Preparation method and application of double-doped biochar

Abstract

The invention discloses a preparation method and application of double-doped biochar, and belongs to the technical field of biochar preparation, and the preparation method comprises the following steps: cleaning, drying and crushing apple branches to obtain branch powder with uniform particles; uniformly blending the branch powder, urea and potassium formate with deionized water, drying, and carrying out calcination reaction at 600-800 DEG C; cooling to room temperature, sequentially washing with diluted hydrochloric acid and deionized water until the pH is constant, and drying to obtain N-doped biochar; and uniformly blending the N-doped biochar and ammonium fluoride by using deionized water, drying, and carrying out calcination reaction at 400-600 DEG C to obtain the double-doped biochar. Compared with single N doping, the preparation method of the N and F double-doped biochar provided by the invention can more efficiently regulate and control pore development of the biochar, the step-by-step preparation method can accurately regulate and control the introduction effect of doped elements, the specific surface area of the prepared N and F double-doped biochar is greatly increased, and the preparation method is suitable for large-scale industrial production. And a sufficient structure bearing foundation is provided for the high-efficiency adsorption performance of the material.

Description

Technical Field

[0001] This invention relates to the field of biochar preparation technology, and in particular to a method for preparing dual-doped biochar and its application. Background Technology

[0002] The widespread presence and continuous accumulation of antibiotics in aquatic environments has become a global environmental and health crisis. Norfloxacin, a typical representative of third-generation fluoroquinolone antibiotics, is frequently detected in water bodies due to its broad antibacterial spectrum, low toxicity, and wide range of applications. Environmental residues of norfloxacin may not only induce the emergence of antibiotic-resistant bacteria and disrupt the ecological balance, but also pose a potential threat to drinking water safety and human health, necessitating the development of efficient, economical, and environmentally friendly removal technologies. Adsorption methods are considered a highly promising solution due to their ease of operation, controllable cost, and low likelihood of secondary pollution; the core of this approach lies in the development of high-performance adsorption materials.

[0003] Biochar possesses significant advantages such as a large specific surface area, well-developed pore structure, abundant surface functional groups, environmental friendliness, and the ability to utilize waste agricultural and forestry biomass as raw material, and has been widely used for the adsorption of various pollutants. Apple tree branches, as a major waste generated from orchard pruning, are produced in huge quantities annually but are often discarded or used for low-value purposes. Converting them into biochar not only aligns with the circular economy concept of "treating pollution with waste," but their structural characteristics of being rich in cellulose, hemicellulose, and lignin also suggest their potential as a precursor for excellent porous carbon-based materials. However, the adsorption performance and selectivity of raw biochar for complex organic pollutants such as norfloxacin are often limited, making it difficult to meet practical application needs. Therefore, controlling the physicochemical properties of biochar (such as specific surface area, pore size distribution, charge distribution, etc.) through physical or chemical modification strategies to enhance its interaction with target pollutants has become key to improving its adsorption performance.

[0004] Heteroatom doping is an effective means to improve the adsorption performance of biochar. Nitrogen doping has been extensively studied, as it can alter the surface chemistry of biochar (such as increasing specific surface area and introducing N-containing functional groups), change the electronic configuration of the matrix, induce the generation of new defects and active centers, and significantly improve its ability to adsorb organic pollutants such as norfloxacin. On the other hand, in recent years, fluorine (F) doping has emerged in the field of material modification due to its unique strong electronegativity and hydrophobicity. The high electronegativity and strong electron affinity of fluorine atoms can lead to localization of surface charge distribution, forming electron-rich and electron-deficient regions, disrupting the symmetry of surface electron distribution. This asymmetry is beneficial for the adsorption of organic pollutants and improves its performance. In existing technologies, polyvinylidene fluoride is used as the fluorine source, and the carbon source is not agricultural or forestry waste, which has problems such as high cost and small specific surface area, thus limiting its application in the removal of organic pollutants. Summary of the Invention

[0005] The present invention aims to overcome the defect of small specific surface area of ​​biochar prepared by existing technology, and provides a method for preparing dual-doped biochar and its application.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: Firstly, a method for preparing dual-doped biochar is provided, comprising the following steps: (1) Apple tree branches are washed, dried and crushed to obtain tree branch powder with uniform particles; (2) Mix the tree branch powder, urea and potassium formate with deionized water, dry them, and calcine them at 600-800℃. (3) Cool the product obtained in step (2) to room temperature, rinse it with dilute hydrochloric acid and deionized water in sequence until the pH is constant, and dry it to obtain N-doped biochar; (4) The N-doped biochar prepared in step (3) is mixed with ammonium fluoride with deionized water, dried, and calcined at 400~600 °C to obtain double-doped biochar.

[0007] In one embodiment, in step (1), the drying temperature is 105-120°C and the drying time is 12-24h.

[0008] In one embodiment, the sieving process in step (1) is characterized by passing through a 20-40 mesh sieve.

[0009] In one embodiment, in step (2), tree branch powder, urea and potassium formate are added in equal amounts.

[0010] In one embodiment, in step (2), calcination is carried out in nitrogen atmosphere for 1-2 hours.

[0011] In one embodiment, in step (3), the drying temperature is 105-120°C and the drying time is 12-24 h.

[0012] In one embodiment, in step (4), the mass of ammonium fluoride added is 1-6 times that of the product in step (3), the calcination temperature is 400-600 ℃, and the calcination time is 1-2 h.

[0013] Secondly, the present invention also provides an application of dual-doped biochar, wherein the dual-doped biochar prepared by any of the above-described methods is used to remove organic pollutants from water.

[0014] The method for preparing N and F dual-doped biochar provided by this invention can more efficiently control the pore development of biochar compared with single N doping. The stepwise preparation method can precisely control the introduction effect of doping elements, and the specific surface area of ​​the prepared N and F dual-doped biochar is greatly improved, providing a sufficient structural support for the material's high-efficiency adsorption performance.

[0015] The N / F dual-doped biochar material prepared by this invention exhibits adsorption performance far exceeding that of existing single-doped N biochar for similar pollutants. Furthermore, it is highly adaptable to various organic pollution control scenarios, including antibiotics and dyes. In addition, this invention uses waste apple tree branches as a biomass substrate, transforming agricultural and forestry waste into a high-value dual-doped biochar adsorbent material. This not only solves the environmental pollution problem caused by the indiscriminate disposal of agricultural and forestry waste but also replaces the high-cost preparation path of traditional adsorbent materials. While achieving efficient treatment of organic pollutants, it also expands the channels for the resource utilization of waste, realizing a synergistic improvement in both environmental and economic benefits.

[0016] To make the above-mentioned features and advantages of the invention more apparent and understandable, specific embodiments are described below, and detailed descriptions are provided in conjunction with the accompanying drawings. Attached Figure Description

[0017] Figure 1 This is the N2 adsorption-desorption isotherm of the N-doped biochar of this invention; Figure 2 This is the N2 adsorption-desorption isotherm of N,F dual-doped biochar prepared by the one-step pyrolysis method of this invention; Figure 3 This is the N2 adsorption-desorption isotherm of N,F double-doped biochar prepared by the two-step pyrolysis method of this invention with an ammonium fluoride addition ratio of 1:1 to biochar. Figure 4 This is the N2 adsorption-desorption isotherm of N,F double-doped biochar prepared by the two-step pyrolysis method of this invention with an ammonium fluoride addition ratio of 1:3 to biochar. Figure 5 This is the N2 adsorption-desorption isotherm of N,F double-doped biochar prepared by the two-step pyrolysis method of this invention with an ammonium fluoride addition ratio of 1:6 to biochar. Detailed Implementation To make the objectives and technical solutions of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0018] Example 1: This embodiment aims to prepare a nitrogen-doped biochar.

[0019] A method for preparing an N-doped biochar-supported Ni / NiO catalyst includes the following steps: (1) First, wash the apple tree branches with deionized water to remove surface impurities, dry them in an oven at 105℃ for 12 hours, pulverize them with a pulverizer and pass them through a 30-mesh sieve to obtain apple tree branch powder with uniform size.

[0020] (2) Place 2 g of apple branch powder, 2 g of potassium formate and 2 g of urea into a beaker containing 30 mL of deionized water, stir vigorously until homogeneous, and dry in an oven at 105 °C. Place the mixed sample in a tube furnace under a nitrogen atmosphere with a flow rate of 200 mL / min and a heating rate of 3 °C / min, and calcine at 800 °C for 1 h.

[0021] (3) After calcination, the sample was automatically cooled to room temperature and then washed with dilute hydrochloric acid and deionized water until the pH was neutral to remove water-soluble impurities. Then, the sample was placed in a constant temperature drying oven at 120 °C and dried for 12 h to obtain a black powder, namely N-doped apple tree branch-based biochar, which was stored in a sealed glass container.

[0022] like Figure 1 The specific surface area of ​​the N-doped biochar obtained in step (3) of this embodiment is 1937.02 m². 2 / g.

[0023] Example 2 The remaining steps in this embodiment are the same as those in Embodiment 1, except that 2 g of ammonium fluoride was added in step (2).

[0024] like Figure 2 In Example 2, the N,F dual-doped organism prepared by one-step pyrolysis had a specific surface area of ​​829.54 m². 2 / g.

[0025] Example 3 The remaining steps in this embodiment are the same as in embodiment 1, except that step (4) is added: (4) The N-doped biochar obtained in step (3) is mixed with ammonium fluoride at a mass ratio of 1:1, placed in a tube furnace, N2 is introduced, and calcined at 600 °C for 1 h. After washing with deionized water, it is dried in an oven at 105 °C to obtain N,F double-doped biochar (NFBCs-1:1).

[0026] like Figure 3 The specific surface area of ​​the NFBCs-1:1 obtained in Example 3 was 2166.68 m². 2 / g.

[0027] Example 4 The remaining steps in this embodiment are the same as those in embodiment 3, except that in step (4), the mass ratio of N-doped biochar to ammonium fluoride is replaced by a mass ratio of N-doped biochar to ammonium fluoride of 1:3.

[0028] like Figure 4 The specific surface area of ​​NFBCs-1:3 obtained in Example 4 was 2186.60 m2 / g.

[0029] Example 5 The remaining steps in this embodiment are the same as those in Embodiment 1, except that in step (4), the mass ratio of N-doped biochar to ammonium fluoride is replaced by a mass ratio of N-doped biochar to ammonium fluoride of 1:6.

[0030] like Figure 5 The specific surface area of ​​NFBCs-1:6 obtained in Example 5 was 2358.40 m². 2 / g.

[0031] Example 6 The adsorption experiments of typical organic compounds were all carried out in 150 mL conical flasks. In typical experiments, 10 mg NFBCs-1:3 and 50 mg / L norfloxacin were used in a 150 mL conical beaker and shaken at 180 rpm. At certain time intervals (0-100 min), 2 mL of sample was taken, filtered through a 0.45 μm filter membrane, and measured at a wavelength of 273 nm using a UV-Vis spectrophotometer. The adsorption amount of norfloxacin was calculated using the following formula (1): (1) In equation (1), Q e Adsorption capacity, mg / g; V is the initial volume of the norfloxacin solution, in L; C0 is the initial concentration of the norfloxacin solution, in mg / L; C t The real-time concentration of norfloxacin solution, in mg / L, at time t during the experiment; m is the mass of adsorbent NFBCs-1:3 added, in g.

[0032] The equilibrium adsorption capacity of NFBCs-1:3 for norfloxacin was determined to be 429.91 mg / g. Example 7 The adsorption experiments of typical organic compounds were all carried out in 150 mL conical flasks. In typical experiments, 10 mg NFBCs-1:3 and 50 mg / L levofloxacin were used in a 150 mL conical flask and shaken at 180 rpm. At certain time intervals (0-100 min), 2 mL of sample was taken, filtered through a 0.45 μm filter membrane, and measured at a wavelength of 273 nm using a UV-Vis spectrophotometer. The removal rate of levofloxacin was calculated using the following formula (2): (2) In equation (2), η is the removal rate; C0 is the initial concentration of the norfloxacin solution, in mg / L; C e The real-time concentration of norfloxacin solution, in mg / L, when adsorption reaches equilibrium.

[0033] Analysis showed that NFBCs-1:3 achieved a levofloxacin removal rate of 95.09%.

[0034] Example 8 Adsorption experiments for typical organic compounds were conducted in 150 mL Erlenmeyer flasks. In a typical experiment, 10 mg of NFBCs-1:3 and 50 mg / L tetracycline were mixed in a 150 mL Erlenmeyer flask with shaking at 180 rpm. At regular time intervals (0-100 min), 2 mL samples were taken, filtered through a 0.45 μm filter, and measured using a UV-Vis spectrophotometer. The removal rate of tetracycline was calculated using the same method as that for levofloxacin in Example 7. Analysis showed that NFBCs-1:3 achieved a tetracycline removal rate of 97.96%.

[0035] Example 9 Adsorption experiments for typical organic compounds were conducted in 150 mL Erlenmeyer flasks. In typical experiments, 10 mg of NFBCs-1:3 and 50 mg / L methyl orange were used in a 150 mL Erlenmeyer flask, shaken at 180 rpm. At regular time intervals (0-100 min), 2 mL samples were taken, filtered through a 0.45 μm filter membrane, and measured using a UV-Vis spectrophotometer. The removal rate of methyl orange was calculated using the same method as that for levofloxacin in Example 7. Analysis showed that NFBCs-1:3 achieved a methyl orange removal rate of 99.90%.

[0036] In summary, the method for preparing N and F dual-doped biochar provided by this invention can more efficiently control the pore development of biochar compared to single N doping. The biochar prepared in Example 1 has a specific surface area of ​​1937.02 m² / g. Although the one-step dual-doping process used in Example 2 achieves N and F co-doping, the specific surface area of ​​the material is only 829.54 m² / g, and the pore structure optimization effect is limited. However, the stepwise dual-doping process of this invention can precisely control the introduction effect of dopant elements, and the specific surface area of ​​the prepared N and F dual-doped biochar is significantly improved. Specifically, the specific surface area of ​​Example 3 (NFBCs-1:1) is 2166.68 m² / g, Example 4 (NFBCs-1:3) is 2186.60 m² / g, and Example 5 (NFBCs-1:6) is as high as 2358.40 m² / g, which is about 21.8% higher than that of Example 1, providing a sufficient structural support for the high-efficiency adsorption performance of the material.

[0037] Based on the optimized pore structure described above, the NFBCs material prepared in this invention exhibits significant advantages in adsorption performance. The equilibrium adsorption capacity of NFBCs-1:3 for norfloxacin reaches 429.91 mg / g, far exceeding the adsorption level of existing single-doped N-based biochar for similar pollutants. Furthermore, this material is applicable to a wider range of pollution systems. Experimental results in Examples 7-9 show that it achieves a removal rate of 95.09% for levofloxacin, 97.96% for tetracycline, and 99.90% for methyl orange, making it highly suitable for treating various organic pollution scenarios, including antibiotics and dyes.

[0038] Furthermore, this invention uses discarded apple tree branches as a biomass substrate to transform agricultural and forestry waste into high-value dual-doped biochar adsorbent materials. This not only solves the environmental pollution problem caused by the indiscriminate disposal of agricultural and forestry waste, but also replaces the high-cost preparation path of traditional adsorbent materials. While achieving efficient treatment of organic pollutants, it expands the channels for the resource utilization of waste and realizes the synergistic improvement of environmental and economic benefits.

[0039] Although the invention has been described and illustrated in detail with reference to preferred embodiments, the invention is not limited to the disclosed examples, and those skilled in the art can derive other variations therefrom without departing from the scope of protection of the invention.

Claims

1. A method for preparing dual-doped biochar, characterized in that, Includes the following steps: (1) Apple tree branches are washed, dried and crushed to obtain tree branch powder with uniform particles; (2) Mix the tree branch powder, urea and potassium formate with deionized water, dry them, and calcine them at 600-800℃. (3) Cool the product obtained in step (2) to room temperature, rinse it with dilute hydrochloric acid and deionized water in sequence until the pH is constant, and dry it to obtain N-doped biochar; (4) The N-doped biochar prepared in step (3) is mixed with ammonium fluoride with deionized water, dried, and calcined at 400~600 °C to obtain double-doped biochar.

2. The method for preparing dual-doped biochar according to claim 1, characterized in that, In step (1), the drying temperature is 105-120℃ and the drying time is 12-24h.

3. The method for preparing dual-doped biochar according to claim 2, characterized in that, In step (1), the sieving is performed through a 20-40 mesh sieve.

4. The method for preparing dual-doped biochar according to claim 3, characterized in that, In step (2), tree branch powder, urea and potassium formate are added in equal amounts.

5. The method for preparing dual-doped biochar according to claim 4, characterized in that, In step (2), calcination is carried out in nitrogen gas for 1-2 hours.

6. The method for preparing dual-doped biochar according to claim 5, characterized in that, In step (3), the drying temperature is 105-120℃ and the drying time is 12-24 h.

7. The method for preparing dual-doped biochar according to claim 6, characterized in that, In step (4), the mass of ammonium fluoride added is 1-6 times that of the product in step (3), the calcination temperature is 400-600 ℃, and the calcination time is 1-2 h.

8. An application of dual-doped biochar, characterized in that, The dual-doped biochar prepared by the method described in any one of claims 1-7 is used to remove organic pollutants from water.

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