Biomass-based degradable afforestation water-retaining agent and preparation method thereof

Abstract

The invention discloses a biomass-based degradable afforestation water-retaining agent and a preparation method thereof, and belongs to the technical field of water-retaining agents. The raw materials of the composite microbial degradation agent comprise plant starch, alkali modified cellulose, a composite microbial degradation agent subjected to microcapsule embedding treatment, poly (N-isopropylacrylamide), a sodium polyacrylate-acrylamide copolymer, a salt-alkali buffer agent, MOFs-sodium alginate, a photosensitizer, a cross-linking agent and an initiator. The wall material of the microcapsule is sodium alginate-chitosan. The biomass-based degradable afforestation water-retaining agent provided by the invention is an innovative functional material developed for growth requirements of drought-enduring plants such as haloxylon ammodendron and populus euphratica aiming at extreme environments such as high temperature and drought, high salinity and alkalinity and strong wind and sand erosion in desert areas. According to the water-retaining agent, through multi-component collaborative design, the technical bottlenecks of traditional materials in the aspects of long-acting water retention, controllable degradation and the like are broken through.

Description

Technical Field

[0001] The invention relates to the technical field of water-retaining agents, in particular to a biomass-based degradable afforestation water-retaining agent and a preparation method thereof. Background Art

[0002] While existing biodegradable water-retaining agents for afforestation are environmentally friendly, energy-saving, and possess a certain degree of water-retention capacity, they still suffer from numerous drawbacks. First, their performance parameters are relatively limited, lacking specific designs tailored to the needs of different desert tree species. For example, Haloxylon ammodendron has a well-developed root system and requires relatively little water in its early stages of growth, but requires high water stability. Populus euphratica is drought- and saline-tolerant but sensitive to changes in soil salinity during its seedling stage. Existing water-retaining agents cannot fully meet these specific needs.

[0003] Secondly, in an extremely dry desert environment with large temperature differences between day and night, the water absorption and release rates of water retaining agents are difficult to match the growth rhythm of trees, resulting in low water utilization efficiency.

[0004] Third, microbial degradation agents have poor stability in the complex soil environment of the desert, which affects the degradation effect of water-retaining agents. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a biomass-based degradable afforestation water-retaining agent and a preparation method thereof, so as to at least achieve the purpose of improving water retention performance and controllable degradation.

[0006] The object of the present invention is achieved through the following technical solutions: A biomass-based degradable afforestation water-retaining agent, the raw materials of which include the following components in parts by weight: 40-60 parts of plant starch, 30-40 parts of alkali-modified cellulose, 3-8 parts of microencapsulated composite microbial degradation agent, 2-5 parts of poly (N-isopropylacrylamide), 2-5 parts of sodium polyacrylate-acrylamide copolymer, 1-3 parts of saline-alkali buffer, 2-5 parts of MOFs-sodium alginate, 1-3 parts of photosensitizer, 1-3 parts of cross-linking agent, and 0.5-1.5 parts of initiator; The wall material of the microcapsule is sodium alginate-chitosan.

[0007] As some possible implementation methods of the present application, the raw materials include the following components in parts by weight: 42-55 parts of plant starch, 32-38 parts of alkali-modified cellulose, 4-8 parts of microencapsulated composite microbial degradation agent, 2-4 parts of poly (N-isopropylacrylamide), 2-4 parts of sodium polyacrylate-acrylamide copolymer, 2-2.5 parts of saline-alkali buffer, 3-4.5 parts of MOFs-sodium alginate, 1-2.5 parts of photosensitizer, 1-2.5 parts of cross-linking agent and 0.5-1.2 parts of initiator.

[0008] As some possible implementation methods of the present application, in the MOFs-sodium alginate, the MOFs organic ligand is sodium lignin sulfonate, and the metal salt is magnesium chloride or calcium chloride.

[0009] As some possible implementation methods of the present application, a polydopamine layer is coated on the surface of the MOFs-sodium alginate composite material.

[0010] As some possible implementation methods of the present application, nano-titanium dioxide is introduced into the polydopamine layer.

[0011] As some possible implementation methods of the present application, PEG is grafted onto the surface of the polydopamine layer introduced with nano-titanium dioxide.

[0012] As some possible implementation methods of the present application, nanocellulose and nanosilica are introduced into the microcapsule wall material.

[0013] In addition, to achieve the above-mentioned purpose, the present invention also provides a preparation method of a biomass-based degradable afforestation water-retaining agent, comprising adding plant starch, alkali-modified cellulose and MOFs-sodium alginate to deionized water, stirring thoroughly, sequentially adding a crosslinker, an initiator, a saline-alkali buffer and a photosensitizer, adding poly N-isopropylacrylamide and sodium polyacrylate-acrylamide copolymer after thorough dispersion, stirring evenly, and performing a photopolymerization reaction under ultraviolet light, followed by adding a microcapsulated composite microbial degradation agent, mixing thoroughly, and drying to obtain a biomass-based degradable afforestation water-retaining agent.

[0014] The beneficial effects of the present invention are: 1. The biomass-based biodegradable water-retaining agent provided by this invention is a functional material developed to meet the specific growth requirements of desert plants such as Haloxylon ammodendron and Populus euphratica, particularly in desert environments characterized by high temperatures, drought, high salinity, and strong wind and sand erosion. This water-retaining agent utilizes a multi-component collaborative design to overcome the technical bottlenecks of traditional materials in terms of long-term water retention and controlled degradation. Specifically, plant starch and alkali-modified cellulose form a "skeleton-filler" network, with MOFs (sodium alginate) embedded within the network pores, achieving adaptive water retention in the extreme desert environment. The plant starch, due to its hydrophilicity, forms a gel matrix, while the alkali-modified cellulose enhances the network's mechanical strength through hydroxyl activation. Together, the two create a three-dimensional structure. The MOFs (sodium alginate) leverage the high specific surface area of ​​MOFs and the ionic crosslinking properties of sodium alginate to enhance water absorption and salt tolerance. Poly (N-isopropylacrylamide) and sodium polyacrylate-acrylamide copolymers utilize dual thermo- and salt-sensitive properties to regulate water release at varying temperatures and salt concentrations. The saline-alkali buffer and microencapsulated microorganisms synergistically improve the rhizosphere environment. Testing has shown that the water-retaining agent exhibits a water absorption rate of ≥507 g / g in deionized water and ≥152 g / g in 0.9% NaCl solution. It also maintains a water retention rate of ≥81.7% for 72 hours at 40°C and a water release period of ≥72 hours, breaking through the water retention bottleneck of traditional materials in high-salt, arid environments. Furthermore, the water-retaining agent of this invention is suitable not only for desert regions but also for high-temperature, arid regions such as Qiubei, Yunnan.

[0015] 2. The introduction of nano-SiO2 and cellulose into the microcapsule wall effectively enhances its compressive strength while increasing porosity, promoting contact between microorganisms and the water-retention network. The composite wall formed by these nanomaterials resists the inactivation of microorganisms in the desert's high salinity and strong UV environments, significantly increasing the number of viable microorganisms and accelerating degradation rates.

[0016] 3. When MOFs (sodium alginate) are coated with a polydopamine layer, its catechol structure hydrogen bonds with water molecules, forming a molecular-scale salt barrier. This also strengthens the interfacial bonding between the MOFs and other components, reducing structural damage caused by wind and sand erosion. When PEG is grafted onto the polydopamine layer, a hydrophilic-hydrophobic microphase separation structure forms. This structure contracts in high-salt environments, slowing water release, while expanding in low-salt environments, accelerating water release, effectively matching the diurnal salinity fluctuations in the desert. When TiO2 is introduced into the polydopamine layer, its photocatalytic heat production and the thermosensitivity of PEG synergistically regulate the water release rate. Simultaneously, the photocatalytically generated hydroxyl radicals react with microorganisms in a "photo-biological" synergistic degradation process, effectively increasing the degradation rate. Furthermore, the UV resistance of TiO2 extends the material's service life, accelerating degradation. Combined with the long-term water release of PEG, this significantly increases the water release cycle and significantly reduces soil salinity. DETAILED DESCRIPTION

[0017] A biomass-based degradable afforestation water-retaining agent, the raw materials of which include the following components in parts by weight: 40-60 parts of plant starch, 30-40 parts of alkali-modified cellulose, 3-8 parts of microencapsulated composite microbial degradation agent, 2-5 parts of poly (N-isopropylacrylamide), 2-5 parts of sodium polyacrylate-acrylamide copolymer, 1-3 parts of saline-alkali buffer, 2-5 parts of MOFs-sodium alginate, 1-3 parts of photosensitizer, 1-3 parts of cross-linking agent, and 0.5-1.5 parts of initiator; The wall material of the microcapsule is sodium alginate-chitosan.

[0018] The functions of the components in the water-retaining agent of the present invention are as follows: Plant starch: It has good water absorption and certain film-forming properties. In desert environments, it can form a gel-like structure after absorbing water, storing water and slowly releasing it, providing a continuous water supply for plants such as Haloxylon ammodendron and Populus euphratica.

[0019] Alkali-modified cellulose: The hydroxyl activity of cellulose treated with alkali is enhanced, and its compatibility with other components is improved, which helps to build a stable three-dimensional network structure, enhance the mechanical strength and water retention capacity of the water-retaining agent, and at the same time improve the soil structure and increase the soil permeability, which is beneficial to the growth and respiration of the roots of Haloxylon ammodendron and Populus euphratica.

[0020] The microencapsulated composite microbial degradation agent, sodium alginate-chitosan, is a natural, biodegradable, and environmentally friendly material. In the harsh desert environment of high temperature, high salt concentrations, and strong ultraviolet rays, the microcapsules effectively protect the microorganisms, preventing them from losing activity or even losing their activity. Over time, the wall material gradually degrades, releasing microorganisms that degrade the water-retaining agent, allowing it to decompose naturally after completing its water-retaining mission. Furthermore, the microbial activity improves the soil microbial community structure, promotes soil nutrient cycling, and creates a more favorable soil environment for the growth of desert trees like Haloxylon ammodendron.

[0021] Poly (N-isopropylacrylamide): Poly (N-isopropylacrylamide) is temperature-sensitive. In the desert environment with large temperature differences between day and night, when the temperature rises during the day, its molecular structure changes, prompting the water-retaining agent to accelerate water release to meet the increased water demand of Haloxylon ammodendron and Populus euphratica due to transpiration; when the temperature drops at night, it can reduce water release to prevent excessive water loss.

[0022] Sodium polyacrylate-acrylamide copolymer: It is salt-sensitive. When the soil salinity changes, it can adjust the water release rate of the water retaining agent to ensure the absorption of water by the tree roots and avoid difficulties in water absorption due to excessive soil salinity.

[0023] Salt-alkali buffers are used to regulate soil pH. Desert soils are generally highly salinized, and excessive salinity can inhibit the growth of Haloxylon ammodendron and Populus euphratica. Salt-alkali buffers specifically address this issue, regulating soil pH and creating a suitable growth environment for salt-sensitive plants like Populus euphratica seedlings.

[0024] MOFs - Sodium Alginate: Sodium alginate has excellent water absorption and retention properties, effectively increasing the water absorption rate of water-retaining agents, providing more abundant and lasting water for Haloxylon ammodendron and Populus euphratica. Furthermore, the gel properties of sodium alginate, combined with saline-alkali buffers, slow the diffusion of saline and alkali components in the soil, enhancing soil pH regulation and creating a more stable soil environment for Populus euphratica seedlings. However, sodium alginate's water absorption and water retention capacity are insufficient. In the extremely arid desert environment, water evaporates rapidly, making it difficult to meet the long-term and high-volume water needs of trees, resulting in rapid water loss and poor water retention. MOFs, with their ultra-high surface area and rich pore structure, can absorb large amounts of water. When combined with sodium alginate, they significantly enhance their water absorption and retention capacity, providing a more abundant and lasting water supply for trees. Furthermore, MOFs can effectively improve the weak mechanical strength of the gel structure formed by sodium alginate, which easily breaks under the impact of wind and sand.

[0025] In summary, the biomass-based biodegradable water-retaining agent provided by this invention is an innovative functional material developed to address the extreme environments of desert regions, such as high temperature, drought, high salinity, and strong wind and sand erosion, specifically the growth needs of drought-tolerant plants such as Haloxylon ammodendron and Populus euphratica. Through a multi-component collaborative design, this water-retaining agent overcomes the technical bottlenecks of traditional materials in terms of long-term water retention and controlled degradation, achieving an organic integration of material performance and ecological function.

[0026] In order to further improve the water absorption and retention effect of the water retaining agent, as some possible implementation methods of this application, the amount of raw materials is further limited, that is, the raw materials include the following components in parts by weight: 42-55 parts of plant starch, 32-38 parts of alkali-modified cellulose, 4-8 parts of microencapsulated composite microbial degradation agent, 2-4 parts of poly (N-isopropylacrylamide), 2-4 parts of sodium polyacrylate-acrylamide copolymer, 2-2.5 parts of saline-alkali buffer, 3-4.5 parts of MOFs-sodium alginate, 1-2.5 parts of photosensitizer, 1-2.5 parts of cross-linking agent and 0.5-1.2 parts of initiator.

[0027] To effectively reduce raw material costs and improve water absorption and retention, some possible implementations of this application define the materials of MOFs-sodium alginate. Specifically, the MOFs-sodium alginate comprises sodium lignin sulfonate as the organic ligand and magnesium chloride or calcium chloride as the metal salt. Sodium lignin sulfonate is widely available, relatively low in cost, and exhibits good dispersibility and certain adsorption properties. Its combination with sodium alginate can further optimize the performance of MOFs-sodium alginate. Magnesium chloride or calcium chloride, as metal salts, can form specific coordination structures with sodium lignin sulfonate and sodium alginate, affecting the pore structure and adsorption properties of the MOFs-sodium alginate, thereby enhancing the overall performance of the water-retention agent. In desert environments, this optimized MOFs-sodium alginate can more effectively absorb and store water, providing a more adequate water supply for Haloxylon ammodendron and Populus euphratica. Furthermore, the water release process is more stable and sustained, helping to improve the survival of the trees in drought conditions.

[0028] The structure of MOFs materials will collapse or decompose in complex desert soil environments such as high salt. At the same time, MOFs-sodium alginate has weak interfacial bonding with other components in harsh desert environments such as strong ultraviolet rays and wind and sand, and is easily eroded, affecting its water retention function and service life, and thus unable to provide long-term and stable water supply to Haloxylon ammodendron and Populus euphratica.

[0029] Based on this, as some possible implementations of this application, a polydopamine layer is coated on the surface of the MOFs-sodium alginate composite material. This polydopamine layer can enhance the interaction between the MOFs-sodium alginate and other components, strengthen the three-dimensional network structure of the water-retaining agent, improve mechanical strength and deformation resistance, and enhance the structural stability of the MOFs material in harsh environments. Furthermore, the biocompatibility of polydopamine promotes microbial attachment and growth, facilitating the function of the composite microbial degradation agent and accelerating the late-stage degradation of the water-retaining agent.

[0030] However, after polydopamine is degraded in the soil, it will produce some small molecular substances. These substances may accumulate in the soil, causing potential secondary pollution to the soil environment, which is contrary to the original intention of the environmental protection design of the water-retaining agent. Based on this, as some possible implementation methods of the present application, nano-titanium dioxide is introduced into the polydopamine layer. Nano-titanium dioxide has photocatalytic activity and can promote the degradation of polydopamine under light conditions. At the same time, it can also enhance the antibacterial properties of the water-retaining agent and reduce the invasion of harmful microorganisms on the roots of trees. In addition, the addition of nano-titanium dioxide can also improve the mechanical properties of the polydopamine coating and improve its stability.

[0031] In addition, the polydopamine layer may reduce the permeability of the three-dimensional water-retaining network structure constructed by MOFs-sodium alginate and plant starch and alkali-modified cellulose, thereby reducing the diffusion rate of water inside the water-retaining agent, affecting the timely acquisition of water by trees such as Haloxylon ammodendron and Populus euphratica. Based on this, as some possible implementation methods of the present application, PEG is grafted on the surface of the polydopamine layer introduced with nano-titanium dioxide. The introduction of hydrophilic groups can improve the hydrophilicity of the polydopamine coating, increase the water transmission rate in the coating, and reduce the obstruction to the diffusion of water inside the water-retaining agent. At the same time, the PEG flexible chain segment can improve the interaction between the water-retaining agent and soil particles, reduce the agglomeration of the water-retaining agent in the soil, and improve the dispersibility and uniformity of the water-retaining agent in the soil.

[0032] In a desert sandy environment, microcapsules may be subjected to external mechanical forces, and the insufficient mechanical properties of the original wall material can easily lead to rupture, causing the microorganisms to be inactivated prematurely, affecting the degradation of the water-retaining agent and the soil improvement effect. Based on this, as some possible implementation methods of the present application, nanocellulose and nanosilica are introduced into the microcapsule wall material. Nanocellulose has a high specific surface area, high strength and good hydrophilicity, which can enhance the mechanical properties and water retention capacity of the microcapsule wall material; nanosilica has good chemical stability and reinforcing effects, which can improve the weather resistance and rigidity of the microcapsule wall material. In the harsh environment of the desert, microcapsules need to have good performance to protect the composite microbial degradation agent.

[0033] In addition, to achieve the above-mentioned purpose, the present invention also provides a preparation method of a biomass-based degradable afforestation water-retaining agent, comprising adding plant starch, alkali-modified cellulose and MOFs-sodium alginate to deionized water, stirring thoroughly, sequentially adding a crosslinker, an initiator, a saline-alkali buffer and a photosensitizer, adding poly N-isopropylacrylamide and sodium polyacrylate-acrylamide copolymer after thorough dispersion, stirring evenly, and performing a photopolymerization reaction under ultraviolet light, followed by adding a microcapsule-embedded composite microbial degradation agent, mixing thoroughly, and drying to obtain a biomass-based degradable afforestation water-retaining agent.

[0034] This preparation method limits the order of adding each raw material to ensure sufficient mixing, so that the crosslinking agent and initiator can effectively play their role, promote polymerization and crosslinking reactions, form a stable and excellent three-dimensional network structure, and provide reliable materials for desert afforestation.

[0035] Next, the preparation method of the water-retaining agent is further described in detail through examples.

[0036] Example 1 S1. Preparation of raw materials.

[0037] A. The preparation method of alkali-modified cellulose is as follows: The straw cellulose was crushed to 80 mesh, added with 18% NaOH solution (solid-liquid ratio 1:10), alkalized at 30°C for 2 hours, filtered and washed with deionized water until neutral, then added with epichlorohydrin (5% of the cellulose mass), and etherified at 45°C for 3 hours. The product was washed with ethanol, dried and crushed to 100 mesh to obtain alkali-modified cellulose.

[0038] B. The preparation method of MOFs-sodium alginate is as follows: B1. Dissolve 20 g of sodium lignin sulfonate in 100 mL of DMF, add 15 g of anhydrous MgCl2, and stir at 70°C for 12 h. The mixture is then centrifuged, washed, and activated at 150°C for 6 h to obtain a lignin-based MOF. B2. Dissolve 5g of sodium alginate in 100mL of deionized water, add 3g of lignin-based MOFs material, and ultrasonically disperse for 30min. Then, add 50mL of a 2% CaCl2 solution dropwise. Cross-link and cure for 1h. The product is freeze-dried and crushed to 200 mesh to obtain MOFs-sodium alginate.

[0039] C. The preparation method of the microcapsulated composite microbial degradation agent is as follows: C1. Weigh 4 g of sodium alginate (viscosity 200-400 mPa·s) and slowly add it to 100 mL of deionized water. Stir continuously at 45°C for 2.5 h to obtain a sodium alginate solution. Take 4 g of chitosan (deacetylation degree ≥ 90%) and dissolve it in 2% acetic acid solution (100 mL). Stir at 35°C for 3 h. After complete dissolution, adjust the pH to 5.0-5.5 with 1 M NaOH solution. Filter to remove insoluble matter to obtain chitosan solution. Bacillus, cellulolytic bacteria, and desert halomonas were selected and inoculated into the corresponding liquid culture medium. Bacillus was cultured in LB medium, cellulolytic bacteria in a medium with cellulose as the sole carbon source, and desert halomonas in a high-salt medium (NaCl concentration 3% - 5%). The culture was shaken at 30°C and 200 r / min for 20 hours until the logarithmic growth phase. The cultured bacterial suspensions of each strain were centrifuged at 4°C and 5000 r / min for 15 minutes, the supernatant was discarded, and the cells were resuspended in sterile saline. The centrifugation and washing were repeated 2-3 times. The bacterial suspensions of each strain were then mixed in a volume ratio of 1:1:1, and the concentration of the mixed bacterial suspension was adjusted to 1×10 9 CFU / mL.

[0040] C2. Slowly add 8 mL of the above mixed bacterial suspension to the sodium alginate solution and stir at 200 r / min for 20 min. Then slowly drip the resulting mixture into the chitosan solution. After the addition is complete, stir and react for 30-40 min. Then add 8 mL of 0.1 M calcium chloride solution and react for 12 min. Finally, filter through a 100-mesh filter, wash, and pre-freeze at -40°C for 2.5 h. Then, dry at -20°C under vacuum <10 Pa for 18 h to obtain the microcapsule-encapsulated composite microbial degradation agent.

[0041] D. The preparation method of sodium polyacrylate-acrylamide copolymer is as follows: D1. Raw material preparation: Weigh 15 g of sodium acrylate and dissolve it in 100 mL of deionized water; weigh 5 g of acrylamide and dissolve it in 50 mL of deionized water; then mix the two monomer solutions and adjust the pH to 7.0-7.5 with 1 M NaOH solution to obtain a monomer solution. Weigh 0.2 g of ammonium persulfate and dissolve it in 10 mL of deionized water to obtain an initiator solution; Weigh 0.08 g of N,N'-methylenebisacrylamide and dissolve it in 5 mL of deionized water to obtain a crosslinker solution; D2. Add the monomer mixture to a four-necked flask equipped with a condenser, thermometer, and stirrer. Then, introduce nitrogen for 30 minutes. Cool the flask to 10°C, add 5 mL of the crosslinker solution, stir evenly, and slowly add 10 mL of the initiator solution dropwise. After the addition is complete, continue the reaction at 10°C for 1 hour, then raise the temperature to 50°C and react for 3 hours. After the reaction is complete, age the product at 60°C for 2 hours, cool it to room temperature, cut it into small pieces, soak it in anhydrous ethanol for 24 hours, filter it, and vacuum-dry it at 60°C to constant weight. Finally, pulverize it through a 40-mesh sieve to obtain sodium polyacrylate-acrylamide copolymer.

[0042] S2. Synthesis of water-retaining agent.

[0043] 55g corn starch, 38g alkali-modified cellulose, and 4g MOFs-sodium alginate were added to 500mL deionized water and mechanically stirred at 60°C for 2h to form a uniform suspension. 2g N,N'-methylenebisacrylamide, 1g potassium persulfate, 2g saline-alkali buffer (a mixture of sodium bicarbonate and potassium dihydrogen phosphate in a mass ratio of 3:1), and 2g benzoin dimethyl ether were then added in sequence. After stirring and dispersing for 30min, 3g N-isopropylacrylamide (molecular weight of 50,000-60,000) and 4g sodium polyacrylate-acrylamide copolymer were added. After stirring for another 1h, the mixture was transferred to a photoreactor and irradiated with 365nm UV light (intensity 50mW / cm²) for 40min. Then, 8 g of microcapsulated composite microbial degradation agent was added to the reaction system and stirred at low speed for 15 minutes. The mixture was then vacuum dried at 45°C to a moisture content of ≤10%. The product was crushed and passed through a 40-mesh sieve to obtain a granular biomass-based degradable afforestation water-retaining agent.

[0044] Example 2 Based on Example 1, the amount of each raw material of the water-retaining agent was adjusted. The amount of each raw material after adjustment is as follows: 58g plant starch, 35g alkali-modified cellulose, 8g microcapsule-encapsulated composite microbial degradation agent, 3g poly (N-isopropylacrylamide), 3g sodium polyacrylate-acrylamide copolymer, 2g saline-alkali buffer, 5g MOFs-sodium alginate, 1.5g photosensitizer, 2g cross-linking agent and 1g initiator.

[0045] The remaining steps and parameters are the same as in Example 1.

[0046] Example 3 On the basis of Example 1, the microcapsulated composite microbial degradation agent was replaced with a modified composite microbial degradation agent. The remaining parameters and methods were the same as those in Example 1.

[0047] In this embodiment, the preparation method of the modified composite microbial degradation agent is as follows: C1. Weigh 0.4 g of nanosilica (particle size 30 nm) and disperse it in anhydrous ethanol. Add APTES (6% by mass of the nanosilica). Stir and react at 60°C for 4 h. After the reaction, centrifuge, wash, and dry to obtain the modified silica.

[0048] Weigh 4 g of sodium alginate (viscosity 300 mPa·s) and slowly add it to 100 mL of deionized water. Stir continuously at 45°C for 2.5 h. Then add 0.1 g of nanocellulose (diameter 10-15 nm, length 500-1000 nm). Ultrasonicate at 300 W power and 30°C for 20 min to obtain a sodium alginate-cellulose solution. Take 4 g of chitosan (deacetylation degree ≥ 90%) and dissolve it in 2% acetic acid solution (100 mL). Stir at 35°C for 3 hours. After complete dissolution, adjust the pH to 5.0-5.5 with 1 M NaOH solution. Filter to remove insoluble matter, then add 0.2 g of modified nano-silica and stir thoroughly to obtain chitosan-silica solution.

[0049] Bacillus, cellulolytic bacteria, and desert halomonas were selected and inoculated into their respective liquid cultures. Bacillus was cultured in LB medium, cellulolytic bacteria in a medium with cellulose as the sole carbon source, and desert halomonas in a high-salt medium (4% NaCl concentration). Cultures were shaken at 30°C and 200 rpm for 20 hours until the logarithmic growth phase. The cultured bacterial suspensions of each strain were centrifuged at 4°C and 5000 rpm for 15 minutes, the supernatant discarded, and the cells resuspended in sterile saline. The centrifugation and washing were repeated three times. The bacterial suspensions of each strain were then mixed in a 1:1:1 volume ratio and the concentration of the mixed suspension was adjusted to 1×10 9 CFU / mL.

[0050] C2. Slowly add 8 mL of the above mixed bacterial suspension to the sodium alginate-cellulose solution and stir at 200 r / min for 20 min. Then slowly drop the resulting mixture into the chitosan-silica solution. After the addition is complete, stir and react for 40 min. Then add 8 mL of 0.1 M calcium chloride solution and react for 12 min. Finally, filter through a 100-mesh filter, wash, and pre-freeze at -40°C for 2.5 h. Then, dry at -20°C under vacuum <10 Pa for 18 h to obtain a microcapsule-encapsulated composite microbial degradation agent.

[0051] Example 4 Based on Example 3, MOFs-sodium alginate was replaced with the first modified MOFs-sodium alginate. The remaining parameters and steps were the same as in Example 1.

[0052] In this embodiment, the preparation method of the first modified MOFs - sodium alginate is as follows: B1. Dissolve 20 g of sodium lignin sulfonate in 100 mL of DMF, add 15 g of anhydrous MgCl2, and stir at 70°C for 12 h. The mixture is then centrifuged, washed, and activated at 150°C for 6 h to obtain a lignin-based MOF. B2. Dissolve 5g of sodium alginate in 100mL of deionized water, add 3g of lignin-based MOFs material and ultrasonically disperse for 30min. Then, add 50mL of a 2% CaCl2 solution dropwise and cross-link and cure for 1h. The product is freeze-dried and crushed to 200-mesh size. The microspheres are washed three times with deionized water, collected, and freeze-dried (-50°C, 10Pa, 24h). The freeze-dried product is then crushed and passed through a 200-mesh sieve to obtain MOFs-sodium alginate composite microspheres.

[0053] B3. Weigh 1.21g Tris base, dissolve in 800mL deionized water, adjust the pH to 8.5 with HCl, and dilute to 1L Tris-HCl buffer. 5g of MOFs-alginate composite microspheres were added to 200mL of buffer (1.21g of Tris base was weighed, dissolved in 800mL of deionized water, the pH adjusted to 8.5 with HCl, and the volume was adjusted to 1L of Tris-HCl buffer) and ultrasonically dispersed for 10 minutes. Subsequently, 0.5g of dopamine hydrochloride was added and stirred at room temperature in the dark for 24 hours. After the reaction, the product was washed and pre-frozen at -40°C for 3 hours. It was then freeze-dried (10Pa, -20°C, 24 hours), pulverized, and passed through a 200-mesh sieve to obtain the first modified MOFs-alginate.

[0054] Example 5 Based on Example 3, MOFs-sodium alginate was replaced with a second modified MOFs-sodium alginate. The remaining parameters and steps were the same as in Example 3.

[0055] In this embodiment, the preparation method of the second modified MOFs - sodium alginate is as follows: B1-B3 are the same as in Example 4; B4. Weigh 2 g of PEG-2000 and dissolve it in 100 mL of deionized water. Add 0.5 g of N-hydroxysuccinimide and 0.8 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. Stir at room temperature for 2 h to obtain an activation solution. 5 g of the first modified MOFs-sodium alginate was added to 200 mL of phosphate buffer and ultrasonically dispersed for 10 minutes; then the activation solution was added and stirred at 37°C in the dark for 12 hours. After the reaction, the product was washed and pre-frozen at -40°C for 3 hours, freeze-dried (10 Pa, -20°C, 24 hours), and crushed through a 200-mesh sieve to obtain the second modified MOFs-sodium alginate.

[0056] Example 6 Based on Example 3, MOFs-sodium alginate was replaced with the third modified MOFs-sodium alginate. The remaining parameters and steps were the same as in Example 3.

[0057] In this embodiment, the preparation method of the third modified MOFs - sodium alginate is as follows: B1-B2. Same as Example 4, MOFs-sodium alginate composite microspheres were prepared.

[0058] B3. Weigh 0.4 g of nano-titanium dioxide (anatase type, particle size 20-30 nm) and add 50 mL of deionized water. Then, add 8% by weight of 3-aminopropyltriethoxysilane to the nano-silicon dioxide. Incubate with magnetic stirring at 60°C for 4 h. After the reaction is complete, centrifuge at 8000 rpm for 10 min, discard the supernatant, and wash with anhydrous ethanol to obtain modified nano-titanium dioxide.

[0059] 5 g of MOFs-sodium alginate composite microspheres were added to 200 mL of buffer solution (1.21 g of Tris base was weighed and dissolved in 800 mL of deionized water, the pH was adjusted to 8.5 with HCl, and the volume was made up to 1 L of Tris-HCl buffer), and ultrasonically dispersed for 10 min (power 300 W). Subsequently, 0.5 g of dopamine hydrochloride and 0.3 g of modified nano-titanium dioxide were added. The mixture was stirred at room temperature in the dark for 24 h, and ultrasonically dispersed for 5 min (power 200 W) every 2 h. After the reaction, the mixture was washed and pre-frozen at -40 °C for 3 h, freeze-dried (10 Pa, -20 °C, 24 h), and crushed to pass through a 200-mesh sieve.

[0060] B4. Weigh 2 g of PEG-2000 and dissolve it in 100 mL of deionized water. Add 0.5 g of N-hydroxysuccinimide and 0.8 g of EDC. Stir at room temperature for 2 h to prepare an activation solution.

[0061] 5 g of the product obtained from B3 was added to 200 mL of PBS buffer (pH = 7.4), ultrasonically dispersed for 10 min, and activated solution was added. The mixture was stirred at 37 ° C in the dark for 12 h, then washed and freeze-dried to obtain the third modified MOFs - sodium alginate.

[0062] Comparative Example 1 On the basis of Example 1, MOFs-sodium alginate was replaced by sodium alginate, and the remaining parameters and steps were the same as Example 1.

[0063] Comparative Example 2 On the basis of Example 1, the composite microbial degradation agent embedded in the microcapsule was directly changed to the composite microbial degradation agent, that is, the composite microbial degradation agent was not embedded but directly added into the system, and the added amount was the same as that in Example 1.

[0064] The remaining parameters and steps are the same as in Example 1.

[0065] Experimental example The water-retaining agents in Examples 1-6 and Comparative Examples 1-2 were used to perform the following experiments.

[0066] 1. Water retention performance test (test results are shown in Table 1) ① Water absorption rate (SAR): Weigh 0.5g water retaining agent and add 200mL deionized water and 0.9% NaCl solution. Let it stand for 24h and then filter. Calculate the water absorption rate SAR = (wet weight - dry weight) / dry weight.

[0067] ② Water retention rate: Place the water-saturated water-retaining agent in a 40℃ oven, weigh it every 24 hours, and calculate the water retention rate (water retention rate = residual water / initial water absorption × 100%).

[0068] ③ Water release cycle: the time required from the start of water absorption to the water retention rate dropping to 30% of the initial water absorption.

[0069] Table 1: It can be seen from Table 1 that the water retention performance of Examples 1-6 is significantly higher than that of Comparative Examples 1-2.

[0070] The specific analysis is as follows: Example 1-2: Construction of a basic three-dimensional water retention network by MOFs-sodium alginate and alkali-modified cellulose.

[0071] Example 3: Nano-SiO2 and cellulose are introduced into the microcapsule wall material to enhance the compressive strength of the wall material through the "skeleton reinforcement effect", reduce the collapse of the water retention network in a high-salt environment, and thus improve the salt-resistant water absorption rate and water release cycle.

[0072] Example 4: A polydopamine layer is coated on the surface of MOFs-sodium alginate. Leveraging the hydrophilicity and salting-out resistance of the catechol structure, it forms a molecular barrier that blocks salt ion penetration, improving water retention in high-salt environments. Simultaneously, the polydopamine layer enhances the wall's compressive strength, reducing the collapse of the water-retention network in high-salt environments and thereby increasing the water-release cycle.

[0073] Example 5: The polydopamine layer is grafted with PEG segments to achieve "salt-sensitive water release" through the hydrophilic-hydrophobic microphase separation structure. It shrinks and slows water release at high salt concentrations, and stretches and accelerates water release at low salt concentrations, thereby optimizing the water release regulation ability.

[0074] Example 6: PEG-PDA-SiO2 synergistic modification, SiO2 photocatalytic heat generation and PEG temperature sensitivity synergistically regulate the water release rate, while SiO2's anti-ultraviolet properties enhance the material's weather resistance, achieving long-term water retention and extended water release cycles.

[0075] Comparative Example 1: The network formed by the single component of sodium alginate cannot effectively adsorb salt ions. The water-retaining network is easy to disintegrate in a high-salt environment, resulting in a significant decrease in water absorption and retention performance.

[0076] Comparative Example 2: Without microcapsule embedding, the microbial metabolites destroyed the water retention network structure. At the same time, the harsh desert environment caused the microbial activity to decay, indirectly reducing the water retention performance.

[0077] 2. Degradation performance test (test results are shown in Table 2) ①Degradation rate: bury 10g of water retaining agent in sandy loam (native sandy loam in the Taklimakan Desert, with a moisture content of 2.3%, pH 8.5, a salt content of 0.6%, and a depth of 10cm), and take samples regularly to calculate the degradation rate.

[0078] ② Microbial activity detection: Use the dilution coating plate method to detect the number of viable microorganisms (CFU / g) in the water-retaining agent after 90 days of burial.

[0079] Table 2: It can be seen from Table 2 that the degradation rate and viable bacteria count of Examples 1-6 are higher than those of Comparative Examples 1-2.

[0080] The specific analysis is as follows: Example 1-2: Sodium alginate-chitosan microcapsules protect microorganisms through physical barriers, reduce the inactivation of microorganisms by the high salt and strong ultraviolet environment in the desert, maintain the activity of degrading bacteria, and achieve basic degradation functions.

[0081] Example 3: Nano-SiO2 / cellulose enhances the porosity of the microcapsule wall material, promotes the contact area between microorganisms and the water retention network, accelerates the release of microorganisms, and increases the degradation rate.

[0082] Example 4: The polydopamine coating regulates the degradation rhythm through the "barrier first, then degradation" mechanism, delaying the invasion of microorganisms in the early stage, and then gradually decomposing the coating to expose the degradation sites in the later stage, achieving gradient degradation.

[0083] Example 5: PEG-grafted polydopamine coating improves microbial attachment efficiency, promotes the contact between microbial enzymes and the water retention network, and enhances the synergistic degradation efficiency.

[0084] Example 6: TiO2 photocatalytically produces hydroxyl radicals that destroy the chemical bonds of the water-retaining network, forming a "photo-biological" synergistic effect with microbial degradation. At the same time, the anti-ultraviolet properties of TiO2 extend the service life of the material and accelerate degradation.

[0085] Comparative Example 1: No MOFs adsorbed soil salt. High salinity and alkalinity inhibited microbial activity, resulting in ineffective reproduction of degrading bacteria. The degradation rate was significantly lower than that of the example.

[0086] Comparative Example 2: Microorganisms were directly exposed to the desert environment, where ultraviolet rays and high salinity caused the number of viable bacteria to decrease significantly, resulting in a lack of sustained degradation ability and low degradation efficiency.

[0087] 3. Tree growth indicators (test results are shown in Table 3) Test plants: Haloxylon ammodendron (seedlings 6 months old, plant height 33-37 cm).

[0088] Simulated desert environment: artificial climate chamber temperature 25-40°C (15°C difference between day and night), humidity 20±5%, light intensity 12h / day (UV intensity 50mW / cm²); soil matrix is ​​native sandy loam of the Taklimakan Desert (moisture content 2.3%, pH 8.5, salt content 0.6%).

[0089] Planting method: 30 plants were planted in each group. The water retaining agent and soil were mixed at a mass ratio of 1:50. Water was applied at 50 mL / plant per week for the first 30 days, and then once every two weeks.

[0090] Measurement indicators: Survival rate, plant height, main root length and number of lateral roots were counted 120 days after planting.

[0091] Table 3: Table 3 shows that the survival rate, plant height, main root length and lateral root number of Examples 1, 3, 5 and 6 are significantly higher than those of Comparative Examples 1-2 and the blank control, indicating that the water retaining agent can effectively improve soil moisture conditions and promote tree growth.

[0092] The specific analysis is as follows: Example 1: The basic water retention network maintains water supply around the root system and promotes the development of the root system and the growth of the above-ground parts of Haloxylon ammodendron.

[0093] Example 3: The nanomaterials released by the microcapsules improve the soil aggregate structure, create a favorable environment for root growth by increasing porosity and permeability, and promote the extension of main roots and germination of lateral roots.

[0094] Example 5: PEG grafting regulates the water release cycle to match the transpiration rhythm of trees, accelerating water release during high temperatures during the day to meet transpiration needs, and slowing water release during low temperatures at night to reduce water loss.

[0095] Example 6: TiO2 photocatalytically degrades soil pollutants, PEG provides long-term water release, and PDA regulates salinity and alkalinity, significantly improving tree survival rate and growth.

[0096] Comparative Example 1: The salt adsorption function of MOFs is missing, and the high salinity and alkalinity of the soil inhibits the root system from absorbing water and nutrients, resulting in the stunted growth of trees.

[0097] Comparative Example 2: The microorganisms were not embedded, resulting in attenuation of their activity, making it impossible to improve the soil organic matter content through metabolic activities, and the trees lacked a good rhizosphere ecological environment.

Claims

1. A biomass-based degradable afforestation water-retaining agent, characterized in that: Its raw materials include the following components by weight: 40-60 parts of plant starch, 30-40 parts of alkali-modified cellulose, 3-8 parts of microencapsulated composite microbial degradation agent, 2-5 parts of poly (N-isopropylacrylamide), 2-5 parts of sodium polyacrylate-acrylamide copolymer, 1-3 parts of saline-alkali buffer, 2-5 parts of MOFs-sodium alginate, 1-3 parts of photosensitizer, 1-3 parts of cross-linking agent, and 0.5-1.5 parts of initiator; The wall material of the microcapsule is sodium alginate-chitosan.

2. A biomass-based degradable afforestation water-retaining agent according to claim 1, characterized in that: Its raw materials include the following components by weight: 42-55 parts of plant starch, 32-38 parts of alkali-modified cellulose, 4-8 parts of microencapsulated composite microbial degradation agent, 2-4 parts of poly (N-isopropylacrylamide), 2-4 parts of sodium polyacrylate-acrylamide copolymer, 2-2.5 parts of saline-alkali buffer, 3-4.5 parts of MOFs-sodium alginate, 1-2.5 parts of photosensitizer, 1-2.5 parts of cross-linking agent, and 0.5-1.2 parts of initiator; The wall material of the microcapsule is sodium alginate-chitosan.

3. A biomass-based degradable afforestation water-retaining agent and a preparation method thereof according to claim 1, characterized in that: In the MOFs-sodium alginate, the MOFs organic ligand is sodium lignin sulfonate, and the metal salt is magnesium chloride or calcium chloride.

4. A biomass-based degradable afforestation water-retaining agent and a preparation method thereof according to claim 3, characterized in that: A polydopamine layer is coated on the surface of the MOFs-sodium alginate composite material.

5. A biomass-based degradable afforestation water-retaining agent and a preparation method thereof according to claim 4, characterized in that: Nano-titanium dioxide is introduced into the polydopamine layer.

6. A biomass-based degradable afforestation water-retaining agent and a preparation method thereof according to claim 5, characterized in that: The surface of the polydopamine layer into which nano-titanium dioxide is introduced is grafted with PEG.

7. The biomass-based degradable afforestation water-retaining agent and its preparation method according to claim 1, characterized in that: Nano cellulose and nano silicon dioxide are introduced into the microcapsule wall material.

8. The method for preparing the biomass-based degradable afforestation water-retaining agent according to any one of claims 1 to 7, characterized in that: Plant starch, alkali-modified cellulose and MOFs-sodium alginate are added to deionized water, and after thorough stirring, a cross-linking agent, an initiator, a saline-alkali buffer and a photosensitizer are added in sequence. Poly (N-isopropylacrylamide) and sodium polyacrylate-acrylamide copolymer are fully dispersed and added. After stirring evenly, a photopolymerization reaction is carried out under ultraviolet light. Subsequently, a microcapsulated composite microbial degradation agent is added, and the mixture is thoroughly mixed and dried to obtain a biomass-based degradable afforestation water-retaining agent.

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