A multi-level pore biochar-based cathode material and a preparation method and application thereof

Abstract

The application discloses a kind of multistage hole biochar-based cathode materials and its preparation method and application, multistage hole biochar-based cathode material constructs nonmetallic heteroatom doped site and nanometer cobalt oxide metal site in the multistage hole structure of biochar, simultaneously provides high-density active site and fast mass transfer channel for the electrochemical generation and activation reaction of hydrogen peroxide;Biochar is provided with mesopore, macropore, the diameter of mesopore is 2-50nm, and the diameter of macropore is 50-2000nm.Preparation method includes the following steps: hydrothermal method is handled to dry oil crop residue precursor;Preparation of defect-rich multistage hole biochar;Preparation of multistage hole biochar-based cathode material.The application obtains defect-rich biochar with developed mesopore and macropore structure as the ideal carrier of electro-fenton cathode material by series of pretreatment, and realizes defect control by adjusting biomass precursor type, acid and biomass precursor mass ratio, hydrothermal reaction temperature.

Description

Technical Field

[0001] This invention pertains to cathode materials, their preparation methods and applications, specifically a hierarchical porous biochar-based cathode material, its preparation method and application. Background Technology

[0002] In recent years, with the rapid development of industry, wastewater from chemical, pharmaceutical, and pesticide industries contains various recalcitrant organic pollutants such as antibiotics and dyes, which are highly toxic and difficult to remove. These pollutants are generally difficult to biodegrade and typically require advanced oxidation technologies to improve their biodegradability. Electro-Fenton technology can generate hydrogen peroxide in situ, avoiding the risks of storing and transporting high-concentration hydrogen peroxide and improving its utilization efficiency. However, traditional homogeneous electro-Fenton processes have stringent pH requirements (2.5–3.5), and the addition of ferrous ions generates a large amount of iron sludge, increasing the difficulty of subsequent treatment. To address these challenges, a series of heterogeneous catalysts, including metal oxides and iron ore, have been developed. Chinese Patent Application No. 202010028202.2 discloses the preparation of an activated carbon-supported catalyst for the heterogeneous electro-Fenton degradation of organic wastewater, but its kinetic rate is slow, and its catalytic activity for the oxygen reduction reaction to generate hydrogen peroxide is low.

[0003] Nanocarbon materials offer significant advantages as catalysts for oxygen reduction reactions (ORRs). Their high specific surface area, good conductivity, and excellent electrochemical stability facilitate electron transport and maintain stability over long-term use. Furthermore, their lower oxygen adsorption energy compared to metal sites promotes the desorption of OCR intermediates, leading to the selective generation of hydrogen peroxide. However, the application of nanocarbon materials in electro-Fenton technology still faces numerous challenges. The pores of nanocarbon materials are primarily distributed in mesopores / micropores, which hinders mass transfer between hydrogen peroxide and pollutants. Moreover, the synthesis and control of nanocarbon structures are complex and challenging. Existing modified biochar can achieve efficient hydrogen peroxide generation in simulated wastewater environments, but its activation effect on hydrogen peroxide is weak, making it difficult to fully utilize accumulated high concentrations of hydrogen peroxide. It has not overcome the key technological bottlenecks of rapid hydrogen peroxide generation and efficient activation. Existing phosphorus-doped biochar used in water treatment to produce H2O2 only achieves H2O2 generation; it is difficult to further activate H2O2 into active species and degrade pollutants, resulting in poor removal efficiency. Summary of the Invention

[0004] Purpose of the invention: In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a hierarchical porous biochar-based cathode material. Another purpose of this invention is to provide a method for preparing a hierarchical porous biochar-based cathode material. Yet another purpose of this invention is to provide an application of a hierarchical porous biochar-based cathode material in electro-Fenton degradation of pollutants.

[0005] Technical solution: The present invention discloses a hierarchical porous biochar-based cathode material, which constructs non-metallic heteroatom doping sites and nano-cobalt oxide metal sites in the hierarchical porous structure of biochar, providing high-density active sites and fast mass transfer channels for the electrochemical generation and activation reaction of hydrogen peroxide; the biochar is provided with mesopores and macropores, the diameter of the mesopores being 2-50 nm and the diameter of the macropores being 50-2000 nm.

[0006] Furthermore, the mesopore volume accounts for 35-40%.

[0007] The preparation method of the above-mentioned hierarchical porous biochar-based cathode material includes the following steps:

[0008] Step 1, hydrothermal treatment of dried oilseed crop residue precursors: After drying the oilseed crop residues, soak them in a phosphoric acid solution, heat them at 140-210℃ for hydrolysis, and then filter and separate the hydrolysis products to obtain biomass pellets.

[0009] Step 2, Preparation of defect-rich hierarchical biochar (DBC): The biomass particles obtained in Step 1 are calcined at 500-1000℃ in an inert gas atmosphere, cooled, washed and dried to obtain defect-rich hierarchical biochar.

[0010] Step 3: Preparation of hierarchical porous biochar-based cathode material: The defect-rich hierarchical porous biochar obtained in Step 2 is soaked in cobalt salt organic solvent and subjected to hydrothermal reaction at 120-180℃ to obtain cobalt salt-loaded defect-rich hierarchical porous biochar. Then, it is calcined again at 240-600℃, cooled, washed, and dried to obtain hierarchical porous biochar-based cathode material.

[0011] Further, in step one, the mass ratio of oilseed crop residue to phosphoric acid solution is 0.3–5:1, and the concentration of phosphoric acid solution is 8–25 g / L. The oilseed crop residue can be any one of the following: tung oil seed, peanut, soybean, sesame, or rapeseed. The heating and hydrolysis reaction time is 7–18 hours.

[0012] Furthermore, in step two, the drying temperature is 40–80℃, and the drying time is 7–24 h. The calcination heating rate is 5℃ / min, and the calcination time is 1–5 h.

[0013] Further, in step three, the cobalt salt is any one or more of cobalt naphthenate, cobalt neodecanoate, and cobalt stearate. The concentration of the cobalt salt organic solution is 1.25–15 g / L, and the final loading of the cobalt salt on the biochar is 0.2–10 wt%. The hydrothermal reaction time is 3–10 h, and the secondary calcination time is 1–5 h. The drying temperature is 60 °C.

[0014] The application of the hierarchical porous biochar-based cathode material described in this invention in the electro-Fenton degradation of pollutants.

[0015] Preparation principle: Using oilseed crop waste as a natural biomass precursor, firstly, defect-rich biochar with a rich meso / macroporous structure is obtained by hydrothermal treatment with phosphoric acid and high-temperature calcination. Cobalt neodecanoate is used as a precursor for metal active site doping. The abundant phosphorus functional groups of the biochar material are used to anchor the cobalt sites. During the pyrolysis process, the reducing atmosphere formed by organic ligands is used to grow a nanostructure with a carbon layer encapsulating cobalt oxide on the inner wall of the biochar pores. A mesoporous / microporous carbon layer is further constructed on the surface of the biochar to build a composite carbon material with a multi-level porous structure. When this multi-level porous material is used as the cathode of the electro-Fenton technology, relying on the abundant intrinsic defects and heteroatom sites of the carbon material itself, it can achieve highly selective hydrogen peroxide generation at a high current efficiency. The hydrogen peroxide accumulates in the meso / macroporous structure of the biochar and is further activated by the cobalt oxide in the surface meso / microporous carbon layer to generate reactive oxygen species, thereby achieving efficient degradation of organic pollutants in water.

[0016] Compared with existing electro-Fenton catalytic cathode materials, this invention utilizes an improved neodecanoic acid metal brine thermal method to load cobalt oxide into the well-developed meso / macroporous structure of defect-rich hierarchical biochar. When this material is applied to electro-Fenton cathode materials, the abundant intrinsic defects and phosphorus functional groups within the defect-rich biochar channels serve as highly efficient active sites for two-electron oxygen reduction. This allows for the rapid accumulation of high concentrations of hydrogen peroxide within the well-developed meso / macroporous structure of the biochar, and further, under the catalysis of cobalt, the hydrogen peroxide continuously generates oxygen-active species through an external circuit, thereby efficiently oxidizing and degrading organic pollutants.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0018] 1. Through a series of pretreatments, defect-rich biochar with well-developed mesoporous and macroporous structures is obtained as an ideal carrier for electro-Fenton cathode materials. Defect control is achieved by adjusting the type of biomass precursor, the mass ratio of acid to biomass precursor, and the hydrothermal reaction temperature.

[0019] 2. Under hydrothermal conditions, the abundant defects in the pores of biochar and the phosphorus and oxygen functional groups on the surface further enhance the bonding between neodecanoate metal salt and biochar.

[0020] 3. The well-developed macro / mesoporous structure of biochar can promote the rapid diffusion of hydrogen peroxide in the pores and the enrichment of pollutants, thereby accelerating the generation and utilization of oxygen-reactive species.

[0021] 4. Cobalt oxides loaded on the surface of biochar can effectively activate hydrogen peroxide generated in situ, thereby achieving the degradation and removal of pollutants. Attached Figure Description

[0022] Figure 1 This describes the microstructure of defect-rich hierarchical porous biochar modified with phosphoric acid in Example 1 of this invention.

[0023] Figure 2 This describes the microstructure of cobalt oxide supported on defect-rich hierarchical porous biochar in Example 1 of the present invention.

[0024] Figure 3 The Co valence state distribution of cobalt coated with a carbon layer grown within the pores of defect-rich hierarchical biochar in Example 1 of this invention;

[0025] Figure 4 This is a BET pore size distribution diagram of the product obtained in Example 1 of the present invention;

[0026] Figure 5 This is a macropore distribution diagram obtained by mercury intrusion porosimetry in Example 1 of the present invention.

[0027] Figure 6 These are the effect diagrams of the degradation of sulfamethoxazole by the multi-level porous biochar-based cathode materials in Examples 1-5 of the present invention;

[0028] Figure 7 These are the effect diagrams of pollutant degradation by the multi-level porous biochar-based cathode materials in Examples 6-10 of the present invention;

[0029] Figure 8 The results are from Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention. Detailed Implementation

[0030] In the following embodiments, D represents hierarchical pores and BC represents biochar.

[0031] Example 1

[0032] A method for preparing a hierarchical porous biochar-based cathode material includes the following steps:

[0033] (1) Hydrothermal treatment of dried oilseed crop residue precursor, *Tetracentron sinense* seeds: 1 g of *Tetracentron sinense* seeds and 2 g of phosphoric acid were mixed in 80 mL of deionized water. The phosphoric acid solution concentration was 25 g / L, and the mass ratio of oilseed crop residue to phosphoric acid solution was 0.5:1. The mixture was hydrolyzed in a sealed hydrothermal reactor at 180 °C for 12 h. Biomass particles were obtained by filtration, such as… Figure 1 As shown.

[0034] (2) Preparation of defect-rich hierarchical biochar (DBC): The spherical biomass particles obtained in step (1) were vacuum dried and then placed in a tube furnace. The furnace was calcined at 800℃ for 3 hours under an argon flow at a heating rate of 5℃ / min. After cooling, the particles were repeatedly washed with ethanol and deionized water and dried at 60℃ for 12 hours to obtain defect-rich hierarchical biochar (DBC). The microstructure of DBC is shown in the figure. Figure 2 As shown, its Co valence state analysis is as follows: Figure 3 As shown. By Figures 2-3It can be seen that Co is encapsulated in carbon layers in divalent and trivalent forms.

[0035] (3) Preparation of hierarchical porous biochar-based cathode material: 0.5 g of cobalt neodecanoate was added to 40 mL of heptane to prepare a precursor solution with a concentration of 12.5 g / L. 0.1 g of DBC (after thorough grinding) was added to the precursor suspension and stirred for 30 min until the precursor loading reached 5 wt%. The solution was hydrothermally heated at 130 °C for 6 h. The DBC loaded with the precursor was then calcined in a tube furnace at 400 °C for 3 h under air conditions, with a heating rate of 5 °C / min. Vacuum drying yielded cobalt oxide-supported defect-rich biochar (Co-DBC-1).

[0036] Application Example 1

[0037] Electro-Fenton degradation of sulfamethoxazole was carried out in a 25 mL gas cathode reactor. 10 mg of Co-DBC-1 obtained in Example 1 was loaded onto a carbon cloth surface as the working cathode. The reaction was operated in a three-cathode system, with a saturated calomel cathode as the reference cathode and a platinum mesh as the counter cathode, E = -0.5 (vs SCE). O2 was introduced into the gas chamber of the reactor at a flow rate of 50 mL / min. 0.05 mM Na2SO4 was used as the supporting electrolyte. The reaction was carried out under neutral conditions, with pre-adsorption for 30 min before electrolysis. The degradation effect was as follows: Figure 6 As shown.

[0038] like Figures 4-5 The average size of the mesopores in the material obtained in Example 1 is approximately 5.15 nm, and the average size of the macropores is 474.24 nm. The diameter of the mesopores ranges from 2 to 50 nm, and the diameter of the macropores ranges from 50 to 2000 nm.

[0039] Example 2

[0040] The remaining steps in this embodiment are the same as in Embodiment 1, except that peanut is selected as the precursor for oilseed crop residue. The product is denoted as Co-DBC-2.

[0041] Application Example 2

[0042] The electro-Fenton degradation steps for sulfamethoxazole are the same as in Application Example 1, and the degradation effect is as follows: Figure 6 As shown.

[0043] Example 3

[0044] The remaining steps in this embodiment are the same as in Embodiment 1, except that soybean is selected as the oilseed crop residue precursor. The product is denoted as Co-DBC-3.

[0045] Application Example 3

[0046] The electro-Fenton degradation steps for sulfamethoxazole are the same as in Application Example 1, and the degradation effect is as follows: Figure 6 As shown.

[0047] Example 4

[0048] The remaining steps in this embodiment are the same as in Example 1, except that sesame is selected as the precursor for oilseed crop residue. The product is denoted as Co-DBC-4.

[0049] Application Example 4

[0050] The electro-Fenton degradation steps for sulfamethoxazole are the same as in Application Example 1, and the degradation effect is as follows: Figure 6 As shown.

[0051] Example 5

[0052] The remaining steps in this embodiment are the same as in Embodiment 1, except that rapeseed is selected as the precursor for oilseed crop residue. The product is denoted as Co-DBC-5.

[0053] Application Example 5

[0054] The electro-Fenton degradation steps for sulfamethoxazole are the same as in Application Example 1, and the degradation effect is as follows: Figure 6 As shown.

[0055] Depend on Figure 6 It can be seen that the hierarchical porous biochar-based cathode material has a good effect on SMZ degradation, with Co-DBC-1 removing 92% of SMZ in 30 minutes.

[0056] Application Example 6

[0057] The electro-Fenton degradation experiment was identical to that in Application Example 1, the only difference being that the pollutant was replaced with tetracycline hydrochloride. The degradation effect was as follows: Figure 7 As shown.

[0058] Application Example 7

[0059] The electro-Fenton degradation experiment was identical to that in Application Example 1, the only difference being that the pollutant was replaced with ciprofloxacin, and the degradation effect was as follows: Figure 7 As shown.

[0060] Application Example 8

[0061] The electro-Fenton degradation experiment was identical to that in Application Example 1, the only difference being that the pollutant was replaced with norfloxacin, and the degradation effect was as follows: Figure 7 As shown.

[0062] Application Example 9

[0063] The electro-Fenton degradation experiment was identical to that in Application Example 1, the only difference being that the pollutant was replaced with trichlorophenol, and the degradation effect was as follows: Figure 7 As shown.

[0064] Application Example 10

[0065] The electro-Fenton degradation experiment was identical to that in Application Example 1, the only difference being that the pollutant was replaced with 2,4-dichlorophenol, and the degradation effect was as follows: Figure 4 As shown.

[0066] Depend on Figure 7 It can be seen that the hierarchical porous biochar-based cathode material has good broad-spectrum performance, and the removal rate of various pollutants reaches more than 95% within 90 minutes.

[0067] Of the above application examples, application example 10 is the best application example.

[0068] Example 6

[0069] A method for preparing a hierarchical porous biochar-based cathode material includes the following steps:

[0070] (1) Hydrothermal treatment of dried oilseed crop residue precursor soybean: 0.192 g soybean and 0.64 g phosphoric acid were mixed in 80 mL deionized water. The phosphoric acid solution concentration was 8 g / L, and the mass ratio of oilseed crop residue to phosphoric acid solution was 0.3:1. The mixture was hydrolyzed in a hydrothermal reactor at 140 °C for 18 h. Biomass particles were obtained by filtration.

[0071] (2) Preparation of defect-rich hierarchical biochar (DBC): The spherical biomass particles obtained in step (1) were placed in a tube furnace after vacuum drying and calcined at 500°C for 5 hours under an argon flow at a heating rate of 5°C / min. After cooling, the particles were repeatedly washed with ethanol and deionized water and dried at 40°C for 24 hours to obtain defect-rich hierarchical biochar (DBC).

[0072] (3) Preparation of hierarchical porous biochar-based cathode material: 0.05 g of cobalt naphthenate was added to 40 mL of heptane to prepare a precursor solution with a concentration of 1.25 g / L. 0.1 g of DBC (after thorough grinding) was added to the precursor suspension and stirred for 30 min until the precursor loading reached 0.2 wt%. The solution was then hydrothermally heated at 120 °C for 10 h. The DBC loaded with the precursor was placed in a tube furnace and calcined at 240 °C for 5 h under air conditions, with a heating rate of 5 °C / min. Vacuum drying yielded cobalt oxide-supported defect-rich biochar (Co-DBC-6).

[0073] Example 7

[0074] A method for preparing a hierarchical porous biochar-based cathode material includes the following steps:

[0075] (1) Hydrothermal treatment of dried rapeseed precursor from oilseed crop residue: 4.8 g of rapeseed and 0.96 g of phosphoric acid were mixed in 80 mL of deionized water. The concentration of the phosphoric acid solution was 12 g / L, and the mass ratio of oilseed crop residue to phosphoric acid solution was 5:1. The mixture was hydrolyzed in a hydrothermal reactor at 210 °C for 7 h. Biomass particles were obtained by filtration.

[0076] (2) Preparation of defect-rich hierarchical biochar (DBC): The spherical biomass particles obtained in step (1) were placed in a tube furnace after vacuum drying and calcined at 1000℃ for 1-5 hours under an argon flow at a heating rate of 5℃ / min. After cooling, the particles were repeatedly rinsed with ethanol and deionized water and dried at 80℃ for 7 hours to obtain defect-rich hierarchical biochar (DBC).

[0077] (3) Preparation of hierarchical porous biochar-based cathode material: 0.5 g of cobalt stearate was added to 40 mL of heptane to prepare a precursor solution with a concentration of 15 g / L. 0.1 g of DBC (after thorough grinding) was added to the precursor suspension and stirred for 30 min until the precursor loading reached 10 wt%. The solution was hydrothermally heated at 180 °C for 3 h. The DBC loaded with the precursor was then calcined in a tube furnace at 600 °C for 1 h under air conditions, with a heating rate of 5 °C / min. Vacuum drying yielded cobalt oxide-supported defect-rich biochar (Co-DBC-7).

[0078] Comparative Example 1

[0079] The remaining steps of this comparative example are the same as those of Example 1, except that cobalt neodecanoate is replaced with iron neodecanoate.

[0080] Comparative Example 2

[0081] The remaining steps of this comparative example are the same as those of Example 1, except that cobalt neodecanoate is replaced with copper neodecanoate.

[0082] like Figure 8 Examples 1, 1, and 2 were all used in an electro-Fenton degradation experiment to degrade SMZ. The results showed that the biochar substrate could effectively carry out 2e degradation in the system. - The ORR reaction generates H2O2, which accumulates sufficiently in the system. The hierarchical pores of biochar can adsorb and confine pollutants. The in-situ generated H2O2 is activated by cobalt oxides loaded on the biochar substrate. Co loses electrons and generates species with high oxidizing power, thereby achieving the degradation and removal of pollutants. Under the action of cathode current, Co can gain electrons to achieve recycling.

Claims

1. A method for preparing a hierarchical porous biochar-based cathode material for electro-Fenton degradation of antibiotic pollutants, characterized in that, Includes the following steps: Step 1: After drying the oilseed crop residue, soak it in a phosphoric acid solution, heat it at 140~210℃ to hydrolyze it, and then filter and separate the hydrolysis products to obtain biomass pellets. Step 2: The biomass particles obtained in Step 1 are calcined at 500~1000℃ in an inert gas atmosphere, cooled, washed and dried to obtain defect-rich hierarchical porous biochar. Step 3: The defect-rich hierarchical biochar obtained in Step 2 is soaked in cobalt salt organic solvent and subjected to hydrothermal reaction at 120~180℃ to obtain cobalt salt-loaded defect-rich hierarchical biochar. Then, it is calcined again at 240~600℃, cooled, washed and dried to obtain hierarchical biochar-based cathode material. In step three, the cobalt salt is any one or more of cobalt naphthenate, cobalt neodecanoate, and cobalt stearate; the concentration of the cobalt salt organic solution is 1.25~15 g / L, and the final loading of the cobalt salt on the biochar is 0.2~10 wt%. The hierarchical porous biochar-based cathode material constructs non-metallic heteroatom doping sites and nano-cobalt oxide metal sites within the hierarchical porous structure of biochar, providing both high-density active sites and rapid mass transfer channels for the electrochemical generation and activation of hydrogen peroxide. The biochar is provided with mesopores and macropores, the diameter of the mesopores being 2-50 nm and the diameter of the macropores being 50-2000 nm; the mesopore volume ratio is 35-40%.

2. The method for preparing a hierarchical porous biochar-based cathode material for electro-Fenton degradation of antibiotic pollutants according to claim 1, characterized in that: In step one, the mass ratio of oilseed crop residue to phosphoric acid solution is 0.3~5:1, and the concentration of phosphoric acid solution is 8~25 g / L.

3. The method for preparing a hierarchical porous biochar-based cathode material for electro-Fenton degradation of antibiotic pollutants according to claim 1, characterized in that: In step two, the drying temperature is 40~80℃ and the drying time is 7~24 h.

4. The method for preparing a hierarchical porous biochar-based cathode material for electro-Fenton degradation of antibiotic pollutants according to claim 1, characterized in that: In step two, the heating rate of calcination is 5℃ / min, and the calcination time is 1~5 h.

5. A method for preparing a hierarchical porous biochar-based cathode material for electro-Fenton degradation of antibiotic pollutants according to claim 1, characterized in that: In step three, the hydrothermal reaction takes 3 to 10 hours, and the secondary calcination takes 1 to 5 hours.

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