Preparation method and application of calcium modified biochar catalyst
By using calcium hydroxide-modified biochar catalyst, the problems of low activity and coking phenomenon of traditional biochar catalysts were solved, the pore structure was optimized, and the effect of efficient removal of tetracycline was achieved.
Patent Information
- Application Number
- CN202511049950.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-29
- Publication Date
- 2025-11-07
AI Technical Summary
Traditional biochar catalysts have low catalytic activity, high preparation costs, and are prone to coking during pyrolysis, making it difficult to effectively remove tetracycline pollution. Furthermore, existing modification methods use toxic or expensive reagents, which damage the biochar structure.
Calcium hydroxide was used as a modifier to prepare calcium-modified biochar catalysts by mixing it with walnut shell powder, lignin, or carbohydrate residues. This process avoids coking, optimizes the pore structure, and enhances catalytic activity.
The specific surface area and pore structure of biochar were significantly improved, enhancing the adsorption and degradation efficiency of tetracycline. The degradation kinetic constant was increased by 36 to 43 times, achieving efficient and environmentally friendly tetracycline removal.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of sewage treatment materials, and particularly relates to a preparation method of a calcium-modified biochar catalyst and application thereof. BACKGROUND
[0002] Tetracycline has a wide range of pollution and has a certain hydrophilicity, and is easy to migrate and diffuse with water bodies. At the same time, its antibacterial property inhibits the activity of microbial communities in water bodies, interferes with key ecological processes such as organic matter decomposition and nitrogen and phosphorus cycling, and seriously weakens the self-purification ability of water bodies, which has a serious harm to aquatic ecosystems and human health.
[0003] Biochar has attracted much attention in the field of wastewater treatment due to its wide raw material sources, environmental friendliness and low cost. However, the physicochemical properties of traditional biochar have obvious shortcomings, such as low specific surface area (usually < 50 m 2 / g), insufficient pore structure development (especially lack of mesopores), which leads to limited adsorption capacity, and uneven distribution and limited number of surface oxygen-containing functional groups (such as carboxyl and phenolic hydroxyl groups), which weakens the affinity and catalytic activity for pollutants. The removal rate of tetracycline (TCH) by biochar directly pyrolyzed from biomass is extremely low, which is difficult to meet the actual demand.
[0004] At present, the exploration of the catalytic performance of biochar usually involves selected biomass precursors, which need to be modified by chemical reagents. They can effectively improve the removal effect of pollutants through traditional modification methods, but they usually need to use toxic or expensive reagents. This not only increases the processing cost, but also has the possibility of destroying the internal structure of biomass and making it disordered, which aggravates the complexity of the preparation process of biochar. Therefore, these methods may mask the basic understanding of the structure-activity relationship of biochar and complicate its application.
[0005] Lignin itself has a high carbon content and a high degree of aromaticity, and is a good precursor of catalysts. However, natural lignin biomass is a highly heterogeneous complex polymer with wide molecular weight distribution, large differences in functional group content and type, and diverse linkages. Fractionation can separate this mixture into components with relatively more uniform structure and more controllable properties. In addition, during the pyrolysis process of lignin as a precursor, the rich oxygen-containing functional groups of lignin easily trigger significant cross-linking reactions at high temperatures, which not only hinders the heat transfer and mass diffusion efficiency between molecules, but also leads to serious agglomeration of lignin molecules, which may cause melting and coking phenomena.
[0006] Therefore, it is necessary to develop a calcium-modified biochar catalyst with low preparation cost, which can alleviate the coking phenomenon in the pyrolysis process, optimize the pore structure of carbon materials, and efficiently catalyze the degradation of tetracycline. SUMMARY
[0007] The technical problems to be solved by the present application provide a preparation method of calcium modified biochar catalyst and application thereof, which can effectively solve the problems of low catalytic activity, high preparation cost and easy coking phenomenon during pyrolysis of traditional biochar, and has good treatment effect when the calcium modified biochar catalyst is used for activating persulfate to degrade tetracycline.
[0008] The present application solves the above technical problems by the following technical solutions:
[0009] The present application provides a preparation method of calcium modified biochar catalyst, which comprises the following operation steps:
[0010] S1, preparing a precursor: preparing walnut shell powder or raw lignin or carbohydrate residues as a precursor;
[0011] S2, preparing a calcium modified biochar catalyst, the specific operation steps are as follows:
[0012] Step 1, mixing the precursor of step S1 and calcium hydroxide in a weight ratio of 1:20 to obtain a mixture;
[0013] Step 2, adding ultrapure water according to the solid-liquid ratio of 1:100 (g / mL) of the mixture of step 1, stirring uniformly and then transferring to a blast oven until the water is evaporated, to obtain calcium modified biomass;
[0014] Step 3, grinding the calcium modified biomass through a 60 mesh sieve and placing it in an alumina boat;
[0015] Step 4, placing the alumina boat into a tube furnace and pyrolyzing under nitrogen atmosphere, the tube furnace program is set to heat to 900 DEG C at a heating rate of 5 DEG C / min and keep for 2h, to obtain calcium modified biochar;
[0016] Step 5, when the temperature in the tube furnace decreases to room temperature, the calcium modified biochar is repeatedly washed with deionized water to remove ash and soluble organic compounds to obtain a calcium modified biochar catalyst.
[0017] In step S1 of the present application, the preparation method of the walnut shell powder is: selecting walnut shell, crushing into powder through a 60 mesh sieve to obtain walnut shell powder.
[0018] In step S1 of the present application, the preparation method of the carbohydrate residues comprises the following operation steps:
[0019] Step 1, mixing choline chloride and urea in a molar ratio of 1:2 in a round-bottom flask, stirring by magnetic force and heating at 85 DEG C until a transparent viscous liquid without obvious particles is obtained, i.e. a deep eutectic solvent (DES) is obtained;
[0020] Step 2, the walnut shell powder passing through a 60-mesh sieve is mechanically stirred with the prepared DES at a mass ratio of 1:5, and then is transferred into a polytetrafluoroethylene (PTFE) liner of a high-pressure reactor, and is kept at 155 DEG C for 9h;
[0021] Step 3, the product of Step 2 is filtered to separate insoluble components, and then is dried at 60 DEG C for 2h to obtain a carbohydrate residue.
[0022] In Step S1 of the present application, the preparation method of the original lignin comprises the following operation steps:
[0023] Step 1, choline chloride and urea are mixed in a round-bottom flask at a molar ratio of 1:2, and then are subjected to magnetic stirring and heating at 85 DEG C until a transparent viscous liquid without obvious particles is obtained, i.e., a DES is obtained;
[0024] Step 2, the walnut shell powder passing through a 60-mesh sieve is mechanically stirred with the prepared DES at a mass ratio of 1:5, and then is transferred into a polytetrafluoroethylene (PTFE) liner of a high-pressure reactor, and is kept at 155 DEG C for 9h;
[0025] Step 3, the product of Step 2 is filtered to separate insoluble components, and then is dried at 60 DEG C for 2h to obtain a carbohydrate residue.
[0026] Step 4, after the filtrate of Step 3 is cooled to room temperature, an excess of deionized water is added to precipitate lignin, and after the precipitation is complete, the lignin in the solution is filtered and is washed with deionized water multiple times to ensure that ethanol is effectively removed.
[0027] Step 5, the lignin of Step 4 is dried at room temperature for 24h to obtain original lignin.
[0028] In the preparation method of the carbohydrate residue and the original lignin according to the present application, the mechanical stirring time in Step 2 is 6h.
[0029] The calcium-modified biochar catalyst according to the present application is used for activating persulfate to degrade tetracycline.
[0030] Compared with the prior art, the present application has the following beneficial effects:
[0031] 1. The present application uses environmentally friendly and low-toxic calcium hydroxide to replace traditional strong corrosive activators (such as KOH), avoids the destruction of the carbon skeleton, effectively inhibits the caking, melting and charring phenomena in the lignin pyrolysis process, improves the specific surface area of the biochar, optimizes the pore structure, and retains the intrinsic structure of the biomass fraction components.
[0032] 2. The present application regulates the charge distribution characteristics of the material surface by introducing calcium species, significantly improves the positive electrical properties of the surface, and improves the adsorption and degradation of tetracycline, so that the adsorption efficiency of calcium modified biochar for tetracycline is improved by 4 times, and the degradation kinetics constant of activated persulfate (PDS) is improved by 36-43 times.
[0033] 3. The present application optimizes the structure characteristics of different biomass components by calcium modification process; calcium species as an electronic bridge mediates the efficient activation of PDS, which is conducive to regulating the active site density and improving the adsorption and catalytic ability of tetracycline; and the modification process avoids the destruction of strong alkali to the carbon skeleton, and the stability is significantly better than that of sodium-based modified materials.
[0034] 4. The raw material used in the present application is biomass waste walnut shell powder, which realizes the high-value utilization of agricultural and forestry waste, conforms to the concept of circular economy and sustainable development, and can efficiently degrade antibiotic pollutants, and is suitable for complex water quality treatment. BRIEF DESCRIPTION OF DRAWINGS
[0035] Figure 1 The scanning electron microscope (SEM) spectrum and C, O, Ca element EDS energy spectrum analysis spectrum of the calcium modified biochar catalyst prepared in examples 1-3 of the present application.
[0036] Figure 2 The N2 adsorption-desorption curve and the corresponding pore size distribution diagram of the calcium modified biochar catalyst prepared in examples 1-3 of the present application and the biochar prepared in comparative example 1.
[0037] Figure 3 The XRD diagram of the calcium modified biochar catalyst prepared in examples 1-3 of the present application.
[0038] Figure 4 The removal efficiency diagram of tetracycline (TCH) of the calcium modified biochar catalyst prepared in examples 1-3 of the present application and the biochar prepared in comparative examples 1, 3 and 5.
[0039] Figure 5 The removal efficiency diagram of tetracycline (TCH) of the biochar prepared in comparative examples 2, 4 and 6, which is used to explore the effect of calcium modification on the degradation efficiency of tetracycline. DETAILED DESCRIPTION
[0040] The technical solutions of the present application are further illustrated below with examples, but in no way limit the present application. The following content is only an exemplary illustration of the scope of the present application, and those skilled in the art can make various changes and modifications to the present application according to the disclosed content, which shall also belong to the scope of the present application claimed. Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as generally understood by those skilled in the art to which the present application belongs.
[0041] The various chemical reagents used in the embodiments of the present application are obtained through conventional commercial channels unless otherwise specified. The products from different manufacturers do not have a significant effect on the results. Unless otherwise specified, it is understood to be carried out at room temperature.
[0042] The relevant terms involved in the present application are explained as follows:
[0043] PDS: Peroxydisulfate
[0044] TCH: Tetracycline hydrochloride
[0045] CaBC: Calcium-modified biochar
[0046] CaHBC: Calcium-modified biochar catalyst prepared with walnut shell powder as precursor
[0047] CaHLBC: Calcium-modified biochar catalyst prepared with raw lignin as precursor
[0048] CaHRBC: Calcium-modified biochar catalyst prepared with carbohydrate residue as precursor
[0049] Example 1:
[0050] The calcium-modified biochar catalyst prepared with raw lignin as precursor in the present application comprises the following operation steps:
[0051] S1, Preparation of precursor:
[0052] 1. Mix choline chloride and urea in a molar ratio of 1:2 in a round-bottom flask, stir magnetically and heat at 85℃ until a transparent viscous liquid without obvious particles is obtained, i.e. a deep eutectic solvent (DES) is obtained;
[0053] 2. Select walnut shell, crush into powder and pass through a 60-mesh sieve, collect the walnut shell powder, and mechanically stir and mix the walnut shell powder with the prepared deep eutectic solvent (DES) at a mass ratio of 1:5 for 6h, then transfer to a polytetrafluoroethylene (PTFE) liner in a high-pressure reactor and keep at 155℃ for 9h;
[0054] 3. The insoluble components, i.e. the carbohydrate residue, were separated by filtration, and then dried at 60 °C for 2 h, while the filtrate was subjected to rotary evaporation to recover ethanol;
[0055] 4. After the filtrate of step 3 was cooled to room temperature, excess deionized water was added to precipitate the lignin. After the precipitation was complete, the lignin was filtered from the aqueous solution and washed with deionized water several times to ensure effective removal of ethanol. The lignin was then dried at room temperature for 24 h to obtain the raw lignin.
[0056] S2, Preparation of calcium-modified biochar catalyst, including the following steps:
[0057] Step 1, the raw lignin obtained in step S1 was mixed with calcium hydroxide in a weight ratio of 1:20;
[0058] Step 2, the mixture of step 1 was added to ultrapure water at a solid-liquid ratio of 1:100 (g / mL) and stirred uniformly, then transferred to a forced air oven until the water was evaporated;
[0059] Step 3, the impregnated calcium-modified biomass was collected, ground through a 60 mesh sieve, and placed in an alumina boat;
[0060] Step 4, the alumina boat was placed in a tube furnace and pyrolyzed under a nitrogen atmosphere. The tube furnace was programmed to heat to 900 °C at a rate of 5 °C / min and hold for 2 h to obtain calcium-modified biochar;
[0061] Step 5, after the tube furnace was cooled to room temperature, the calcium-modified biochar was repeatedly washed with deionized water to effectively remove ash and soluble organic compounds to obtain the calcium-modified biochar catalyst, designated as CaHLBC.
[0062] The experiment of coupling calcium-modified biochar catalyst CaHLBC with PDS to degrade TCH, including the following experimental steps:
[0063] The experiment was carried out in a conical flask, and the temperature of the constant temperature shaker was 25 °C, and the shaking speed was 155 rpm. 10 mg of calcium-modified biochar catalyst CaHLBC was dispersed in 100 mL of TCH solution (10 mg / L, pH 4.5) for 30 min to achieve adsorption and desorption equilibrium, which was determined by a 24 h pre-experiment. Samples were taken at regular intervals, and each time the sample was filtered with a 0.45 μm disposable PVDF filter before being transferred to a vial containing sodium thiosulfate. The collected samples were then analyzed at a wavelength of 357 nm using ultraviolet spectrophotometry and high performance liquid chromatography (HPLC).
[0064] Comparative Example 1:
[0065] A method for preparing a lignin biochar, comprising the following preparation steps:
[0066] S1, preparation of a precursor:
[0067] Choline chloride and urea were mixed in a round-bottom flask at a molar ratio of 1:2, stirred magnetically and heated at 85℃ until a transparent viscous liquid without obvious particles was obtained, which was called deep eutectic solvent (DES); 60 mesh walnut shell powder was then mechanically stirred with the prepared deep eutectic solvent (DES) at a mass ratio of 1:5 for 6h, and then transferred into a polytetrafluoroethylene (PTFE) liner of a high-pressure reactor and kept at 155℃ for 9h; the insoluble components, mainly carbohydrate residues, were separated by filtration, and then dried at 60℃ for 2h; the filtrate was subjected to rotary evaporation to recover ethanol; after cooling to room temperature, the solution was collected, and then an excess of deionized water was added to precipitate lignin; after the precipitation was complete, the lignin in the aqueous solution was filtered and washed with deionized water multiple times to ensure effective removal of ethanol; and then dried at room temperature for 24h to collect the raw lignin.
[0068] S2, preparation and modification of biochar:
[0069] Step 1, the raw lignin of step S1 was ground through a 60 mesh sieve and placed in an alumina boat, and the alumina boat was placed in a tube furnace for pyrolysis under a nitrogen atmosphere, the tube furnace was heated to 900℃ at a heating rate of 5℃ / min and kept for 2h;
[0070] Step 2, after cooling, the raw lignin powder was repeatedly washed with deionized water to effectively remove ash and soluble organic compounds, and stored in a sealed plastic bag to obtain lignin biochar, designated as HLBC.
[0071] The experiment of coupling lignin biochar HLBC with PDS to degrade TCH, including the following experimental steps: the experiment was carried out in a conical flask, the temperature of the constant temperature shaker was 25℃, and the shaking speed was 155rpm. 10mg of lignin biochar HLBC was dispersed in 100mL of TCH solution (10mg / L, pH 4.5) for 30min to achieve adsorption and desorption equilibrium, which was determined by a pre-experiment lasting for 24h. Sampling was taken every fixed time, and each time the sample was first filtered with a 0.45μm disposable PVDF filter, and then transferred to a vial containing sodium thiosulfate. Subsequently, the collected samples were analyzed at a wavelength of 357nm using ultraviolet spectrophotometry and high performance liquid chromatography (HPLC).
[0072] Comparative Example 2:
[0073] A method for preparing a sodium-modified lignin biochar, comprising the following preparation steps:
[0074] S1, Preparation of precursor:
[0075] Choline chloride and urea were mixed in a 1:2 molar ratio in a round-bottom flask, stirred magnetically and heated at 85°C until a transparent viscous liquid without apparent particles was obtained, this liquid was called deep eutectic solvent (DES); 60 mesh walnut shell powder was then mixed with the prepared deep eutectic solvent (DES) in a mass ratio of 1:5 and mechanically stirred for 6 h, then transferred to a polytetrafluoroethylene (PTFE) liner in a high-pressure reactor and kept at 155°C for 9 h; the insoluble components, mainly carbohydrate residues, were then separated by filtration, and then at 60°C for 2 h; the filtrate was subjected to rotary evaporation to recover ethanol; after cooling to room temperature, the solution was collected, then an excess of deionized water was added to precipitate the lignin, after the precipitation was complete, the lignin in the aqueous solution was filtered and washed with deionized water several times to ensure effective removal of ethanol; then dried at room temperature for 24 h, and the raw lignin was collected.
[0076] S2, Preparation and modification of biochar:
[0077] Step 1, mix the raw lignin of step S1 and sodium hydroxide in a weight ratio of 1:20;
[0078] Step 2, after stirring uniformly with ultrapure water, transfer to a forced air oven until the water is evaporated;
[0079] Step 3, collect the sodium-modified biomass after immersion, grind through a 60 mesh sieve and place in an alumina boat;
[0080] Step 4, place the alumina boat in a tube furnace and pyrolyze under a nitrogen atmosphere, with the tube furnace program set to heat to 900°C at a rate of 5°C / min and hold for 2 h;
[0081] Step 5, after cooling to room temperature, rinse the sodium-modified biomass with deionized water repeatedly to effectively remove ash and soluble organic compounds, and collect the sodium-modified lignin biochar, designated as NaHLBC.
[0082] The experiment of coupling sodium-modified lignin biochar NaHLBC with PDS to degrade TCH, including the following experimental steps:
[0083] The experiment was carried out in a conical flask, and the temperature of the constant temperature shaker was 25℃, and the shaking speed was 155 rpm. 10 mg of sodium modified lignin biochar NaHLBC was dispersed in 100 mL TCH solution (10 mg / L, pH 4.5) for 30 min to achieve adsorption and desorption equilibrium, which was determined by a pre-experiment lasting for 24 h. Sampling was taken every fixed time, and each sampling was first filtered with a 0.45 μm disposable PVDF filter, and then transferred to a vial containing sodium thiosulfate. Subsequently, the collected samples were analyzed at a wavelength of 357 nm using ultraviolet spectrophotometry and high performance liquid chromatography (HPLC).
[0084] Example 2:
[0085] The calcium modified biochar catalyst prepared by taking walnut shell powder as a precursor comprises the following operation steps:
[0086] S1, preparation of the precursor: select walnut shell, crush into powder and pass through a 60 mesh sieve, and collect the walnut shell powder;
[0087] S2, preparation of the calcium modified biochar catalyst, comprising the following operation steps:
[0088] Step 1, mix the walnut shell powder passing through a 60 mesh sieve and calcium hydroxide according to a weight ratio of 1:20;
[0089] Step 2, add ultrapure water according to a solid-liquid ratio of 1:100 (g / mL) of the mixture of step 1, stir uniformly, and then transfer to a blast oven until the moisture is evaporated;
[0090] Step 3, collect the calcium modified biomass after impregnation, grind and pass through a 60 mesh sieve, and then put into an alumina boat;
[0091] Step 4, put the alumina boat into a tube furnace, and perform pyrolysis under a nitrogen atmosphere, and the tube furnace program is set to heat to 900℃ at a heating rate of 5℃ / min and keep for 2 h, to obtain the calcium modified biochar;
[0092] Step 5, after the tube furnace is reduced to room temperature, repeatedly rinse the calcium modified biochar with deionized water to effectively remove ash and soluble organic compounds, and collect the calcium modified biochar, to obtain the calcium modified biochar catalyst, which is named as CaHBC.
[0093] The experiment of coupling degradation of TCH by the calcium modified biochar catalyst CaHBC and PDS includes the following experimental steps:
[0094] The experiment was carried out in a conical flask, and the temperature of the constant temperature shaker was 25℃, and the shaking speed was 155 rpm. 10 mg of calcium modified biochar catalyst CaHBC was dispersed in 100 mL TCH solution (10 mg / L, pH 4.5) for 30 min to achieve adsorption and desorption equilibrium, which was determined by a 24 h pre-experiment. Sampling was taken every fixed time, and each sampling was first filtered with a 0.45 μm disposable PVDF filter, and then transferred to a vial containing sodium thiosulfate. Subsequently, the collected samples were analyzed at a wavelength of 357 nm using ultraviolet spectrophotometry and high performance liquid chromatography (HPLC).
[0095] Comparative Example 3:
[0096] A preparation method of walnut shell powder biochar, comprising the following preparation steps:
[0097] S1, preparation of precursor:
[0098] Select walnut shell, crush into powder and pass through a 60 mesh sieve, and collect the walnut shell powder.
[0099] S2, preparation of walnut shell powder biochar, comprising the following operation steps:
[0100] Step 1, grind the walnut shell powder to pass through a 60 mesh sieve, then put it into an alumina boat, and put the alumina boat into a tube furnace, and pyrolyze under nitrogen atmosphere, heat the tube furnace to 900℃ at a heating rate of 5℃ / min and keep for 2h;
[0101] Step 2, after cooling, repeatedly rinse with deionized water to effectively remove ash and soluble organic compounds, and store in a sealed plastic bag to obtain walnut shell powder biochar, named HBC.
[0102] The experiment of coupling walnut shell powder biochar HBC and PDS to degrade TCH, comprising the following experimental steps:
[0103] The experiment was carried out in a conical flask, and the temperature of the constant temperature shaker was 25℃, and the shaking speed was 155 rpm. 10 mg of calcium modified biochar catalyst CaHBC was dispersed in 100 mL TCH solution (10 mg / L, pH 4.5) for 30 min to achieve adsorption and desorption equilibrium, which was determined by a 24 h pre-experiment. Sampling was taken every fixed time, and each sampling was first filtered with a 0.45 μm disposable PVDF filter, and then transferred to a vial containing sodium thiosulfate. Subsequently, the collected samples were analyzed at a wavelength of 357 nm using ultraviolet spectrophotometry and high performance liquid chromatography (HPLC).
[0104] Comparative Example 4:
[0105] A preparation method of sodium modified walnut shell powder biochar, comprising the following preparation steps:
[0106] S1, preparation of the precursor:
[0107] Select walnut shell, crush into powder and pass through a 60-mesh sieve, and collect the walnut shell powder.
[0108] S2, preparation of sodium modified walnut shell powder biochar, comprising the following operation steps:
[0109] Step 1, mix 60-mesh walnut shell powder and sodium hydroxide according to a weight ratio of 1:20;
[0110] Step 2, after adding ultrapure water and stirring uniformly, transfer to a forced air oven until the moisture is evaporated;
[0111] Step 3, collect the impregnated sodium modified biomass, grind through a 60-mesh sieve, and then put into an alumina boat;
[0112] Step 4, place the alumina boat into a tube furnace and pyrolyze under a nitrogen atmosphere, and set the tube furnace program to heat to 900 DEG C at a heating rate of 5 DEG C / min and maintain for 2h.
[0113] Step 5, after the tube furnace is reduced to room temperature, repeatedly rinse the sodium modified biomass with deionized water to effectively remove ash and soluble organic compounds, collect the sodium modified walnut shell powder biochar, and name it NaHBC.
[0114] The experiment of coupling sodium modified walnut shell powder biochar NaHBC and PDS to degrade TCH, comprising the following experimental steps:
[0115] The experiment is carried out in a conical flask, and the temperature of the constant temperature shaker is 25 DEG C and the shaking speed is 155 rpm. 10mg of sodium modified walnut shell powder biochar NaHBC is dispersed in 100mL of TCH solution (10mg / L, pH 4.5) for 30min to achieve adsorption and desorption equilibrium, which is determined by a pre-experiment lasting for 24h. Sample every fixed time, and each sampling is first filtered with a 0.45mu m disposable PVDF filter, and then transferred to a vial containing sodium thiosulfate. Subsequently, the collected samples are analyzed at a wavelength of 357nm using ultraviolet spectrophotometry and high performance liquid chromatography (HPLC).
[0116] Example 3:
[0117] The calcium modified biochar catalyst prepared by taking the carbohydrate residue as the precursor, comprising the following operation steps:
[0118] S1, preparation of the precursor, comprising the following operation steps:
[0119] 1. Mix choline chloride and urea in a 1:2 molar ratio in a round-bottom flask, stir magnetically and heat at 85°C until a clear, viscous liquid without visible particles is obtained, i.e. a deep eutectic solvent (DES) is obtained;
[0120] 2. Select walnut shells, crush them into powder and pass them through a 60-mesh sieve, collect the walnut shell powder, and mix the walnut shell powder with the prepared deep eutectic solvent (DES) in a mass ratio of 1:5 by mechanical stirring for 6 h, then transfer it to the polytetrafluoroethylene (PTFE) liner of a high-pressure reactor and keep it at 155°C for 9 h;
[0121] 3. Then separate the insoluble components, i.e. the carbohydrate residue, by filtration, and then dry it at 60°C for 2 h to obtain the carbohydrate residue, and perform rotary evaporation on the filtrate to recover ethanol.
[0122] S2. Preparation of calcium-modified biochar catalyst, including the following operation steps:
[0123] Step 1. Mix the carbohydrate residue obtained in step S1 and calcium hydroxide in a weight ratio of 1:20;
[0124] Step 2. Add the mixture of step 1 to ultrapure water in a solid-liquid ratio of 1:100 (g / mL) and stir until uniform, then transfer it to a forced air oven until the water is evaporated;
[0125] Step 3. Collect the calcium-modified biomass after soaking, grind it through a 60-mesh sieve and put it into an alumina boat;
[0126] Step 4. Put the alumina boat into a tube furnace and pyrolyze it under a nitrogen atmosphere, with the tube furnace program set to heat to 900°C at a rate of 5°C / min and hold for 2 h to obtain calcium-modified biochar;
[0127] Step 5. After the tube furnace cools to room temperature, rinse the calcium-modified biochar with deionized water repeatedly to effectively remove ash and soluble organic compounds, collect the calcium-modified biochar, i.e. obtain the calcium-modified biochar catalyst, and name it CaHRBC.
[0128] The experiment of coupling CaHRBC and PDS to degrade TCH includes the following experimental steps:
[0129] The experiment was carried out in a conical flask, the temperature of the constant temperature shaker was 25℃, and the shaking speed was 155 rpm. 10 mg of calcium modified biochar catalyst CaHRBC was dispersed in 100 mL of TCH solution (10 mg / L, pH 4.5) for 30 min to achieve adsorption and desorption equilibrium, which was determined by a pre-experiment lasting for 24 h. Sampling was taken every fixed time, and each sampling was first filtered with a 0.45 μm disposable PVDF filter and then transferred to a vial containing sodium thiosulfate. Subsequently, the collected samples were analyzed at a wavelength of 357 nm using ultraviolet spectrophotometry and high-performance liquid chromatography (HPLC).
[0130] Comparative Example 5:
[0131] A method for preparing a carbohydrate residue biochar, comprising the following preparation steps:
[0132] S1, preparation of a precursor:
[0133] Choline chloride and urea were mixed in a 1:2 molar ratio in a round-bottom flask, stirred magnetically and heated at 85℃ until a transparent viscous liquid without obvious particles was obtained, which was called a deep eutectic solvent (DES); 60-mesh walnut shell powder was then mechanically stirred with the prepared deep eutectic solvent (DES) at a mass ratio of 1:5 for 6 h, and then transferred to a polytetrafluoroethylene (PTFE) liner in a high-pressure reactor, and kept at 155℃ for 9 h; the insoluble components, i.e., the carbohydrate-based residues, were then separated by filtration, and then dried at 60℃ for 2 h to collect the carbohydrate residues.
[0134] S2, preparation of a carbohydrate residue biochar, comprising the following operation steps:
[0135] Step 1, the carbohydrate residues were ground through a 60-mesh sieve, placed in an alumina boat, and the alumina boat was placed in a tube furnace for pyrolysis under a nitrogen atmosphere, and the tube furnace was heated to 900℃ at a heating rate of 5℃ / min and kept for 2 h;
[0136] Step 2, after cooling, repeatedly washed with deionized water to effectively remove ash and soluble organic compounds, and stored in a sealed plastic bag to obtain the carbohydrate residue biochar, which was named HRBC.
[0137] The experiment of coupling HRBC and PDS to degrade TCH, comprising the following experimental steps:
[0138] The experiment was carried out in a conical flask, the temperature of the constant temperature shaker was 25℃, and the shaking speed was 155 rpm. 10 mg of carbohydrate residue biochar HRBC was dispersed in 100 mL TCH solution (10 mg / L, pH 4.5) for 30 min to reach adsorption and desorption equilibrium, which was determined by a pre-experiment lasting for 24 h. Sampling was taken every fixed time, and each sampling was first filtered with a 0.45 μm disposable PVDF filter and then transferred to a vial containing sodium thiosulfate. The collected samples were then analyzed at a wavelength of 357 nm using ultraviolet spectrophotometry and high-performance liquid chromatography (HPLC).
[0139] Comparative Example 6:
[0140] A preparation method of a sodium-modified carbohydrate biochar, comprising the following preparation steps:
[0141] S1, preparation of a precursor:
[0142] Choline chloride and urea were mixed in a 1:2 molar ratio in a round-bottom flask, stirred magnetically and heated at 85℃ until a transparent viscous liquid without obvious particles was obtained, which was referred to as a deep eutectic solvent (DES); 60-mesh walnut shell powder was then mechanically stirred with the prepared deep eutectic solvent (DES) at a mass ratio of 1:5 for 6 h, and then transferred to a polytetrafluoroethylene (PTFE) liner in a high-pressure reactor, and kept at 155℃ for 9 h; the insoluble components, i.e., carbohydrate residues, were then separated by filtration, and then dried at 60℃ to collect the carbohydrate residues.
[0143] S2, preparation of a sodium-modified carbohydrate biochar, comprising the following operation steps:
[0144] Step 1, mixing the carbohydrate residues and sodium hydroxide at a weight ratio of 1:20;
[0145] Step 2, adding ultrapure water and stirring uniformly, and then transferring to a forced air oven until the water is evaporated;
[0146] Step 3, collecting the sodium-modified biomass after immersion, grinding through a 60-mesh sieve, and then placing in an alumina boat;
[0147] Step 4, placing the alumina boat in a tube furnace and pyrolyzing under a nitrogen atmosphere, and setting the tube furnace program to heat to 900℃ at a heating rate of 5℃ / min and keep for 2 h;
[0148] Step 5, after the tube furnace is cooled to room temperature, the sodium-modified biomass is repeatedly washed with deionized water to effectively remove ash and soluble organic compounds, and the sodium-modified carbohydrate biochar is collected and named as NaHRBC.
[0149] The experiment of coupling NaHRBC with PDS to degrade TCH includes the following experimental steps:
[0150] The experiment was carried out in a conical flask, and the temperature of the constant temperature shaker was 25℃, and the shaking speed was 155 rpm. 10 mg of sodium-modified carbohydrate biochar NaHRBC was dispersed in 100 mL of TCH solution (10 mg / L, pH 4.5) for 30 min to achieve adsorption and desorption equilibrium, which was determined by a pre-experiment lasting for 24 h. Sampling was taken every fixed time, and each sampling was first filtered with a 0.45 μm disposable PVDF filter, and then transferred to a vial containing sodium thiosulfate. Subsequently, the collected samples were analyzed at a wavelength of 357 nm using ultraviolet spectrophotometry and high-performance liquid chromatography (HPLC).
[0151] Performance analysis:
[0152] 1. Electron microscope characterization analysis
[0153] The morphology structure and chemical composition of the material prepared in combination with Examples 1-3 were analyzed for CaBC, and the analysis results are shown in Figure 1 It can be observed by field emission electron microscopy (SEM) that the calcium-modified biochar catalysts CaHBC( Figure 1 a), CaHRBC( Figure 1 b) and CaHLBC( Figure 1 c) of the present application all exhibit obvious roughness, and there are rich protrusions and wrinkle structures, which are beneficial to expose active sites and enhance the adsorption and activation capacity of reactants on the surface. SEM-EDS element surface scanning Figure 1 d-l) confirms that the calcium element and the C and O elements are uniformly distributed on the surface of the material, verifying that the calcium is successfully loaded on the carbon matrix.
[0154] 2. Specific surface area and pore structure analysis
[0155] As shown in Figure 2 , N2 adsorption-desorption test shows that the calcium-modified biochar catalysts CaHBC, CaHRBC and CaHLBC of the present application all exhibit type IV isotherm, and the mesopore with a pore size of 2-50 nm is the dominant structure, while the original HLBC is type III isotherm and the pore size distribution shows that it is a non-porous material.
[0156] The specific surface area data reveal that the specific surface area of CaHLBC is increased from 2.66 m2 / g to 46.19 m2 / g after the modification of calcium hydroxide, with an increase of 17 times. The phenolic hydroxyl, carboxyl and aldehyde groups contained in lignin cross-link to form dense carbon blocks during direct pyrolysis, which seriously limits the development of pores (the specific surface area of HLBC is only 2.66 m2 / g) and hinders the application of PDS-AOPs. Calcium hydroxide promotes uneven decomposition and carbonization by regulating the pyrolysis path of oxygen-containing functional groups, forms a loose porous structure while retaining the carbon skeleton, and significantly improves the exposure of active sites.
[0157] 3. X-ray diffraction analysis (XRD)
[0158] XRD analysis is used to characterize the crystal structure of the solid phase of the biochar. The crystal structure of the calcium-modified biochar catalyst of the present application is determined by XRD pattern. As shown in Figure 3 , XRD analysis detects the characteristic peaks of cubic CaO at 2θ = 32.2°
(111) crystal plane
(200) crystal plane
(220) crystal plane
[0159] 4. Adsorption and degradation performance analysis of CaBC
[0160] The adsorption and degradation performance of CaBC is analyzed by combining the materials prepared in Examples 1-3, Comparative Example 1, Comparative Example 3, and Comparative Example 5. The analysis results are shown in Figure 4 : The comparative experiments of calcium-modified biochar (CaBC) and unmodified material (BC) in coupling with persulfate (PDS) to degrade tetracycline (TCH) show that the adsorption efficiency of BC on TCH is generally lower than 10%, especially HRBC has almost no adsorption, while Ca(OH)2 modification significantly improves the adsorption performance, and the adsorption rate of CaHBC on TCH reaches 40%. This is because calcium modification optimizes the material structure, increases the specific surface area, reduces the steric hindrance of mesopore development, and enhances the electrostatic attraction between the positive surface of CaBC and the negative ions of TCH.
[0161] As shown in Figure 4 , the comparative experiments of calcium-modified biochar (CaBC) and unmodified material (HBC) in coupling with persulfate (PDS) to degrade tetracycline (TCH) show that in terms of degradation performance, CaBC coupled with PDS shows excellent activity: CaHLBC removes 80% of TCH in 15 minutes, and the removal rate of CaHBC / CaHRBC is significantly improved compared with the unmodified system. All three materials show excellent performance in degrading TCH.
[0162] 5. Analysis of the effect of calcium modification
[0163] The role of calcium modification in the application of biochar was analyzed in combination with the materials prepared in Examples 1-3, Comparative Example 2, Comparative Example 4, and Comparative Example 6, and the analysis results are shown in Figure 4 and Figure 5 .
[0164] To analyze the role of calcium species caused by calcium hydroxide modification and alkali activation, sodium hydroxide modified biochar (NaBC) was introduced as a control experimental group. The degradation performance comparison is shown in Figure 5 . NaOH activation significantly weakens the catalytic activity of the material. The TCH degradation rate of NaHBC is reduced from 64% of CaHBC to 41%, and the TCH degradation rate of NaHLBC is reduced from 84% of CaHBC to 61%. This is because the high reactivity of NaOH excessively destroys the three-dimensional network structure of lignin during pyrolysis, that is, the carbonyl / methoxyl functional groups are broken, resulting in a decrease in molecular weight and a decrease in thermal stability. In contrast, Ca(OH)2 mildly retains the aromatic structure and carbon skeleton due to the low ionization degree in water, and its decomposition products (CaO / CaCO3) can act as a template to promote the construction of pore structure of carbon materials and be loaded on the carbon surface in situ to form active sites.
Claims
1. A method for preparing a calcium-modified biochar catalyst, characterized by, The method comprises the following operation steps: S1, preparing a precursor: preparing walnut shell powder or original lignin or carbohydrate residues as a precursor; S2, preparing a calcium-modified biochar catalyst, the specific operation steps are as follows: Step 1, mix the precursor of step S1 and calcium hydroxide according to the weight ratio of 1:20 to obtain a mixture; Step 2, add ultrapure water according to the solid-liquid ratio of 1:100 (g / mL) with the mixture of step 1, stir uniformly, then transfer to a forced air oven until the moisture is evaporated, obtain calcium-modified biomass; Step 3, grind the calcium-modified biomass through a 60-mesh sieve and put it into an alumina boat; Step 4, put the alumina boat into a tube furnace and pyrolyze under nitrogen atmosphere, the tube furnace program is set to heat to 900℃ at a heating rate of 5℃ / min and keep for 2h, obtain calcium-modified biochar; Step 5, when the temperature in the tube furnace decreases to room temperature, wash the calcium-modified biochar repeatedly with deionized water to remove ash and soluble organic compounds, obtain the calcium-modified biochar catalyst.
2. The method of claim 1, wherein the calcium-modified biochar catalyst is prepared by the steps of: In step S1, the preparation method of the walnut shell powder is: selecting walnut shell, crushing into powder through a 60-mesh sieve, obtaining walnut shell powder.
3. The method of claim 1, wherein the calcium-modified biochar catalyst is prepared by the steps of: In step S1, the preparation method of the carbohydrate residues comprises the following operation steps: Step 1, mix choline chloride and urea in a round-bottom flask at a molar ratio of 1:2, stir magnetically and heat at 85℃ until a transparent viscous liquid without obvious particles is obtained, i.e. a deep eutectic solvent (DES) is obtained; Step 2, mechanically stir the walnut shell powder sieved through a 60-mesh sieve and the prepared deep eutectic solvent (DES) according to a mass ratio of 1:5, then transfer to a polytetrafluoroethylene (PTFE) liner in a high-pressure reactor and keep at 155℃ for 9h; Step 3, filter the product of step 2 to separate out insoluble components, then dry at 60℃ for 2h to obtain carbohydrate residues.
4. The method of claim 1, wherein the calcium-modified biochar catalyst is prepared by the steps of: In step S1, the preparation method of the original lignin comprises the following operation steps: Step 1, mix choline chloride and urea in a round-bottom flask at a molar ratio of 1:2, stir magnetically and heat at 85℃ until a transparent viscous liquid without obvious particles is obtained, i.e. a deep eutectic solvent (DES) is obtained; Step 2, mechanically stir the walnut shell powder sieved through a 60-mesh sieve and the prepared deep eutectic solvent (DES) according to a mass ratio of 1:5, then transfer to a polytetrafluoroethylene (PTFE) liner in a high-pressure reactor and keep at 155℃ for 9h; Step 3, filter the product of step 2 to separate out insoluble components, then dry at 60℃ for 2h to obtain carbohydrate residues, and perform rotary evaporation on the filtrate to recover ethanol; Step 4, cool the filtrate of step 3 to room temperature, then add excess deionized water to precipitate lignin, after the precipitation is complete, filter the lignin in the solution and wash it with deionized water multiple times to ensure effective removal of ethanol; Step 5, dry the lignin of step 4 at room temperature for 24h to obtain original lignin.
5. The method for preparing the calcium-modified biochar catalyst according to claim 3 or 4, characterized in that, In step 2, the mechanical stirring time is 6h.
6. Use of the calcium-modified biochar catalyst according to claims 1-5, characterized in that, The calcium-modified biochar catalyst is used for activating persulfate to degrade tetracycline.