Composite adsorption material, preparation method thereof and application of composite adsorption material in saline-alkali soil remediation

Abstract

The invention belongs to the technical field of soil remediation, and particularly relates to a composite adsorption material, a preparation method thereof and application of the composite adsorption material in saline-alkali soil remediation. The composite adsorption material is prepared from the following raw materials in parts by mass: 30 to 40 parts of chitosan modified biochar, 10 to 20 parts of phosphoric acid / deep eutectic solvent modified porous polymer and 40 to 50 parts of low-acyl gellan gum / gelatin hydrogel, chitosan in the chitosan modified biochar comprises carboxymethyl chitosan, phytic acid modified chitosan and maleic anhydride modified chitosan; the mass ratio of the carboxymethyl chitosan to the phytic acid modified chitosan to the maleic anhydride modified chitosan is 1: (6-10): (2-6). The composite adsorption material can improve the pH and the salt content of saline-alkali soil, and also can improve the porosity, the water content and the organic matter content.

Description

Technical Field

[0001] The invention belongs to the technical field of soil remediation, and specifically relates to a composite adsorption material and a preparation method thereof and application thereof in saline-alkali land remediation. Background Art

[0002] Saline-alkali land is a general term for various types of saline soil, alkaline soil, salinized and alkaline soil. The soil in saline-alkali land is compacted, has low porosity, poor air permeability and water infiltration, which in turn affects the growth, abundance, metabolism of microorganisms and the activity of biological enzymes in the soil, reduces the conversion rate of soil organic matter, and affects the normal growth of plants. Therefore, the restoration of saline-alkali land is of great significance.

[0003] In the prior art, a Chinese patent with publication number CN117737047A discloses a saline-alkali land desulfurized gypsum charcoal-based soil conditioner and its preparation method and application. The raw materials of the saline-alkali land desulfurized gypsum charcoal-based soil conditioner include the following components: desulfurized gypsum, biochar, Hangjin 2# soil, wood vinegar, halophilic Exosulfur Rhodospirillum, and Acidobacterium; the soil conditioner prepared by this technical solution not only repairs the saline-alkali soil but also adds nutrients to the soil, promotes crop growth, and the soil conditioner test group reduces the amount of chemical fertilizer by 20% compared with the control group; however, there are a large number of coal-fired power plants in my country, and the content of harmful elements such as heavy metals in the produced desulfurized gypsum is uneven. The environmental safety of the application of desulfurized gypsum in the agricultural field has always been a matter of great concern to all sectors of society.

[0004] A Chinese patent with publication number CN117903810A discloses a soil remediation agent suitable for saline-alkali land and a preparation method thereof. The soil remediation agent suitable for saline-alkali land is composed of component A and component B, wherein component A is a fermentation product of fresh peel and sugar fermented in water; component B is potassium humate, zeolite powder and biomass charcoal. The soil remediation agent uses discarded peel as raw material, which can turn waste into treasure. Other raw materials are also natural raw materials, which are green and environmentally friendly. The soil remediation agent provided can significantly reduce the pH value and salt content of saline-alkali land. However, the presence of fresh peel in this technical solution limits its large-scale application. Summary of the invention

[0005] In view of the above problems, the present invention provides a composite adsorption material and a preparation method thereof and application in saline-alkali land restoration. The composite adsorption material of the present invention can improve the pH and salt content of saline-alkali soil while also increasing porosity, water content and organic matter content.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of the present invention provides a composite adsorption material, wherein the raw materials include, by weight: 30-40 parts of chitosan-modified biochar, 10-20 parts of phosphoric acid / deep eutectic solvent-modified porous polymer, and 40-50 parts of low-acyl gellan gum / gelatin hydrogel;

[0008] The chitosan in the chitosan-modified biochar includes carboxymethyl chitosan, phytic acid-modified chitosan and maleic anhydride-modified chitosan; the mass ratio of the carboxymethyl chitosan, phytic acid-modified chitosan and maleic anhydride-modified chitosan is 1:(6-10):(2-6).

[0009] Preferably, the mass ratio of the carboxymethyl chitosan, the phytic acid modified chitosan and the maleic anhydride modified chitosan is 1:8:4.

[0010] Biochar has a large number of porous structures and strong adsorption capacity, and has broad application prospects in soil remediation. However, due to its alkalinity, it is generally used in acidic soils. In order to apply biochar to saline-alkali land, the biochar needs to be acidified. The existing technology often uses the method of soaking biochar in strong acid. However, soaking in strong acid will cause its structure to change, affecting its performance.

[0011] The present invention creatively uses carboxymethyl chitosan, phytic acid modified chitosan and maleic anhydride modified chitosan to modify biochar, which can not only neutralize the alkaline groups on the surface of biochar to avoid the destruction of the biochar structure, but also find that the three can synergistically enhance the effect. It is speculated that this is because the linear structure of carboxymethyl chitosan, the polyphosphate group of phytic acid modified chitosan and the rigid structure of maleic anhydride modified chitosan work together to form a complex cross-linked network on the surface of biochar, and the structure is more stable, so that the biochar can not only rely on itself to improve the soil structure, adsorb and fix the salt in the soil At the same time, the acidic functional groups (carboxyl, polyphosphate, and maleic acid) on the surface of the modified biochar can each play their own advantages (carboxyl and maleic acid groups provide acidity, and polyphosphate groups can not only provide acidity, but also form complexes with metal cations in the soil to reduce salt accumulation), comprehensively improving the salt content and pH of saline-alkali soil; in addition, the modified biochar forms a stable network structure between soil particles due to chitosan, further increasing the porosity of the soil; at the same time, due to the high water absorption and water retention of chitosan, the soil moisture content can be increased to a certain extent.

[0012] In some preferred embodiments, the carboxylation degree of the carboxymethyl chitosan is ≥80.

[0013] In some preferred embodiments, the deacetylation degree of the chitosan is ≥90%.

[0014] In some preferred embodiments, the preparation method of the phytic acid modified chitosan is:

[0015] (1) Dissolving chitosan in acetic acid solution to obtain a mixed solution A;

[0016] (2) uniformly mixing the phytic acid solution, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide to obtain a mixed solution B;

[0017] (3) Adding mixed solution A to mixed solution B for reaction, filtering, washing and drying after the reaction is completed.

[0018] In some preferred embodiments, the ratio of chitosan to acetic acid solution in step (1) is (1-2) g: (15-25) mL, preferably 1.5 g: 20 mL; and the concentration of the acetic acid solution is 2%.

[0019] In some preferred embodiments, the ratio of the phytic acid solution, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide in step (2) is (10-15) mL: (1-2) g: (0.4-0.8) g, preferably 12 mL: 1.5 g: 0.6 g.

[0020] In some preferred embodiments, the ratio of chitosan to phytic acid solution is (1-2) g: (1-1.5) mL, preferably 1.5 g: 1.5 mL.

[0021] In some preferred embodiments, the reaction temperature in step (3) is 50-60° C., and the reaction time is 90-120 min.

[0022] In some preferred embodiments, the preparation method of maleic anhydride modified chitosan is: first dissolving chitosan in ethanol to obtain a chitosan solution, then adding maleic anhydride to the chitosan solution for heating and reflux reaction for 120-180 minutes, and filtering, washing and drying after the heating and reflux reaction.

[0023] In some preferred embodiments, the mass ratio of chitosan to ethanol is (1-3):(80-100), preferably 2:98.

[0024] In some preferred embodiments, the mass ratio of chitosan to maleic anhydride is (5-7):(2-4), preferably 6:3.

[0025] In some preferred embodiments, the method for preparing chitosan-modified biochar comprises the following steps:

[0026] S1, pyrolyzing the dried and crushed coconut shell at 600-700°C under anaerobic conditions for 3-5h, drying, grinding, and passing through a 100-mesh sieve after the pyrolysis to obtain biochar;

[0027] S2, dissolving carboxymethyl chitosan, phytic acid-modified chitosan and maleic anhydride-modified chitosan in an acetic acid solution, and then adding biochar and stirring to obtain a suspension;

[0028] S3, adding sodium hydroxide to the suspension to adjust the pH to 8.5-9.5, stirring to react, filtering, washing and drying after the reaction is completed.

[0029] In some preferred embodiments, in step S2, the ratio of the total mass of the carboxymethyl chitosan, phytic acid modified chitosan and maleic anhydride modified chitosan to the acetic acid solution is (1-2) g: (300-400) mL, preferably 1.5 g: 350 mL; and the concentration of the acetic acid solution is 2%.

[0030] In some preferred embodiments, the mass ratio of the total mass of the carboxymethyl chitosan, phytic acid modified chitosan and maleic anhydride modified chitosan to the biochar in step S2 is 1:(5-7), preferably 1:6.

[0031] In some preferred embodiments, the stirring reaction in step S3 has a rotation speed of 200-300 rpm, a stirring reaction temperature of 25-30° C., and a stirring reaction time of 60-90 min.

[0032] In some preferred embodiments, the preparation method of the phosphoric acid / deep eutectic solvent modified porous polymer is:

[0033] Step 1, mixing an aqueous solution of a low eutectic solvent, phloroglucinol and 4,4',4'',4'''-silanetetrayltetrabenzaldehyde, preheating and stirring, and then performing a polymerization reaction, and washing and drying after the reaction to obtain a low eutectic solvent-modified porous polymer;

[0034] Step 2: Mix the low eutectic solvent modified porous polymer, ethyl phosphate solution and thionyl chloride to perform a reflux reaction, and after the reflux reaction is completed, filter and dry to obtain the phosphoric acid / low eutectic solvent modified porous polymer.

[0035] In the prior art, humic acid or humate is often used as an improver to improve the pH of saline-alkali land. However, studies have reported that humic acid has strong competitiveness and will preferentially combine with heavy metal ions to form soluble complexes. Although it can reduce the adsorption of heavy metals in the soil, the formed complexes can be absorbed by the roots of plants, which has a negative impact on plants. However, when only chitosan is used to modify biochar in the present invention, the improvement effect on saline-alkali land is poor. Therefore, the present invention creatively prepares a phosphoric acid / low eutectic solvent modified porous polymer, firstly loads the low eutectic solvent in the skeleton of the porous polymer formed by phloroglucinol-4,4',4'',4'''-silanetetrayltetrabenzaldehyde, and then fixes the phosphoric acid molecules on the hydroxyl groups on the porous polymer; the low eutectic solvent formed by choline chloride and panthenol can not only generate an insoluble complex by reacting with sodium ions, so as to continuously play the effect of fixing sodium ions, help improve soil structure and reduce salt content, but also has good water retention; after phosphoric acid is combined with the hydroxyl groups on the porous polymer, it can slowly release hydrogen ions in the soil, continuously improve the alkalinization of the soil; the porous polymer increases the porosity of the soil; in summary, the phosphoric acid / low eutectic solvent modified porous polymer and the chitosan modified biochar can significantly improve the pH of saline-alkali land, significantly increase the porosity of the soil and increase the soil water content to a certain extent through the synergistic effect.

[0036] In some preferred embodiments, the preparation method of the deep eutectic solvent in step 1 is: mixing choline chloride and panthenol in a molar ratio of 1:1.5-2.5 at 60-80° C. for 1-3 hours to obtain the deep eutectic solvent.

[0037] In some preferred embodiments, the aqueous solution of the low eutectic solvent in step 1 is prepared by mixing the low eutectic solvent and water in a mass ratio of (6-7):(3-4).

[0038] In some preferred embodiments, in step 1, the mass ratio of the low eutectic solvent, phloroglucinol and 4,4',4'',4'''-silanetetrayltetrabenzaldehyde is (3-4):(0.5-1):1, preferably 3.5:0.8:1.

[0039] In some preferred embodiments, the preheating and stirring temperature in step 1 is 60-70° C., and the preheating and stirring time is 30-50 min.

[0040] In some preferred embodiments, the polymerization reaction temperature in step 1 is 90-100° C., and the polymerization reaction time is 5-7 h.

[0041] In some preferred embodiments, the mass ratio of the low eutectic solvent-modified porous polymer, the ethyl phosphate solution and the thionyl chloride in step 2 is 1:(4-8):(0.5-1.5), preferably 1:6:1.

[0042] In some preferred embodiments, the ethyl phosphate solution in step 2 is a dichloromethane solution of ethyl phosphate; the molar concentration of the ethyl phosphate solution is 0.5 mol.

[0043] In some preferred embodiments, the heating reflux reaction time in step 2 is 18-24 hours.

[0044] In some preferred embodiments, the preparation method of the low acyl gellan gum / gelatin hydrogel is: dissolving low acyl gellan gum in water to obtain a low acyl gellan gum aqueous solution, dissolving gelatin in water to obtain a gelatin aqueous solution, mixing and stirring the low acyl gellan gum aqueous solution and the gelatin aqueous solution to obtain a low acyl gellan gum / gelatin aqueous solution; adding acetic acid to the low acyl gellan gum / gelatin aqueous solution, stirring evenly, removing bubbles, and gelling to obtain the obtained solution.

[0045] The inventors found that the phosphoric acid / low eutectic solvent modified porous polymer and chitosan modified biochar have limited increase in soil moisture content through synergistic action, and improve the soil moisture content. The present invention creatively prepares low acyl gellan gum / gelatin hydrogel, and unexpectedly finds that the hydrogel formed by the compounding of low acyl gellan gum and gelatin not only significantly improves the soil moisture content when used in the present invention compared with other hydrogels, but also increases the content of organic matter; the inventors speculate that it is because low acyl gellan gum increases the strength of gelatin, and the obtained hydrogel can ensure that the structure is not destroyed for a long time when the environment changes, thereby helping the soil to retain moisture for a long time. In addition, it can work together with the phosphoric acid / low eutectic solvent modified porous polymer and chitosan modified biochar, and while playing a water-retaining role, the complex structure and moist environment provided by the hydrogel are conducive to the survival and reproduction of beneficial microorganisms, accelerate the decomposition of organic matter, and the generated organic matter can be stored in the porous structure of the phosphoric acid / low eutectic solvent modified porous polymer and chitosan modified biochar, thereby avoiding the rapid mineralization and loss of organic matter. Furthermore, the inventors have also found that the best overall effect is achieved when the mass ratio of the chitosan-modified biochar, the phosphoric acid / low eutectic solvent-modified porous polymer, and the low acyl gellan gum / gelatin hydrogel is controlled to be (2-3):1:(2.5-4).

[0046] In some preferred embodiments, the mass ratio of the low acyl gellan gum to water is (3-6):50; the mass ratio of the gelatin to water is (10-15):100.

[0047] In some preferred embodiments, the volume ratio of the low acyl gellan gum / gelatin aqueous solution to acetic acid is 100:(1-3).

[0048] Preferably, the preparation method of the low acyl gellan gum / gelatin hydrogel is: dissolving low acyl gellan gum in water at 90-95°C to obtain a low acyl gellan gum aqueous solution, soaking gelatin for 10 minutes, and then dissolving it in water at 60-65°C to obtain a gelatin aqueous solution, mixing and stirring the low acyl gellan gum aqueous solution and the gelatin aqueous solution to obtain a low acyl gellan gum / gelatin aqueous solution; adding acetic acid to the low acyl gellan gum / gelatin aqueous solution, stirring evenly, removing bubbles, and gelling at 8°C for 48 hours to obtain the obtained product.

[0049] Preferably, the mass ratio of the chitosan-modified biochar, the phosphoric acid / low eutectic solvent-modified porous polymer and the low acyl gellan gum / gelatin hydrogel is (2-3):1:(2.5-4).

[0050] The second aspect of the present invention provides a method for preparing the above-mentioned composite adsorption material, comprising the following steps: uniformly mixing chitosan-modified biochar, phosphoric acid / low eutectic solvent-modified porous polymer and low acyl gellan gum / gelatin hydrogel to obtain the composite adsorption material.

[0051] The third aspect of the present invention provides the use of the above-mentioned composite adsorption material in saline-alkali land restoration.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] 1. The present invention creatively uses carboxymethyl chitosan, phytic acid modified chitosan and maleic anhydride modified chitosan to modify biochar, which can not only neutralize the alkaline groups on the surface of biochar to avoid the destruction of the biochar structure, but also find that the three can synergistically enhance the effect, improve the salt content and pH of saline-alkali soil, increase the porosity of the soil, and increase the soil water content to a certain extent.

[0054] 2. The present invention creatively prepares a phosphoric acid / low eutectic solvent modified porous polymer. The phosphoric acid / low eutectic solvent modified porous polymer and chitosan modified biochar can significantly improve the pH of saline-alkali land, significantly increase the porosity of the soil, and increase the soil water content to a certain extent through synergistic effect.

[0055] 3. The present invention creatively prepares low acyl gellan gum / gelatin hydrogel, and unexpectedly finds that the hydrogel formed by compounding low acyl gellan gum and gelatin not only significantly improves the soil water content when used in the present invention, but also increases the content of organic matter compared to other hydrogels.

[0056] 4. When the mass ratio of chitosan-modified biochar, phosphoric acid / low eutectic solvent-modified porous polymer and low acyl gellan gum / gelatin hydrogel is controlled to be (2-3):1:(2.5-4), the comprehensive effect is the best. DETAILED DESCRIPTION

[0057] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, a specific implementation scheme is now described in detail.

[0058] The present invention is further described below in conjunction with the embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to the different requirements of specific use, and the implementation conditions not indicated are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0059] In the following examples and comparative examples, unless otherwise specified, the raw materials used are commercially available or prepared by conventional methods in the art. It should also be noted that the manufacturers of all plant extracts used in the examples of the present invention are only for illustrative purposes, and the source of the manufacturer does not affect the main active ingredients and the effects of the present invention.

[0060] Example 1

[0061] A composite adsorption material, wherein the raw materials are composed of 30 parts of chitosan-modified biochar, 10 parts of phosphoric acid / low eutectic solvent-modified porous polymer, and 40 parts of low acyl gellan gum / gelatin hydrogel, by weight.

[0062] The chitosan in the chitosan-modified biochar includes carboxymethyl chitosan, phytic acid-modified chitosan and maleic anhydride-modified chitosan; the mass ratio of the carboxymethyl chitosan, phytic acid-modified chitosan and maleic anhydride-modified chitosan is 1:8:4.

[0063] The carboxylation degree of the carboxymethyl chitosan is ≥80 and is purchased from Shanghai Shifeng Biotechnology Co., Ltd.

[0064] The chitosan has a deacetylation degree of ≥90% and was purchased from Shanghai Shifeng Biotechnology Co., Ltd.

[0065] The preparation method of the phytic acid modified chitosan is:

[0066] (1) Dissolving chitosan in acetic acid solution to obtain a mixed solution A;

[0067] (2) Evenly mix the phytic acid solution, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (CAS No.: 7084-11-9) and N-hydroxysuccinimide (CAS No.: 6066-82-6) to obtain a mixed solution B;

[0068] (3) Adding mixed solution A to mixed solution B for reaction, filtering, washing and drying after the reaction is completed.

[0069] In step (1), the ratio of chitosan to acetic acid solution is 1.5 g:20 mL; the concentration of the acetic acid solution is 2%.

[0070] The ratio of the phytic acid solution, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide in step (2) is 12 mL: 1.5 g: 0.6 g.

[0071] The ratio of the chitosan to phytic acid solution is 1.5 g:1.5 mL.

[0072] Phytic acid solution was purchased from Nanjing Quanlong Biotechnology Co., Ltd. with a specification of 70%.

[0073] The reaction temperature in step (3) is 55°C and the reaction time is 120 min.

[0074] The preparation method of the maleic anhydride modified chitosan is as follows: firstly dissolving chitosan in ethanol to obtain a chitosan solution, then adding maleic anhydride (CAS No.: 108-31-6) to the chitosan solution for heating and reflux reaction for 150 minutes, and filtering, washing and drying after the reflux reaction is completed.

[0075] The mass ratio of chitosan to ethanol is 2:98.

[0076] The mass ratio of chitosan to maleic anhydride is 6:3.

[0077] The preparation method of the chitosan modified biochar is:

[0078] S1, pyrolyzing the dried and crushed coconut shell at 680°C under anaerobic conditions for 4 hours, drying, grinding, and passing through a 100-mesh sieve after the pyrolysis to obtain biochar;

[0079] S2, dissolving carboxymethyl chitosan, phytic acid-modified chitosan and maleic anhydride-modified chitosan in an acetic acid solution, and then adding biochar and stirring to obtain a suspension;

[0080] S3, adding sodium hydroxide to the suspension to adjust the pH to 9.0, stirring to react, filtering, washing and drying after the reaction is completed.

[0081] In step S2, the ratio of the total mass of the carboxymethyl chitosan, the phytic acid modified chitosan and the maleic anhydride modified chitosan to the acetic acid solution is 1.5 g:350 mL; and the concentration of the acetic acid solution is 2%.

[0082] The mass ratio of the total mass of the carboxymethyl chitosan, the phytic acid modified chitosan and the maleic anhydride modified chitosan to the biochar in step S2 is 1:6.

[0083] The stirring reaction in step S3 was carried out at a rotation speed of 250 rpm, a temperature of 28° C., and a time of 70 min.

[0084] The preparation method of the phosphoric acid / deep eutectic solvent modified porous polymer is:

[0085] Step 1, mixing an aqueous solution of a low eutectic solvent, phloroglucinol (CAS No.: 108-73-6) and 4,4',4'',4'''-silanetetrayltetrabenzaldehyde (CAS No.: 1055999-34-2), preheating and stirring, and then performing a polymerization reaction. After the reaction is completed, washing and drying are performed to obtain a low eutectic solvent-modified porous polymer;

[0086] Step 2: Mix the low eutectic solvent modified porous polymer, ethyl phosphate solution and thionyl chloride and reflux for 20 hours. After the reflux reaction is completed, filter and dry to obtain the phosphoric acid / low eutectic solvent modified porous polymer.

[0087] The preparation method of the low eutectic solvent in step 1 is: mixing choline chloride and panthenol in a molar ratio of 1:2 at 70° C. and reacting for 2 hours to obtain the low eutectic solvent.

[0088] The aqueous solution of the low eutectic solvent in step 1 is prepared by mixing the low eutectic solvent and water in a mass ratio of 6:3.

[0089] In step 1, the mass ratio of the low eutectic solvent, phloroglucinol and 4,4',4'',4'''-silanetetrayltetrabenzaldehyde is 3.5:0.8:1.

[0090] The preheating stirring temperature in step 1 is 70° C., and the preheating stirring time is 40 min.

[0091] The polymerization reaction temperature in step 1 is 95° C., and the polymerization reaction time is 6 h.

[0092] The mass ratio of the low eutectic solvent modified porous polymer, ethyl phosphate solution and thionyl chloride in step 2 is 1:6:1.

[0093] The ethyl phosphate solution in step 2 is a solution of ethyl phosphate (CAS No.: 78-40-0) in dichloromethane (CAS No.: 75-09-2); the molar concentration of the ethyl phosphate solution is 0.5 mol.

[0094] The preparation method of the low acyl gellan gum / gelatin hydrogel is as follows: dissolving low acyl gellan gum in water at 90°C to obtain a low acyl gellan gum aqueous solution, soaking gelatin for 10 minutes and then dissolving it in water at 65°C to obtain a gelatin aqueous solution, mixing and stirring the low acyl gellan gum aqueous solution and the gelatin aqueous solution to obtain a low acyl gellan gum / gelatin aqueous solution; adding acetic acid to the low acyl gellan gum / gelatin aqueous solution, stirring evenly, removing bubbles, and gelling at 8°C for 48 hours to obtain the product.

[0095] The mass ratio of the low acyl gellan gum to water is 5:50; the mass ratio of the gelatin to water is 12:100.

[0096] The volume ratio of the low acyl gellan gum / gelatin aqueous solution to acetic acid is 100:2.

[0097] Low acyl gellan gum was purchased from Zhengzhou Opel Biotechnology Co., Ltd., gel type.

[0098] Gelatin was purchased from Shanghai Fushen Biotechnology Co., Ltd. with an average molecular weight of 50,000-10,000.

[0099] The preparation method of the composite adsorption material is as follows: chitosan-modified biochar, phosphoric acid / low eutectic solvent-modified porous polymer and low acyl gellan gum / gelatin hydrogel are uniformly mixed to obtain the composite adsorption material.

[0100] Example 2

[0101] The difference from Example 1 is that the raw materials of the composite adsorption material, calculated by mass, include: 40 parts of chitosan-modified biochar, 20 parts of phosphoric acid / low eutectic solvent-modified porous polymer, and 50 parts of low acyl gellan gum / gelatin hydrogel; the rest are the same.

[0102] The preparation method of the above composite adsorption material is the same as that of Example 1.

[0103] Example 3

[0104] The difference from Example 1 is that the raw materials of the composite adsorption material, calculated by mass, are composed of 36 parts of chitosan-modified biochar, 15 parts of phosphoric acid / low eutectic solvent-modified porous polymer, and 45 parts of low acyl gellan gum / gelatin hydrogel; the rest are the same.

[0105] The preparation method of the above composite adsorption material is the same as that of Example 1.

[0106] Comparative Example 1

[0107] The difference from Example 3 is that the carboxymethyl chitosan and phytic acid modified chitosan are replaced by maleic anhydride modified chitosan of the same mass respectively; the rest are the same.

[0108] Comparative Example 2

[0109] The difference from Example 3 is that the carboxymethyl chitosan and the maleic anhydride modified chitosan are replaced by phytic acid modified chitosan of the same mass respectively; the rest are the same.

[0110] Comparative Example 3

[0111] The difference from Example 3 is that the phytic acid modified chitosan and the maleic anhydride modified chitosan are replaced by carboxymethyl chitosan of the same mass respectively; the rest are the same.

[0112] Comparative Example 4

[0113] The difference from Example 3 is that the phosphoric acid / low eutectic solvent modified porous polymer is replaced by a phosphoric acid modified porous polymer; the preparation method of the phosphoric acid modified porous polymer is as follows: Step 1, mix pyrogallol and 4,4',4'',4'''-silane tetrayl tetrabenzaldehyde and 1,4-dioxane, preheat and stir, then carry out polymerization reaction, wash and dry the porous polymer after the reaction is completed; in step 1, the mass ratio of pyrogallol and 4,4',4'',4'''-silane tetrayl tetrabenzaldehyde and 1,4-dioxane is 0.8:1:20. The preheating and stirring temperature in step 1 is 70°C, and the preheating and stirring time is 40min. The polymerization reaction temperature in step 1 is 90°C, and the polymerization reaction time is 24h.

[0114] Step 2, the porous polymer, ethyl phosphate solution and thionyl chloride are mixed and refluxed for 20 hours. After the reflux reaction is completed, the porous polymer is filtered and dried to obtain a phosphoric acid / deep eutectic solvent modified porous polymer; the rest are the same.

[0115] Comparative Example 5

[0116] The difference from Example 3 is that the phosphoric acid / low eutectic solvent modified porous polymer is replaced by chitosan modified biochar of equal mass; the rest are the same.

[0117] Comparative Example 6

[0118] The difference from Example 3 is that the chitosan-modified biochar is replaced with an equal mass of phosphoric acid / low eutectic solvent-modified porous polymer; the rest are the same.

[0119] Comparative Example 7

[0120] The difference from Example 3 is that low acyl gellan gum is replaced with chitosan of the same mass; the rest are the same.

[0121] Comparative Example 8

[0122] The difference from Example 3 is that the mass ratio of chitosan-modified biochar, phosphoric acid / low eutectic solvent-modified porous polymer and low acyl gellan gum / gelatin hydrogel is 1:3:2.3, that is, the composite adsorption material, by mass, consists of 15 parts of chitosan-modified biochar, 45 parts of phosphoric acid / low eutectic solvent-modified porous polymer and 36 parts of low acyl gellan gum / gelatin hydrogel; the rest are the same.

[0123] Application Examples

[0124] The composite adsorption materials prepared in Examples 1-3 and Comparative Examples 1-8 were applied to the saline-alkali land improvement test in Lanzhou New District, Gansu Province. The test area was plowed at a depth of about 25 cm and divided into 11 areas, each with an area of ​​10×10 m. The composite adsorption materials of Examples 1-3 and Comparative Examples 1-8 were applied respectively, and the application amount was 200 kg per mu; marigold seeds were sown on June 5, 2024, and 0-20 cm soil was taken on September 5, 2024 to detect pH, water-soluble salts, porosity, water content and organic matter. Among them, pH (soil-water mass ratio 10:2.5) was determined according to standard NY / T 1377-2007; water-soluble salts were determined according to standard NY / T1121.16-2006; porosity was determined according to standard NY / T 1121.4-2006; water content was determined according to standard NY / T1121.3-2006; soil organic matter content was determined according to standard NY / T 1121.6-2006; the results are shown in Table 1.

[0125] Table 1 Application results of composite adsorption materials of Examples 1-3 and Comparative Examples 1-8

[0126]

[0127] As can be seen from Table 1, the composite adsorption materials of Examples 1-3 can improve the pH and salt content of saline-alkali soil while also increasing porosity, water content and organic matter content;

[0128] It can be seen from Comparative Examples 1 to 3 that when the same amount of chitosan but only one type is used to modify the biochar, the effects of the three modifications cannot reach the effect of Example 3, indicating that the use of carboxymethyl chitosan, phytic acid-modified chitosan and maleic anhydride-modified chitosan to modify biochar has an effect of 1+1+1>3, and the three have a synergistic effect;

[0129] In Comparative Example 4, since the porous polymer was not modified by a low eutectic solvent, the effect of the obtained composite adsorption material on improving saline-alkali soil was reduced;

[0130] It can be seen from Comparative Examples 5-6 that when only chitosan-modified biochar or phosphoric acid / deep eutectic solvent-modified porous polymer is used, both cannot achieve the effect of Example 3, indicating that the use of chitosan-modified biochar and phosphoric acid / deep eutectic solvent-modified porous polymer has an effect of 1+1>2, and the two have a synergistic effect;

[0131] In Comparative Example 7, since low acyl gellan gum was replaced with chitosan of equal mass, the obtained composite adsorption material had a decreased effect on improving the water content of the soil and a decreased organic matter content;

[0132] It can be seen from Comparative Example 8 that even if chitosan-modified biochar and phosphoric acid / low eutectic solvent-modified porous polymer are used at the same time, when the mass ratio of chitosan-modified biochar, phosphoric acid / low eutectic solvent-modified porous polymer and low acyl gellan gum / gelatin hydrogel is not in the range of (2-3):1:(2.5-4), the modification effect of the composite adsorbent on saline-alkali land decreases.

[0133] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A composite adsorption material, characterized in that: The raw materials include, by weight: 30-40 parts of chitosan-modified biochar, 10-20 parts of phosphoric acid / low eutectic solvent-modified porous polymer, and 40-50 parts of low acyl gellan gum / gelatin hydrogel; The chitosan in the chitosan-modified biochar includes carboxymethyl chitosan, phytic acid-modified chitosan and maleic anhydride-modified chitosan; the mass ratio of the carboxymethyl chitosan, phytic acid-modified chitosan and maleic anhydride-modified chitosan is 1:(6-10):(2-6).

2. The composite adsorption material according to claim 1, characterized in that: The preparation method of the phytic acid modified chitosan is: (1) Dissolving chitosan in acetic acid solution to obtain a mixed solution A; (2) uniformly mixing the phytic acid solution, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide to obtain a mixed solution B; (3) Adding mixed solution A to mixed solution B for reaction, filtering, washing and drying after the reaction is completed.

3. The composite adsorption material according to claim 2, characterized in that: The preparation method of the maleic anhydride modified chitosan is as follows: firstly dissolving chitosan in ethanol to obtain a chitosan solution, then adding maleic anhydride to the chitosan solution to heat and reflux for 120-180 minutes, and filtering, washing and drying after the reflux reaction is completed.

4. The composite adsorption material according to claim 3, characterized in that: The method for preparing chitosan-modified biochar comprises the following steps: S1, pyrolyzing the dried and crushed coconut shell at 600-700°C under anaerobic conditions for 3-5h, drying, grinding, and passing through a 100-mesh sieve after the pyrolysis to obtain biochar; S2, dissolving carboxymethyl chitosan, phytic acid-modified chitosan and maleic anhydride-modified chitosan in an acetic acid solution, and then adding biochar and stirring to obtain a suspension; S3, adding sodium hydroxide to the suspension to adjust the pH to 8.5-9.5, stirring to react, filtering, washing and drying after the reaction is completed.

5. The composite adsorption material according to claim 4, characterized in that: The preparation method of the phosphoric acid / deep eutectic solvent modified porous polymer is: Step 1, mixing an aqueous solution of a low eutectic solvent, phloroglucinol and 4,4',4'',4'''-silanetetrayltetrabenzaldehyde, preheating and stirring, and then performing a polymerization reaction, and washing and drying after the reaction to obtain a low eutectic solvent-modified porous polymer; Step 2: Mix the low eutectic solvent modified porous polymer, ethyl phosphate solution and thionyl chloride and heat them under reflux reaction. After the heating and reflux reaction is completed, filter and dry to obtain the phosphoric acid / low eutectic solvent modified porous polymer.

6. The composite adsorption material according to claim 5, characterized in that: The preparation method of the low eutectic solvent in step 1 is: mixing choline chloride and panthenol in a molar ratio of 1:1.5-2.5 at 60-80° C. for 1-3 hours to obtain the low eutectic solvent.

7. The composite adsorption material according to claim 6, characterized in that: The preparation method of the low acyl gellan gum / gelatin hydrogel comprises the following steps: dissolving low acyl gellan gum in water to obtain a low acyl gellan gum aqueous solution, dissolving gelatin in water to obtain a gelatin aqueous solution, mixing and stirring the low acyl gellan gum aqueous solution and the gelatin aqueous solution to obtain a low acyl gellan gum / gelatin aqueous solution; adding acetic acid to the low acyl gellan gum / gelatin aqueous solution, stirring evenly, removing bubbles, and gelling to obtain the low acyl gellan gum / gelatin aqueous solution.

8. The composite adsorption material according to claim 7, characterized in that: The mass ratio of the chitosan-modified biochar, the phosphoric acid / low eutectic solvent-modified porous polymer and the low-acyl gellan gum / gelatin hydrogel is (2-3):1:(2.5-4).

9. The method for preparing the composite adsorption material according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: uniformly mixing chitosan-modified biochar, phosphoric acid / low eutectic solvent-modified porous polymer and low acyl gellan gum / gelatin hydrogel to obtain the biochar.

10. Use of the composite adsorption material according to any one of claims 1 to 8 in saline-alkali land restoration.

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