natural zeolite was reacted with 1.0M sodium hydroxide solution at 300 r / min with magnetic stirring for 8 h. After the reaction, the mixed slurry was allowed to settle or separated by filtration or centrifugation. The solid phase was collected and then repeatedly washed with deionized water. Each time, sufficient deionized water was added and the mixture was shaken or stirred before filtration until the pH of the washing liquid was close to neutral and there was no obvious alkaline taste, in order to remove residual NaOH and dissolved impurity ions. The washed zeolite was placed in an 80℃ oven and dried for 8 h to constant weight. After drying, it was cooled to room temperature and stored in a sealed bag or desiccator to obtain the modified zeolite.

[0068] The concentration of the pyrrole aqueous solution is 1 mol / L. It is prepared freshly by mixing pyrrole with a purity of >99% and deionized water under light-protected conditions. The solution is prepared at 23°C, and the resistivity of the deionized water is >18.2 MΩ•cm. The pyrrole aqueous solution is prepared by ultrasonic stirring at a frequency of 40 kHz for 5 minutes to ensure uniform dissolution. Finally, the pH of the pyrrole aqueous solution is adjusted to 7.0 with 0.1 M sodium hydroxide solution and 0.1 M nitric acid solution. In addition, the prepared solution must be used within 12 minutes.

[0069] The spore suspension was prepared as follows: *Bacillus pasteurellii* was stored in cryovials. The solutes in composite solution one were beef extract, peptone, manganese sulfate titanium dioxide, and nickel chloride hexahydrate. The solvent was deionized water. The concentrations of beef extract, peptone, manganese sulfate titanium dioxide, and nickel chloride hexahydrate in composite solution one were 4 g / L, 6 g / L, 15 mg / L, and 25 mg / L. *Bacillus pasteurellii* was added to composite solution one to obtain composite solution A. The mass fraction of *Bacillus pasteurellii* in composite solution one was 0.2%. Composite solution A was cultured in a constant temperature incubator at 30℃ and 300 r / min for 20 days. h; The solutes in composite solution two are yeast extract, ammonium chloride, manganese sulfate titanium dioxide, and nickel chloride hexahydrate, and the solvent is deionized water. The concentrations of yeast extract, ammonium chloride, manganese sulfate titanium dioxide, and nickel chloride hexahydrate in composite solution two are 7 g / L, 10 g / L, 10 mg / L, and 25 mg / L. Composite solution A, after 20 h of culture, is inoculated into composite solution two at a volume ratio of 1% (i.e., the volume fraction of composite solution A after 24 h of culture is 1%). After culturing for 64 h, a suspension is obtained. Finally, the suspension is sterilized in an 80℃ water bath for 15 min, and then centrifuged at 6000 r / min for 10 min. The precipitate is then diluted with physiological saline (1.0% sodium chloride solution) to a spore concentration of 2.0 × 10⁻⁶. 10 CFU / mL was used to obtain a spore suspension.

[0070] The sodium alginate-graphene oxide mixed solution was prepared as follows: Sodium alginate was dissolved in deionized water and magnetically stirred at 600 rpm for 40 min until fully dissolved. Then, graphene oxide powder was added, and the mixture was magnetically stirred at 2800 rpm for 50 min to obtain the mixed solution. The sodium alginate accounted for 1% of the mass fraction of the mixed solution, and the graphene oxide accounted for 5% of the mass fraction.

[0071] A method for preparing a photothermal evaporation material for saline loess site remediation specifically includes the following steps:

[0072] (1) The polypropylene nonwoven fabric was cleaned successively with 0.1M nitric acid solution and 0.1M sodium hydroxide solution to improve the interfacial wettability and cleanliness of the material; then, modified zeolite was uniformly dispersed on two opposite surfaces of the polypropylene nonwoven fabric, with a single addition mass of 0.8 g / cm³ on each surface. 2 Then, under light-protected conditions, 1 mol / L pyrrole aqueous solution and 1.5 mol / L ferric chloride aqueous solution were sprayed sequentially onto the two surfaces. The above steps of dispersing modified zeolite on the tidal flat, spraying pyrrole aqueous solution and ferric chloride aqueous solution were repeated three times. The ambient temperature was maintained at 23°C. Cross-linked coatings were formed on the two surfaces of the polypropylene nonwoven fabric by in-situ polymerization.

[0073] (2) The polypropylene nonwoven fabric with a cross-linked coating on its surface was sequentially immersed in a spore suspension and a sodium alginate-graphene oxide mixed solution. The immersion time in the spore suspension or sodium alginate-graphene oxide mixed solution was 4 min each time. After immersion, the polypropylene nonwoven fabric was removed and two surfaces were sprayed with a 1.0% calcium chloride solution. The spraying amount for each surface was 0.5 mL / cm. 2 Afterwards, the material is rinsed with deionized water to remove residual monomers, intermediate products and iron salt byproducts. Finally, the obtained polypropylene nonwoven fabric is dried at 40°C for 10 hours to obtain the photothermal evaporation material.

[0074] The surface of the resulting photothermal evaporation material is black.

[0075] Example 3:

[0076] In this embodiment, the polypropylene nonwoven fabric has a thickness of 1.5 mm, a pore size of 20 mesh, a corresponding equivalent pore size of approximately 250 μm, and a porosity of 80%; the sodium hydroxide solution has a concentration of 0.1 M; the nitric acid solution has a concentration of 0.1 M; the ferric chloride aqueous solution has a concentration of 2 mol / L; and the calcium chloride solution is a 3% (w / w) calcium chloride aqueous solution prepared from analytical grade calcium chloride.

[0077] The modified zeolite was prepared by the following method: 15-mesh natural zeolite was reacted with 1.0M sodium hydroxide solution at 300 r / min with magnetic stirring for 10 h. After the reaction, the mixed slurry was allowed to settle or separated by filtration or centrifugation. The solid phase was collected and then repeatedly washed with deionized water. Each time, sufficient deionized water was added and the mixture was shaken or stirred before filtration until the pH of the washing liquid was close to neutral and there was no obvious alkaline taste, in order to remove residual NaOH and dissolved impurity ions. The washed zeolite was placed in a 100℃ oven and dried for 6 h to constant weight. After drying, it was cooled to room temperature and stored in a sealed bag or desiccator to obtain the modified zeolite.

[0078] The concentration of the pyrrole aqueous solution is 1 mol / L. It is prepared freshly by mixing pyrrole with a purity of >99% and deionized water under light-protected conditions. The solution is prepared at 25°C, and the resistivity of the deionized water is >18.2 MΩ•cm. The pyrrole aqueous solution is prepared by ultrasonic stirring at a frequency of 30 kHz for 5 minutes to ensure uniform dissolution. Finally, the pH of the pyrrole aqueous solution is adjusted to 7.5 with 0.1 M sodium hydroxide solution and 0.1 M nitric acid solution. In addition, the prepared solution must be used within 15 minutes.

[0079] The spore suspension was prepared as follows: *Bacillus pasteurellii* was stored in cryovials. The solutes in composite solution one were beef extract, peptone, manganese sulfate titanium dioxide, and nickel chloride hexahydrate. The solvent was deionized water. The concentrations of beef extract, peptone, manganese sulfate titanium dioxide, and nickel chloride hexahydrate in composite solution one were 10 g / L, 8 g / L, 12 mg / L, and 22 mg / L. *Bacillus pasteurellii* was added to composite solution one to obtain composite solution A. The mass fraction of *Bacillus pasteurellii* in composite solution one was 0.05%. Composite solution A was cultured in a constant temperature incubator at 35℃ and 200 r / min for 3 days. 0h; The solutes in composite solution two are yeast extract, ammonium chloride, manganese sulfate titanium dioxide, and nickel chloride hexahydrate, and the solvent is deionized water. The concentrations of yeast extract, ammonium chloride, manganese sulfate titanium dioxide, and nickel chloride hexahydrate in composite solution two are 7 g / L, ammonium chloride, manganese sulfate, and titanium dioxide, and nickel chloride hexahydrate, respectively. Composite solution A, after 30 h of culture, is inoculated into composite solution two at a volume ratio of 2% (i.e., the volume fraction of composite solution A after 24 h of culture is 2%). After culturing for 96 h, a suspension is obtained. Finally, the suspension is sterilized in an 80℃ water bath for 30 min, and then centrifuged at 8000 r / min for 10 min. The precipitate is then diluted with physiological saline (0.8% sodium chloride solution) to a spore concentration of 3.0 × 10⁻⁶. 10 CFU / mL was used to obtain a spore suspension.

[0080] The sodium alginate-graphene oxide mixed solution was prepared as follows: Sodium alginate was dissolved in deionized water and magnetically stirred at 800 rpm for 50 min until fully dissolved. Then, graphene oxide powder was added, and the mixture was magnetically stirred at 1800 rpm for 60 min to obtain the mixed solution. The sodium alginate accounted for 5% of the mass fraction of the mixed solution, and the graphene oxide accounted for 10% of the mass fraction.

[0081] A method for preparing a photothermal evaporation material for saline loess site remediation specifically includes the following steps:

[0082] (1) The polypropylene nonwoven fabric was cleaned successively with 0.1M nitric acid solution and 0.1M sodium hydroxide solution to improve the interfacial wettability and cleanliness of the material; then, modified zeolite was uniformly dispersed on two opposite surfaces of the polypropylene nonwoven fabric, with a single addition mass of 1.0 g / cm³ on each surface. 2 Then, under light-protected conditions, 1 mol / L pyrrole aqueous solution and 2 mol / L ferric chloride aqueous solution were sprayed sequentially onto the two surfaces. The above steps of dispersing modified zeolite on the tidal flat, spraying pyrrole aqueous solution and ferric chloride aqueous solution were repeated three times. The ambient temperature was maintained at 25°C. Crosslinked coatings were formed on the two surfaces of the polypropylene nonwoven fabric by in-situ polymerization.

[0083] (2) The polypropylene nonwoven fabric with a cross-linked coating on its surface was sequentially immersed in a spore suspension and a sodium alginate-graphene oxide mixed solution. The immersion time in the spore suspension or sodium alginate-graphene oxide mixed solution was 10 min each time. After immersion, the polypropylene nonwoven fabric was removed and two surfaces were sprayed with a 3% calcium chloride solution. The spraying amount for each surface was 2 mL / cm. 2 Afterwards, the material is rinsed with deionized water to remove residual monomers, intermediate products, and iron salt byproducts. Finally, the resulting polypropylene nonwoven fabric is dried at 65°C for 6 hours to obtain the photothermal evaporation material.

[0084] The surface of the resulting photothermal evaporation material is black.

[0085] Application Example 1:

[0086] (1) Take loess samples that have been air-dried and sieved, with a mesh diameter of 2 mm and an initial moisture content of 16%;

[0087] (2) Mix simulated seawater or a NaCl solution with a mass concentration of 13% with the above loess sample to obtain a mixed sample, wherein the mass ratio of simulated seawater or NaCl solution to loess sample is 1:20;

[0088] (3) The above mixed sample was sealed and cured for 3 days to obtain saline loess sample. During the period, it was stirred once every 6 hours to ensure that the salt was evenly distributed.

[0089] (4) The above-mentioned saline loess sample was filled into a columnar soil chamber with a diameter of 10 cm and a height of 10 cm, compacted to the predetermined dry density, and allowed to stand for more than 24 hours to obtain a simulated saline loess sample. In this application example, the predetermined dry density is 1.40 g / cm³. 3 In the simulated saline loess sample, the mass of particles with a diameter <0.075mm / the total mass of the simulated saline loess sample is ≥60%.

[0090] (5) A gel cotton rope is buried and connected to the bottom of the columnar soil chamber as a capillary water transport medium. The length of the gel cotton rope is 10cm.

[0091] (6) The photothermal evaporation material prepared in Example 1 is suspended 2 cm above the surface of the columnar soil chamber to avoid direct contact with the ground surface;

[0092] (7) It operates continuously under natural sunlight, with a wind speed of 0 m / s, an illuminance of 1 sun (i.e., 1.0 kW / m^2), a daily irradiation time of 8 hours, and continuous operation for 10 days.

[0093] (8) When the surface of the photothermal evaporation material is covered by more than 80% crystallized salt, replace the material and collect the salt to complete the soil remediation.

[0094] The gelled cotton rope is prepared as follows: Cotton rope is cut to a fixed length, washed with deionized water, and soaked in a 1wt% NaOH solution for 60 minutes to remove impurities and activate the fibers. It is then washed until neutral and set aside. PVA is dissolved in deionized water at 90°C to prepare a homogeneous precursor solution, with PVA accounting for 9% of the precursor solution's mass fraction. This precursor solution is poured into a paper cup, and the neutralized cotton rope is completely immersed in it and magnetically stirred at 300 r / min for 45 minutes (vacuuming for 5-10 minutes can be used to enhance penetration). The immersed cotton rope is then removed and placed in a paper cup to maintain moisture. It is first frozen at -20°C for 10 hours and then thawed at room temperature for 2 hours. This freeze-thaw cycle is repeated three times to achieve in-situ gelation. Finally, the surface residue is gently washed away with deionized water and the rope is sealed and kept moist to obtain the gelled cotton rope.

[0095] Application Example 2:

[0096] The method in Application Example 1 is used, except that the wind speed in step (7) is 2 m / s, and the rest is the same as in Application Example 1.

[0097] Application Example 3:

[0098] The method in Application Example 1 is used, except that the wind speed in step (7) is 4 m / s, and the rest is the same as in Application Example 1.

[0099] Application Example 4:

[0100] The method in Application Example 1 is used, except that the gel cotton rope in step (5) is replaced with ordinary cotton rope, otherwise it is the same as Application Example 1.

[0101] Application Example 5:

[0102] The method in Application Example 4 is used, except that the wind speed in step (7) is 3 m / s, and the rest is the same as in Application Example 1.

[0103] Figure 1The results show the light absorption rate test results of the nonwoven fabric used in the examples and the photothermal evaporation material for saline loess site remediation prepared in Example 1. The light absorption rate of the nonwoven fabric averages 66.1% in the 200-2500nm wavelength range, while the light absorption rate of the photothermal evaporation material averages 96.8% in the 200-2500nm wavelength range, exhibiting almost complete absorption in the visible light region. This is due to the formation of stable strong covalent bonds and electrostatic interactions between the nonwoven fabric and pyrrole, zeolite, sodium alginate, and graphene oxide in the photothermal evaporation material, resulting in stable adhesion. Compared with the raw materials, the photothermal evaporation material exhibits a significantly improved absorption rate (approximately 30.7%) compared to the nonwoven fabric. The reason lies in the combined effect of the nonwoven fabric skeleton, the conductive polymer layer formed by pyrrole polymerization, the conjugated structure of graphene oxide, and the rough microporous structure of zeolite. This creates a multi-scale micro / nano structure on the material surface, resulting in multiple scattering / trapping effects of light, thereby enhancing broad-spectrum absorption. Simultaneously, the ionic crosslinking / film-forming effect of sodium alginate in the system stably immobilizes functional components such as pyrrole, zeolite, and graphene oxide on the surface of the nonwoven fabric fibers, forming a stable and continuous photothermal conversion interface. Furthermore, hydrogen bonds / coordination interactions can form between the oxygen-containing functional groups on the surface of the nonwoven fabric fibers and graphene oxide and sodium alginate, while π-π interactions and electrostatic adsorption exist between the pyrrole polymer and graphene oxide, thus constructing a multi-interaction network that significantly improves the coating's bonding strength and durability. These results demonstrate that the prepared photothermal evaporation material possesses excellent photothermal conversion performance, providing a strong driving force for subsequent evaporation and desalination processes.

[0104] Figure 2 The tensile strength test results are for the nonwoven fabric used in the examples and the photothermal evaporation material for saline loess site remediation prepared in Example 1. The test was conducted using a universal tensile testing machine with a loading rate of 10 mm / min. The results showed that the tensile strength of the nonwoven fabric in the dry and wet states was 1.41 MPa and 1.45 MPa, respectively. The tensile strength of the photothermal evaporation material in the dry state was 1.85 MPa, and the tensile strength in the wet state was 1.74 MPa. The dry state of the photothermal evaporation material refers to the photothermal evaporation material finally prepared in Example 1, and the wet state refers to the process in Step (2) of Example 1 where the material was rinsed with deionized water without drying. Compared with nonwoven fabrics, photothermal evaporation materials exhibit approximately 31.2% higher tensile strength in the dry state and maintain relatively high strength in the wet state with a smaller decrease (approximately 5.9%). This indicates that photothermal evaporation materials not only do not weaken the toughness of the nonwoven fabric substrate but also play a "reinforcing-co-supporting" role on the fiber skeleton through film / bonding networks. At the same time, photothermal evaporation materials have a high wet strength retention rate, indicating that the material is not prone to coating peeling or structural instability during long-term water absorption and evaporation cycles, and can meet the requirements of outdoor long-term laying, repeated deployment and retrieval, and wind load disturbance.

[0105] Figure 3The evaporation rate test results are shown for the nonwoven fabric used in the examples and the photothermal evaporation material for saline loess site remediation prepared in Example 1. The evaporation capacity per unit area was tested under natural light intensity (1 sun), and the results show that the evaporation rate of the nonwoven fabric is 2.40 kg / m². 2 •h, the evaporation rate of the photothermal evaporation material is 4.43 kg / m 2 •h, an increase of approximately 84.6%, indicates that the material possesses highly efficient interfacial evaporation performance. This improvement stems from two main factors. Figure 1 The enhanced photothermal conversion resulting from the broad-spectrum high absorption is also due to the efficient water supply network jointly constructed by the zeolite microporous structure and the nonwoven capillary channels, which enables water to be transported quickly and continuously to the evaporation interface. At the same time, the local heating of the interface can reduce the liquid film thickness and accelerate the escape of water molecules, thus exhibiting significantly enhanced interfacial evaporation performance.

[0106] Figure 4 The results of the salt exchange mass test of the photothermal evaporation material for saline loess site remediation prepared in Example 1 are shown. Following the methods of Application Examples 1-3, the mass of crystallized salt on the material surface and the change in soil salinity were measured. The results showed that an average of 4 kg of salt could be migrated and fixed per square meter, and the surface salt content of the soil decreased by more than 80% within 10 days, verifying its significant desalination capacity. This material can form a stable migration path of "water-salt upward migration—interfacial crystallization—centralized collection" driven by evaporation, allowing salt to continuously migrate upward from the soil and accumulate and crystallize on the material surface, thereby achieving the transfer and fixation of salt from the soil system to the material end, demonstrating significant desalination efficiency and engineering application potential.

[0107] Figure 5 The results show the surface temperature test results of the photothermal evaporation material for saline loess site remediation prepared in Example 1. Following the methods of Application Examples 1-3, the surface temperature response of the material under 1 Sun conditions was monitored using an infrared thermal imager. It was found that the surface temperature of the evaporator (i.e., the photothermal evaporation material) rapidly rose to 44.4°C within 2 minutes and remained stable, demonstrating its good photothermal response rate and thermal field stability. Rapid heating enables the rapid establishment of evaporation driving force during the start-up phase, while temperature stability helps maintain a continuous and uniform evaporation flux, thereby ensuring the continuity and controllability of the desalination process.

[0108] Figure 6The results of soil pH and electrical conductivity (EC) tests in saline loess remediation using the photothermal evaporation material prepared in Example 1 are shown. After 10 days of operation, the soil pH increased from the initial 6.70 to 7.63, and the electrical conductivity decreased from 2930 μS / cm to 384 μS / cm. This indicates that the technology not only effectively reduces salt concentration but also regulates soil pH and improves the soil physicochemical environment. The significant decrease in EC demonstrates that the material can effectively reduce ionic strength and salt stress in the soil solution; pH regulation helps improve the soil physicochemical environment and plant adaptability, providing support for the ecological restoration and subsequent utilization of saline loess sites.

[0109] In summary, the photothermal evaporation material of this invention has significant desalination capacity, high evaporation efficiency, superior mechanical properties, is environmentally friendly, and non-toxic to plant growth. Specifically:

[0110] (1) Significant desalination capacity: The average soil salinity decreased by 80% within 10 days, and the desalination rate in the 3-4cm deep layer reached as high as 92.5%;

[0111] (2) High evaporation efficiency: The evaporation rate under unit light is 2.50 kg / m³ 2 •h, which can reach 4.43 kg / m at a wind speed of 4 m / s. 2 •h;

[0112] (3) Excellent mechanical properties: dry tensile strength reaches 1.85 MPa, and wet elongation reaches 59.8%;

[0113] (4) Environmentally friendly: The carbon emissions of the material are 34.7% lower than those of similar materials;

[0114] (5) Non-toxic to plant growth: After soil remediation, lettuce roots can grow up to 8.6 cm and the above-ground part can reach 40 mm in height.

[0115] The above description is merely an embodiment of the present invention and is not intended to limit the present invention in any way. The present invention can also have other embodiments based on the above structure and function, which will not be listed hereafter. Therefore, any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a photothermal evaporation material for the remediation of saline loess sites, characterized in that, Specifically, the following steps are included: (1) The polypropylene nonwoven fabric was cleaned with dilute acid solution and dilute alkali solution in turn. Then, the modified zeolite was uniformly dispersed on the two surfaces of the polypropylene nonwoven fabric. Then, under the dark, pyrrole aqueous solution and ferric chloride aqueous solution were sprayed on the two surfaces in turn. Then, the above steps of dispersing the modified zeolite, spraying pyrrole aqueous solution and ferric chloride aqueous solution were repeated many times. The ambient temperature was maintained at 20-25℃. The two surfaces of the polypropylene nonwoven fabric were polymerized in situ to form a cross-linked coating. The mass of modified zeolite added per surface area of ​​polypropylene nonwoven fabric in a single application is 0.5-1.0 g / cm³. 2 ; The polypropylene nonwoven fabric has a thickness of 0.7mm-1.5mm, a pore size of 20-40 mesh, and a porosity of 70-85%; the concentration of the pyrrole aqueous solution is 1mol / L, and the concentration of the ferric chloride aqueous solution is 1-2mol / L. (2) The polypropylene nonwoven fabric with a cross-linked coating on its surface was successively immersed in a spore suspension and a sodium alginate-graphene oxide mixed solution. After immersion, the polypropylene nonwoven fabric was removed and two surfaces were sprayed with calcium chloride solution. The mass fraction of the calcium chloride solution was 1.0-3.0%, and the spraying amount of calcium chloride solution on each surface was 0.5-2.0 mL / cm. 2 After rinsing with deionized water, and finally drying, a photothermal evaporation material for saline loess site remediation is obtained. In step (2), the spore suspension was prepared as follows: *Pasteurella multocida* was stored in cryovials. *Pasteurella multocida* was added to compound solution one to obtain compound solution A. The mass fraction of *Pasteurella multocida* in compound solution one was 0.05-0.2%. Compound solution A was cultured in a constant temperature incubator at 25-35℃ and 180-300 r / min for 20-30 h. The cultured compound solution A was then inoculated into compound solution two at a volume ratio of 1-2%, and cultured for 64-96 h to obtain a suspension. Finally, the suspension was sterilized in a water bath at 80℃ for 15-30 min. The suspension was then centrifuged at 6000-8000 r / min for 10 min. The precipitate was diluted with physiological saline to a spore concentration of 2.0 × 10⁻⁶. 10 -3.0×10 10 CFU / mL was used to obtain spore suspensions; the solutes in compound solution one were beef extract, peptone, manganese titanium dioxide, and nickel chloride hexahydrate, and the solvent was deionized water. The concentrations of beef extract, peptone, manganese titanium dioxide, and nickel chloride hexahydrate in compound solution one were 4-10 g / L, 5-8 g / L, 10-15 mg / L, and 20-25 mg / L, respectively. The solutes in compound solution two were yeast extract, ammonium chloride, manganese titanium dioxide, and nickel chloride hexahydrate, and the solvent was deionized water. The concentrations of yeast extract, ammonium chloride, manganese titanium dioxide, and nickel chloride hexahydrate in compound solution two were 5-10 g / L, 10-20 g / L, 10-15 mg / L, and 20-30 mg / L, respectively. The sodium alginate-graphene oxide mixed solution described in step (2) is prepared by the following method: Sodium alginate is dissolved in deionized water and magnetically stirred at 500-800 r / min for 30-50 min until fully dissolved. Then, graphene oxide powder is added and magnetically stirred at 1500-2800 r / min for 40-60 min to obtain the sodium alginate-graphene oxide mixed solution. In the sodium alginate-graphene oxide mixed solution, sodium alginate accounts for 1-5% of the mass fraction of the mixed solution, and graphene oxide accounts for 5-10% of the mass fraction of the mixed solution.

2. The preparation method of the photothermal evaporation material for saline loess site remediation as described in claim 1, characterized in that, In step (1), the dilute acid solution and the dilute alkaline solution are 0.1M nitric acid solution and 0.1M sodium hydroxide solution, respectively.

3. The preparation method of the photothermal evaporation material for saline loess site remediation as described in claim 1, characterized in that, The modified zeolite in step (1) is prepared by the following method: 10-15 mesh natural zeolite is placed in a 1.0M sodium hydroxide solution and magnetically stirred at 200-300 r / min for 6-10 h. After the reaction is completed, the mixed slurry is separated into solid and liquid phases, the solid phase is collected, and then the solid phase is repeatedly washed with deionized water until the pH of the washing solution is close to neutral and there is no obvious alkaline taste. The washed zeolite is placed in an oven at 60-105℃ and dried for 6-12 h to constant weight. After drying, it is cooled to room temperature to obtain the modified zeolite. The pyrrole aqueous solution described in step (1) is prepared freshly by mixing pyrrole with a purity of >99% and deionized water under light-protected conditions. The solution is prepared at 20-25°C, and the resistivity of the deionized water is >18.2 MΩ•cm. The solution is ultrasonically stirred during preparation to ensure uniform dissolution. The pH of the ultrasonically prepared mixed solution is adjusted to 6.5-7.5 using 0.1M sodium hydroxide solution and nitric acid solution. In addition, the prepared solution must be used within 10-15 minutes.

4. The preparation method of the photothermal evaporation material for saline loess site remediation as described in claim 1, characterized in that, In step (1), the steps of dispersing modified zeolite in the tidal flat, spraying pyrrole aqueous solution and ferric chloride aqueous solution are repeated 3-5 times; in step (2), the soaking time in the spore suspension or sodium alginate-graphene oxide mixed solution is 4-10 min each time; in step (2), drying refers to drying at 40-65℃ for 6-10 hours.

5. A photothermal evaporation material for saline loess site remediation obtained by any one of the preparation methods described in claims 1-4, characterized in that, The photothermal evaporation material has a black surface, an absorbance of 96.0% in the 200-2500nm spectral range, and a dry tensile strength of not less than 1.8MPa.

6. The application of the photothermal evaporation material for saline loess site remediation as described in claim 5 in the remediation of saline loess sites, characterized in that, When applying the material, first bury cotton ropes in the saline loess, then suspend the photothermal evaporation material above the surface of the saline loess, and then carry out site repair under solar radiation; under solar radiation, evaporate for 8 hours a day for 10 days; after the salt crystal coverage on the surface of the photothermal evaporation material reaches 80%, replace the material and collect the salt. The cotton rope is a gel cotton rope or a regular cotton rope, and the saline loess is cylindrical saline loess. The number of cotton ropes shall not be less than the ratio of the diameter to the height of the cylindrical saline loess, and the length of the cotton ropes shall not be less than 10 times the ratio of the height to the diameter of the cylindrical saline loess (in cm). The position of the photothermal evaporation material suspended above the ground surface shall be greater than the ratio of the height to the diameter of the cylindrical saline loess (in cm).

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