All straw components-based hydrogel synthesized by visible light-driven method, and preparation method and use thereof in agriculture

Abstract

An all straw components-based hydrogel synthesized by visible light-driven method, and a preparation method and use thereof in agriculture are provided, belonging to the technical field of materials.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of materials, and in particular relates to an all straw components-based hydrogel synthesized by visible light-driven method, and a preparation method and use thereof in agriculture. BACKGROUND

[0002] The use of fertilizers and pesticides is beneficial in increasing agricultural product output and plays an important role in solving the problem of increasing food demand year by year. However, excessive use of the fertilizers and pesticides has caused serious environmental pollution and posed a serious threat to human health. Studies have shown that excessive use of the fertilizers on farmland can not only increase soil alkalinity and salinity, but also cause excessive levels of nitrogen, phosphorus, and potassium in groundwater, leading to eutrophication of water bodies and phytoplankton bloom. Excessive use of the pesticides can kill beneficial microorganisms in the soil and seriously reduce soil quality. Moreover, the long-term accumulation of non-degradable components may damage the ecosystem and further affect human health. The reduced and controlled release of fertilizers and pesticides can reduce or avoid the above problems and promote the green development of agriculture. However, most of the controlled-release materials currently used are synthetic materials that are difficult to degrade in the soil, making it of great significance to use biodegradable agricultural straw to prepare slow-release fertilizers. China has a large production of agricultural straw. As a renewable biological resource with multiple uses, agricultural straw that mainly composed of natural polymers, such as cellulose, hemicellulose and lignin, can be applied to agricultural production with high added value, promoting agricultural development and protecting the environment.

[0003] Among the remediation materials for soil pollution, natural polymer materials have the advantages of low cost, desirable treatment effect, and no secondary pollution, and are recognized as the most promising materials (Hassanisaadi M, Riseh R S, Rabiei A, et al. Nano / micro-cellulose-based materials as remarkable sorbents for the remediation of agricultural resources from chemical pollutants [J]. International Journal of Biological Macromolecules, 2023, 246: 18.). Natural polymer-based hydrogels combine the unique three-dimensional network structure advantages of hydrogels with the abundant sources, biodegradability, and renewability of natural polymers, and have shown excellent results in the remediation of water resources and soil pollution. However, the cellulose-based hydrogels, lignin-based hydrogels, and hemicellulose-based hydrogels currently being studied are all prepared using a single biomass component, and generally have defects such as high cost, low utilization rate, and serious pollution during the preparation process (Shan S, Sun X-F, Xie Y, Li W, Ji T. High-performance hydrogel adsorbent based on cellulose, hemicellulose, and lignin for copper (II) ion removal [J]. Polymers, 2021, 13(18):3063.). It is also worth noting that when preparing hydrogels with a traditional free radical initiation system, toxic reagents such as ammonium persulfate and potassium persulfate are always used as free radical initiators, while the reaction is difficult to control. In addition, the performance of the prepared hydrogels is poor, which limits the agricultural application of hydrogels.

[0004] In view of the problems such as high cost, low utilization rate, and pollution during the preparation process of the existing single straw component-based hydrogels, especially the problem of toxic hazards of the traditional free radical initiators and the poor performance of the hydrogels, which limit the application of hydrogels, it is urgent to develop a novel all straw components-based hydrogel that is pollution-free and economical. At the same time, an environmentally friendly and high-performance synthesis method of the all straw components-based hydrogel is developed by using non-toxic initiators to improve the preparation method and hydrogel performance, so as to achieve soil pollution remediation and slow release of fertilizers and pesticides, and then improve agricultural production efficiency and economic benefits. SUMMARY

[0005] In order to overcome the above shortcomings of the prior art, the present disclosure is to provide an all straw components-based hydrogel synthesized by visible light-driven method, and a preparation method and use thereof in agriculture to solve the problems of high cost, low utilization rate, and serious pollution of existing single straw component-based hydrogels, as well as the high toxicity and difficult reaction control of traditional preparation methods by free radical initiation, resulting in limited the application of the hydrogels.

[0006] To achieve the above objects, the present disclosure adopts the following technical solutions:

[0007] The present disclosure provides a method for preparing an all straw components-based hydrogel synthesized by visible light-driven method, including:

[0008] 1) adding a straw powder to deionized water, subjecting a resulting mixture to homogeneous dispersion, adding mpg-CsN4 thereto, subjecting a resulting material to ultrasonic treatment, then adding a hydrogen peroxide solution thereto, and then stirring a resulting solution in a water bath under irradiation of a xenon lamp to obtain an aqueous solution containing all straw components ; and

[0009] 2) adding glycerol, a monomer acrylic acid (AA), acrylamide (AM), and A,M-methylenebisacrylamide (MBA) to the aqueous solution containing all straw components obtained in step 1), subjecting a resulting mixed material to homogenization, then irradiating with the xenon lamp to form a hydrogel, and then subjecting the hydrogel to immersion and freeze-drying to obtain the all straw components-based hydrogel synthesized by visible light-driven method.

[0010] In some embodiments, in step 1), a mass ratio of the straw powder to the mpg-CsN4 is in a range of 1: (0.1-0.4), a volume ratio of the deionized water to the hydrogen peroxide solution is in a range of 1: (0.01-0.2), and the hydrogen peroxide solution has a mass percentage of 30%.

[0011] In some embodiments, in step 1), the homogeneous dispersion is conducted for 10 min to 30 min, and the ultrasonic treatment is conducted for 30 min to 60 min.

[0012] In some embodiments, in step 1), the xenon lamp has a power of 150 W to 300 W, and the stirring in the water bath is conducted for 24 h to 30 h.

[0013] In some embodiments, in step 2), a dosage ratio of the aqueous solution containing all straw components, the glycerol, the AA, the AM, and the MBA is in a range of 10 mL: (1-10) mL: (0.1-0.9) g: (0.1-0.9) g: 0.01 g.

[0014] In some embodiments, in step 2), the xenon lamp has a power of 150 W to 300 W, and the irradiating with the xenon lamp is conducted for 4 h to 8 h.

[0015] In some embodiments, in step 2), the immersion is conducted in distilled water for 48 h to 72 h, and the freeze-drying is conducted for 24 h to 36 h.

[0016] The present disclosure further provides an all straw components-based hydrogel synthesized by visible light-driven method prepared by the above method, where the all straw components-based hydrogel synthesized by visible light-driven method is in a porous structure, the porous structure is internally provided with interconnected porous channels, and a plurality of blocky layer-shaped mpg-CsN4 and long rod-shaped short fibers are distributed on an inner wall of each of the porous channels.

[0017] The present disclosure further provides use of the all straw components-based hydrogel synthesized by visible light-driven method prepared by the above method in water holding and water retention in soil.

[0018] The present disclosure further provides use of the all straw components-based hydrogel synthesized by visible light-driven method prepared by the above method in adsorption of nitrogen, phosphorus, and a pesticide and slow release of the nitrogen, the phosphorus, and the pesticide.

[0019] Compared with the prior art, the present disclosure has the following beneficial effects:

[0020] The present disclosure provides a method for preparing an all straw components-based hydrogel synthesized by visible light-driven method. The method includes: adding a straw powder to deionized water, subjecting a resulting mixture to homogeneous dispersion of the straw powder, adding mpg-CsN4 thereto as a photoinitiator, conducting ultrasonic treatment, then adding a hydrogen peroxide solution thereto, and stirring in a water bath under irradiation of a xenon lamp to obtain an aqueous solution containing all straw components; and adding glycerol, MBA, AA, and AM in sequence to the aqueous solution containing all straw components, subjecting a resulting mixed material to homogenization, irradiating with the xenon lamp to form a hydrogel, and then subjecting the hydrogel to immersion and freeze-drying in sequence to obtain the all straw components-based hydrogel synthesized by visible light-driven method. The preparation process of the all straw components-based hydrogel synthesized by visible light-driven method mainly includes the following three stages: the first is a visible light-driven decomposition stage of the straw cell wall, which is conducted by: under illumination conditions, when the illumination energy is greater than the band gap of mpg-CrNr, the electron-hole pairs generated by mpg-CsN4 react with dissolved oxygen and water molecules in the aqueous solution to produce a large number of active free radicals such as • O: and • OH, which further trigger the decomposition of hydrogen peroxide to produce new and more free radicals, such as HOO . These free radicals decompose the straw cell wall into cellulose, hemicellulose, and lignin to form an aqueous solution containing all straw components. The second is a chain initiation and chain growth stage. Under continued illumination conditions, the active free radicals continuously generated by mpg-CsN4 capture the hydrogen atoms of the hydroxyl groups in cellulose, hemicellulose, and lignin in the aqueous solution containing all straw components to produce corresponding alkoxy free radicals. These alkoxy free radicals and OH may attack the double bonds of AA and AM, causing the double bonds to open and undergo addition reactions, thereby forming a polymer main chain and completing chain growth. While the chain is growing, a cross-linking agent MBA and glycerol also participate in the polymerization to form a three-dimensional network structure of the hydrogel. Meanwhile, mpg-CsN4 and cellulose in the solution can be doped into the three-dimensional network skeleton of the hydrogel through hydrogen bonding and other effects, thereby increasing the cross-linking density of the hydrogel. The final stage 3 is a chain termination stage. As the reaction proceeds, the monomer content decreases until the reaction ends. The all straw components-based hydrogel synthesized by visible light-driven method adopts the straw powder as the raw material and the mpg-CiN4 as the photoinitiator. By using the all straw components as a raw material, agricultural waste is fully utilized and resource recycling is achieved; moreover, the visible light-driven synthesis does not require high temperature or high pressure, reduces energy consumption and environmental pollution, and is in line with the development trend of green chemistry. Changing the content of each component in the all straw components-based hydrogel synthesized by visible light-driven method results in significant changes in its performance. The AA and AM contents decrease, the pores of the all straw components-based hydrogel synthesized by visible light-driven method become larger, and the swelling performance improves, which is beneficial for improving the water holding and water retention capacity of the soil and the adsorption of pesticides. The AA and AM contents increase, the carboxylic acid group and amide group increase, and the adsorption of N and P is effectively improved. The cross-linking density increases, the pores become more, and the specific surface area of all straw components-based hydrogel synthesized by visible light-driven method increases, which is beneficial for the all straw components-based hydrogel synthesized by visible light-driven method to load pesticides and fertilizers, so that the release rates of nitrogen fertilizer, phosphate fertilizer and pesticides are significantly reduced. The preparation method has the advantages of simple process and easy control of conditions. The all straw components-based hydrogel synthesized by visible light-driven method is prepared directly from straw powder by visible light-driven method, that is, it is prepared by free radical polymerization initiated by visible light in a one-pot manner. The water retention performance and fertilizer adsorption capacity of this all straw components-based hydrogel synthesized by visible light-driven method change significantly with the change of the content of each component. Through reasonable regulation, there are desirable water holding capacity and water retention capacity, stronger adsorption performance, and the release rate of fertilizers and pesticides can be effectively controlled, thereby improving the utilization rate of fertilizers and pesticides and reducing their pollution. The present disclosure solves the problems of high cost, low utilization rate, and serious pollution during the preparation process of polymer-based hydrogels prepared from existing single natural macromolecular component, as well as the poor performance of the hydrogel, which limits the application of straw hydrogels.

[0021] Further, a mass ratio of the straw powder to the mpg-CsN4 is in a range of 1: (0.1-0.4), a volume ratio of the deionized water to the hydrogen peroxide solution is in a range of 1: (0.01-0.2), and preferably, a volume ratio of the deionized water to the hydrogen peroxide solution is in a range of 1: (0.05-0.2) to ensure the separation of the straw biomass components, such that the aqueous solution containing all straw components is successfully prepared.

[0022] Further, the homogeneous dispersion is conducted for 10 min to 30 min, such that the straw powder is fully mixed and dispersed, the production efficiency is improved under the premise of ensuring the quality, and the energy consumption and time cost of production are reduced. The ultrasonic treatment is conducted for 30 min to 60 min, which can effectively improve the microstructure of the material, reduce the particle size, increase the specific surface area, remove impurities and air bubbles, and improve the purity of the product.

[0023] Further, the xenon lamp has a power of 150 W to 300 W, which can provide stable and moderate light intensity, improve the accuracy of the experiment, achieve efficient energy conversion, reduce energy consumption, and meet the requirements of energy retention and environmental protection. The stirring in the water bath is conducted for 24 h to 30 h to ensure that the reactants are fully mixed and reacted in the water bath, which can improve the uniformity of reaction system. The temperature of reaction system is kept stable by controlling the temperature of water bath, which helps to improve the reaction efficiency and product quality.

[0024] Further, a dosage ratio of the aqueous solution containing all straw components, the glycerol, the AA, the AM, and the MBA is in a range of 10 mL: (1-10) mL: (0.1-0.9) g: (0.1-0.9) g: 0.01 g; the dosage of each component is adjusted to ensure the successful preparation of the all straw components-based hydrogel synthesized by visible light-driven method.

[0025] Further, the xenon lamp has a power of 150 W to 300 W, the irradiating with the xenon lamp is conducted for 4 h to 8 h to ensure that the reaction system is sufficiently exposed to light, avoiding changes in sample properties or excessive reactions caused by excessive light exposure, thereby reducing unnecessary energy consumption and time costs.

[0026] Furthermore, the immersion is conducted in distilled water for 48 h to 72 h; the distilled water immersion can ensure that the hydrogel fully absorbs water and helps to remove impurities, pollutants, or residues on the surface of the hydrogel. Through immersion, these impure substances can be dissolved or washed away, thereby improving the purity of the hydrogel. The freeze-drying is conducted for 24 h to 36 h. Compared with the traditional drying method, the method of removing water from the hydrogel by freeze-drying and sublimation can better maintain the original structure and morphology of the hydrogel. Through freeze-drying, the water in the hydrogel is completely removed, thereby avoiding chemical reactions or degradation that may be caused by the presence of water, making the hydrogel have more stability and longer shelf life.

[0027] The present disclosure provides an all straw components-based hydrogel synthesized by visible light-driven method prepared by the above method, where the all straw components-based hydrogel synthesized by visible light-driven method presents a porous structure with interconnected porous channels inside. This structure provides a convenient channel for molecule transfer, increases the surface area, and helps the all straw components-based hydrogel synthesized by visible light-driven method to efficiently exchange and react with the external environment; a large number of blocky layer-shaped mpg-CsN4 and long rod-shaped short fibers are distributed on an inner wall of each of the porous channel. The mpg-CsN4 is an excellent photocatalyst that can promote the decomposition of straw and the preparation of the all straw components-based hydrogel synthesized by visible light-driven method under the drive of visible light; the long rod-shaped short fibers enhance the mechanical properties of the hydrogel and improve its tensile strength and toughness. This makes the hydrogel more stable and durable when being subjected to external forces or deformation.

[0028] The present disclosure further provides use of the all straw components-based hydrogel synthesized by visible light-driven method prepared by the above method in water holding and water retention in soil, where the swelling properties of the all straw components-based hydrogel synthesized by visible light-driven method mainly depend on the osmotic pressure, the affinity of water and polymer, and the cross-linking density of the network. The all straw components-based hydrogel synthesized by visible light-driven method has the largest content of wheat straw components, and the hydrophilic groups mainly come from cellulose, hemicellulose, and lignin in wheat straw. With the increases of AA and AM contents, the carboxylic acid group and amide group increase, and the carbon-carbon double bond is very easy to polymerize under photoinitiation conditions, which 5 participates in the synthesis of the network skeleton of the all straw components-based hydrogel synthesized by visible light-driven method, increases the cross-linking density of the all straw components-based hydrogel synthesized by visible light-driven method and reduces the swelling rate. When the AA and AM contents are 0.1 g, the maximum swelling rates of the all straw components-based hydrogel synthesized by visible light-driven method can reach 6044.86% and 4676.86%, respectively; when the contents of the all straw components-based hydrogel synthesized by visible light-driven method in the soil are 0% and 3%, the maximum water holding rates of the soil are 68.62% and 228.51%, respectively, and the water retention capacities of the soil are 16.3% and 48.8%, respectively.

[0029] Compared with the soil without the addition of the all straw components-based hydrogel synthesized by visible light-driven method, the water content of the soil with the addition of the all straw components-based hydrogel synthesized by visible light-driven method is significantly increased. With the increase in the content of the all straw components-based hydrogel synthesized by visible light-driven method, the water retention capacity of the soil is gradually enhanced, which can effectively reduce the evaporation of water in the soil and reduce the evaporation rate of water in agriculture. This is of potential application value in soil remediation and the development of agriculture in arid areas.

[0030] The present disclosure further provides use of the all straw components-based hydrogel synthesized by visible light-driven method prepared by the above method in adsorption of nitrogen, phosphorus, and a pesticide and slow release of the nitrogen, the phosphorus, and the pesticide. When adsorbing nitrogen, phosphorus, and the pesticide thiophanate methyl (TM) in water and slowly releasing N, P and pesticide in soil, the AM content affects the adsorption of P by the all straw components-based hydrogel synthesized by visible light-driven method, and the AA content affects the adsorption of N by the all straw components-based hydrogel synthesized by visible light-driven method. As the content of AM or AA increases, the adsorption of P and N by the all straw components-based hydrogel synthesized by visible light-driven method gradually increases. When the AA content is 0.9 g, the adsorption rate of N reaches a maximum of 31.93%; when the AM content is 0.9 g, the adsorption rate of P reaches a maximum of 29.48%. The main influencing factor for the adsorption of fungicide TM is the swelling properties of the all straw components-based hydrogel synthesized by visible light-driven method. The better the swelling properties of the all straw components-based hydrogel synthesized by visible light-driven method, the better the adsorption performance of the straw hydrogel for TM. In terms of slow release of fertilizers and pesticides, compared with untreated nitrogen fertilizers, phosphate fertilizers, and pesticides, slow-release fertilizers of the all straw components-based hydrogel synthesized by visible light-driven method loaded with nitrogen fertilizers, phosphate fertilizers, and pesticides, using the all straw components-based hydrogel synthesized by visible light-driven method as a carrier, show slow release in the soil, and the release rate is significantly reduced. In agricultural applications, the hydrogel can effectively improve the fertilizer utilization efficiency and extend the fertilizer application period. This has potential application value in improving a series of environmental problems caused by conventional water-soluble fertilizers. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 shows a schematic diagram of the preparation process of the all straw components-based hydrogel synthesized by visible light-driven method provided in the present disclosure.

[0032] FIG. 2 shows X-ray diffraction (XRD) patterns of various materials provided in Example 1 of the present disclosure, where (a) shows an XRD pattern of mpg-CsN^ and (b) shows an XRD pattern of the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 1.

[0033] FIG. 3-1 shows an X-ray photoelectron spectroscopy (XPS) pattern of the mpg-C3N4, where (a) shows a full XPS spectrum; (b) shows a spectrum of Cis; (c) shows a spectrum of Nls; and (d) shows a spectrum of Ols.

[0034] FIG. 3-2 shows an XPS pattern of the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 1, where (a) shows a full XPS spectrum; (b) shows a spectrum of Cis; (c) shows a spectrum of Nls; and (d) shows a spectrum of Ols.

[0035] FIG. 4 shows scanning electron microscopy (SEM) images of various materials provided in various examples of the present disclosure, where (a) shows the mpg-CsN^ (b) shows an SEM magnified image of the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 4; (c) shows the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 1; (d) shows the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 2; (e) shows the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 3; and (f) shows the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 4.

[0036] FIG. 5 shows Fourier transform infrared spectroscopy (FT-IR) graphs of various materials provided in various examples of the present disclosure, where (a) shows the mpg-CiNu (b) shows the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 5; (c) shows the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 1; and (d) shows the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 4.

[0037] FIG. 6 is a graph showing the effect of AM and AA contents on the swelling properties of the all straw components-based hydrogel synthesized by visible light-driven method, where (a) shows the effect of AM content on the swelling properties of the all straw components-based hydrogel synthesized by visible light-driven method; and (b) shows the effect of AA content on the swelling properties of the all straw components-based hydrogel synthesized by visible light-driven method.

[0038] FIG. 7 is a graph showing the maximum water holding rate and soil water retention rate of the all straw components-based hydrogel synthesized by visible light-driven method provided in Example 1 of the present disclosure at different contents, where (a) shows the maximum water holding rate of the soil at different contents of the all straw components-based hydrogel synthesized by visible light-driven method; and (b) shows the water retention rate of the soil at different contents of the all straw components-based hydrogel synthesized by visible light-driven method.

[0039] FIG. 8-1 is a graph showing the effect of AM and AA contents on the adsorption of N in water by the all straw components-based hydrogel synthesized by visible light-driven method.

[0040] FIG. 8-2 is a graph showing the effect of AM and AA contents on the adsorption of P in water by the all straw components-based hydrogel synthesized by visible light-driven method.

[0041] FIG. 8-3 is a graph showing the effect of AM and AA contents on the adsorption of TM in water by the all straw components-based hydrogel synthesized by visible light-driven method.

[0042] FIG. 9 is a graph showing the changes in the release rate of direct application of fertilizers and the all straw components-based hydrogel fertilizers in the soil, where (a) shows the change in the release of NH4CI and NTWS-AA-Example 3 in the soil over time; (b) shows the change in the release of KH2PO4 and PTWS-AM-Example 4 in the soil over time; and (c) shows the change in the release of TM and TM-Example 1 in the soil over time. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] To make persons skilled in the art better understand the present disclosure, the following clearly and completely describes the technical solutions in the embodiments of the present disclosure with reference to the accompanying drawings in the embodiments of the present disclosure. Apparently, the described embodiments are merely some rather than all of the embodiments of the present disclosure. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts shall fall within the scope of protection of the present disclosure.

[0044] It should be noted that terms such as "first" and "second" in the specification, claims, and drawings of the present disclosure are intended to distinguish between similar objects but do not necessarily indicate a specific order or sequence. It should be understood that the objects used in such a way may be interchanged under appropriate conditions to make it possible to implement the described embodiments of the present disclosure in other sequences apart from those illustrated or described herein. Moreover, the terms "include", "comprise", and any other variants mean to cover the non-exclusive inclusion, for example, a process, method, system, product, or apparatus including a list of steps or units is not necessarily limited to those steps or units which are clearly listed, but may include other steps or units which are not explicitly listed or which are inherent in such process, method, system, product, or apparatus. The experimental methods described in the following examples are conventional methods unless otherwise specified; and the reagents and materials can be obtained from commercial sources unless otherwise specified.

[0045] The present disclosure will be further described in detail below with reference to the drawings.

[0046] In the present disclosure, wheat straw is used as a raw material, mesoporous graphite-phase carbon nitride is used as a photoinitiator, and an all straw components-based hydrogel is prepared by visible light-driven method. The hydrogel presents a porous structure with interconnected porous channels inside, and a large number of blocky layer-shaped mpg-CsN4 and long rod-shaped short fibers are distributed on an inner wall of each of the porous channels. This all straw components-based hydrogel synthesized by visible light-driven method can significantly improve the water retention capacity of the soil, effectively adsorb N, P, and TM in the water, and slowly release N, P, and TM in the soil. The hydrogel also has the function of repairing water resources and soil pollution and has a positive impact on the development of green agriculture.

[0047] The present disclosure further provides an all straw components-based hydrogel synthesized by visible light-driven method, where the all straw components-based hydrogel is in a three-dimensional network porous structure, the porous structure is internally provided with interconnected porous channels, and a plurality of blocky layer-shaped mpg-CsN4 and long rod-shaped short fibers are distributed on an inner wall of each of the porous channels.

[0048] The present disclosure further provides a method for preparing the all straw components-based hydrogel synthesized by visible light-driven method as described above, including the following steps:

[0049] 1) adding a straw powder to deionized water, subjecting a resulting mixture to homogeneous dispersion, adding mpg-CsN4 thereto, then subjecting a resulting material to ultrasonic treatment, then adding a hydrogen peroxide solution thereto, and then irradiating a resulting solution with a xenon lamp and stirring to obtain an aqueous solution containing all straw components under a water bath condition; and

[0050] 2) adding glycerol, AA, AM, and MBA to the aqueous solution containing all straw components obtained in step 1), subjecting a resulting mixed material to homogenization, then irradiating with the xenon lamp to form a hydrogel, cutting the hydrogel into blocks, and then subjecting a cut hydrogel to immersion and freeze-drying in sequence to obtain the all straw components-based hydrogel synthesized by visible light-driven method.

[0051] In step 1),

[0052] a mass ratio of the straw powder to the mpg-CsN4 is in a range of 1: (0.1-0.4);

[0053] the straw powder is prepared by a process including: crushing a wheat straw with a cell crusher, passing through a 200-mesh sieve to obtain the straw powder;

[0054] the mpg-CsN4 is prepared by a process including: weighing 30 g of urea into a crucible with a lid, completely wrapping the crucible with a tin foil and placing in a muffle furnace, heating to a temperature of 600°C to 650°C at a heating rate of 10°C / min to 20°C / min and then holding at the temperature for 4 h to 6 h, cooling to a room temperature, and grinding to obtain the mpg-Cs^;

[0055] the homogeneous dispersion is conducted for 10 min to 30 min, and the ultrasonic treatment is conducted for 30 min to 60 min;

[0056] a volume ratio of the deionized water to the hydrogen peroxide solution is in a range of 1: (0.05-0.2);

[0057] in some embodiments, a volume ratio of the deionized water to the hydrogen peroxide solution is in a range of 1: (0.01-0.2);

[0058] the hydrogen peroxide solution has a mass percentage of 30%; and

[0059] the xenon lamp has a power of 150 W to 300 W, and the stirring in the water bath is conducted for 24 h to 30 h.

[0060] In step 2),

[0061] a dosage ratio of the aqueous solution containing all straw components, the glycerol, the AA, the AM, and the MBA is in a range of 10 mL: (1-10) mL: (0.1-0.9) g: (0.1-0.9) g: 0.01 g;

[0062] AA represents monomer acrylic acid, AM represents acrylamide, MBA represents A,M-methylenebisacrylamide, and TM represents pesticide thiophanate-methyl;

[0063] the xenon lamp has a power of 150 W to 300 W, and the irradiating with the xenon lamp is conducted for 4 h to 8 h;

[0064] the immersion is conducted in distilled water for 48 h to 72 h, and the freeze-drying is conducted for 24 h to 36 h.

[0065] The present disclosure further provides use of the all straw components-based hydrogel synthesized by visible light-driven method prepared by the above method in water holding and water retention in soil.

[0066] The present disclosure further provides use of the all straw components-based hydrogel synthesized by visible light-driven method prepared by the above method in adsorption of nitrogen, phosphorus, and a pesticide and slow release of the nitrogen, the phosphorus, and the pesticide.

[0067] FIG. 1 shows a schematic diagram of the preparation process of the all straw components-based hydrogel synthesized by visible light-driven method provided in the present disclosure. As shown in the figure, the preparation process of the all straw components-based hydrogel synthesized by visible light-driven method mainly includes the following three stages: First, the visible light-driven decomposition of the straw cell wall stage, which is conducted by: under illumination conditions, when the illumination energy is greater than the band gap of mpg-C3N4, the electron-hole pairs generated by mpg-CsN4 react with dissolved oxygen and water molecules in the aqueous solution to produce a large number of active free radicals such as CL and OH, which further trigger the decomposition of hydrogen peroxide to produce new and more free radicals, such as HOO . These free radicals decompose the straw cell wall into cellulose, hemicellulose, and lignin to form an aqueous solution containing all straw components. The second is chain initiation and chain growth stage. Under continued illumination conditions, the active free radicals continuously generated by mpg-CsN4 capture the hydrogen atoms of the hydroxyl groups in cellulose, hemicellulose, and lignin in the aqueous solution containing all straw components to produce corresponding alkoxy free radicals. These alkoxy free radicals and OH may attack the double bonds of AA and AM, causing the double bonds to open and undergo addition reactions, thereby forming a polymer main chain and completing chain growth. While the chain is growing, a cross-linking agent MBA and glycerol also participate in the polymerization to form a three-dimensional network structure of the all straw components-based hydrogel synthesized by visible light-driven method. Meanwhile, mpg-CsN4 and cellulose in the solution can be doped into the three-dimensional network skeleton of the all straw components-based hydrogel synthesized by visible light-driven method through hydrogen bonding and other effects, thereby increasing the cross-linking density of the all straw components-based hydrogel synthesized by visible light-driven method. The final stage is the chain termination stage. As the reaction proceeds, the monomer content decreases until the reaction ends. The whole preparation method involves simple processes and easily controllable conditions.

[0068] Example 1

[0069] An all straw components-based hydrogel synthesized by visible light-driven method was prepared by the following steps:

[0070] Step 1. 1 g of a straw powder was weighed and added to 50 mL of deionized water. A resulting mixture was subjected to homogeneous for 20 min, and then 0.1 g of mpg-CsN4 was added thereto. A resulting material was subjected to ultrasonic treatment for 50 min, and then 6 mL of a hydrogen peroxide solution (30 wt%) was added thereto. A resulting solution was irradiated with a xenon lamp at 300 W and stirred, and reacted under a water bath condition for 30 h to obtain an aqueous solution containing all straw components.

[0071] Step 2. 10 mL of the aqueous solution containing all straw components was taken, and 1 mL of glycerol, 0.5 g of AM, 0.5 g of AA, and 10 mg of MBA were added thereto. A resulting material was subjected to homogenization, and then irradiated with the xenon lamp at 300 W for 4 h to form a hydrogel. The hydrogel was taken out and cut into evenly sized blocks, immersed in distilled water for 48 h, and dried in a freeze-dryer for 24 h to obtain the all straw components-based hydrogel synthesized by visible light-driven method.

[0072] Example 2

[0073] An all straw components-based hydrogel synthesized by visible light-driven method was prepared by the following steps:

[0074] Step 1. 1 g of a straw powder was weighed and added to 50 mL of deionized water. A resulting mixture was subjected to homogeneous for 10 min, and then 0.2 g of mpg-CsN4 was added thereto. A resulting material was subjected to ultrasonic treatment for 30 min, and then 6 mL of a hydrogen peroxide solution (30 wt%) was added thereto. A resulting solution was irradiated with a xenon lamp at 300 W and stirred, and reacted under a water bath condition for 24 h to obtain an aqueous solution containing all straw components.

[0075] Step 2. 10 mL of the aqueous solution containing all straw components was taken, and 2 mL of glycerol, 0.5 g of AM, 0.1 g of AA, and 10 mg of MBA were added thereto. A resulting material was subjected to homogenization, and then irradiated with the xenon lamp at 300 W for 4 h to form a hydrogel. The hydrogel was taken out and cut into evenly sized blocks, immersed in distilled water for 48 h, and dried in a freeze-dryer for 24 h to obtain the all straw components-based hydrogel synthesized by visible light-driven method.

[0076] Example 3

[0077] An all straw components-based hydrogel synthesized by visible light-driven method was prepared by the following steps:

[0078] Step 1. 1 g of a straw powder was weighed and added to 50 mL of deionized water. A resulting mixture was subjected to homogeneous for 30 min, and then 0.3 g of mpg-CsN4 was added thereto. A resulting material was subjected to ultrasonic treatment for 60 min, and then 6 mL of a hydrogen peroxide solution (30 wt%) was added thereto. A resulting solution was irradiated with a xenon lamp at 150 W and stirred, and reacted under a water bath condition for 30 h to obtain an aqueous solution containing all straw components.

[0079] Step 2. 10 mL of the aqueous solution containing all straw components was taken, and 3 mL of glycerol, 0.5 g of AM, 0.9 g of AA, and 10 mg of MBA were added thereto. A resulting material was subjected to homogenization, and then irradiated with the xenon lamp at 150 W for 6 h to form a hydrogel. The hydrogel was taken out and cut into evenly sized blocks, immersed in distilled water for 60 h, and dried in a freeze-dryer for 30 h to obtain the all straw components-based hydrogel synthesized by visible light-driven method.

[0080] Example 4

[0081] An all straw components-based hydrogel synthesized by visible light-driven method was prepared by the following steps:

[0082] Step 1. 1 g of a straw powder was weighed and added to 50 mL of deionized water. A resulting mixture was subjected to homogeneous for 30 min, and then 0.4 g of mpg-CsN4 was added thereto. A resulting material was subjected to ultrasonic treatment for 60 min, and then 6 mL of a hydrogen peroxide solution (30 wt%) was added thereto. A resulting solution was irradiated with a xenon lamp at 150 W and stirred, and reacted under a water bath condition for 30 h to obtain an aqueous solution containing all straw components.

[0083] Step 2. 10 mL of the aqueous solution containing all straw components was taken, and 5 mL of glycerol, 0.9 g of AM, 0.5 g of AA, and 10 mg of MBA were added thereto. A resulting material was subjected to homogenization, and then irradiated with the xenon lamp at 150 W for 6 h to form a hydrogel. The hydrogel was taken out and cut into evenly sized blocks, immersed in distilled water for 60 h, and dried in a freeze-dryer for 30 h to obtain the all straw full-components-based hydrogel synthesized by visible light-driven method.

[0084] Example 5

[0085] An all straw components-based hydrogel synthesized by visible light-driven method was prepared by the following steps:

[0086] Step 1.1 g of a straw powder was weighed and added to 50 mL of deionized water. A resulting mixture was subjected to homogeneous for 10 min, and then 0.1 g of mpg-CsN4 was added thereto. A resulting material was subjected to ultrasonic treatment for 30 min, and then 5 mL of a hydrogen peroxide solution (30 wt%) was added thereto. A resulting solution was irradiated with a xenon lamp at 300 W and stirred, and reacted under a water bath condition for 27 h to obtain an aqueous solution containing all straw components.

[0087] Step 2. 10 mL of the aqueous solution containing all straw components was taken, and 4 mL of glycerol, 0.1 g of AM, 0.5 g of AA, and 10 mg of MBA were added thereto. A resulting material was subjected to homogenization, and then irradiated with the xenon lamp at 300 W for 8 h to form a hydrogel. The hydrogel was taken out and cut into evenly sized blocks, immersed in distilled water for 72 h, and dried in a freeze-dryer for 33 h to obtain the all straw components-based hydrogel synthesized by visible light-driven method.

[0088] Example 6

[0089] An all straw components-based hydrogel synthesized by visible light-driven method was prepared by the following steps:

[0090] Step 1. 1 g of a straw powder was weighed and added to 50 mL of deionized water. A resulting mixture was subjected to homogeneous for 15 min, and then 0.3 g of mpg-CsN4 was added thereto. A resulting material was subjected to ultrasonic treatment for 50 min, and then 5 mL of a hydrogen peroxide solution (30 wt%) was added thereto. A resulting solution was irradiated with a xenon lamp at 150 W and stirred, and reacted under a water bath condition for 27 h to obtain an aqueous solution containing all straw components.

[0091] Step 2. 10 mL of the aqueous solution containing all straw components was taken, and 10 mL of glycerol, 0.3 g of AM, 0.5 g of AA, and 10 mg of MBA were added thereto. A resulting material was subjected to homogenization, and then irradiated with the xenon lamp at 150 W for 8 h to form a hydrogel. The hydrogel was taken out and cut into evenly sized blocks, immersed in distilled water for 72 h, and dried in a freeze-dryer for 33 h to obtain the all straw components-based hydrogel synthesized by visible light-driven method.

[0092] Example 7

[0093] An all straw components-based hydrogel synthesized by visible light-driven method was prepared by the following steps:

[0094] Step 1. 1 g of a straw powder was weighed and added to 50 mL of deionized water. A resulting mixture was subjected to homogeneous for 30 min, and then 0.3 g of mpg-CsN4 was added thereto. A resulting material was subjected to ultrasonic treatment for 60 min, and then 10 mL of a hydrogen peroxide solution (30 wt%) was added thereto. A resulting solution was irradiated with a xenon lamp at 150 W and stirred, and reacted under a water bath condition for 27 h to obtain an aqueous solution containing all straw components.

[0095] Step 2. 10 mL of the aqueous solution containing all straw components was taken, and 6 mL of glycerol, 0.5 g of AM, 0.7 g of AA, and 10 mg of MBA were added thereto. A resulting material was subjected to homogenization, and then irradiated with the xenon lamp at 150 W for 8 h to form a hydrogel. The hydrogel was taken out and cut into evenly sized blocks, immersed in distilled water for 72 h, and dried in a freeze-dryer for 36 h to obtain the all straw components-based hydrogel synthesized by visible light-driven method.

[0096] Example 8

[0097] An straw components-based hydrogel synthesized by visible light-driven method was prepared by the following steps:

[0098] Step 1.1 g of a straw powder was weighed and added to 50 mL of deionized water. A resulting mixture was subjected to homogeneous for 15 min, and then 0.3 g of mpg-CsN4 was added thereto. A resulting material was subjected to ultrasonic treatment for 50 min, and then 6 mL of a hydrogen peroxide solution (30 wt%) was added thereto. A resulting solution was irradiated with a xenon lamp at 150 W and stirred, and reacted under a water bath condition for 30 h to obtain an aqueous solution containing all straw components.

[0099] Step 2. 10 mL of the aqueous solution containing all straw components was taken, and 8 mL of glycerol, 0.5 g of AM, 0.3 g of AA, and 10 mg of MBA were added thereto. A resulting material was subjected to homogenization, and then irradiated with the xenon lamp at 150 W for 6 h to form a hydrogel. The hydrogel was taken out and cut into evenly sized blocks, immersed in distilled water for 60 h, and dried in a freeze-dryer for 36 h to obtain the all straw components-based hydrogel synthesized by visible light-driven method.

[0100] Example 9

[0101] An all straw components-based hydrogel synthesized by visible light-driven method was prepared by the following steps:

[0102] Step 1. 1 g of a straw powder was weighed and added to 50 mL of deionized water. A resulting mixture was subjected to homogeneous for 15 min, and then 0.2 g of mpg-CsN4 was added thereto. A resulting material was subjected to ultrasonic treatment for 50 min, and then 5 mL of a hydrogen peroxide solution (30 wt%) was added thereto. A resulting solution was irradiated with a xenon lamp at 150 W and stirred, and reacted under a water bath condition for 27 h to obtain an aqueous solution containing all straw components.

[0103] Step 2. 10 mL of the aqueous solution containing all straw components was taken, and 10 mL of glycerol, 0.3 g of AM, 0.5 g of AA, and 10 mg of MBA were added thereto. A resulting material was subjected to homogenization, and then irradiated with the xenon lamp at 150 W for 8 h to form a hydrogel. The hydrogel was taken out and cut into evenly sized blocks, immersed in distilled water for 72 h, and dried in a freeze-dryer for 33 h to obtain the all straw components-based hydrogel synthesized by visible light-driven method.

[0104] Example 10

[0105] An all straw components-based hydrogel synthesized visible light-driven was prepared by the following steps:

[0106] Step 1. 1 g of a straw powder was weighed and added to 50 mL of deionized water. A resulting mixture was subjected to homogeneous for 15 min, and then 0.2 g of mpg-CsN4 was added thereto. A resulting material was subjected to ultrasonic treatment for 40 min, and then 0.5 mL of a hydrogen peroxide solution (30 wt%) was added thereto. A resulting solution was irradiated with a xenon lamp at 200 W and stirred, and reacted under a water bath condition for 26 h to obtain an aqueous solution containing all straw components.

[0107] Step 2. 10 mL of the aqueous solution containing all straw components was taken, and 10 mL of glycerol, 0.3 g of AM, 0.5 g of AA, and 10 mg of MBA were added thereto. A resulting material was subjected to homogenization, and then irradiated with the xenon lamp at 200 W for 5 h to form a hydrogel, The hydrogel was taken out and cut into evenly sized blocks, immersed in distilled water for 66 h, and dried in a freeze-dryer for 33 h to obtain the all straw components-based hydrogel synthesized by visible light-driven method.

[0108] Comparative Example 1

[0109] In a swelling performance test, the examples with different component contents were compared with each other. In a water retention performance test, the comparison condition was the application amount of the all straw components-based hydrogel synthesized by visible light-driven method in the soil.

[0110] Comparative Example 2

[0111] In a test of adsorption of N, P, and TM in water, the examples with different component contents were compared with each other. In a study of slow-release of fertilizers and pesticides, the comparison condition was the soil without application of all straw components-based hydrogel synthesized by visible light-driven method.

[0112] In order to illustrate the various properties of the all straw components-based hydrogel synthesized by visible light-driven method provided in the present disclosure, the all straw components-based hydrogels synthesized by visible light-driven method provided in Examples 1 to 9 were tested for related performances, and Comparative Example 1 and Comparative Example 2 were used as control groups, as shown in FIG. 2 to FIG. 5.

[0113] FIG. 2 shows XRD patterns of various materials provided in Example 1 of the present disclosure; where (a) shows an XRD pattern of mpg-CsN^ and (b) shows an XRD pattern of the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 1. As shown in FIG. 2, some characteristic peaks could be observed in the XRD pattern of mpg-C3N4, indicating that mpg-CsN4 is successfully prepared and has desirable purity and crystallinity. In the XRD pattern of the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 1, typical diffraction peaks of cellulose type I in wheat straw and characteristic peaks of mpg-CsN4 could be observed, indicating that the all straw components-based hydrogel synthesized by visible light-driven method is successfully prepared.

[0114] FIG. 3-1 shows an XPS pattern of the mpg-CsN4, where (a) shows a full XPS spectrum; (b) shows a spectrum of Cis; (c) shows a spectrum of Nls; and (d) shows a spectrum of Ols.

[0115] FIG. 3-2 shows an XPS pattern of the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 1, where (a) shows a full XPS spectrum; (b) shows a spectrum of Cis; (c) shows a spectrum of N1 s; and (d) shows a spectrum of 01 s. Characteristic peaks belonging to AM, AA, mpg-C3N4, and cellulose in wheat straw could be observed in the figure, indicating that mpg-CsN4 is successfully incorporated into the network structure of the all straw components-based hydrogel synthesized by visible light-driven method, which fully demonstrates the successful synthesis of the all straw components-based hydrogel synthesized by visible light-drive.

[0116] FIG. 4 shows SEM images of various materials provided in various examples of the present disclosure, where (a) shows the mpg-Cs^; (b) shows an SEM magnified image of the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 4; (c) shows the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 1; (d) shows the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 2; (e) shows the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 3; and (f) shows 14 the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 4. It can be seen from the figure that mpg-CsN4 presents a blocky layer-shaped structure, and the straw component hydrogel synthesized by visible light-driven method presents a porous structure with interconnected porous channels inside. A large number of blocky layer-shaped mpg-CsN4 and long rod-shaped short fibers are distributed on an inner wall of the porous channels. With the increase of AA and AM contents, the pores of the all straw components-based hydrogel synthesized by visible light-driven method become smaller, resulting in a decrease in the swelling performance of the all straw components-based hydrogel synthesized by visible light-driven method; moreover, the cross-linking density of the all straw components-based hydrogel synthesized by visible light-driven method gradually increases, the number of pores increases, and the specific surface area of the all straw components-based hydrogel synthesized by visible light-driven method is increased, which is more conducive to the contact between the all straw components-based hydrogel synthesized by visible light-driven method and the reactants.

[0117] FIG. 5 shows FT-IR graphs of various materials provided in various examples of the present disclosure, where (a) shows the mpg-CsN4; (b) shows the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 5; (c) shows the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 1; and (d) shows the all straw components-based hydrogel synthesized by visible light-driven method disclosed in Example 4. By comparing the infrared spectra of the all straw components-based hydrogel synthesized by visible light-driven method and mpg-CsN4, the characteristic absorption peak of the mpg-CsN4 could be seen in the spectrum of the all straw components-based hydrogel synthesized by visible light-driven method, indicating that the all straw components-based hydrogel synthesized by visible light-driven method has been successfully prepared by visible light-driven method.

[0118] In order to further illustrate the water holding capacity and water retention capacity of the all straw components-based hydrogel synthesized by visible light-driven method provided by the present disclosure, the effects of AM and AA contents on the swelling properties of the all straw components-based hydrogel synthesized by visible light-driven method were first investigated in the examples, and then the water retention performance of the all straw components-based hydrogel synthesized by visible light-driven method was tested, with the application amount of the all straw components-based hydrogel synthesized by visible light-driven method as the control, as shown in FIG. 6 and FIG. 7.

[0119] The effect of AM and AA contents on the swelling properties of the all straw components-based hydrogel synthesized by visible light-driven methods was determined by the following procedure: the prepared all straw components-based hydrogel synthesized by visible light-driven method was fully immersed, cut into blocks and freeze-dried to obtain a hydrogel for later use; a certain mass of the hydrogel was weighed and added to 100 ml of deionized water, and allowed to absorb water and swell at room temperature; the swollen all straw components-based hydrogel synthesized by visible light-driven method was taken out at regular intervals, wiped with filter paper to remove water droplets on the surface of all straw components-based hydrogel synthesized by visible light-driven method, and weighed immediately. The swelling rate of the all straw components-based hydrogel synthesized by visible light-driven method was calculated according to Formula (1):

[0120] St = x 100% (1) Qd

[0121] In the formula: Qt represents a mass of the all straw components-based hydrogel synthesized by visible light-driven method at swelling time t, in g; Qd represents a mass of the hydrogel before swelling, in g; St represents the swelling rate of the all straw components-based hydrogel synthesized by visible light-driven method at time t, in %.

[0122] FIG. 6 is a graph showing the effect of AM and AA contents on the swelling properties of the all straw components-based hydrogel synthesized by visible light-driven method, where (a) shows the effect of AM content on the swelling properties of the all straw components-based hydrogel synthesized by visible light-driven method; and (b) shows the effect of AA content on the swelling properties of the all straw components-based hydrogel synthesized by visible light-driven method. When the AA and AM contents are 0.1 g, the maximum swelling rates of the all straw components-based hydrogel synthesized by visible light-driven method could reach 6044.86% and 4676.86%, respectively; with the increase of AM and AA contents, the swelling rate of the all straw components-based hydrogel synthesized by visible light-driven method decreases. The main reason is that the increase in AM and AA contents leads to an increase in the cross-linking density of the network skeleton of the all straw components-based hydrogel synthesized by visible light-driven method, which in turn leads to a decrease in the swelling rate.

[0123] The water holding and water retention properties of the all straw components-based hydrogel synthesized by visible light-driven method were determined by the following procedure: soil samples were prepared with different application rates of the all straw components-based hydrogel synthesized by visible light-driven method (0%, 1%, 2% and 3%): the samples of the all straw components-based hydrogel synthesized by visible light-driven method of different masses were mixed evenly with 100 g of dry soil after sieving (18-mesh sieve), and then a mixture was placed in a PVC tube with a diameter of 4.5 cm and a length of 15 cm. The bottom of the tube was sealed with a 300-mesh nylon cloth and the mixture was weighed (marked as Mi). The soil column was hung vertically on an iron bracket, and tap water was dripped from an upper end of the soil column until water seeped out from the bottom. When there was no more water seeping from the bottom of the soil column, the mixture was weighed again (marked as M2). The maximum water holding ratio of the soil was calculated by Formula (2):

[0124] W(%) = x 100% (2)

[0125] The mixture was placed in a glass beaker and weighed (marked as Mo), immersed in tap water until saturated (the amount of water was calculated based on the above experimental results), and weighed again (marked as Mi). Four experimental samples were placed in the same environment and weighed every 2 d (marked as Mi). All measurements were completed within 30 d. The water retention rate of soil was calculated by Formula (3):

[0126] W(%) = x 100% (3)

[0127] In the formula: WH represents the maximum water holding ratio of soil, in %; WR represents the water retention rate of soil, in %.

[0128] FIG. 7 is a graph showing the maximum water holding rate and soil water retention rate of the all straw components-based hydrogel synthesized by visible light-driven method provided in Example 1 of the present disclosure at different contents, where (a) shows the maximum water holding rate of the soil at different contents of the all straw components-based hydrogel synthesized by visible light-driven method; and (b) shows the water retention rate of the soil at different contents of the all straw components-based hydrogel synthesized by visible light-driven method. As shown in FIG. (a), when the contents of the all straw components-based hydrogel synthesized by visible light-driven method in the soil are 0% and 3%, the maximum water holding rates of the soil are 68.62% and 228.51%, respectively. Compared with the soil without the addition of the all straw components-based hydrogel synthesized by visible light-driven method, the water content of the soil with the addition of the all straw components-based hydrogel synthesized by visible light-driven method has been effectively improved, and the water content of the soil gradually increases with the increase in the content of the all straw components-based hydrogel synthesized by visible light-driven method. However, the swelling rate of the all straw components-based hydrogel synthesized by visible light-driven method in soil is much smaller than that in water. The reason for this may be that each particle of the all straw components-based hydrogel synthesized by visible light-driven method is surrounded by soil particles, which hinders the expansion of the all straw components-based hydrogel synthesized by visible light-driven method. In addition, highly charged metal ions (such as Ca2+, Mg2+, Al3+, and Fe3+) in the soil solution have an extremely high complexing ability with the hydrophilic groups of the all straw components-based hydrogel synthesized by visible light-driven method, which may also be the reason why the swelling rate in soil is lower than that in water. As shown in FIG. (b), the soil without the addition of the all straw components-based hydrogel synthesized by visible light-driven method loses almost all of the absorbed water after 20 d, while the soil samples with the addition of 1%, 2%, and 3% of the all straw components-based hydrogel synthesized by visible light-driven method still retain 4.7%, 15.3%, and 26.6% of the water, respectively. This is because the free enthalpy of the entire system decreases after water enteres the all straw components-based hydrogel synthesized by visible light-driven method. If water escapes from the all straw components-based hydrogel synthesized by visible light-driven method, the free enthalpy of the system could increase, which is not conducive to the stability of the system.

[0129] In order to further illustrate the performance of the slow-release fertilizer, the all straw components-based hydrogel synthesized by visible light-driven method provided in the present disclosure, the examples first investigated the effects of AM and AA contents on the adsorption of ammonia nitrogen, phosphorus, and pesticide (TM) by the all straw components-based hydrogel synthesized by visible light-driven method in water, and then a slow-release experiment of ammonia nitrogen, phosphorus, or TM was conducted, with Comparative Example 2 serving as a control group, as shown in FIG. 8-1 to FIG. 8-3 and FIG. 9.

[0130] The effect of AM and AA contents on the adsorption of ammonia nitrogen, phosphorus, and TM in water by the all straw components-based hydrogel synthesized by visible light-driven method was determined by the following procedure:

[0131] The all straw components-based hydrogel synthesized by visible light-driven method was fully swollen and freeze-dried to obtain the hydrogel. 0.1 g of the all straw components-based hydrogel synthesized by visible light-driven method in each example was placed in a conical flask, 30 mL of a certain concentration of NH4CI solution was added, and the mixture was shaken at 150 rpm at 25 °C for 48 h, and then filtered to determine the concentration of NH4+ in a resulting filtrate. The adsorption amount of NH4+ was calculated according to Formula (4):

[0132] qe = (4)

[0133] In the formula: qe represents the adsorption amount of NH4+ by the all straw components-based hydrogel synthesized by visible light-driven method; Co represents a concentration of NH4+ in the initial solution, in mg / L; Ce represens a concentration of NH4+in the filtrate, in mg / L; V represents a volume of the solution, in L; M represents a mass of the hydrogel, in g.

[0134] The adsorption operation method of P and TM by the all straw components-based hydrogel synthesized by visible light-driven method with different component contents is the same as that in N.

[0135] FIG. 8-1 is a graph showing the effect of AM and AA contents on the adsorption of N in water by the all straw components-based hydrogel synthesized by visible light-driven method. FIG. 8-2 is a graph showing the effect of AM and AA contents on the adsorption of P in water by the straw component-based hydrogel synthesized by visible light-driven method. FIG. 8-3 is a graph showing the effect of AM and AA contents on the adsorption of TM in water by the straw components-based hydrogel synthesized by visible light-driven method. The results show that when the AA content is 0.9 g, the adsorption rate of N reaches a maximum of 31.93%; when the AM content is 0.9 g, the adsorption rate of P reaches a maximum of 29.48%. The contents of AM and AA affect the adsorption of P and N by the straw components-based hydrogel synthesized by visible light-driven method, respectively, and with the increase of AM and AA contents, the adsorption of P and N by the straw components-based hydrogel synthesized by visible light-driven method gradually increases. As for the adsorption of TM in water, the experimental results show that the main influencing factor for the adsorption of fungicide TM is the swelling properties of the straw components-based hydrogel synthesized by visible light-driven method. The better the swelling properties of the all straw components-based hydrogel synthesized by visible light-driven method, the better the adsorption performance of TM.

[0136] The slow-release N, P and TM of the all straw components-based hydrogel synthesized by visible light-driven method was determined by the following procedure: This experiment adopted the slow-release nitrogen fertilizer made from the all straw components-based hydrogel synthesized by visible light-driven method (NTWS-AA-Example 3) in Example 3, the slow-release phosphorus fertilizer made from the all straw components-based hydrogel synthesized by visible light-driven method (PTWS-AM-Example 4) in Example 4, and the slow-release pesticide made from the all straw components-based hydrogel synthesized by visible light-driven method (TM-Example 1) in Example 1. Taking the slow-release nitrogen fertilizer as an example: 2 g of the hydrogel was added to 100 mL of a certain concentration of NH4CI solution, shaken at 25°C, filtered to separate the straw components-based hydrogel synthesized by visible light-driven method loaded with nitrogen, freeze-dried to obtain the slow-release nitrogen fertilizer of the straw components-based hydrogel synthesized by visible light-driven method, and the nitrogen content in the slow-release nitrogen fertilizer of the straw components-based hydrogel synthesized by visible light-driven method was determined by measuring the nitrogen concentration in the filtrate. 1 g of freeze-dried all straw components-based hydrogel synthesized by visible light-driven method loaded with fertilizer and drug was mixed with 100 g of dry soil, and water samples were separated from a resulting mixture using a plastic container with a filter membrane, a valve, and a lid. When the mixture was filled into the container, the valve was closed and then 70 mL of deionized water was added to the soil container until a soil-water saturation point was reached. During the entire experiment, deionized water was continuously replenished to keep the water content in the container constant. At different time periods (days 0.5, 1, 2, 4, 6, 8, and 10), 5 mL of a water sample was filtered through a filter membrane, and 18 the valve was opened to collect the water sample.

[0137] FIG. 9 is a graph showing the changes in the release rate of direct application of fertilizers and the all straw components-based hydrogel fertilizers in the soil, where (a) shows the change in the NH4+ release of NH4CI and NTWS-AA-Example 3 in the soil over time; (b) shows the change in the PO43 release of KH2PO4 and PTWS-AM-Example 4 in the soil over time; and (c) shows the change in the TM release of TM and TM-Example 1 in the soil over time. The results show that after loading nitrogen fertilizer, phosphorus fertilizer, and pesticide with the all straw components-based hydrogel synthesized by visible light-driven method as a carrier, they show slow release in the soil. Compared with untreated nitrogen fertilizer, phosphorus fertilizer, and pesticide, the release rate is significantly reduced. In agricultural applications, the hydrogel could effectively improve the fertilizer utilization efficiency and extend the fertilizer application period.

[0138] The experimental results show that when the AA and AM contents of the all straw components-based hydrogel decrease, the pores of the all straw components-based hydrogel become larger and the swelling performance improves, which is beneficial for improving the water holding capacity and water retention capacity of the soil and facilitating the adsorption of the fungicide TM. When the AA and AM contents increases, the carboxylic acid group and amide group increase, effectively improving the recovery rate of N and P in the wastewater. After loading nitrogen fertilizer, phosphate fertilizer, and pesticide, the release rate in the soil decreases significantly, indicating that the preparation method provided in the present disclosure is feasible and could obtain the all straw components-based hydrogel synthesized by visible light-driven method with better performance.

[0139] The present disclosure describes the preferred examples and their effects. Although some preferred examples of the present disclosure have been described, persons skilled in the art can make changes and modifications to these examples once they learn the basic inventive concept. Therefore, the appended claims are intended to be construed to include the preferred examples and all alterations and modifications that fall within the scope of the present disclosure.

[0140] Although the embodiments of the present disclosure have been illustrated and described, it should be understood that those of ordinary skill in the art may make various changes, modifications, replacements and variations to the above embodiments without departing from the principle and spirit of the present disclosure, and the scope of the present disclosure is limited by the appended claims and their legal equivalents.

[0141] The above contents are merely used to illustrate the technical ideas of the present disclosure, rather than to limit the scope of the present disclosure. Any variations made based on the technical solutions according to the technical ideas proposed by the present disclosure shall fall within the scope as defined by the claims of the present disclosure.

Claims

1. A method for preparing an all straw components-based hydrogel synthesized by visible light-driven method, comprising:1) adding a straw powder to deionized water, subjecting a resulting mixture to homogeneous dispersion, adding mpg-CiN4 thereto, subjecting a resulting material to ultrasonic treatment, then adding a hydrogen peroxide solution thereto, and then stirring a resulting solution in a water bath under irradiation of a xenon lamp to obtain an aqueous solution containing all straw components; and2) adding glycerol, a monomer acrylic acid (AA), acrylamide (AM), and A,M-methylenebisacrylamide (MBA) to the aqueous solution containing all straw components obtained in step 1), subjecting a resulting mixed material to homogenization, then irradiating with the xenon lamp to form a hydrogel, and then subjecting the hydrogel to immersion and freeze-drying to obtain the all straw components-based hydrogel synthesized by visible light-driven method.

2. The method of claim 1, wherein in step 1), a mass ratio of the straw powder to the mpg-CsN4 is in a range of 1: (0.1-0.4), a volume ratio of the deionized water to the hydrogen peroxide solution is in a range of 1: (0.01-0.2), and the hydrogen peroxide solution has a mass percentage of 30%.

3. The method of claim 1, wherein in step 1), the homogeneous dispersion is conducted for 10 minutes to 30 minutes, and the ultrasonic treatment is conducted for 30 minutes to 60 minutes.

4. The method of claim 1, wherein in step 1), the xenon lamp has a power of 150 W (Watt) to 300 W, and the stirring in the water bath is conducted for 24 hours to 30 hours.

5. The method of claim 1, wherein in step 2), a dosage ratio of the aqueous solution containing all straw components, the glycerol, the monomer AA, the AM, and the MBA is in a range of 10 mL (milliliter): (1-10) mL: (0.1-0.9) g (gram): (0.1-0.9) g: 0.01 g.

6. The method of claim 1, wherein in step 2), the xenon lamp has a power of 150 W to 300 W, and the irradiation with the xenon lamp is conducted for 4 hours to 8 hours.

7. The method of claim 1, wherein in step 2), the immersion is conducted in distilled water for 48 hours to 72 hours, and the freeze-drying is conducted for 24 hours to 36 hours.

8. An all straw components-based hydrogel synthesized by visible light-driven method prepared by the method of any one of claims 1 to 7, wherein the all straw components-based hydrogel synthesized by visible light-driven method is in a porous structure, the porous structure is internally provided with interconnected porous channels, and a plurality of blocky layer-shaped mpg-CiN4 and long rod-shaped short fibers are distributed on an inner wall of each of the porous channels.

9. Use of the all straw components-based hydrogel synthesized by visible light-driven method prepared by the method of any one of claims 1 to 7 in water holding and water retention in soil.

10. Use of the all straw components-based hydrogel synthesized by visible light-driven method prepared by the method of any one of claims 1 to 7 in adsorption of nitrogen, phosphorus, and a pesticide and slow release of the nitrogen, the phosphorus, and the pesticide.

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