Protonated chitosan modified sustained-release material as well as preparation method and application thereof

Abstract

The invention relates to the field of soil remediation and improvement, and discloses a protonated chitosan modified sustained-release material and a preparation method and application thereof.The protonated chitosan modified sustained-release material is of a core-shell structure, an inner core contains sulfate, and a shell layer contains protonated chitosan modified porous carbon; the raw materials for preparing the protonated chitosan modified porous carbon contain biomass. The protonated chitosan modified sustained-release material provided by the invention can continuously provide electron acceptors for indigenous sulfate reducing bacteria by continuously releasing sulfate radicals and stimulate the sulfate reducing bacteria to continuously utilize an organic carbon source in an environment for metabolic proliferation, so that the effects of degrading and stabilizing pollutants are achieved, and the protonated chitosan modified sustained-release material has a relatively good application value.

Description

Technical Field

[0001] The present invention relates to the field of soil remediation and improvement, and particularly to a slow-release material modified by protonated chitosan, its preparation method and application. Background Art

[0002] During the processes of oil exploration, transportation, processing, utilization, etc., relatively serious site pollution often occurs. The remediation of organic pollution sites such as petroleum hydrocarbons and benzene series is an urgent, arduous and long-term task in the context of ecological civilization construction. The breakthrough of green and efficient remediation technologies has great milestone significance for the long-term development of the industry and the continuous promotion of ecological civilization.

[0003] As a bioenergy with great potential for resource utilization, waste biomass has received great attention under the background of advocating comprehensive resource utilization. As a porous solid with an aromatic structure after thermal processing of waste biomass, biochar has strong biological and chemical stability and can exist in the environment for a long time without being decomposed and mineralized by microorganisms. Existing research has found that the porous structure after biomass carbonization not only enables it to have a better soil improvement effect, but also some studies use biochar as a matrix to obtain a carbon-based slow-release material with a certain drug slow-release function through operations such as blending and compounding to participate in the remediation of contaminated soil. After the slow release is completed, the biochar matrix can continue to play a certain role in the process of soil improvement, and through the addition of the slow-release function, the biochar is transformed into a soil conditioner with a certain remediation function.

[0004] Sulfate-reducing bacteria are a dominant strain that can degrade pollutants using sulfate as an electron acceptor and are widely present in various environments such as soil, seawater, oil and gas fields, and river bottom sludge. Its electron acceptors are sulfur oxides such as sulfate, sulfite, and thiosulfate. Organic pollutants in the environment can serve as the carbon source for its life activities and be degraded through its dissimilatory action, and further converted into CO3 2- etc. At the same time, sulfate is reduced to S 2- , and part of the carbon source S 2- and CO3 2- can interact with metal ions to form insoluble precipitates, and through the life activities of sulfate-reducing bacteria, the conversion and removal of pollutants can be comprehensively achieved. However, in existing technologies related to the bio-stimulation of sulfate-reducing bacteria, most focus on ensuring the stimulation of basic nutrient elements such as carbon source and nitrogen source, and there are few related studies on continuously ensuring the life activities of sulfate-reducing bacteria in the original environment through electron donors. There is also no report on technical research aiming at realizing the slow release of sulfate alone.

[0005] The main types of traditional sustained-release agents include coating type, polymer matrix type, adsorptive type, etc. Among them, the coating technology plays a hindering role in the process of drug diffusion and release, prolonging the drug effect period. Because it is simple to implement and has strong operability, it is widely used. The common coating materials are mainly divided into two categories: organic and inorganic. Common inorganic coatings mainly include sulfur, calcium magnesium phosphate fertilizer, insoluble phosphate, etc. Organic coatings are mostly chitosan, sodium alginate, starch, cellulose, etc. Inorganic coatings have high brittleness and poor toughness. Organic coatings mostly come from natural biomass and are mostly microbial nutrient organic matter. During their reuse in soil, they are easily preferentially utilized by microorganisms as metabolic substrates, greatly weakening their coating function, thus affecting the drug sustained-release effect.

[0006] Relying on sulfate-reducing bacteria widely existing in nature, a system with biochar as the matrix and effective sulfate sustained-release is provided. Pollutant removal is achieved by continuously stimulating the life activities of sulfate-reducing bacteria, and there is currently a large research space. Summary of the Invention

[0007] The purpose of the present invention is to overcome the problems in the existing sustained-release technology that the coating of the sustained-release material is easily decomposed, thus affecting the drug sustained-release effect, etc. A sustained-release material modified by protonated chitosan, its preparation method and application are provided. Starting from fully developing the value of biochar itself in the field of realizing sustained-release function, relying on the pore size and surface characteristics of biochar and the structural characteristics of chitosan, with the purpose of realizing long-term sulfate sustained-release, a chitosan-modified carbon-based "coating" sustained-release material for extending the action period of sulfate in the environment is developed. This sustained-release material has great significance for the remediation of organic pollution based on sulfate-reducing bacteria. By in-situ adding the prepared sustained-release material modified by protonated chitosan and continuously stimulating the life activities of sulfate-reducing bacteria in the polluted site, the improvement, treatment and remediation of the polluted site can be better realized.

[0008] To achieve the above purpose, on the one hand, the present invention provides a sustained-release material modified by protonated chitosan. The sustained-release material modified by protonated chitosan has a core-shell structure, in which the core contains sulfate and the shell contains porous carbon modified by protonated chitosan;

[0009] The raw materials for preparing the porous carbon modified by protonated chitosan contain biomass.

[0010] Preferably, the sulfate is selected from one or more of magnesium sulfate, calcium sulfate, potassium sulfate, sodium sulfate, ferric sulfate and lithium sulfate.

[0011] Preferably, the particle size of the sustained-release material modified by protonated chitosan is 10-50 μm, preferably 25-40 μm.

[0012] Preferably, the pore size of the protonated chitosan-modified porous carbon is 1-20 nm, preferably 1-10 nm.

[0013] Preferably, the thickness of the shell layer is 0.3-0.6 times the radius of the protonated chitosan-modified sustained-release material.

[0014] The second aspect of the present invention provides a preparation method of the above-mentioned protonated chitosan-modified sustained-release material, and the preparation method includes the following steps:

[0015] (1) Mix the biomass with an alkaline solution and then perform heat treatment, and then filter, and adjust the pH value of the obtained filtrate to 7-7.5 to obtain a carbonaceous precursor;

[0016] (2) Mix the carbonaceous precursor with a template agent micelle and then perform heat treatment to obtain hollow microspheres;

[0017] (3) Mix the hollow microspheres with a sulfate and then perform carbonization treatment, and then perform washing to obtain composite microspheres;

[0018] (4) Mix the composite microspheres with chitosan, an acetic acid solution, and a cross-linking agent, and then perform cross-linking, and then adjust the pH value of the system to alkaline to obtain chitosan-modified composite microspheres;

[0019] (5) Mix the chitosan-modified composite microspheres with an acidic solution, stir and then let stand.

[0020] Preferably, in step (1), the alkaline solution is selected from sodium hydroxide solution and / or potassium hydroxide solution;

[0021] Preferably, the concentration of the alkaline solution is 0.1-0.3 mol / L;

[0022] Preferably, the solid-liquid ratio of the dosage of the biomass to the alkaline solution is 1 g:5-15 mL, preferably 1 g:9-12 mL.

[0023] Preferably, in step (1), the conditions of the heat treatment are: the temperature is 50-70 °C and the time is 2-4 h.

[0024] Preferably, in step (2), the template agent micelle contains a main template agent and a co-template agent;

[0025] Preferably, the molar ratio of the dosage of the main template agent to the co-template agent is 1:1-40;

[0026] Preferably, the main template agent is triblock copolymer P123;

[0027] Preferably, the co-template agent is sodium dodecyl sulfate.

[0028] Preferably, in step (2), the method for preparing the template agent micelles includes: mixing the main template agent solution and the co-template agent solution;

[0029] Preferably, the volume ratio of the carbonaceous precursor to the template agent micelles is 1-5:1.

[0030] Preferably, in step (2), the heat treatment is hydrothermal treatment;

[0031] Preferably, the conditions of the hydrothermal treatment include: the temperature is 150-200 °C and the time is 8-16 h.

[0032] Preferably, in step (3), the weight ratio of the hollow microspheres to the sulfate is 1:5-10.

[0033] Preferably, in step (3), the conditions of the carbonization treatment include: heating to 150-180 °C at a heating rate of 2-10 °C / min, holding for 5-7 h, and then heating to 700-800 °C at a heating rate of 5-15 °C / min and holding for 3-5 h.

[0034] Preferably, in step (4), the specific process of mixing the composite microspheres with chitosan, glacial acetic acid solution and crosslinking agent includes: mixing chitosan and glacial acetic acid solution to obtain an acidified chitosan solution, then mixing the acidified chitosan solution with the composite microspheres, and then mixing with the crosslinking agent;

[0035] Preferably, the content of chitosan in the acidified chitosan solution is 2-6 wt%.

[0036] Preferably, in step (4), the content of glacial acetic acid in the glacial acetic acid solution is 2-5 vol%;

[0037] Preferably, the weight ratio of chitosan to the composite microspheres is 1:2-5.

[0038] Preferably, in step (4), the crosslinking agent is selected from one or more of formaldehyde, glutaraldehyde and epichlorohydrin;

[0039] Preferably, the weight-to-volume ratio of chitosan to the crosslinking agent is 1 g: 2-5 mL.

[0040] Preferably, in step (4), the crosslinking operation includes: stirring at 35-45 °C for 35-50 min, and then standing for 6-8 h.

[0041] Preferably, in step (5), the concentration of the acidic solution is 0.1-0.5 mol / L.

[0042] Preferably, the acidic solution is selected from one or more of nitric acid solution, hydrochloric acid solution and sulfuric acid solution.

[0043] Preferably, in step (5), the solid-liquid ratio of the amount of the chitosan-modified composite microspheres to the acidic solution is 1 g: 10 - 30 mL, preferably 1 g: 10 - 20 mL;

[0044] Preferably, the standing time is 8 - 12 h;

[0045] Preferably, the stirring time is 20 - 40 min.

[0046] The third aspect of the present invention provides an application of the above-mentioned protonated chitosan-modified slow-release material in the remediation of organic contaminated soil and groundwater.

[0047] Through technical means design, for long-term sulfate slow release, the waste biomass is resourcefully converted into a "coated" carbon that can be used for sulfate slow release. Through structural design, during the sulfate release process, this "coated" carbon can delay its release process through ion exchange, complexation, etc. with sulfate, and through protonation modification design, the slow release effect is strengthened. The protonated chitosan-modified slow-release material proposed by the present invention can continuously release sulfate, continuously provide electron acceptors for indigenous sulfate-reducing bacteria, stimulate the sulfate-reducing bacteria to continuously utilize the organic carbon source in the environment for metabolic proliferation, play a role in pollutant degradation and stabilization, and has good application value. Description of the Drawings

[0048] Figure 1 is the process flow chart of the preparation of the protonated chitosan-modified slow-release material;

[0049] Figure 2 is the structural schematic diagram of the test device used in Test Examples 2 - 4.

[0050] Description of the Reference Numerals

[0051] 1 Stirrer 2 Water storage container

[0052] 3 Peristaltic pump 4 Sample loading port

[0053] 5 Reaction soil column 6 Outlet water storage device

[0054] 7 Nitrogen gas balloon Detailed Embodiments

[0055] The following detailed description of the specific embodiments of the present invention is provided in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the present invention.

[0056] The endpoints and any values in the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0057] On the one hand, the present invention provides a sustained-release material modified with protonated chitosan. The sustained-release material modified with protonated chitosan has a core-shell structure, wherein the inner core contains sulfate, and the shell layer contains porous carbon modified with protonated chitosan;

[0058] The raw materials for preparing the porous carbon modified with protonated chitosan contain biomass.

[0059] In the sustained-release material modified with protonated chitosan of the present invention, the sulfate in the inner core continuously dissolves to release the sulfate radicals it contains. The porous carbon modified with protonated chitosan in the shell layer can form a cationic polyelectrolyte - NH3 + , which can adsorb sulfate ions in the environment through electrostatic attraction. When the sulfate radicals in the inner core start to be released, on the one hand, the porous carbon modified with protonated chitosan in the shell layer serves as a sulfate radical release channel, which can prolong the release time of sulfate radicals. On the other hand, it can interact with the sulfate radicals released from the inner layer through processes such as electrostatic attraction and ion exchange, reducing the free concentration of sulfate radicals in the environment and further improving the effective action period of sulfate radicals.

[0060] In order to further improve the sustained-release ability, preferably, the sulfate is selected from one or more of magnesium sulfate, calcium sulfate, potassium sulfate, sodium sulfate, iron sulfate, and lithium sulfate.

[0061] In the present invention, the particle size of the sustained-release material modified with protonated chitosan is 10 - 50 μm, preferably 25 - 40 μm.

[0062] In the present invention, in order to achieve a better sustained-release effect, the pore diameter of the porous carbon modified with protonated chitosan (the pore channels are mainly mesopore channels and micropore channels) is 1 - 20 nm, preferably 1 - 10 nm.

[0063] In a preferred embodiment, the sustained-release material modified with protonated chitosan of the present invention is spherical, and the inner core is also spherical. Further preferably, the thickness of the shell layer is 0.3 - 0.6 times the radius of the sustained-release material modified with protonated chitosan, and specifically can be 0.3 times, 0.4 times, 0.5 times, or 0.6 times.

[0064] In a preferred embodiment, in the present invention, biomass is selected as the raw material for calcination to prepare porous carbon modified with protonated chitosan, which can realize the functional development and reuse of biomass, and can take into account the resource utilization of biomass and the development of functional medicaments.

[0065] The second aspect of the present invention provides a method for preparing the above-mentioned slow-release material modified with protonated chitosan, and its process flow chart is as Figure 1 shown, and the preparation method includes the following steps:

[0066] (1) Mix biomass with an alkaline solution and then perform heat treatment, and then filter, and adjust the pH value of the obtained filtrate to 7-7.5 to obtain a carbonaceous precursor;

[0067] (2) Mix the carbonaceous precursor with a template agent micelle and then perform heat treatment to obtain hollow microspheres;

[0068] (3) Mix the hollow microspheres with sulfates and then perform carbonization treatment, and then perform washing to obtain composite microspheres;

[0069] (4) Mix the composite microspheres with chitosan, glacial acetic acid solution and a cross-linking agent, and then perform cross-linking, and then adjust the pH value of the system to alkaline to obtain chitosan-modified composite microspheres;

[0070] (5) Mix the chitosan-modified composite microspheres with an acidic solution, stir and then let stand.

[0071] In a preferred embodiment of the present invention, the biomass used in step (1) can be derived from waste biomass rich in carbon polysaccharides such as cellulose, hemicellulose and lignin commonly used in the art, such as one or more of fruit shells, straws and bamboo and wood.

[0072] The main purpose of the operation in step (1) of the present invention is to perform alkali treatment on biomass. The process of decomposing, degrading and transforming biomass through alkali treatment technology is mainly to separate components such as lignocellulose, hemicellulose and lignin for subsequent utilization. The purpose of mixing with an alkaline solution and performing heat treatment is to destroy the biomass cell structure, release soluble polysaccharides, obtain a carbon polysaccharide solution, and obtain a carbonaceous precursor therefrom for the preparation of carbon microspheres.

[0073] In step (1) of the present invention, the alkaline solution is selected from sodium hydroxide solution and / or potassium hydroxide solution.

[0074] In order to ensure the efficient separation of components in biomass, it is necessary to select appropriate concentrations of the alkaline solution and the heat treatment time in step (1).

[0075] Preferably, in step (1), the concentration of the alkaline solution is 0.1 - 0.3 mol / L, specifically it can be 0.1 mol / L, 0.2 mol / L or 0.3 mol / L.

[0076] In a specific embodiment, the concentration of the alkaline solution in step (1) is 0.2 mol / L.

[0077] Preferably, in step (1), the solid-liquid ratio of the dosage of the biomass to the alkaline solution is 1 g : 5 - 15 mL, preferably 1 g : 9 - 12 mL, specifically it can be 1 g : 9 mL, 1 g : 10 mL, 1 g : 11 mL or 1 g : 12 mL.

[0078] In step (1) of the present invention, the conditions of the heat treatment are: the temperature is 50 - 70 °C, and the time is 2 - 4 h.

[0079] In a specific embodiment of step (1), the temperature of the heat treatment can be 50 °C, 55 °C, 60 °C, 65 °C or 70 °C, and the time of the heat treatment can be 2 h, 2.5 h, 3 h, 3.5 h or 4 h.

[0080] In a specific embodiment of step (1), the temperature of the heat treatment is 60 °C, and the time of the heat treatment is 3 h.

[0081] In step (1) of the present invention, the product after the heat treatment has a high alkalinity. In order to avoid the influence on the subsequent operations, therefore, it is also necessary to adjust the pH value of the filtrate obtained by filtration to neutral, and further adjust the pH value of the obtained filtrate to 7 - 7.5.

[0082] Preferably, the pH value of the filtrate obtained by filtration can be adjusted to neutral using hydrochloric acid solution and / or sulfuric acid solution.

[0083] In step (2) of the present invention, the purpose of using the template agent micelles is to obtain hollow microspheres with uniform particle sizes. Preferably, in order to further obtain stable hollow microspheres with uniform particle sizes, the template agent micelles contain a main template agent and a co-template agent.

[0084] Preferably, in step (2) of the present invention, in order to further obtain better effects, the molar ratio of the dosage of the main template agent to the co-template agent is 1 : 1 - 40, specifically it can be 1 : 1, 1 : 10, 1 : 20, 1 : 30 or 1 : 40.

[0085] In a specific embodiment, the molar ratio of the dosage of the main template agent to the co-template agent is 1 : 5.

[0086] Preferably, the main template agent is the triblock copolymer P123.

[0087] Preferably, the co-template agent is sodium dodecyl sulfonate.

[0088] In a preferred embodiment of the present invention, in step (2), the method for preparing the template agent micelles includes: mixing the main template agent solution and the co-template agent solution.

[0089] To further ensure sufficient mixing of all materials, in a specific embodiment of step (2), the main template agent and the co-template agent are respectively mixed with water to obtain the main template agent solution and the co-template agent solution, and then the main template agent solution and the co-template agent solution are mixed to obtain the template agent micelles, which are then mixed with the carbonaceous precursor and subjected to heat treatment.

[0090] In a preferred embodiment, the concentration of the main template agent solution is 0.1 - 1 mmol / L, and the concentration of the co-template agent solution is 2.4 - 4 mmol / L.

[0091] Preferably, in step (2), the volume ratio of the amount of the carbonaceous precursor to the template agent micelles is 1 - 5:1, specifically it can be 1:1, 2:1, 3:1, 4:1 or 5:1.

[0092] In a specific embodiment, the volume ratio of the amount of the carbonaceous precursor to the template agent micelles is 3:1.

[0093] In step (2) of the present invention, after mixing the carbonaceous precursor and the template agent, it is also necessary to stir for 15 - 25 min to ensure uniform mixing.

[0094] Preferably, in step (2), the heat treatment is hydrothermal treatment.

[0095] Preferably, in step (2), the conditions of the hydrothermal treatment include: the temperature is 150 - 200 °C, and the time is 8 - 16 h.

[0096] In a specific embodiment, in step (2), the temperature of the hydrothermal treatment can be 150 °C, 160 °C, 170 °C, 180 °C, 190 °C or 200 °C, and the time of the hydrothermal treatment can be 8 h, 10 h, 12 h, 14 h or 16 h.

[0097] In a specific embodiment, in step (2), the temperature of the hydrothermal treatment is 180 °C, and the time of the hydrothermal treatment can be 10 h.

[0098] In step (2) of the present invention, after the heat treatment operation is completed, in order to further obtain hollow microspheres, the material obtained after heat treatment needs to be cooled to room temperature, then centrifuged, and then filtered. The obtained solid is washed alternately with deionized water and absolute ethanol until the supernatant is clear to remove the unreacted template agent, and then the washed solid is dried to obtain hollow microspheres.

[0099] In the present invention, the room temperature mentioned refers to 20 - 30 °C.

[0100] Preferably, in step (3), the weight ratio of the hollow microspheres to the sulfate is 1:5 - 10, specifically it can be 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10.

[0101] In a specific embodiment, in step (3), the weight ratio of the hollow microspheres to the sulfate is 1:6.

[0102] In the preferred case, the carbonization treatment in step (3) of the present invention is carried out under an inert atmosphere.

[0103] In order to further improve the slow - release performance, in the preferred case of the present invention, in step (3), the conditions of the carbonization treatment include: heating up to 150 - 180 °C at a heating rate of 2 - 10 °C / min, holding for 5 - 7 h, and then heating up to 700 - 800 °C at a heating rate of 5 - 15 °C / min, and holding for 3 - 5 h.

[0104] In step (3), the carbonization treatment is a continuous two - stage heat treatment process, where the first - stage heat treatment is the carbonization of the hollow microspheres, and the second - stage heat treatment is the melting and etching of the sulfate and the filling of the microspheres.

[0105] In a specific embodiment, the conditions of the carbonization treatment in step (3) include: heating up to 160 °C at a heating rate of 6 °C / min, holding for 7 h, and then heating up to 700 °C at a heating rate of 10 °C / min, and holding for 5 h.

[0106] In step (3) of the present invention, after mixing the hollow microspheres with the sulfate, the carbonization treatment is carried out under an inert atmosphere. During the heating process, the hollow microspheres start to carbonize in advance to form hollow porous carbon with certain pores. After reaching the melting temperature of the sulfate, the sulfate starts to melt, undergoes a phase transition, and the molten sulfate enters the interior of the hollow carbon microspheres and further etches the pore structure of the carbon layer. After the carbonization treatment, the obtained material is washed until the supernatant has no obvious suspended ash to remove the surface layer and excess sulfate (exposing the carbon layer surface to facilitate subsequent chitosan modification), so as to obtain composite microspheres with a sulfate@porous carbon core - shell structure.

[0107] Furthermore, in order to obtain a better slow - release effect, in step (3), the sulfate is a mixture of sodium sulfate, potassium sulfate and magnesium sulfate. Based on the total amount of sodium sulfate, potassium sulfate and magnesium sulfate being 100 wt%, the amount of sodium sulfate is 45 - 55 wt%, the amount of potassium sulfate is 5 - 15 wt%, and the amount of magnesium sulfate is 35 - 50 wt%.

[0108] In a specific embodiment, the sulfate in step (3) is a mixture of sodium sulfate, potassium sulfate and magnesium sulfate. Based on the total amount of sodium sulfate, potassium sulfate and magnesium sulfate being 100 wt%, the amount of sodium sulfate is 51 wt%, the amount of potassium sulfate is 6 wt%, and the amount of magnesium sulfate is 43 wt%.

[0109] After obtaining the composite microspheres in the present invention, it is also necessary to further modify them with chitosan. The dosage ratio of chitosan to the composite microspheres affects the modification effect of chitosan on the one hand and the sulfate loading of the subsequent hollow microspheres on the other hand. Therefore, it is necessary to control the weight ratio of chitosan to the composite microspheres. Preferably, in step (4), the weight ratio of the chitosan to the composite microspheres is 1:2 - 5, specifically it can be 1:2, 1:3, 1:4 or 1:5.

[0110] In a specific embodiment, the weight ratio of the chitosan to the composite microspheres in step (4) is 1:3.

[0111] Due to the abundant active groups of chitosan, it is easy to be lost in the environment. Therefore, in the present invention, a cross-linking agent is also used to further assemble and modify chitosan with the help of the cross-linking agent to ensure its stability in the environment.

[0112] In step (4) of the present invention, in order to ensure that the various materials are mixed evenly to achieve a better modification effect, the specific process of mixing the composite microspheres with chitosan, glacial acetic acid solution and cross-linking agent includes: mixing chitosan with glacial acetic acid solution to obtain an acidified chitosan solution, then mixing the acidified chitosan solution with the composite microspheres, and then mixing with the cross-linking agent.

[0113] In step (4) of the present invention, since chitosan can be homogeneously dissolved in an acidic environment, while strong acids such as hydrochloric acid and sulfuric acid are easy to damage the structure of chitosan itself, and glacial acetic acid can dissolve chitosan friendly and create a more homogeneous cross-linking condition, so glacial acetic acid solution is selected to dissolve chitosan. Further preferably, the content of glacial acetic acid in the glacial acetic acid solution in step (4) is 2 - 5 vol%.

[0114] In the preferred case, in order to obtain a better modification effect, the content of chitosan in the acidified chitosan solution in step (4) is 2 - 6 wt%, specifically it can be 2 wt%, 3 wt%, 4 wt%, 5 wt% or 6 wt%.

[0115] In a specific embodiment, the content of chitosan in the acidified chitosan solution in step (4) is 4 wt%

[0116] In step (4) of the present invention, the cross-linking agent is selected from one or more of formaldehyde, glutaraldehyde and epichlorohydrin, and further preferably glutaraldehyde.

[0117] Preferably, the weight - volume ratio of the chitosan to the cross - linker used in step (4) is 1 g: 2 - 5 mL, specifically it can be 1 g: 2 mL, 1 g: 3 mL, 1 g: 4 mL or 1 g: 5 mL.

[0118] More preferably, in step (4), the cross - linking operation includes: stirring at 35 - 45 °C for 35 - 50 min, and then continuing to stand at the same temperature for 6 - 8 h.

[0119] In a specific embodiment of step (4), the cross - linking temperature can be 35 °C, 37 °C, 40 °C, 42 °C or 45 °C, the stirring time can be 35 min, 38 min, 41 min, 44 min, 47 min or 50 min, and the standing time can be 6 h, 6.5 h, 7 h, 7.5 h or 8 h.

[0120] In step (4) of the present invention, the purpose of adjusting the pH value of the system to alkaline is to neutralize the acidic solution. Preferably, it is more appropriate to adjust the pH value of the system to slightly alkaline. More preferably, an alkaline solution can be used to adjust the pH value of the system to 8 - 9.

[0121] Preferably, in step (4), after adjusting the pH value of the system to alkaline, filtration is required, and the obtained solid is washed thoroughly to remove the residual agent to obtain the chitosan - modified composite microspheres.

[0122] The chitosan - modified composite microspheres obtained in the present invention further need to be protonated and modified to improve the slow - release performance of the material, wherein the protonation modification is achieved by the electrostatic attraction between the protonated amino group of chitosan and the acid radical.

[0123] Preferably, in step (5), the acidic solution is selected from one or more of nitric acid solution, hydrochloric acid solution and sulfuric acid solution. More preferably, the concentration of the acidic solution is 0.1 - 0.5 mol / L, specifically it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L.

[0124] In step (5) of the present invention, there is no special requirement for the dosage of the acidic solution, as long as the acidic solution is in excess. Preferably, the solid-liquid ratio of the chitosan-modified composite microspheres to the dosage of the acidic solution is 1 g: 10 - 30 mL, preferably 1 g: 10 - 20 mL, and specifically can be 1 g: 10 mL, 1 g: 11 mL, 1 g: 12 mL, 1 g: 13 mL, 1 g: 14 mL, 1 g: 15 mL, 1 g: 16 mL, 1 g: 17 mL, 1 g: 18 mL, 1 g: 19 mL or 1 g: 20 mL.

[0125] In step (5) of the present invention, the standing time is 8 - 12 h, and specifically can be 8 h, 9 h, 10 h, 11 h or 12 h.

[0126] Preferably, the stirring time in step (5) is 20 - 40 min, and specifically can be 20 min, 25 min, 30 min, 35 min or 40 min.

[0127] In step (5) of the present invention, after standing, filtration is carried out, and the obtained solid after filtration is dried to obtain the protonated chitosan-modified slow-release material of the present invention.

[0128] The preparation method of the present invention obtains the protonated chitosan-modified slow-release material through operations such as biomass pretreatment, preparation and molten salt carbonization of hollow microspheres, modification of composite microsphere chitosan and protonation treatment, etc., which can continuously release sulfate radicals in a certain environment, and the slow-release concentration can still reach 40 ppm at 100 d. The effective slow-release period can be estimated to be more than 120 days through the concentration change during the slow-release process, and the slow-release performance is good. In a certain polluted environment, the addition of the protonated chitosan-modified slow-release material can stimulate the vital activity of indigenous sulfate-reducing bacteria, realize pollutant degradation and stabilization, and has great practical significance for realizing pollutant control.

[0129] The third aspect of the present invention provides an application of the above-mentioned protonated chitosan-modified slow-release material in the remediation of organic-polluted soil and groundwater, and is further preferably applied to the remediation of organic-polluted soil and groundwater such as petroleum hydrocarbons and benzene series.

[0130] The present invention provides an innovative solution to the problem of soil remediation and treatment. At the same time, it also finds a high-value resource recycling path for a large number of stored waste biomasses. Through technical means, the biomass is transformed into a functional product that can effectively stimulate the vital activities of indigenous sulfate-reducing bacteria in the polluted environment, strengthening the self-remediation ability of the polluted environment. Specifically, it provides a protonated chitosan-modified slow-release material with sulfate radical slow-release function. In particular, the realization of the slow-release function of this slow-release material completely depends on the porous carbon functionalized by the biomass, making full use of the potential advantages of the biomass.

[0131] Combining the research status of biochar in the field of fertilizer slow-release, but different from the conventional slow-release purposes such as NPK, a new slow-release mission of biochar is given - sulfate slow-release. Starting from realizing the efficient resource conversion of biomass and the slow-release of sulfate ions, a slow-release material modified by protonated chitosan capable of loading sulfate is prepared. Using the shell carbon as the matrix, chitosan cross-linking and protonation modification are carried out. Chitosan is the product of the deacetylation of chitin and is the only natural polysaccharide with a large stock in nature and being alkaline. It is rich in free amino groups. Protonated chitosan is obtained by acidifying chitosan, so that the amino groups in chitosan combine with free H + in the environment to form a cationic polyelectrolyte - NH3 + , -NH3 + which can adsorb sulfate anions in the environment through electrostatic attraction, further enabling the shell to play a better controlled-release role in the process of realizing sulfate slow-release.

[0132] The resource conversion of biomass into a carbon-fixing functional carbon aggregate in the present invention has good economic significance and is conducive to the recycling and resource utilization of solid waste. Utilizing the structural and functional characteristics of biomass charcoal, it can be transformed into a substance carrier to continuously transport a certain effective component to the defective environment to continuously stimulate the latent ability of the original environment. Sulfate-reducing bacteria are widely present in environments such as soil, wastewater, and waste residue. Sulfate-reducing bacteria use sulfate as an electron acceptor and can use organic pollutants in the environment as a carbon source for life activities, reducing the risk of organic pollution. At the same time, the S 2- generated by sulfate reduction can interact with metal ions to form a stabilized precipitate and separate from the soil ecosystem, controlling the environmental concentration of heavy metals.

[0133] The present invention uses protonated modified biochar as the slow-release shell and sulfate as the slow-release center to prepare a composite microsphere with a core-shell structure of sulfate@protonated chitosan-modified porous carbon. Relying on sulfate-reducing bacteria widely present in nature, an effective sulfate slow-release system is provided. By continuously stimulating the life activities of sulfate-reducing bacteria, pollutant removal is achieved. On the one hand, the comprehensive utilization of waste biomass is realized, enabling it to directly contribute to the overall goal of carbon sequestration and emission reduction under the "dual carbon" background in the form of soil carbon sequestration. On the other hand, by efficiently empowering biomass products, they become an effective carrier for solving the problem of polluted soil in specific scenarios.

[0134] The present invention will be described in detail below through examples, but the scope protected by the present invention is not limited thereto.

[0135] Hereinafter, room temperature refers to 25°C, and the waste biomass used is corn straw.

[0136] Example 1

[0137] (1) The waste biomass was pre - crushed to 50 mesh by a crusher to obtain crushed biomass, and then evenly mixed with 0.2 mol / L NaOH solution (the solid - liquid ratio of crushed biomass to NaOH solution was 1 g:10 mL), and then heat - treated in a constant - temperature water bath (temperature was 60 °C, time was 3 h), and then filtered. The pH value of the filtrate obtained after filtration was adjusted to 7 to obtain a carbonaceous precursor;

[0138] (2) The triblock copolymer P123 (main template agent) was mixed with water to obtain a triblock copolymer P123 solution with a concentration of 0.1 mmol / L, and sodium dodecyl sulfate (co - template agent) was mixed with water to obtain a sodium dodecyl sulfate solution with a concentration of 4 mmol / L. 20 mL of the triblock copolymer P123 solution and 20 mL of the sodium dodecyl sulfate solution were taken respectively and thoroughly mixed to obtain a template agent micelle. The carbonaceous precursor and the template agent micelle were fully mixed in a volume ratio of 3:1 to form an emulsion. After stirring for 20 min, it was transferred to a reaction kettle for hydrothermal treatment. The conditions of the hydrothermal treatment included: temperature was 180 °C, time was constant temperature for 10 h. After the hydrothermal treatment was completed, the material obtained after hydrothermal treatment was cooled to room temperature, then centrifuged, and then filtered. The obtained solid was washed alternately with deionized water and absolute ethanol until the supernatant was clear to remove the unreacted template agent, and then the washed solid was dried to obtain hollow microspheres;

[0139] (3) Sodium sulfate, potassium sulfate and magnesium sulfate were fully mixed to obtain a mixed sulfate (calculated based on the total amount of sodium sulfate, potassium sulfate and magnesium sulfate being 100 wt%, the amount of sodium sulfate was 51 wt%, the amount of potassium sulfate was 6 wt%, and the amount of magnesium sulfate was 43 wt%). The hollow microspheres and the mixed sulfate were fully mixed in a weight ratio of 1:6 and placed in a tubular furnace with a N2 atmosphere for carbonization treatment. The conditions of the carbonization treatment were set as follows: heated to 160 °C at a heating rate of 6 °C / min, held for 7 h, and then heated to 700 °C at a heating rate of 10 °C / min and held for 5 h. The material obtained after carbonization was washed until there was no obvious suspended ash in the supernatant to obtain composite microspheres;

[0140] (4) Chitosan was added to an acetic acid solution (the content of acetic acid was 2 vol%), and was fully dissolved under the condition of a 40 °C water bath to obtain an acidified chitosan solution (the content of chitosan in the acidified chitosan solution was 4 wt%). Subsequently, composite microspheres were added, and the weight ratio of the composite microspheres to chitosan was 3:1. After fully stirring and mixing evenly, 5 mL of glutaraldehyde (crosslinking agent) was slowly added under the condition of stirring. The weight-to-volume ratio of chitosan to the dosage of the crosslinking agent was 1 g:5 mL. Stirring was continued at 40 °C for 40 min to mix evenly, and then the mixture was left standing at this temperature for 7 h. Then, the pH value of the system was adjusted to 8 with a sodium hydroxide solution, followed by filtration, and the obtained solid was washed thoroughly to obtain chitosan-modified composite microspheres;

[0141] (5) The chitosan-modified composite microspheres were added to a 0.2 mol / L sulfuric acid solution (the solid-liquid ratio of the dosage of the chitosan-modified composite microspheres to the acidic solution was 1 g:15 mL), and stirred thoroughly for 30 min, and then left standing for 10 h. The material obtained after standing was filtered, and the obtained solid was dried to obtain a protonated chitosan-modified sustained-release material M1, which had a core-shell structure, with the inner core being mixed sulfates and the shell layer being porous carbon modified with protonated chitosan.

[0142] Example 2

[0143] Implemented according to the method of Example 1, the difference being that in step (2), the concentration of the triblock copolymer P123 solution was 0.2 mmol / L and the concentration of the sodium dodecyl sulfate solution was 3.6 mmol / L to obtain a protonated chitosan-modified sustained-release material M2.

[0144] Example 3

[0145] Implemented according to the method of Example 1, the difference being that in step (2), the concentration of the triblock copolymer P123 solution was 0.4 mmol / L and the concentration of the sodium dodecyl sulfate solution was 3.3 mmol / L to obtain a protonated chitosan-modified sustained-release material M3.

[0146] Example 4

[0147] Implemented according to the method of Example 1, the difference being that in step (2), the concentration of the triblock copolymer P123 solution was 0.6 mmol / L and the concentration of the sodium dodecyl sulfate solution was 3 mmol / L to obtain a protonated chitosan-modified sustained-release material M4;

[0148] It was found by statistical analysis of the particle size distribution of M4 using a laser particle size analyzer that its particle size is concentrated between 25 - 40 μm; by pore size analysis using a physical adsorption instrument, its pore size is distributed between 1 - 10 nm, mainly micropores and mesopores; by characterization analysis using a transmission electron microscope, the thickness of the shell layer is 0.3 times the radius of the protonated chitosan-modified sustained-release material.

[0149] Example 5

[0150] Implemented according to the method of Example 1, the difference is that in step (2), the concentration of the triblock copolymer P123 solution is 0.8 mmol / L, and the concentration of the sodium dodecyl sulfate solution is 2.6 mmol / L, to obtain the protonated chitosan-modified sustained-release material M5.

[0151] Example 6

[0152] Implemented according to the method of Example 4, the difference is that in step (2), the carbonaceous precursor and the template agent micelles are fully mixed in a volume ratio of 1:1 to form an emulsion, to obtain the protonated chitosan-modified sustained-release material M6.

[0153] Example 7

[0154] Implemented according to the method of Example 4, the difference is that in step (2), the carbonaceous precursor and the template agent micelles are fully mixed in a volume ratio of 5:1 to form an emulsion, to obtain the protonated chitosan-modified sustained-release material M7.

[0155] Example 8

[0156] Implemented according to the method of Example 4, the difference is that in step (3), the conditions for carbonization treatment are set as follows: heating to 160 °C at a heating rate of 2 °C / min, holding for 7 h, then heating to 700 °C at a heating rate of 5 °C / min, and holding for 5 h, to obtain the protonated chitosan-modified sustained-release material M8.

[0157] Example 9

[0158] Implemented according to the method of Example 4, the difference is that in step (3), the conditions for carbonization treatment are set as follows: heating to 160 °C at a heating rate of 10 °C / min, holding for 7 h, then heating to 700 °C at a heating rate of 15 °C / min, and holding for 5 h, to obtain the protonated chitosan-modified sustained-release material M9.

[0159] Example 10

[0160] It was carried out according to the method of Example 4, except that in step (3), the carbonization treatment conditions were set as follows: heating to 160 °C at a heating rate of 6 °C / min, holding for 5 h, then heating to 700 °C at a heating rate of 10 °C / min, and holding for 3 h, to obtain the sustained-release material M10 modified with protonated chitosan.

[0161] Example 11

[0162] It was carried out according to the method of Example 4, except that in step (4), the weight ratio of the composite microspheres to chitosan was 2:1, to obtain the sustained-release material M11 modified with protonated chitosan.

[0163] Example 12

[0164] It was carried out according to the method of Example 4, except that in step (4), the weight ratio of the composite microspheres to chitosan was 4:1, to obtain the sustained-release material M12 modified with protonated chitosan.

[0165] Comparative Example 1

[0166] It was carried out according to the method of Example 4, except that a pulverizer was used to pulverize the waste biomass to 200 meshes to obtain pulverized biomass. The pulverized biomass was not subjected to alkali hydrolysis and was directly used as a carbonaceous precursor (the dosage of the pulverized biomass was the same as that in Example 4, and the dosage of the template agent micelles was also the same as that in Example 4), to obtain the sustained-release material D1 modified with protonated chitosan.

[0167] Comparative Example 2

[0168] It was carried out according to the method of Example 1, except that no template agent micelles were additionally used for the preparation of hollow carbon microspheres, that is, in step (2), the carbonaceous precursor was directly transferred to the reaction kettle for hydrothermal treatment to obtain hydrothermal carbon. In step (3), the hollow microspheres were replaced with the same weight of hydrothermal carbon to obtain sulfate composite carbon. In step (4), the composite microspheres were replaced with the same weight of sulfate composite carbon to obtain chitosan-modified sulfate composite carbon. In step (5), the chitosan-modified composite microspheres were replaced with the same weight of chitosan-modified sulfate composite carbon to obtain the protonated chitosan-modified sulfate composite carbon D2.

[0169] Test Example 1

[0170] The 24-hour sulfate sustained-release rate W of M1-M12 and D1-D2 was measured respectively to evaluate the sustained-release performance of the materials, and the calculation formula of W was as follows:

[0171]

[0172] Among them,

[0173] R 24The amount of sulfate radicals precipitated in the aqueous phase under light-shielding conditions for 24 hours on a constant-speed shaker (mg / g).

[0174] T is the total amount of sulfate radicals fixed by the slow-release material (mg / g).

[0175] During the test implementation process, 2 g of M1 - M12 and D1 - D2 were respectively taken and placed in a conical flask containing 250 mL of ultrapure water. Under light-shielding conditions, they were continuously shaken in a shaker at 150 rad / min for 24 hours, and the sulfate radical concentration in the supernatant was measured and recorded as R 24 . 10 g of M1 - M12 and D1 - D2 were respectively taken and placed in an alumina crucible, heated to 1000 °C in a muffle furnace and calcined for 2 hours to release the fixed sulfate radicals. After cooling, the calcined samples were taken out and redissolved, and the sulfate radical concentration in the supernatant was measured and recorded as T, which is the total amount of sulfate radicals fixed by the slow-release material. The test method for sulfate radical concentration refers to HJ84 - 2016 "Determination of Inorganic Anions in Water - Ion Chromatography Method".

[0176] The results are shown in Table 1.

[0177] Table 1

[0178]

[0179] Test Example 2

[0180] To determine the slow-release effect of M1 - M12 and D1 - D2 in the soil - groundwater environment, the test was carried out using the test device as Figure 2 shown to simulate and measure a simple permeable reactive barrier. The test device includes: a water storage container 2, a stirrer 1, a peristaltic pump 3, a reaction soil column 5 (with a length of 30 cm and a diameter of 10 cm), an outlet water storage container 6, and a nitrogen gas balloon 7; among them, the stirrer 1, the water storage container 2, the peristaltic pump 3, the reaction soil column 5, and the outlet water storage container 6 are connected in sequence. The reaction soil column 5 is provided with a sample loading port 4, an inlet and an outlet. The inlet is connected to the peristaltic pump 3, the outlet is connected to the outlet water storage container 6, and the nitrogen gas balloon 7 is connected to the water storage container 2;

[0181] The reaction soil column 5 of the test device is filled with a mixed filler of humic acid, soil, and quartz sand. After loading the sample through the sample loading port 4, it is spread evenly on the entire cross-section. As Figure 2 shown, after the sample is loaded through the sample loading port 4, the internal flow of soil and groundwater can be simulated in the device, and relevant indicators can be monitored to evaluate the slow-release performance of the material.

[0182] Slow-release performance test: After samples M1-M12 and D1-D2 were respectively loaded through the sample loading port 4, the filling thickness of the samples in the reaction soil column 5 was 1 cm. Tap water was contained in the lower part of the water storage container 2, and at the same time, nitrogen gas was filled into the water storage container 2 through the nitrogen gas balloon 7 so that the upper part of the water storage container 2 was filled with nitrogen gas to remove the oxygen in the upper headspace of the aqueous solution. Tap water in the water storage container 2 was continuously injected into the reaction soil column 5 from the water inlet of the reaction soil column 5 at a certain rate through the peristaltic pump 3 to simulate the permeable reactive barrier technology. The outflow concentration of sulfate in the effluent water in the outlet water storage device 6 (i.e., sulfate in the outlet of the reaction soil column 5) was regularly monitored to evaluate the slow-release effect of sulfate in the material, and the slow-release time of the material in the simulated soil groundwater was determined. During the test, the water inflow of the peristaltic pump 3 was adjusted to make the effluent rate in the outlet water storage device 6 3 mL / h.

[0183] Among them, the outflow concentrations of sulfate in the effluent water in the outlet water storage device 6 monitored at different times after injecting the samples are shown in Table 2.

[0184] Table 2

[0185]

[0186]

[0187] According to Table 1, it can be seen that M4 has better sulfate slow-release performance, and the slow-release rate in the aqueous phase in 24 hours is 52.17%. Combining with the long-term slow-release performance test results in Table 2, it is not difficult to see that the sulfate slow-release concentration of M4 can still reach 40 ppm at 100 d. Through the monitoring of the release of sulfate concentration, it is not difficult to estimate that its slow-release period can reach more than 120 d. It can be seen that the slow-release material modified by protonated chitosan of the present invention has good slow-release performance.

[0188] Test Example 3

[0189] The actual pollutant removal performance of the samples was detected using the same test device as in Test Example 2.

[0190] The following contaminated aquifer sediments used were obtained from the petroleum hydrocarbon-contaminated aquifer sediments in the contaminated soil of an enterprise site. The initial concentration of petroleum hydrocarbons was measured to be 103 mg / kg using GS-MS, and the water content of the contaminated aquifer sediments was 32%. The contaminated aquifer sediments taken for the test were placed in a tube and directly placed in a glove box after being sent to the laboratory, and air contact was avoided during the whole process.

[0191] The reactive soil column 5 is filled with contaminated aquifer sediment, which is loaded into M4 through the sample loading port 4 and then spread evenly over the entire cross-section, so that the filling thickness of the sample in the reactive soil column 5 is 1 cm, with contaminated aquifer sediment on both sides, simulating a permeable reactive barrier. The lower part of the water storage container 2 is filled with an aqueous solution of petroleum hydrocarbons with a concentration of 100 mg / L. Similarly, nitrogen is filled into the water storage container 2 through the nitrogen gas balloon 7, so that the upper part of the water storage container 2 is filled with nitrogen, removing the oxygen in the headspace above the aqueous solution of petroleum hydrocarbons. The aqueous solution of petroleum hydrocarbons in the water storage container 2 is continuously injected into the reactive soil column 5 from the water inlet of the reactive soil column 5 at a certain rate through the peristaltic pump 3, simulating the technology of the permeable reactive barrier. By regularly monitoring the data of the sulfate concentration and petroleum hydrocarbon pollutant concentration in the effluent of the water outlet water storage device 6, the actual pollutant removal effect of the material is evaluated. During the test, the water inflow of the peristaltic pump 3 is adjusted to make the effluent rate of the water outlet water storage device 6 3 mL / h. The results are shown in Table 3.

[0192] Table 3

[0193]

[0194] As can be seen from Table 3, in the initial stage of adding the material, due to reasons such as non-uniformity during the mixing process of the sediment and the reagent, systematic errors existing in the testing process, and sulfate-reducing bacteria that have not been fully activated, the level of sulfate utilization is low, the change in pollutant concentration is small, and it basically remains at about 100 ppm. Starting from the 10th day, the pollutant concentration changes greatly, and the increase in sulfate concentration slows down. This is because after a certain adaptation period, the vital activities of sulfate-reducing bacteria are gradually activated, and they can use the pollutants in the environment as a carbon source and sulfate as an electron acceptor for their own metabolic proliferation. By the 100th day, about 60%-70% of the pollutants have been basically degraded; in the later stage of the test, the pollutant concentration is basically at a low level, basically remaining at about 20 ppm, and the degradation rate slows down.

[0195] Test Example 4

[0196] M4 was tested according to the test method of Test Example 3, except that the pollutant was changed from petroleum hydrocarbons to a benzene solution with a concentration of 100 mg / kg, and the other steps were the same. The data of the sulfate concentration and benzene pollutant concentration in the effluent of the water outlet water storage device 6 were regularly monitored, and the results are shown in Table 4.

[0197] Table 4

[0198]

[0199] In Table 4, taking benzene as the degradation object, the degradation trend of benzene during the slow release process of sulfate was investigated, and the overall degradation effect was similar to that of petroleum hydrocarbons, corroborating the wide applicability of the slow-release material modified with protonated chitosan described in the present invention.

[0200] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A sustained-release material modified by protonated chitosan, characterized in that, The protonated chitosan-modified sustained-release material has a core-shell structure, where the core contains sulfate and the shell contains porous carbon modified with protonated chitosan; The raw materials for preparing the porous carbon modified with protonated chitosan contain biomass.

2. The sustained-release material modified with protonated chitosan according to claim 1, characterized in that, The sulfate is selected from one or more of magnesium sulfate, calcium sulfate, potassium sulfate, sodium sulfate, iron sulfate and lithium sulfate.

3. The sustained-release material modified with protonated chitosan according to claim 1 or 2, characterized in that The particle size of the protonated chitosan-modified sustained-release material is 10 - 50 μm, preferably 25 - 40 μm.

4. The sustained-release material modified with protonated chitosan according to claim 1 or 2, characterized in that, The pore size of the porous carbon modified with protonated chitosan is 1 - 20 nm, preferably 1 - 10 nm.

5. The sustained-release material modified with protonated chitosan according to claim 1, characterized in that, The thickness of the shell is 0.3 - 0.6 times the radius of the protonated chitosan-modified sustained-release material.

6. The preparation method of the sustained-release material modified by protonated chitosan according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: (1) Mix biomass with an alkaline solution and then conduct heat treatment, then filter, and adjust the pH value of the obtained filtrate to 7 - 7.5 to obtain a carbonaceous precursor; (2) Mix the carbonaceous precursor with a template agent micelle and then conduct heat treatment to obtain hollow microspheres; (3) Mix the hollow microspheres with sulfate and then conduct carbonization treatment, and then wash to obtain composite microspheres; (4) Mix the composite microspheres with chitosan, glacial acetic acid solution and a crosslinking agent, then conduct crosslinking, and then adjust the pH value of the system to alkaline to obtain chitosan-modified composite microspheres; (5) Mix the chitosan-modified composite microspheres with an acidic solution, stir and then let stand.

7. The preparation method according to claim 6, characterized in that, In step (1), the alkaline solution is selected from sodium hydroxide solution and / or potassium hydroxide solution; Preferably, the concentration of the alkaline solution is 0.1 - 0.3 mol / L; Preferably, the solid-liquid ratio of the dosage of biomass to the alkaline solution is 1 g: 5 - 15 mL, preferably 1 g: 9 - 12 mL.

8. The preparation method according to claim 6 or 7, characterized in that, In step (1), the conditions of the heat treatment are: temperature is 50 - 70 °C, time is 2 - 4 h.

9. The preparation method according to claim 6, wherein In step (2), the template agent micelle contains a main template agent and a co-template agent; Preferably, the molar ratio of the dosage of the main template agent to the co-template agent is 1: 1 - 40; Preferably, the main template agent is triblock copolymer P123; Preferably, the co-template agent is sodium dodecyl sulfate.

10. The preparation method according to claim 9, wherein, In step (2), the preparation method of the template agent micelle includes: mixing the main template agent solution with the co-template agent solution; Preferably, the volume ratio of the dosage of the carbonaceous precursor to the template agent micelle is 1 - 5:

1.

11. The preparation method according to any one of claims 6, 7, 9 or 10, characterized in that, In step (2), the heat treatment is hydrothermal treatment; Preferably, the conditions of the hydrothermal treatment include: temperature is 150 - 200 °C, time is 8 - 16 h.

12. The preparation method according to claim 6, characterized in that, In step (3), the weight ratio of the dosage of the hollow microspheres to the sulfate is 1: 5 - 10.

13. The preparation method according to claim 6 or 12, characterized in that, In step (3), the conditions of the carbonization treatment include: heating at a heating rate of 2 - 10 °C / min to 150 - 180 °C, holding for 5 - 7 h, and then heating at a heating rate of 5 - 15 °C / min to 700 - 800 °C, holding for 3 - 5 h.

14. The preparation method according to claim 6, characterized in that, In step (4), the specific process of mixing the composite microspheres with chitosan, glacial acetic acid solution and crosslinking agent includes: mixing chitosan with glacial acetic acid solution to obtain an acidified chitosan solution, then mixing the acidified chitosan solution with the composite microspheres, and then mixing with the crosslinking agent; Preferably, the content of chitosan in the acidified chitosan solution is 2-6 wt%.

15. The preparation method according to claim 6 or 14, characterized in that, In step (4), the content of glacial acetic acid in the glacial acetic acid solution is 2-5 vol%; Preferably, the weight ratio of the dosage of chitosan to the composite microspheres is 1:2-5.

16. The preparation method according to claim 6 or 14, characterized in that, In step (4), the crosslinking agent is selected from one or more of formaldehyde, glutaraldehyde and epichlorohydrin; Preferably, the weight-to-volume ratio of the dosage of chitosan to the crosslinking agent is 1 g:2-5 mL.

17. The preparation method according to claim 6 or 14, characterized in that, In step (4), the crosslinking operation includes: stirring at 35-45 °C for 35-50 min, and then standing for 6-8 h.

18. The preparation method according to claim 6, characterized in that, In step (5), the concentration of the acidic solution is 0.1-0.5 mol / L. Preferably, the acidic solution is selected from one or more of nitric acid solution, hydrochloric acid solution and sulfuric acid solution.

19. The preparation method according to claim 6 or 18, characterized in that, In step (5), the solid-liquid ratio of the dosage of the chitosan-modified composite microspheres to the acidic solution is 1 g:10-30 mL, preferably 1 g:10-20 mL; Preferably, the stirring time is 20-40 min; Preferably, the standing time is 8-12 h.

20. Use of the protonated chitosan-modified sustained-release material according to any one of claims 1-5 in the remediation of organic-polluted soil and groundwater.

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