A directional light-heat aerogel material for saline-alkali land optimization and a preparation method thereof

Abstract

This invention discloses a directional photothermal aerogel material for optimizing saline-alkali land and its preparation method. The material uses cellulose nanofibers (CNF) and water-soluble polyvinyl alcohol (PVA) as the matrix, polypyrrole (PPy) as the photothermal functional component, and is supplemented with bioactive additives, prepared through in-situ polymerization and directional freeze-drying. This aerogel possesses high porosity, strong hydrophilicity, and excellent photothermal conversion performance, combining water retention, salt conduction, and photothermal evaporation functions. A surface micro-engineering system constructed using this material can achieve directional migration and surface precipitation of soil salts under solar energy drive, improving the water retention and desalination effects of saline-alkali land. The material is biodegradable, and its formulation parameters can be adjusted according to different saline-alkali land types and soil textures to achieve customized applications. This invention can be used for the green and efficient improvement and ecological restoration of saline-alkali land.

Description

Technical Field

[0001] This invention belongs to the field of saline-alkali land improvement materials and ecological restoration technology, specifically involving a hydrophilic functional modified cellulose aerogel with directional pore structure and its preparation method, and the application of this material in water retention, salt conduction and desalination improvement of saline-alkali land. Background Technology

[0003] Existing methods for saline-alkali land management mainly include water leaching, chemical remediation, biological remediation, and remediation assisted by superabsorbent polymers. Traditional water leaching methods consume large amounts of water, which is in stark contrast to the water scarcity in saline-alkali areas. Chemical remediation methods are prone to soil compaction and damage to soil aggregate structure, and pose a risk of secondary pollution. Biological remediation methods have a long treatment cycle and limited effectiveness in rapidly reducing salinity in the root zone. Although synthetic superabsorbent polymers have a certain water retention effect, they suffer from slow degradation, potential microplastic residues, and insufficient ecological safety.

[0004] In addition, existing technologies mostly focus on single-function improvements, lacking a synergistic governance solution that integrates water retention, salt conduction, salt removal and ecological restoration. Furthermore, they are not adaptable enough to different types of saline-alkali land and soil conditions, making it difficult to meet the needs of refined governance.

[0005] In recent years, cellulose-based aerogel materials have shown promising applications in interfacial evaporative desalination and other fields due to their high porosity, strong hydrophilicity, biodegradability, and good photothermal conversion potential. However, existing cellulose-based aerogel materials are mainly designed for water treatment scenarios and have not yet been systematically functionalized and structurally controlled for saline-alkali land remediation environments. They still have shortcomings in directional pore construction, directional salt migration control, and synergistic adaptation with soil systems. Furthermore, surface micro-engineering systems based on these materials have not yet formed a complete technical system, making it difficult to achieve the synergistic advancement of salt migration, surface precipitation, and ecological restoration.

[0006] Therefore, it is necessary to develop a modified aerogel material that combines water retention, salt conduction, and photothermal evaporation functions, and to construct a matching surface micro-engineering system to achieve synergistic management of water retention, salt removal, and ecological restoration in saline-alkali land. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a directional photothermal aerogel material for optimizing saline-alkali land and its preparation method, as well as a related water-retaining and desalination surface micro-engineering system and supporting application methods.

[0008] Includes the following steps: (1) Preparation of CNF suspension Weigh 1.5 g of cellulose nanofibers (CNF), add them to 100 mL of deionized water, stir to swell, and then mechanically stir at room temperature for 12 h to obtain a 1.5% CNF suspension.

[0009] (2) Preparation of PVA solution Weigh 5 g of polyvinyl alcohol (PVA), add it to 100 mL of deionized water, and stir at 90℃ and 500 r / min for 2 h until completely dissolved to obtain a 5% PVA solution.

[0010] (3) Preparation of PVA / CNF composite aerogel 60 mL of 1.5% CNF suspension, 18 mL of 5% PVA solution, and 12 mL of deionized water were mixed and mechanically stirred for 1 h. Then, 450 μL of 50% glutaraldehyde was added as a crosslinking agent, and the pH was adjusted to 4–6 with 1% dilute sulfuric acid. Stirring was continued for 1 h, followed by ultrasonic degassing for 1 h. The resulting gel was transferred to an aluminum tray and freeze-dried under vacuum for 36 h to obtain a PVA / CNF composite aerogel. The mass ratio of PVA to CNF was 1:1.

[0011] (4) In-situ coating of PPy 5.48 g of ammonium persulfate was dissolved in 10 mL of deionized water to obtain solution A, which was then refrigerated for later use. 1.68 mL of pyrrole and 3.68 mL of phytic acid (45%) were added to 10 mL of isopropanol to obtain solution B, which was then cooled to 0°C for later use. After both solutions A and B had cooled to 0°C, they were alternately and uniformly coated onto the surface of the PVA / CNF composite aerogel until the sample surface turned completely black. The sample was then freeze-dried under vacuum for 12 h to obtain the PPy / PVA / CNF composite aerogel.

[0012] (5) Verification of the application effect of directional hydrophilic aerogel in the leaching and desalination of saline-alkali soil Saline-alkali soil was used as the test soil and filled in 15 cm × 10 cm × 5 cm containers with a total volume of 750 mL. Using the amount of directional hydrophilic aerogel added as a variable, control group, experimental group 1, and experimental group 2 were set up. The control group did not add aerogel, experimental group 1 added 4 aerogel particles, and experimental group 2 added 6 aerogel particles. The area ratio and volume ratio of each group are shown in the table.

[0013] Each group was rinsed with 300 mL of deionized water in three separate applications, 100 mL each, with a 15-minute interval between applications. After rinsing, the eluent was collected, and the chloride ion concentration was semi-quantitatively determined using a chloride test strip. Each group was measured in triplicate, and the average value was taken.

[0014] The results showed that the chloride ion concentrations in the leachate of the control group, experimental group 1, and experimental group 2 were 200 mg / L, 200 mg / L, and 150 mg / L, respectively. These results indicate that the chloride ion concentration in the leachate decreased with increasing aerogel addition, suggesting that the directional hydrophilic aerogel can promote salt accumulation and migration, and has a positive effect on the leaching and desalination of saline-alkali soils. It can be used for water retention and salinity reduction improvement of saline-alkali soils.

[0015] Preferably, in step (1), the mass concentration of the cellulose nanofiber dispersion is 1-5%, and the mass concentration of the polyvinyl alcohol solution is 5-15%.

[0016] Preferably, in step (2), the polymerization reaction temperature is 15-35℃.

[0017] Preferably, in step (3), the freezing direction of the directional freezing is perpendicular to the sol surface. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with the implementation of the invention to explain it, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the preparation process of the PPy / PVA / CNF aerogel of the present invention.

[0019] Figure 2 Infrared spectrum of PPy / PVA / CNF aerogel.

[0020] Figure 3 In the image, (a) and (b) are cross-sectional SEM images of PVA / CNF aerogel samples, and (c) is a surface SEM image of PPy / PVA / CNF aerogel samples.

[0021] Figure 4 The swelling ratio of PPy / PVA / CNF aerogel.

[0022] Figure 5 The image shows the UV-Vis-NIR absorption spectrum of PPy / PVA / CNF aerogel.

[0023] Figure 6 The water contact angle of the PPy / PVA / CNF aerogel surface.

[0024] Figure 7 The thermal conductivity of PPy / PVA / CNF aerogel.

[0025] Figure 8 The operating temperature of the PPy / PVA / CNF composite aerogel evaporator.

[0026] Figure 9The evaporator mass-time curve for the PPy / PVA / CNF aerogel evaporator.

[0027] Figure 10 Comparison of chloride ion concentrations under different aerogel distributions. Detailed Implementation

[0028] The following embodiments are provided to better understand the present invention, but are not intended to limit the invention. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0029] The method for synthesizing the directional hydrophilic aerogel saline-alkali land improvement material of the present invention includes the following steps: (1) Preparation of matrix sol The cellulose nanofiber dispersion was mixed with a polyvinyl alcohol solution and stirred until homogeneous to obtain a matrix sol.

[0030] (2) Introduction of photothermal components Pyrrole monomers and initiators were added to the above matrix sol to carry out a polymerization reaction, and polypyrrole was generated in situ on the surface of the matrix skeleton to obtain a photothermal composite sol.

[0031] Among them, the introduction of polypyrrole as a photothermal absorber is a key step in realizing the functionalization of materials, giving them the ability to respond to sunlight and actively generate heat.

[0032] (3) Targeted freeze drying and post-treatment The photothermal composite sol was subjected to directional freezing treatment using a unidirectional temperature gradient control, with the freezing temperature ranging from -20°C to -50°C. Subsequently, it was subjected to vacuum freeze-drying to obtain an aerogel dry body with a vertically oriented pore structure. After further processing, the directional hydrophilic aerogel saline-alkali land improvement material was obtained.

[0033] The directional freeze-drying technique is used to construct a three-dimensional network skeleton with vertical orientation and interconnected micropores.

[0034] Example 1 (1) Preparation of cellulose nanofiber (CNF) suspension Weigh 1.5 g of cellulose nanofibers (CNF), add them to 100 mL of deionized water, stir with a glass rod to swell, and mechanically stir at room temperature for 12 hours to obtain a uniformly dispersed 1.5% CNF suspension.

[0035] (2) Preparation of polyvinyl alcohol (PVA) solution Weigh 5 g of polyvinyl alcohol (PVA), add it to 100 mL of deionized water, heat in a 90°C water bath, and stir at 500 r / min for 2 hours to fully dissolve it, to obtain a 5% PVA aqueous solution.

[0036] (3) Preparation of PVA / CNF composite aerogel First, 60 mL of 1.5% CNF suspension, 18 mL of 5% PVA aqueous solution, and 12 mL of deionized water were added to a beaker in the specified ratio and mixed thoroughly by mechanical stirring for 1 hour. For PVA / CNF aerogel, the mass ratio of PVA to CNF was 1:1. Next, 450 μl of a 50% glutaraldehyde crosslinking agent solution was added uniformly to the mixture. 1% dilute sulfuric acid was added to the mixture to adjust the pH to between 4 and 6. Finally, the weakly acidic mixture was mechanically stirred for another 1 hour to ensure thorough mixing, and then sonicated for 1 hour to remove air bubbles. The resulting aqueous gel was transferred to an aluminum tray and freeze-dried under vacuum for 36 h to obtain the PVA / CNF composite aerogel sample.

[0037] (4) In-situ coating of polypyrrole (PPy) First, weigh 5.48 g of ammonium persulfate and add it to 10 mL of deionized water. Stir thoroughly until completely dissolved to obtain solution A, and refrigerate. Next, add 1.68 mL of pyrrole and 3.68 mL of phytic acid (45%) to 10 mL of isopropanol to prepare solution B, and cool in a refrigerator. After solutions A and B have cooled to 0°C, alternately and evenly coat them onto the surface of a white PVA / CNF composite aerogel sample until the surface of the PVA / CNF composite aerogel sample turns completely black. Vacuum freeze-dry for 12 h to obtain PPy / PVA / CNF composite aerogel.

[0038] (5) Verification of the application effect of directional hydrophilic aerogel in the leaching and desalination of saline-alkali soil Saline-alkali soil was used as the test soil and packed into containers measuring 15 cm × 10 cm × 5 cm, with a total volume of 750 mL. Directional hydrophilic aerogels were prepared according to the method in Example 1. Three groups were set up, with the amount of aerogel added as a variable: a control group (no aerogel added); experimental group 1 (4 aerogel particles added); and experimental group 2 (6 aerogel particles added). Each group was rinsed with 300 mL of deionized water. After rinsing, the leachate was collected, and the chloride ion concentration was measured. The chloride ion concentration was semi-quantitatively determined using a chloride test strip. During the measurement, the reaction area of ​​the test strip was immersed in the test solution for 1 second, then removed and allowed to stand for 60 seconds for color development. The result was then compared with a standard colorimetric card. Each group was measured in triplicate, and the average value was taken.

[0039] The results showed that as the amount of aerogel added increased, the concentration of chloride ions in the leaching solution decreased, indicating that the directional hydrophilic aerogel can promote salt enrichment and migration, and has a positive effect on the leaching and desalination of saline-alkali soil. It can be used for water retention and salt reduction improvement of saline-alkali soil.

Claims

1. A method for preparing a directional photothermal aerogel material for optimizing saline-alkali land, characterized in that, Includes the following steps: S1. Mix the cellulose nanofiber dispersion with the polyvinyl alcohol solution and stir until homogeneous to obtain the matrix sol; S2. Add pyrrole monomer and initiator to the matrix sol to cause in-situ polymerization of pyrrole to obtain photothermal composite sol; S3. The photothermal composite sol is subjected to directional freezing treatment. After freezing under a unidirectional temperature gradient, it is subjected to vacuum freeze-drying and post-processing to obtain the directional hydrophilic aerogel saline-alkali land improvement material. The freezing temperature of the directional freezing process is -20°C to -50°C.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass concentration of the cellulose nanofiber dispersion is 1% to 5%, and the mass concentration of the polyvinyl alcohol solution is 5% to 15%.

3. The preparation method according to claim 1, characterized in that, In step S2, the in-situ polymerization reaction temperature is 15℃~35℃.

4. The preparation method according to claim 1, characterized in that, In step S3, the freezing direction of the directional freezing is perpendicular to the sol surface.

5. A directional hydrophilic aerogel material for improving saline-alkali land, characterized in that, The directional hydrophilic aerogel saline-alkali land improvement material is prepared by the preparation method according to any one of claims 1 to 4. The material comprises a three-dimensional porous framework formed by cellulose nanofibers and polyvinyl alcohol, and a polypyrrole photothermal functional component loaded on the three-dimensional porous framework. The material has a vertically oriented pore structure.

6. The directional hydrophilic aerogel saline-alkali land improvement material according to claim 5, characterized in that, The porosity of the material is higher than 90%.

7. A water-retaining and desalination surface micro-engineering system, characterized in that, The material comprises the directional hydrophilic aerogel saline-alkali land improvement material as described in any one of claims 5-7, and through the synergistic effect of its components A, B and C, constructs a technical closed loop of underground adsorption and fixation, surface photothermal-driven salt release, and subsequent ecological transformation.

8. A method for treating saline-alkali land using the system described in claim 7, characterized in that, The process includes the following steps: Step 1: Test the saline-alkali land to be treated and obtain its key soil indicators; Step 2: Based on the indicators obtained in Step 1, match and determine the formulation and application plan of the directional hydrophilic aerogel saline-alkali land improvement material.

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