Composite biochar material with gradient pore structure and preparation method thereof

Abstract

The application provides a composite biochar material with a gradient pore structure and a preparation method thereof. The composite biochar material is obtained by high-temperature carbonization of a composite gel with a gradient pore structure, the composite gel with the gradient pore structure is obtained by centrifugal separation and directional photocuring, and the composite gel is composed of pre-activated dolomite and alkali pretreated soybean dregs. In the application, the density difference between the soybean dregs and the dolomite forms a gradient distribution of a layered structure during centrifugation, and the layered structure is solidified to maintain the gradient pore structure of the material in the subsequent carbonization process.

Description

Technical Field

[0001] This invention relates to the field of biochar materials, specifically to a composite biochar material with a gradient pore structure and its preparation method. Background Technology

[0002] With rapid industrialization and economic development, aquatic ecosystems are increasingly disturbed, and water environment issues are drawing growing attention. Eutrophication is a common pollution phenomenon, typically caused by excessive levels of nitrogen, phosphorus, and other compounds in the water, leading to overgrowth of aquatic organisms, particularly algae and phytoplankton. Excessive phosphate levels are a major contributing factor to eutrophication. High concentrations of phosphate exacerbate algal growth, thus deteriorating the quality of aquatic ecosystems. The severity of phosphorus pollution and the progress in its prevention and control have attracted widespread attention from researchers.

[0003] Currently, adsorption has become a commonly used and effective method for phosphorus removal in water treatment due to its advantages such as simple operation, environmental friendliness, cost-effectiveness, and applicability to various water quality conditions. It also demonstrates strong adaptability to changes in water quality and does not significantly interfere with microorganisms during the biochemical treatment process. Numerous studies have been conducted on phosphate adsorbents, including the synthesis of metal oxides / hydroxides, carbonate minerals, clay minerals, activated carbon and biochar, polymers, as well as bio-derived materials and industrial waste. The selection and modification optimization of adsorbent materials has always been a research hotspot in phosphate adsorption. Factors such as the economic viability of adsorbent raw materials, the complexity of the preparation process, the adsorption capacity for phosphates, and the recovery and reuse of adsorbed phosphorus all influence the selection.

[0004] Biochar is a solid material obtained by thermochemically converting biomass under oxygen-limited conditions to 200–900℃. Biochar materials are simple and inexpensive to obtain, including agricultural waste, forestry waste, animal manure, and sludge. my country generates a large amount of waste biomass annually, requiring disposal, and this vast quantity represents a natural, green, and low-cost raw material. In recent years, research reports on modified biochar have been continuously updated, showing improvements in adsorption performance, production costs, and reusability. However, the extensive use of chemical reagents has directly increased production costs and indirectly caused environmental pollution.

[0005] Therefore, to address the aforementioned issues, this study employs dolomite instead of chemical reagents to prepare a mineral-soybean residue biochar composite material for removing phosphates from water. Natural dolomite is a carbonate mineral rich in elements such as Ca, Mg, Fe, and Mn, with its main chemical component being CaMg(CO3)2. It is characterized by its low cost, wide distribution, and ease of acquisition. Furthermore, soybean cultivation and related processing industries have a long history in my country. Soybean residue, a byproduct of soybean product production, is produced in my country annually in quantities of approximately 20 million tons. Due to its high moisture content and susceptibility to mold and decay, most soybean residue is used as animal feed or even discarded directly, resulting in low recycling and utilization rates. This not only occupies land resources and causes environmental pollution but also leads to resource waste due to its high protein, fat, and mineral content. Therefore, preparing a highly efficient phosphorus removal adsorbent from non-toxic, side-effect-free, and abundant soybean residue biomass using a dolomite-soybean residue biochar composite adsorbent holds promise for reducing greenhouse gases and solving problems such as phosphorus pollution in wastewater and the difficulty of disposing of waste biomass. Summary of the Invention

[0006] Technical problem to be solved: This invention provides a composite biochar material with a gradient porous structure and its preparation method, which utilizes the gradient porous structure of the composite biochar material and the metal ions contained in dolomite to achieve the adsorption of phosphorus in water.

[0007] Technical solution:

[0008] A composite biochar material with a gradient pore structure is obtained by high-temperature carbonization of a composite gel with a gradient pore structure. The composite gel with a gradient pore structure is obtained by centrifugation and directional photocuring. The composite gel is composed of pre-activated dolomite and soybean residue pretreated with alkali.

[0009] Preferably, the preparation method includes the following steps:

[0010] S1. After pre-cooling the pre-activated dolomite / sodium methacrylate solution, inject it into a centrifuge tube, then add the alkali-pretreated soybean residue / sodium methacrylate solution, and centrifuge to obtain a mixed solution with upper and lower layers.

[0011] S2. The product obtained in S1 is heated and then subjected to directional photocuring to obtain a composite gel with a gradient porous structure.

[0012] S3. The composite gel obtained in S2 is subjected to high-temperature carbonization. After removing the product, it is washed with water until neutral to obtain a composite biochar material with a gradient porous structure.

[0013] Preferably, the mass ratio of the pre-activated dolomite / sodium methacrylate solution and the alkali-pretreated soybean residue / sodium methacrylate solution in S1 is 1-9:1-9.

[0014] Preferably, the method for preparing the sodium alginate methacrylate solution in S1 includes the following steps:

[0015] S11. Sodium alginate and methacrylic anhydride are reacted in a molar ratio of 1-4:0.3-0.8 to obtain sodium methacrylate;

[0016] S12. Add the sodium alginate methacrylate obtained in S11 to water, and add lithium phenyl-2,4,6-trimethylbenzoylphosphinic acid to obtain a sodium alginate methacrylate solution with a mass fraction of 2-6 wt%.

[0017] Preferably, the preparation of the pre-activated dolomite / sodium methacrylate solution in S1 includes the following steps:

[0018] S21. Dolomite and deionized water are mixed at a mass ratio of 1-3:2-7, and microwaved for 3-6 minutes to obtain pre-activated dolomite; S22. The pre-activated dolomite obtained in S21 is added to a sodium alginate methacrylate solution, and 1-4 wt% of Pluronic F127 thermosensitive gel is added to obtain a pre-activated dolomite / sodium alginate methacrylate solution with a mass fraction of 60-80 wt%. Preferably, the preparation of the alkali-pretreated soybean residue / sodium alginate methacrylate solution in S1 includes the following steps:

[0019] S31. Soak soybean residue in sodium bicarbonate solution with pH 8-9 for 1-2 hours, then wash and dry to obtain alkali-pretreated soybean residue; S32. Add the alkali-pretreated soybean residue to sodium methacrylate solution to obtain a alkali-pretreated soybean residue / sodium methacrylate solution with a mass fraction of 60-80 wt%.

[0020] Preferably, in step S2, the upper layer photocuring is performed by irradiating the top with 330-370nm UV light for 50-70 seconds, and the lower layer photocuring is performed by irradiating the bottom of the transparent tube with 390-410nm laser light for 25-35 seconds.

[0021] Preferably, the temperature for the heating process in S2 is 25–40°C, and the time is 4–8 minutes.

[0022] Preferably, the carbonization temperature in step S3 is 500–900°C, the heating rate is 8–12°C / min, and the holding time is 1.5–2.5 h. Beneficial effects: This invention has the following advantages:

[0023] 1. The calcium and magnesium ions in dolomite provide active sites for phosphate adsorption, while soybean residue, as an agricultural waste, has a large amount of organic components that form a porous structure and rich functional groups after pyrolysis. The synergistic effect of the two not only solves the waste treatment problem, but also improves the overall adsorption performance of the material.

[0024] 2. In this invention, the density difference between soybean residue and dolomite is utilized to form a gradient-distributed layered structure during centrifugation. Subsequently, the synergistic effect of thermosensitive gel and photocuring, i.e., the dual synergy of physicochemical processes, is utilized to form a physical gel after centrifugation by heating, which temporarily fixes the layered structure. Then, chemical cross-linking is achieved through directional photocuring, and the upper layer is cured with UV light to gently cross-link the soybean residue-sodium alginate layer, forming an open microporous network. The lower layer is cured with laser light to penetrate the dolomite layer. High-density cross-linking locks the position of mineral particles, preventing particle migration during carbonization and pore collapse, thus maintaining the gradient pore structure of the material during subsequent carbonization.

[0025] 3. The composite biochar obtained in this invention has a gradient pore structure, charge, and chemical site triple synergistic mechanism, which enables highly efficient adsorption of phosphorus in water (adsorption efficiency reaches 99.3%). Moreover, the adsorbed phosphorus can be continuously released, prolonging the effective release cycle of phosphorus in the soil, improving the utilization rate of phosphate fertilizer, and breaking the application dilemma of traditional phosphate fertilizer. Attached Figure Description

[0026] Figure 1 The adsorption capacity and removal rate of phosphorus in water by the biochar composite material obtained in Example 8 in initial solutions with different pH values ​​are shown.

[0027] Figure 2 The adsorption capacity and removal rate of phosphorus in water by dolomite-soybean residue biochar composite materials prepared with different composite ratios. Detailed Implementation

[0028] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments:

[0029] Example 1

[0030] A composite biochar material with a gradient pore structure and its preparation method, the preparation method comprising the following steps:

[0031] S1. After pre-cooling the pre-activated dolomite / sodium methacrylate solution to 0°C, inject it into a centrifuge tube, and then add the alkali-pretreated soybean residue / sodium methacrylate solution. The mass ratio of the pre-activated dolomite / sodium methacrylate solution to the alkali-pretreated soybean residue / sodium methacrylate solution is 7:3. After centrifugation, a mixed solution with upper and lower layers is obtained.

[0032] S2. The product obtained in S1 is heated to 25℃ for 4 min and then subjected to directional photocuring. The upper layer is photocured by irradiating the top with 330nm UV for 50s, and the lower layer is photocured by irradiating the bottom of the transparent tube with 390nm laser for 25s, to obtain a composite gel with a gradient porous structure.

[0033] S3. The composite gel obtained in S2 is subjected to high-temperature carbonization at a temperature of 500℃, a heating rate of 8℃ / min, and a holding time of 1.5h. After removing the product, it is washed with water until neutral to obtain a composite biochar material with a gradient porous structure.

[0034] The preparation method of the sodium alginate methacrylate solution in S1 includes the following steps:

[0035] S11. Sodium alginate and methacrylic anhydride are reacted at a molar ratio of 1:0.3 to obtain sodium methacrylate;

[0036] S12. Add the sodium alginate methacrylate obtained in S11 to water, and add lithium phenyl-2,4,6-trimethylbenzoylphosphinic acid to obtain a sodium alginate methacrylate solution with a mass fraction of 2%.

[0037] The preparation of the pre-activated dolomite / sodium methacrylate solution in S1 includes the following steps:

[0038] S21. Mix dolomite and deionized water at a mass ratio of 2:5 and microwave for 3 minutes to obtain pre-activated dolomite;

[0039] S22. Add the preactivated dolomite obtained in S21 to the sodium methacrylated alginate solution and add 1 wt% of Pluronic F127 thermosensitive gel to obtain a preactivated dolomite / sodium methacrylated alginate solution with a mass fraction of 60 wt%.

[0040] The preparation of the alkali-pretreated soybean residue / sodium methacrylate solution in S1 includes the following steps:

[0041] S31. Soak soybean residue in sodium bicarbonate solution with a pH of 8 for 1 hour, then wash and dry to obtain soybean residue pretreated with alkali.

[0042] S32. Add the alkali-pretreated soybean residue to a sodium methacrylate solution to obtain a 60 wt% alkali-pretreated soybean residue / sodium methacrylate solution.

[0043] Example 2

[0044] A composite biochar material with a gradient pore structure and its preparation method, the preparation method comprising the following steps:

[0045] S1. After pre-cooling the pre-activated dolomite / sodium methacrylate solution to 1°C, inject it into a centrifuge tube, and then add the alkali-pretreated soybean residue / sodium methacrylate solution. The mass ratio of the pre-activated dolomite / sodium methacrylate solution to the alkali-pretreated soybean residue / sodium methacrylate solution is 5:5. After centrifugation, a mixed solution with upper and lower layers is obtained.

[0046] S2. The product obtained in S1 is heated to 30℃ for 4 min and then subjected to directional photocuring. The upper layer is photocured by irradiating the top with 340nm UV for 55s, and the lower layer is photocured by irradiating the bottom of the transparent tube with 390nm laser for 30s, to obtain a composite gel with a gradient porous structure.

[0047] S3. The composite gel obtained in S2 is subjected to high-temperature carbonization at a temperature of 600℃, a heating rate of 10℃ / min, and a holding time of 1.5h. After removing the product, it is washed with water until neutral to obtain a composite biochar material with a gradient porous structure.

[0048] The preparation method of the sodium alginate methacrylate solution in S1 includes the following steps:

[0049] S11. Sodium alginate and methacrylic anhydride are reacted at a molar ratio of 2:0.8 to obtain sodium methacrylate;

[0050] S12. Add the sodium alginate methacrylate obtained in S11 to water, and add lithium phenyl-2,4,6-trimethylbenzoylphosphinic acid to obtain a sodium alginate methacrylate solution with a mass fraction of 3 wt%.

[0051] The preparation of the pre-activated dolomite / sodium methacrylate solution in S1 includes the following steps:

[0052] S21. Mix dolomite and deionized water at a mass ratio of 3:2 and microwave for 4 minutes to obtain pre-activated dolomite;

[0053] S22. Add the preactivated dolomite obtained in S21 to the sodium methacrylated alginate solution and add 2 wt% of Pluronic F127 thermosensitive gel to obtain a preactivated dolomite / sodium methacrylated alginate solution with a mass fraction of 70 wt%.

[0054] The preparation of the alkali-pretreated soybean residue / sodium methacrylate solution in S1 includes the following steps:

[0055] S31. Soak soybean residue in sodium bicarbonate solution with a pH of 8 for 1 hour, then wash and dry to obtain soybean residue pretreated with alkali.

[0056] S32. Add the alkali-pretreated soybean residue to a sodium methacrylate solution to obtain a 70 wt% alkali-pretreated soybean residue / sodium methacrylate solution.

[0057] Example 3

[0058] A composite biochar material with a gradient pore structure and its preparation method, the preparation method comprising the following steps:

[0059] S1. After pre-cooling the pre-activated dolomite / sodium methacrylate solution to 2°C, inject it into a centrifuge tube, and then add the alkali-pretreated soybean residue / sodium methacrylate solution. The mass ratio of the pre-activated dolomite / sodium methacrylate solution to the alkali-pretreated soybean residue / sodium methacrylate solution is 3:7. After centrifugation, a mixed solution with upper and lower layers is obtained.

[0060] S2. The product obtained in S1 is heated to 30℃ for 5 min and then subjected to directional photocuring. The upper layer is photocured by irradiating the top with 340nm UV for 60s, and the lower layer is photocured by irradiating the bottom of the transparent tube with 400nm laser for 30s, to obtain a composite gel with a gradient porous structure.

[0061] S3. The composite gel obtained in S2 is subjected to high-temperature carbonization at a temperature of 700℃, a heating rate of 12℃ / min, and a holding time of 2h. After removing the product, it is washed with water until neutral to obtain a composite biochar material with a gradient porous structure.

[0062] The preparation method of the sodium alginate methacrylate solution in S1 includes the following steps:

[0063] S11. Sodium alginate and methacrylic anhydride are reacted at a molar ratio of 3:0.3 to obtain sodium methacrylate;

[0064] S12. Add the sodium alginate methacrylate obtained in S11 to water, and add phenyl-2,4,6-trimethylbenzoyl lithium phosphinate to obtain a sodium alginate methacrylate solution with a mass fraction of 4 wt%.

[0065] The preparation of the pre-activated dolomite / sodium methacrylate solution in S1 includes the following steps:

[0066] S21. Mix dolomite and deionized water at a mass ratio of 2:7 and microwave for 4 minutes to obtain pre-activated dolomite;

[0067] S22. Add the preactivated dolomite obtained in S21 to the sodium methacrylated alginate solution and add 3 wt% Pluronic F127 thermosensitive gel to obtain a preactivated dolomite / sodium methacrylated alginate solution with a mass fraction of 65 wt%.

[0068] The preparation of the alkali-pretreated soybean residue / sodium methacrylate solution in S1 includes the following steps:

[0069] S31. Soak soybean residue in sodium bicarbonate solution with a pH of 9 for 1.5 hours, then wash and dry to obtain alkali-pretreated soybean residue;

[0070] S32. Add the alkali-pretreated soybean residue to a sodium methacrylate solution to obtain a 70 wt% alkali-pretreated soybean residue / sodium methacrylate solution.

[0071] Example 4

[0072] A composite biochar material with a gradient pore structure and its preparation method, the preparation method comprising the following steps:

[0073] S1. After pre-cooling the pre-activated dolomite / sodium methacrylate solution to 2°C, inject it into a centrifuge tube, and then add the alkali-pretreated soybean residue / sodium methacrylate solution. The mass ratio of the pre-activated dolomite / sodium methacrylate solution to the alkali-pretreated soybean residue / sodium methacrylate solution is 2:8. After centrifugation, a mixed solution with upper and lower layers is obtained.

[0074] S2. The product obtained in S1 is heated to 30℃ for 5 min and then subjected to directional photocuring. The upper layer is photocured by irradiating the top with 350nm UV for 55s, and the lower layer is photocured by irradiating the bottom of the transparent tube with 400nm laser for 30s, to obtain a composite gel with a gradient porous structure.

[0075] S3. The composite gel obtained in S2 is subjected to high-temperature carbonization at a temperature of 600℃, a heating rate of 8℃ / min, and a holding time of 1.5h. After removing the product, it is washed with water until neutral to obtain a composite biochar material with a gradient porous structure.

[0076] The preparation method of the sodium alginate methacrylate solution in S1 includes the following steps:

[0077] S11. Sodium alginate and methacrylic anhydride are reacted at a molar ratio of 2:0.5 to obtain sodium methacrylate;

[0078] S12. Add the sodium alginate methacrylate obtained in S11 to water, and add lithium phenyl-2,4,6-trimethylbenzoylphosphinic acid to obtain a sodium alginate methacrylate solution with a mass fraction of 3 wt%.

[0079] The preparation of the pre-activated dolomite / sodium methacrylate solution in S1 includes the following steps:

[0080] S21. Mix dolomite and deionized water at a mass ratio of 2:5 and microwave for 4 min to obtain pre-activated dolomite;

[0081] S22. Add the preactivated dolomite obtained in S21 to the sodium methacrylated alginate solution and add 2 wt% of Pluronic F127 thermosensitive gel to obtain a preactivated dolomite / sodium methacrylated alginate solution with a mass fraction of 70 wt%.

[0082] The preparation of the alkali-pretreated soybean residue / sodium methacrylate solution in S1 includes the following steps:

[0083] S31. Soak soybean residue in sodium bicarbonate solution with a pH of 9 for 1.5 hours, then wash and dry to obtain alkali-pretreated soybean residue;

[0084] S32. Add the alkali-pretreated soybean residue to a sodium methacrylate solution to obtain a 75 wt% alkali-pretreated soybean residue / sodium methacrylate solution.

[0085] Example 5

[0086] A composite biochar material with a gradient pore structure and its preparation method, the preparation method comprising the following steps:

[0087] S1. After pre-cooling the pre-activated dolomite / sodium methacrylate solution to 2°C, inject it into a centrifuge tube, and then add the alkali-pretreated soybean residue / sodium methacrylate solution. The mass ratio of the pre-activated dolomite / sodium methacrylate solution to the alkali-pretreated soybean residue / sodium methacrylate solution is 2:8. After centrifugation, a mixed solution with upper and lower layers is obtained.

[0088] S2. The product obtained in S1 is heated to 30℃ for 6 min and then subjected to directional photocuring. The upper layer is photocured by irradiating the top with 360nm UV for 60s, and the lower layer is photocured by irradiating the bottom of the transparent tube with 400nm laser for 35s, to obtain a composite gel with a gradient porous structure.

[0089] S3. The composite gel obtained in S2 is subjected to high-temperature carbonization at a temperature of 700℃, a heating rate of 10℃ / min, and a holding time of 2h. After removing the product, it is washed with water until neutral to obtain a composite biochar material with a gradient porous structure.

[0090] The preparation method of the sodium alginate methacrylate solution in S1 includes the following steps:

[0091] S11. Sodium alginate and methacrylic anhydride are reacted at a molar ratio of 3:0.6 to obtain sodium methacrylate;

[0092] S12. Add the sodium alginate methacrylate obtained in S11 to water, and add lithium phenyl-2,4,6-trimethylbenzoylphosphinic acid to obtain a sodium alginate methacrylate solution with a mass fraction of 5 wt%.

[0093] The preparation of the pre-activated dolomite / sodium methacrylate solution in S1 includes the following steps:

[0094] S21. Mix dolomite and deionized water at a mass ratio of 2:5 and microwave for 5 minutes to obtain pre-activated dolomite;

[0095] S22. Add the preactivated dolomite obtained in S21 to the sodium methacrylated alginate solution and add 2 wt% of Pluronic F127 thermosensitive gel to obtain a preactivated dolomite / sodium methacrylated alginate solution with a mass fraction of 65 wt%.

[0096] The preparation of the alkali-pretreated soybean residue / sodium methacrylate solution in S1 includes the following steps:

[0097] S31. Soak soybean residue in sodium bicarbonate solution with a pH of 9 for 1.5 hours, then wash and dry to obtain alkali-pretreated soybean residue;

[0098] S32. Add the alkali-pretreated soybean residue to a sodium methacrylate solution to obtain a 65wt% alkali-pretreated soybean residue / sodium methacrylate solution.

[0099] Example 6

[0100] A composite biochar material with a gradient pore structure and its preparation method, the preparation method comprising the following steps:

[0101] S1. After pre-cooling the pre-activated dolomite / sodium methacrylate solution to 2°C, inject it into a centrifuge tube, and then add the alkali-pretreated soybean residue / sodium methacrylate solution. The mass ratio of the pre-activated dolomite / sodium methacrylate solution to the alkali-pretreated soybean residue / sodium methacrylate solution is 7:5. After centrifugation, a mixed solution with upper and lower layers is obtained.

[0102] S2. The product obtained in S1 is heated to 25℃ for 5 min and then subjected to directional photocuring. The upper layer is photocured by irradiating the top with 340nm UV for 60s, and the lower layer is photocured by irradiating the bottom of the transparent tube with 400nm laser for 25s, to obtain a composite gel with a gradient porous structure.

[0103] S3. The composite gel obtained in S2 is subjected to high-temperature carbonization at a temperature of 900℃, a heating rate of 8℃ / min, and a holding time of 1.5h. After removing the product, it is washed with water until neutral to obtain a composite biochar material with a gradient porous structure.

[0104] The preparation method of the sodium alginate methacrylate solution in S1 includes the following steps:

[0105] S11. Sodium alginate and methacrylic anhydride are reacted at a molar ratio of 2:0.8 to obtain sodium methacrylate;

[0106] S12. Add the sodium alginate methacrylate obtained in S11 to water, and add lithium phenyl-2,4,6-trimethylbenzoylphosphinic acid to obtain a sodium alginate methacrylate solution with a mass fraction of 2 wt%.

[0107] The preparation of the pre-activated dolomite / sodium methacrylate solution in S1 includes the following steps:

[0108] S21. Mix dolomite and deionized water at a mass ratio of 3:7 and microwave for 5 minutes to obtain pre-activated dolomite;

[0109] S22. Add the preactivated dolomite obtained in S21 to the sodium methacrylated alginate solution and add 2 wt% of Pluronic F127 thermosensitive gel to obtain a preactivated dolomite / sodium methacrylated alginate solution with a mass fraction of 65 wt%.

[0110] The preparation of the alkali-pretreated soybean residue / sodium methacrylate solution in S1 includes the following steps:

[0111] S31. Soak soybean residue in sodium bicarbonate solution with a pH of 8 for 1.5 hours, then wash and dry to obtain alkali-pretreated soybean residue;

[0112] S32. Add the alkali-pretreated soybean residue to a sodium methacrylate solution to obtain a 70 wt% alkali-pretreated soybean residue / sodium methacrylate solution.

[0113] Example 7

[0114] A composite biochar material with a gradient pore structure and its preparation method, the preparation method comprising the following steps:

[0115] S1. After pre-cooling the pre-activated dolomite / sodium methacrylate solution to 2°C, inject it into a centrifuge tube, and then add the alkali-pretreated soybean residue / sodium methacrylate solution. The mass ratio of the pre-activated dolomite / sodium methacrylate solution to the alkali-pretreated soybean residue / sodium methacrylate solution is 7:2. After centrifugation, a mixed solution with upper and lower layers is obtained.

[0116] S2. The product obtained in S1 is heated to 30℃ for 5 min and then subjected to directional photocuring. The upper layer is photocured by irradiating the top with 345nm UV for 60s, and the lower layer is photocured by irradiating the bottom of the transparent tube with 405nm laser for 35s, to obtain a composite gel with a gradient porous structure.

[0117] S3. The composite gel obtained in S2 is subjected to high-temperature carbonization at a temperature of 650℃, a heating rate of 10℃ / min, and a holding time of 2h. After removing the product, it is washed with water until neutral to obtain a composite biochar material with a gradient porous structure.

[0118] The preparation method of the sodium alginate methacrylate solution in S1 includes the following steps:

[0119] S11. Sodium alginate and methacrylic anhydride are reacted at a molar ratio of 3:0.7 to obtain sodium methacrylate;

[0120] S12. Add the sodium alginate methacrylate obtained in S11 to water, and add lithium phenyl-2,4,6-trimethylbenzoylphosphinic acid to obtain a sodium alginate methacrylate solution with a mass fraction of 5 wt%.

[0121] The preparation of the pre-activated dolomite / sodium methacrylate solution in S1 includes the following steps:

[0122] S21. Mix dolomite and deionized water at a mass ratio of 3:5 and microwave for 4 minutes to obtain pre-activated dolomite;

[0123] S22. Add the preactivated dolomite obtained in S21 to the sodium methacrylated alginate solution and add 3 wt% of Pluronic F127 thermosensitive gel to obtain a preactivated dolomite / sodium methacrylated alginate solution with a mass fraction of 70 wt%.

[0124] The preparation of the alkali-pretreated soybean residue / sodium methacrylate solution in S1 includes the following steps:

[0125] S31. Soak soybean residue in sodium bicarbonate solution with a pH of 9 for 1.5 hours, then wash and dry to obtain alkali-pretreated soybean residue;

[0126] S32. Add the alkali-pretreated soybean residue to a sodium methacrylate solution to obtain a 70 wt% alkali-pretreated soybean residue / sodium methacrylate solution.

[0127] Example 8

[0128] A composite biochar material with a gradient pore structure and its preparation method, the preparation method comprising the following steps:

[0129] S1. After pre-cooling the pre-activated dolomite / sodium methacrylate solution to 0°C, inject it into a centrifuge tube, and then add the alkali-pretreated soybean residue / sodium methacrylate solution. The mass ratio of the pre-activated dolomite / sodium methacrylate solution to the alkali-pretreated soybean residue / sodium methacrylate solution is 9:1. After centrifugation, a mixed solution with upper and lower layers is obtained.

[0130] S2. The product obtained in S1 is heated to 25℃ for 5 min and then subjected to directional photocuring. The upper layer is photocured by irradiating the top with 340nm UV for 65s, and the lower layer is photocured by irradiating the bottom of the transparent tube with 405nm laser for 25s, to obtain a composite gel with a gradient porous structure.

[0131] S3. The composite gel obtained in S2 is subjected to high-temperature carbonization at a temperature of 900℃, a heating rate of 10℃ / min, and a holding time of 2h. After removing the product, it is washed with water until neutral to obtain a composite biochar material with a gradient porous structure.

[0132] The preparation method of the sodium alginate methacrylate solution in S1 includes the following steps:

[0133] S11. Sodium alginate and methacrylic anhydride are reacted at a molar ratio of 3:0.7 to obtain sodium methacrylate;

[0134] S12. Add the sodium alginate methacrylate obtained in S11 to water, and add phenyl-2,4,6-trimethylbenzoyl lithium phosphinate to obtain a sodium alginate methacrylate solution with a mass fraction of 4 wt%.

[0135] The preparation of the pre-activated dolomite / sodium methacrylate solution in S1 includes the following steps:

[0136] S21. Mix dolomite and deionized water at a mass ratio of 3:5 and microwave for 5 minutes to obtain pre-activated dolomite;

[0137] S22. Add the preactivated dolomite obtained in S21 to the sodium methacrylated alginate solution and add 3 wt% of Pluronic F127 thermosensitive gel to obtain a preactivated dolomite / sodium methacrylated alginate solution with a mass fraction of 70 wt%.

[0138] The preparation of the alkali-pretreated soybean residue / sodium methacrylate solution in S1 includes the following steps:

[0139] S31. Soak soybean residue in sodium bicarbonate solution with a pH of 9 for 1.5 hours, then wash and dry to obtain alkali-pretreated soybean residue;

[0140] S32. Add the alkali-pretreated soybean residue to a sodium methacrylate solution to obtain a 75 wt% alkali-pretreated soybean residue / sodium methacrylate solution.

[0141] Comparative Example 1

[0142] The difference between Comparative Example 1 and Example 8 is that in S1, dolomite and soybean residue were placed in a quartz boat at a mass ratio of 9:1 and then sent into a tube furnace for carbonization.

[0143] Comparative Example 2

[0144] The difference between Comparative Example 2 and Example 8 is that the soybean residue in S1 was not pretreated with alkali.

[0145] Comparative Example 3

[0146] The difference between Comparative Example 3 and Example 8 is that both the upper and lower layers in S2 are cured using 340nm UV.

[0147] Comparative Example 4

[0148] The difference between Comparative Example 4 and Example 8 is that both the upper and lower layers in S2 are cured using a 405nm laser.

[0149] Comparative Example 5

[0150] The difference between Comparative Example 5 and Example 8 is that phenyl-2,4,6-trimethylbenzoyl lithium phosphinate was not added in S12.

[0151] Comparative Example 6

[0152] The difference between Comparative Example 6 and Example 8 is that Pluronic F127 thermosensitive gel was not added in S22.

[0153] Comparative Example 7

[0154] The difference between Comparative Example 7 and Example 8 is that the alkali-pretreated soybean residue was placed directly in a quartz boat for carbonization, without the addition of dolomite.

[0155] Comparative Example 8

[0156] The difference between Comparative Example 8 and Example 8 is that the dolomite was placed directly in a quartz boat for carbonization, without the addition of soybean residue.

[0157] Comparative Example 9

[0158] The difference between Comparative Example 9 and Example 8 is that in S1, the pre-activated dolomite / sodium methacrylate solution was pre-cooled to 0°C and then injected into the centrifuge tube, without adding the alkali-pretreated soybean residue / sodium methacrylate solution; and in S2, only a 405nm laser was used to irradiate the bottom of the transparent tube for 25 seconds.

[0159] Comparative Example 10

[0160] The difference between Comparative Example 10 and Example 8 is that in S1, the soybean residue / sodium methacrylate solution pretreated with alkali was used instead of the pre-activated dolomite / sodium methacrylate solution; and in S2, only 340nm UV was used to irradiate the top for 65s.

[0161] Performance testing

[0162] The adsorption capacity of phosphorus in water of the materials obtained in Examples 1-8 and Comparative Examples 1-10 was tested, and the results are shown in the table below.

[0163]

[0164]

[0165] The phosphorus release rate and cumulative release rate over 28 days of the materials obtained in Examples 1-8 and Comparative Examples 1-10 after adsorbing phosphorus were tested, and the results are shown in the table below.

[0166]

[0167] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A composite biochar material with a gradient pore structure, characterized in that: The composite biochar material is obtained by high-temperature carbonization of a composite gel with a gradient pore structure. The composite gel with a gradient pore structure is obtained by centrifugation and directional photocuring. The composite gel is composed of pre-activated dolomite and soybean residue pretreated with alkali. The method for preparing the composite biochar material with a gradient pore structure includes the following steps: S1. After pre-cooling the pre-activated dolomite / sodium methacrylate solution, inject it into a centrifuge tube, then add the alkali-pretreated soybean residue / sodium methacrylate solution, and centrifuge to obtain a mixed solution with upper and lower layers. S2. The product obtained in S1 is heated and subjected to directional photocuring. The upper layer is photocured by irradiating the top with 330~370nm UV for 50~70s, and the lower layer is photocured by irradiating the bottom of the transparent tube with 390~410nm laser for 25~35s. Then a composite gel with a gradient porous structure is obtained. S3. The composite gel obtained in S2 is carbonized at high temperature. After removing the product, it is washed with water until neutral to obtain a composite biochar material with a gradient porous structure. The preparation method of the sodium alginate methacrylate solution in S1 includes the following steps: S11. Sodium alginate and methacrylic anhydride are reacted in a molar ratio of 1~4:0.3~0.8 to obtain sodium methacrylate; S12. Add the sodium alginate methacrylate obtained in S11 to water, and add lithium phenyl-2,4,6-trimethylbenzoylphosphinic acid to obtain a sodium alginate methacrylate solution with a mass fraction of 2~6wt%. The preparation of the pre-activated dolomite / sodium methacrylate solution in S1 includes the following steps: S21. Mix dolomite and deionized water at a mass ratio of 1~3:2~7 and microwave for 3~6 minutes to obtain pre-activated dolomite; S22. Add the pre-activated dolomite obtained in S21 to the sodium methacrylated alginate solution, and add 1~4wt% of Pluronic F127 thermosensitive gel to obtain a pre-activated dolomite / sodium methacrylated alginate solution with a mass fraction of 60~80wt%.

2. The composite biochar material with a gradient pore structure according to claim 1, characterized in that: The mass ratio of the pre-activated dolomite / sodium methacrylate solution and the alkali-pretreated soybean residue / sodium methacrylate solution in S1 is 1~9:1~9, and the pre-cooling temperature is 0~4℃.

3. The composite biochar material with a gradient pore structure according to claim 1, characterized in that: The preparation of the alkali-pretreated soybean residue / sodium methacrylate solution in S1 includes the following steps: S31. Soak soybean residue in sodium bicarbonate solution with a pH of 8-9 for 1-2 hours, then wash and dry to obtain alkali-pretreated soybean residue; S32. Add the alkali-pretreated soybean residue to a sodium methacrylate solution to obtain an alkali-pretreated soybean residue / sodium methacrylate solution with a mass fraction of 60-80 wt%.

4. The composite biochar material with a gradient pore structure according to claim 1, characterized in that: The temperature for the heating process in S2 is 25–40°C, and the time is 4–8 minutes.

5. The composite biochar material with a gradient pore structure according to claim 1, characterized in that: The carbonization temperature in S3 is 500~900℃, the heating rate is 8~12℃ / min, and the holding time is 1.5~2.5h.

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