Bio-based nitrogen-doped carbon material, preparation method thereof and application of bio-based nitrogen-doped carbon material in treatment of printing and dyeing wastewater

Abstract

The invention relates to the technical field of wastewater treatment, and particularly discloses a bio-based nitrogen-doped carbon material, a preparation method thereof and application of the bio-based nitrogen-doped carbon material in treatment of printing and dyeing wastewater. The bio-based nitrogen-doped carbon material is prepared by mixing portulaca oleracea carbonized powder and carbon-nitrogen mixed powder prepared by co-carbonizing portulaca oleracea powder and silkworm chrysalis shell powder according to a specific proportion. The bio-based nitrogen-doped carbon material is used as a cathode material to be applied to treatment of indigo dyeing wastewater in an electric flocculation and electrochemical oxidation coupled system, carboxyl and hydroxyl rich in carbonized purslane can effectively neutralize the increased pH value in the electric flocculation process, continuous flocculation is guaranteed, proper conditions are provided for oxygen reduction reaction, and the method is suitable for industrial production. The hydrogen evolution reaction is reduced, the OH <-> generation amount is reduced, and the treatment efficiency and stability are synergistically improved. Meanwhile, the carbon-nitrogen mixed powder has a rich mesoporous structure, the structure can promote the double-electron oxygen reduction reaction of O2, and the electrooxidation catalytic efficiency in a wastewater treatment system is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a bio-based nitrogen-doped carbon material, its preparation method, and its application in treating dyeing and printing wastewater. Background Technology

[0002] As a key link in the textile industry chain, the dyeing and printing industry generates a large amount of industrial wastewater with complex composition and high pollutant concentration during the production process. Among them, indigo dyeing wastewater is extremely difficult to treat because it contains stable dye molecules, reducing inorganic pollutants and auxiliary agent residues. Direct discharge will pose a serious threat to aquatic ecosystems and human health. Therefore, the development of efficient and stable indigo dyeing wastewater treatment technology has become an urgent need in the field of environmental protection.

[0003] Among existing indigo dyeing wastewater treatment technologies, electrocoagulation technology has gained widespread attention due to its unique advantages. This technology utilizes the Al dissolution of aluminum anodes under an electric field. 3+ Hydrolysis and polymerization form hydroxyaluminum-based flocs with strong adsorption properties, which can effectively capture suspended solids and some dissolved dye molecules in wastewater, achieving solid-liquid separation of pollutants. However, single electrocoagulation technology is less effective for reducing pollutants in wastewater (such as S2O4). 2- Insufficient oxidation capacity leads to a low chemical oxygen demand (COD) removal rate, making it difficult to meet emission standards.

[0004] Electrocatalytic oxidation technology generates H2O2 and reactive oxygen species in situ through the oxygen reduction reaction (ORR) at the cathode, which can enhance the degradation of reducing pollutants. However, currently, the most efficient catalysts driving the ORR reaction are mostly precious metals such as Pt and Au. Their high preparation cost and scarcity greatly increase the operating cost of wastewater treatment, hindering the large-scale application of this technology. Bio-based materials, as renewable resources derived from biomass in nature, have outstanding advantages such as abundant reserves, low price, good biocompatibility, and degradability. After disposal, they can be naturally degraded or assimilated by organisms, without causing long-term environmental burden. Preparing carbon-based electrode materials by carbonizing bio-based materials aligns with the concept of green and sustainable development.

[0005] Although bio-based carbon materials have shown great application potential as ORR catalysts, providing a new direction for optimizing the electrocoagulation-electrocatalytic oxidation combined treatment system, the existing combined treatment system still faces key technical problems: during the electrocoagulation reaction, the hydrolysis of aluminum anode and the hydrogen evolution reaction at cathode cause the pH value of the system to rise continuously. The increase in pH value not only inhibits the formation and adsorption activity of aluminum-based flocs, weakening the electrocoagulation effect, but also the ORR reaction rate and catalytic efficiency are extremely sensitive to the pH value of the reaction system. A slightly alkaline environment will significantly reduce the adsorption capacity of O2 on the electrode surface and the electron transfer efficiency, inhibit the generation of H2O2 and reactive oxygen species, and lead to the degradation of electrocatalytic oxidation performance.

[0006] Therefore, how to screen suitable bio-based carbon materials, prepare electrode materials with excellent ORR catalytic performance and pH adaptability, and construct a wastewater treatment system that can synergistically enhance the effects of electrocoagulation and electrocatalytic oxidation is of great significance for promoting the development of efficient treatment technology for indigo dyeing wastewater. Summary of the Invention

[0007] To address the problem of continuously rising pH levels during the treatment process in existing electrocoagulation-electrocatalytic oxidation combined wastewater treatment systems, leading to a dual degradation of electrocoagulation and electrocatalytic oxidation performance, this invention provides a bio-based nitrogen-doped carbon material, its preparation method, and its application in treating dyeing and printing wastewater. This bio-based nitrogen-doped carbon material uses natural biomass purslane and silkworm pupa shells as precursors. Through nitrogen doping modification to regulate the material's structure and electronic properties, when used as an electrocatalytic oxidation cathode, it maintains excellent ORR catalytic activity over a wide pH range. This synergistic effect with the electrocoagulation system achieves efficient treatment of indigo dyeing wastewater while reducing treatment costs, aligning with green development requirements.

[0008] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: In a first aspect, the present invention provides a method for preparing a bio-based nitrogen-doped carbon material, comprising the following steps: Step a: Under an inert atmosphere, carbonize purslane powder at 140℃~160℃ to obtain carbonized purslane powder; Step b: Mix purslane powder and silkworm pupa shell powder evenly at a mass ratio of 5:1 to 15:1, and carbonize at 500℃ to 600℃ in an inert atmosphere to obtain carbon-nitrogen mixed powder. Step c: Mix the purslane carbonized powder and carbon-nitrogen mixed powder evenly to obtain a bio-based nitrogen-doped carbon material.

[0009] Compared to existing technologies, the method for preparing bio-based nitrogen-doped carbon materials provided by this invention first involves low-temperature carbonization of purslane powder at 140℃~160℃, fully preserving the natural oxygen-containing functional groups in purslane. This results in the carbonized purslane powder surface being rich in carboxyl groups (-COOH) and hydroxyl groups (-OH). These acidic functional groups can neutralize the OH groups generated by the hydrolysis of aluminum anode and the hydrogen evolution reaction at cathode in the electrocoagulation system. - This effectively inhibits excessive pH increases in the system, ensuring the continuous formation of aluminum-based flocs and maintaining high adsorption activity; simultaneously, it provides a near-neutral suitable pH environment for the ORR reaction, reducing the occurrence of hydrogen evolution side reactions and OH-. - It effectively addresses the problem of dual degradation in electrocoagulation and electrocatalytic oxidation performance in the combined system by mitigating interference with oxygen adsorption.

[0010] In step b, purslane is used as the carbon source and silkworm pupa shells as the nitrogen source, achieving in-situ doping of nitrogen into the carbon material through co-carbonization. By controlling the ratio of purslane to silkworm pupa shells, high-density active centers are constructed in the carbon material, thereby improving oxygen adsorption and electron transfer efficiency. Simultaneously, controlling the carbonization temperature to 500℃~600℃ allows for the formation of abundant mesoporous structures in the carbon material. These mesoporous structures not only facilitate mass transfer and diffusion of oxygen, pollutant molecules, and reaction intermediates, but also promote efficient two-electron reduction reactions of oxygen through spatial confinement effects, significantly improving the selectivity and yield of H₂O₂ formation. This, in turn, enhances the formation efficiency of reactive oxygen species such as ·OH, effectively driving the formation of S₂O₄. 2- This process facilitates the oxidative degradation of reducing pollutants, thereby significantly improving the efficiency of electrocatalytic oxidation.

[0011] Purslane carbonized powder can form a good conductive framework and pH buffer matrix, while carbon-nitrogen mixed powder serves as a highly active catalytic center. The combination of the two can enable the final electrode material to achieve a synergistic effect of conductivity, pH buffering capacity and catalytic activity, allowing the material to maintain stable working conditions and high-efficiency electrochemical performance in complex actual wastewater treatment environments.

[0012] The inert atmosphere described in this invention is provided by an inert gas, which can be a conventional inert gas in the art, such as argon or nitrogen.

[0013] Optionally, the purslane and silkworm pupa shells can be cleaned in an ultrasonic bath, dried, crushed, and then carbonized.

[0014] Further, in step a, the carbonization is carried out by a programmed temperature increase to 140℃~160℃, with a heating rate of 5℃ / min~15℃ / min.

[0015] The optimized heating rate facilitates the uniform and gradual pyrolysis of organic components in purslane powder, avoiding localized overheating or drastic structural changes caused by excessively rapid heating, thereby improving the stability and controllability of the carbonization process. Simultaneously, this medium-to-low temperature carbonization range helps to maximize the retention of inherent oxygen-containing functional groups (such as -COOH and -OH) in the precursor while forming the initial carbon framework, providing a structural basis for the subsequent surface modification and pH buffering functions of the material in the electrochemical system.

[0016] Furthermore, in step a, the carbonization time is 20 min to 40 min.

[0017] The optimal carbonization time can maximize the preservation of active functional groups on the material surface while ensuring thorough carbonization.

[0018] Furthermore, in step b, the carbonization is carried out by a programmed temperature increase to 500℃~600℃, with a heating rate of 5℃ / min~15℃ / min.

[0019] The optimized heating rate facilitates uniform and controllable thermal decomposition of the purslane and silkworm pupa shell mixture during carbonization. A gradual heating process avoids precursor structural damage or component loss due to sudden heat changes, ensuring that nitrogen-containing components in the silkworm pupa shell can stably and effectively participate in the reaction and be incorporated into the carbon framework, achieving in-situ nitrogen doping. Simultaneously, this controlled heating promotes the orderly release of volatile products, creating conditions for the subsequent formation of a rich and stable mesoporous structure at the target temperature.

[0020] Furthermore, in step b, the carbonization time is 40 min to 60 min.

[0021] Further, in step c, the mass ratio of the purslane carbonized powder to the carbon-nitrogen mixed powder is (0.5~1):(1.5~2).

[0022] The optimized ratio allows the final bio-based nitrogen-doped carbon material to achieve a balance between catalytic activity, pH buffering capacity, and conductivity, providing an ideal cathode material for the electrocoagulation-electrochemical oxidation system.

[0023] Secondly, the present invention also provides a bio-based nitrogen-doped carbon material, which is prepared by the preparation method of the bio-based nitrogen-doped carbon material described in any one of the above claims.

[0024] Thirdly, the present invention also provides a bio-based nitrogen-doped carbon cathode, comprising the above-mentioned bio-based nitrogen-doped carbon material.

[0025] As a specific embodiment of the present invention, the preparation method of the above-mentioned bio-based nitrogen-doped carbon cathode includes the following steps: The above-mentioned bio-based nitrogen-doped carbon material, binder and solvent are mixed evenly to obtain a slurry; The slurry is loaded onto the surface of a conductive substrate and cured to obtain the bio-based nitrogen-doped carbon cathode.

[0026] Specifically, the adhesive is a 4%~6% (w / w) Nafion solution, and the solvent is isopropanol. The conductive substrate is graphite felt.

[0027] It should be noted that before use, the graphite felt should be ultrasonically cleaned in acetone for 20-40 minutes, then ultrasonically cleaned in deionized water for 20-40 minutes, dried, and ready for use.

[0028] Specifically, the curing temperature is 140℃~160℃, and the time is 25min~35min.

[0029] Fourthly, the present invention also provides the application of the above-mentioned bio-based nitrogen-doped carbon cathode in the electrocoagulation coupled electrochemical oxidation treatment of dyeing and printing wastewater.

[0030] Specifically, the dyeing wastewater is indigo dyeing wastewater.

[0031] Fifthly, the present invention also provides a method for treating dyeing and printing wastewater by electrocoagulation coupled with electrochemical oxidation, comprising the following steps: S1, adjust the pH value of the dyeing and printing wastewater to be treated to acidic; S2, using aluminum as the anode and the above-mentioned bio-based nitrogen-doped carbon cathode as the cathode, electrolyzes the dyeing and printing wastewater, while simultaneously introducing oxygen into the cathode region, allowing the electrolyzed wastewater to settle and separate solids and liquids to obtain the treated wastewater.

[0032] Specifically, in S1, acidity refers to a pH value of 5.8 to 6.2.

[0033] Specifically, the area of ​​the electrode immersed in the wastewater is 15.5 cm². 2 ~16.5cm 2 .

[0034] Specifically, the electrolysis voltage is 8V~12V, and the electrolysis time is 40min~60min.

[0035] Specifically, the oxygen flow rate is 350 mL / min to 450 mL / min.

[0036] Specifically, the settling time is 0.5h to 1.5h.

[0037] It should be noted that the aforementioned bio-based nitrogen-doped carbon cathode can reduce O2 to hydrogen peroxide (H2O2), superoxide radicals (·O- 2), and singlet oxygen in the electrochemical system.1 Reactive oxygen species such as O2 and hydroxyl radicals (·OH) are present. These reactive oxygen species co-oxidize dithionite (S2O2-4) in the solution to generate sulfate (SO2-4), thus removing the reducing substances.

[0038] The bio-based nitrogen-doped carbon material provided by this invention retains oxygen-containing functional groups (carboxyl groups, hydroxyl groups, etc.) on its surface, which effectively stabilize the pH value of the system. This ensures the continuous formation of aluminum-based flocs during electrocoagulation and creates a suitable reaction environment for subsequent electrocatalytic oxidation. Simultaneously, the synergistic effect of the high-density active centers constructed by nitrogen doping and the abundant mesoporous structure significantly improves the efficiency of oxygen reduction to H2O2, thereby promoting the generation of highly oxidizing active species such as ·OH, thus achieving efficient degradation of organic pollutants such as indigo. Furthermore, this material uses biomass such as purslane and silkworm pupa shells as raw materials, which are widely available, inexpensive, and have a simple preparation process, resulting in high economic and environmental benefits. Attached Figure Description

[0039] Figure 1 The nitrogen isotherm adsorption-desorption curve of the bio-based nitrogen-doped carbon material prepared in Example 1 of this invention; Figure 2 The pore size distribution diagram is shown for the bio-based nitrogen-doped carbon material prepared in Example 1 of this invention. Figure 3 The images are SEM images of the bio-based nitrogen-doped carbon material prepared in Example 1 of this invention at different magnifications. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0041] To better illustrate the present invention, further examples are provided below.

[0042] The methods for detecting the decolorization rate in the following examples and comparative examples are as follows: The absorbance of the wastewater was measured using a UV-Vis spectrophotometer. The maximum absorption wavelength of the indigo wastewater was detected at 670 nm, and the decolorization rate of the solution was calculated.

[0043] Decolorization rate (%) = (Absorbance of original wastewater - Absorbance of treated wastewater) / Absorbance of treated wastewater × 100% Example 1 This embodiment provides a method for preparing a bio-based nitrogen-doped carbon material, including the following steps: Step a: Use an ultrasonic cleaner to ultrasonically clean purslane and silkworm pupa shells for 30 minutes, then put them in a forced-air drying oven at 100℃ to dry, and let them cool naturally to room temperature. Grind and pulverize them separately to obtain purslane powder and silkworm pupa shell powder. Step b: Under a nitrogen atmosphere, the purslane powder is heated to 150°C at a rate of 10°C / min and carbonized for 30 min to obtain carbonized purslane powder. Step c: Mix purslane powder and silkworm pupa shell powder evenly at a mass ratio of 10:1, add to a tube furnace under nitrogen atmosphere, heat to 550℃ at a rate of 10℃ / min, carbonize for 50min, cool, wash with deionized water until pH is 7.0, and dry in a forced-air drying oven at 100℃ to obtain carbon-nitrogen mixed powder. Step d: The carbonized purslane powder and the carbon-nitrogen mixed powder are mixed evenly at a mass ratio of 0.75:1.5 to obtain a bio-based nitrogen-doped carbon material.

[0044] The above-mentioned bio-based nitrogen-doped carbon material is used to prepare a bio-based nitrogen-doped carbon cathode, and the steps are as follows: Cut the graphite felt into 4cm×4cm squares, immerse it in acetone and sonicate for 20-40 minutes, then immerse it in deionized water and sonicate for 30 minutes, and then dry it in an oven at 80℃ for 8 hours. Take 2.5g of the bio-based nitrogen-doped carbon material prepared above, 1.6mL of 5% Nafion solution and 0.8mL of isopropanol, mix them evenly, disperse them by ultrasonication for 5min, and then drop them onto the surface of graphite felt using the drop coating method. After air drying, transfer them to a muffle furnace and cure them at 150℃ for 30min to obtain a bio-based nitrogen-doped carbon cathode.

[0045] The application of the above-mentioned bio-based nitrogen-doped carbon cathode in an electrocoagulation-coupled electrochemical oxidation system for treating indigo dyeing wastewater includes the following steps: The pH of the indigo dyeing wastewater was adjusted to 6.0 with sulfuric acid. 250 mL of the pH-adjusted indigo dyeing wastewater was poured into the electrolyte. Aluminum was used as the anode and the bio-based nitrogen-doped carbon cathode prepared above was used as the cathode. The electrodes were vertically inserted into the electrolytic cell with a 2 cm gap between them. The stirring rate was set to 180 r / min, and electrolysis was carried out for 50 min within a voltage range of 10 V. During the treatment, oxygen was introduced to the cathode surface at a flow rate of 400 mL / min. After the treatment was completed, the mixture was allowed to stand and precipitate for 1 h. Solid-liquid separation was then performed to obtain the treated wastewater.

[0046] Figure 1 The N2 isotherm adsorption-desorption curve of the bio-based nitrogen-doped carbon powder prepared in this embodiment. Figure 2 This is a pore size distribution diagram of bio-based nitrogen-doped carbon powder. Figure 3 Scanning electron microscope (SEM) images of bio-based nitrogen-doped carbon powder at different magnifications. Figure 1It can be seen that the N2 isotherm adsorption-desorption curve of the bio-based nitrogen-doped carbon material belongs to the type IV adsorption-desorption isotherm, without a clear saturation adsorption plateau, and is a type H3 hysteresis loop, indicating that the material has a mesoporous structure. Figure 2 It is known that bio-based nitrogen-doped carbon powder has a large number of mesoporous structures. From Figure 3 It can be seen that the prepared bio-based nitrogen-doped carbon powder has an irregular shape, a rough surface, and an obvious and abundant pore structure.

[0047] The bio-based nitrogen-doped carbon powder obtained above was subjected to BET analysis, and its specific surface area was 44.59 m². 2 / g, mesopore volume 0.4553cm³ 3 / g.

[0048] The treated indigo dyeing wastewater was tested, and the COD removal rate was 87.40%, the decolorization rate was 99.97%, and the energy consumption during the experiment was 15.11 kWh / cm³. 3 The pH rose to 6.5.

[0049] Example 2 This embodiment provides a method for preparing a bio-based nitrogen-doped carbon material, including the following steps: Step a: Use an ultrasonic cleaner to ultrasonically clean purslane and silkworm pupa shells for 20 minutes, then put them in a forced-air drying oven at 90°C to dry, and let them cool naturally to room temperature. Grind and pulverize them separately to obtain purslane powder and silkworm pupa shell powder. Step b: Under a nitrogen atmosphere, the purslane powder is heated to 140°C at a rate of 5°C / min and carbonized for 40 min to obtain carbonized purslane powder. Step c: Mix purslane powder and silkworm pupa shell powder evenly at a mass ratio of 15:1, add to a tube furnace under nitrogen atmosphere, heat to 500℃ at a rate of 5℃ / min, carbonize for 60min, cool, wash with deionized water until pH is 6.8, and dry in a forced-air drying oven at 90℃ to obtain carbon-nitrogen mixed powder. Step d: The carbonized purslane powder and the carbon-nitrogen mixed powder are mixed evenly at a mass ratio of 0.5:1.5 to obtain a bio-based nitrogen-doped carbon material.

[0050] The above-mentioned bio-based nitrogen-doped carbon material is used to prepare a bio-based nitrogen-doped carbon cathode, and the steps are as follows: The graphite felt was cut into 4cm×4cm squares, first immersed in acetone and sonicated for 20 minutes, then immersed in deionized water and sonicated for 20 minutes, and then placed in an oven at 70℃ to dry for 8.5 hours. Take 2.0g of the bio-based nitrogen-doped carbon material prepared above, 1.5mL of 5% Nafion solution and 0.7mL of isopropanol, mix them evenly, ultrasonically disperse for 4min, and drop-coat the mixture onto the surface of graphite felt using the drop-coating method. After air drying, transfer it to a muffle furnace and cure it at 140℃ for 35min to obtain a bio-based nitrogen-doped carbon cathode.

[0051] The application of the above-mentioned bio-based nitrogen-doped carbon cathode in an electrocoagulation-coupled electrochemical oxidation system for treating indigo dyeing wastewater includes the following steps: The pH of the indigo dyeing wastewater was adjusted to 5.8 with sulfuric acid. 250 mL of the pH-adjusted indigo dyeing wastewater was poured into the electrolyte. Aluminum was used as the anode and the bio-based nitrogen-doped carbon cathode prepared above was used as the cathode. The electrodes were vertically inserted into the electrolytic cell with a 2 cm gap between them. The stirring rate was set to 180 r / min, and electrolysis was carried out for 60 min within a voltage range of 8 V. During the treatment, oxygen was introduced to the cathode surface at a flow rate of 350 mL / min. After the treatment was completed, the mixture was allowed to stand and precipitate for 0.5 h. Solid-liquid separation was then performed to obtain the treated wastewater.

[0052] The bio-based nitrogen-doped carbon powder obtained above was subjected to BET analysis, and its specific surface area was 37.20 m². 2 / g, mesopore volume 0.3527cm³ 3 / g.

[0053] The treated indigo dyeing wastewater was tested, and the COD removal rate was 80.51%, the decolorization rate was 98.88%, and the energy consumption during the experiment was 16.24 kWh / cm³. 3 The pH rose to 6.9.

[0054] Example 3 This embodiment provides a method for preparing a bio-based nitrogen-doped carbon material, including the following steps: Step a: Use an ultrasonic cleaner to ultrasonically clean purslane and silkworm pupa shells for 40 minutes, then put them in a forced-air drying oven at 110℃ to dry, and let them cool naturally to room temperature. Grind and pulverize them separately to obtain purslane powder and silkworm pupa shell powder. Step b: Under a nitrogen atmosphere, the purslane powder is heated to 160°C at a rate of 15°C / min and carbonized for 20 min to obtain carbonized purslane powder. Step c: Mix purslane powder and silkworm pupa shell powder evenly at a mass ratio of 5:1, add to a tube furnace under nitrogen atmosphere, heat to 600℃ at a rate of 15℃ / min, carbonize for 40min, cool, wash with deionized water until pH is 7.2, and dry in a forced-air drying oven at 110℃ to obtain carbon-nitrogen mixed powder. Step d: Mix purslane carbonized powder and carbon-nitrogen mixed powder at a mass ratio of 1:2 to obtain bio-based nitrogen-doped carbon material.

[0055] The above-mentioned bio-based nitrogen-doped carbon material is used to prepare a bio-based nitrogen-doped carbon cathode, and the steps are as follows: The graphite felt was cut into 4cm×4cm squares, first immersed in acetone and sonicated for 40 minutes, then immersed in deionized water and sonicated for 40 minutes, and then placed in an oven at 90℃ to dry for 7.5 hours. Take 3.0g of the bio-based nitrogen-doped carbon material prepared above, 1.7mL of 5% Nafion solution and 0.9mL of isopropanol, mix them evenly, ultrasonically disperse for 6min, and drop-coat the mixture onto the surface of graphite felt using the drop-coating method. After air drying, transfer it to a muffle furnace and cure it at 160℃ for 25min to obtain a bio-based nitrogen-doped carbon cathode.

[0056] The application of the above-mentioned bio-based nitrogen-doped carbon cathode in an electrocoagulation-coupled electrochemical oxidation system for treating indigo dyeing wastewater includes the following steps: The pH of the indigo dyeing wastewater was adjusted to 6.2 with sulfuric acid. 250 mL of the pH-adjusted indigo dyeing wastewater was poured into the electrolyte. Aluminum was used as the anode and the bio-based nitrogen-doped carbon cathode prepared above was used as the cathode. The electrodes were vertically inserted into the electrolytic cell with a 2 cm gap between them. The stirring rate was set to 180 r / min, and electrolysis was carried out for 40 min within a voltage range of 12 V. During the treatment, oxygen was introduced to the cathode surface at a flow rate of 450 mL / min. After the treatment was completed, the mixture was allowed to stand and precipitate for 1.5 h. Solid-liquid separation was then performed to obtain the treated wastewater.

[0057] The bio-based nitrogen-doped carbon powder obtained above was subjected to BET analysis, and its specific surface area was 35.49 m². 2 / g, mesopore volume 0.3424cm³ 3 / g.

[0058] The treated indigo dyeing wastewater was tested, and the COD removal rate was 82.01%, the decolorization rate was 98.54%, and the energy consumption during the experiment was 16.37 kWh / cm³. 3 The pH rose to 6.8.

[0059] Comparative Example 1 This comparative example provides a method for preparing bio-based carbon materials, which differs from the examples only in that silkworm pupa shells are not added. The method specifically includes the following steps: Step a: Use an ultrasonic cleaner to ultrasonically clean the purslane with water for 30 minutes, then put it in a forced-air drying oven to dry at 100℃, let it cool naturally to room temperature, grind and pulverize it to obtain purslane powder; Step b: Under a nitrogen atmosphere, the purslane powder is heated to 150°C at a rate of 10°C / min and carbonized for 30 min to obtain carbonized purslane powder a. Step c: Add purslane powder to a tube furnace under nitrogen atmosphere, heat to 550℃ at a rate of 10℃ / min, carbonize for 50min, cool, wash with deionized water until pH is 7.0, and dry in a forced-air drying oven at 100℃ to obtain purslane carbonized powder b. Step d: Mix purslane carbonized powder a and purslane carbonized powder b at a mass ratio of 0.75:1.5 to obtain bio-based carbon material.

[0060] The bio-based carbon material prepared above was used to prepare a carbon cathode in the same way as in Example 1, and was used in an electrocoagulation coupled electrochemical oxidation system to treat indigo dyeing wastewater. The treatment conditions were exactly the same as in Example 1, and will not be repeated here.

[0061] The bio-based carbon material obtained above was subjected to BET testing, and its specific surface area was 33.18 m². 2 / g, mesopore volume 0.3096cm³ 3 / g.

[0062] The treated indigo dyeing wastewater was tested, and the COD removal rate was 67.84%, the decolorization rate was 88.23%, and the energy consumption during the experiment was 23.13 kWh / cm³. 3 The pH rose to 7.1.

[0063] Comparative Example 2 This comparative example provides a method for preparing a bio-based nitrogen-doped carbon material. The only difference from Example 1 is that in step c, only silkworm pupa shells are used for carbonization, without carbon-nitrogen co-carbonization. The specific steps are as follows: Step a: Use an ultrasonic cleaner to ultrasonically clean purslane and silkworm pupa shells for 30 minutes, then put them in a forced-air drying oven at 100℃ to dry, and let them cool naturally to room temperature. Grind and pulverize them separately to obtain purslane powder and silkworm pupa shell powder. Step b: Under a nitrogen atmosphere, the purslane powder is heated to 150°C at a rate of 10°C / min and carbonized for 30 min to obtain carbonized purslane powder. Step c: Add silkworm pupa shell powder to a tube furnace under nitrogen atmosphere, heat to 550°C at a rate of 10°C / min, carbonize for 50 min, cool, wash with deionized water until pH is 7.0, and dry in a forced-air drying oven at 100°C to obtain silkworm pupa shell carbonized powder. Step d: Mix purslane carbonized powder and silkworm pupa shell carbonized powder evenly at a mass ratio of 0.75:1.5 to obtain bio-based nitrogen-doped carbon material.

[0064] The bio-based nitrogen-doped carbon material prepared above was used to prepare a carbon cathode in the same way as in Example 1, and was used in an electrocoagulation coupled electrochemical oxidation system to treat indigo dyeing wastewater. The treatment conditions were exactly the same as in Example 1, and will not be repeated here.

[0065] The bio-based nitrogen-doped carbon material obtained above was subjected to BET analysis, and its specific surface area was 18.83 m². 2 / g, mesopore volume 0.0944cm³ 3 / g.

[0066] The treated indigo dyeing wastewater was tested, and the COD removal rate was 67.62%, the decolorization rate was 87.51%, and the energy consumption during the experiment was 18.32 kWh / cm³. 3 The pH rose to 7.2.

[0067] Comparative Example 3 This comparative example provides a method for preparing carbonized silkworm pupa shell powder, the specific steps of which are as follows: Step a: Use an ultrasonic cleaner to ultrasonically clean the silkworm pupa shells for 30 minutes, then put them in a forced-air drying oven to dry at 100℃, let them cool naturally to room temperature, grind and pulverize them to obtain silkworm pupa shell powder. Step b: Add silkworm pupa shell powder to a tube furnace under nitrogen atmosphere, heat to 550℃ at a rate of 10℃ / min, carbonize for 50 min, cool, wash with deionized water until pH is 7.0, and dry in a forced-air drying oven at 100℃ to obtain silkworm pupa shell carbonized powder.

[0068] The carbonized silkworm pupa shell powder prepared above was used to prepare a carbon cathode in the same way as in Example 1, and was used in an electrocoagulation coupled electrochemical oxidation system to treat indigo dyeing wastewater. The treatment conditions were exactly the same as in Example 1, and will not be repeated here.

[0069] The carbonized silkworm pupa shell powder obtained above was subjected to BET analysis, and its specific surface area was 18.03 m². 2 / g, mesopore volume 0.0823cm³ 3 / g.

[0070] The treated indigo dyeing wastewater was tested, and the COD removal rate was 68.94%, the decolorization rate was 88.87%, and the energy consumption during the experiment was 16.67 kWh / cm³. 3 The pH rose to 7.7.

[0071] Comparative Example 4 This comparative example provides a method for preparing a bio-based nitrogen-doped carbon material, which differs from Example 1 only in that the carbonization temperature of purslane is increased. The specific steps are as follows: Step a: Use an ultrasonic cleaner to ultrasonically clean purslane and silkworm pupa shells for 30 minutes, then put them in a forced-air drying oven at 100℃ to dry, and let them cool naturally to room temperature. Grind and pulverize them separately to obtain purslane powder and silkworm pupa shell powder. Step b: Under a nitrogen atmosphere, the purslane powder is heated to 550°C at a rate of 10°C / min and carbonized for 30 min to obtain carbonized purslane powder. Step c: Mix purslane powder and silkworm pupa shell powder evenly at a mass ratio of 10:1, add to a tube furnace under nitrogen atmosphere, heat to 550℃ at a rate of 10℃ / min, carbonize for 50min, cool, wash with deionized water until pH is 7.0, and dry in a forced-air drying oven at 100℃ to obtain carbon-nitrogen mixed powder. Step d: The carbonized purslane powder and the carbon-nitrogen mixed powder are mixed evenly at a mass ratio of 0.75:1.5 to obtain a bio-based nitrogen-doped carbon material.

[0072] The bio-based carbon material prepared above was used to prepare a carbon cathode in the same way as in Example 1, and was used in an electrocoagulation coupled electrochemical oxidation system to treat indigo dyeing wastewater. The treatment conditions were exactly the same as in Example 1, and will not be repeated here.

[0073] The bio-based nitrogen-doped carbon powder obtained above was subjected to BET analysis, and its specific surface area was 43.51 m². 2 / g, mesopore volume 0.4482cm³ 3 / g.

[0074] The treated indigo dyeing wastewater was tested, and the COD removal rate was 65.12%, the decolorization rate was 88.79%, and the energy consumption during the experiment was 16.54 kWh / cm³. 3 The pH rose to 7.6.

[0075] Comparative Example 5 This comparative example provides a method for preparing a bio-based nitrogen-doped carbon material. The only difference from Example 1 is the change in the mass ratio of purslane powder and silkworm pupa shell powder in step c. The specific steps are as follows: Step a: Use an ultrasonic cleaner to ultrasonically clean purslane and silkworm pupa shells for 30 minutes, then put them in a forced-air drying oven at 100℃ to dry, and let them cool naturally to room temperature. Grind and pulverize them separately to obtain purslane powder and silkworm pupa shell powder. Step b: Under a nitrogen atmosphere, the purslane powder is heated to 150°C at a rate of 10°C / min and carbonized for 30 min to obtain carbonized purslane powder. Step c: Mix purslane powder and silkworm pupa shell powder evenly at a mass ratio of 20:1, add to a tube furnace under nitrogen atmosphere, heat to 550℃ at a rate of 10℃ / min, carbonize for 50min, cool, wash with deionized water until pH is 7.0, and dry in a forced-air drying oven at 100℃ to obtain carbon-nitrogen mixed powder. Step d: The carbonized purslane powder and the carbon-nitrogen mixed powder are mixed evenly at a mass ratio of 0.75:1.5 to obtain a bio-based nitrogen-doped carbon material.

[0076] The bio-based carbon material prepared above was used to prepare a carbon cathode in the same way as in Example 1, and was used in an electrocoagulation coupled electrochemical oxidation system to treat indigo dyeing wastewater. The treatment conditions were exactly the same as in Example 1, and will not be repeated here.

[0077] The bio-based nitrogen-doped carbon powder obtained above was subjected to BET analysis, and its specific surface area was 34.51 m². 2 / g, mesopore volume 0.2792cm³ 3 / g.

[0078] The treated indigo dyeing wastewater was tested, and the COD removal rate was 70.62%, the decolorization rate was 88.89%, and the energy consumption during the experiment was 19.73 kWh / cm³. 3 The pH rose to 7.2.

[0079] Comparative Example 6 This comparative example provides a method for preparing a bio-based nitrogen-doped carbon material. The only difference from Example 1 is the change in the mass ratio of purslane powder and silkworm pupa shell powder in step c. The specific steps are as follows: Step a: Use an ultrasonic cleaner to ultrasonically clean purslane and silkworm pupa shells for 30 minutes, then put them in a forced-air drying oven at 100℃ to dry, and let them cool naturally to room temperature. Grind and pulverize them separately to obtain purslane powder and silkworm pupa shell powder. Step b: Under a nitrogen atmosphere, the purslane powder is heated to 150°C at a rate of 10°C / min and carbonized for 30 min to obtain carbonized purslane powder. Step c: Mix purslane powder and silkworm pupa shell powder evenly at a mass ratio of 5:2, add to a tube furnace under nitrogen atmosphere, heat to 550℃ at a rate of 10℃ / min, carbonize for 50min, cool, wash with deionized water until pH is 7.0, and dry in a forced-air drying oven at 100℃ to obtain carbon-nitrogen mixed powder. Step d: The carbonized purslane powder and the carbon-nitrogen mixed powder are mixed evenly at a mass ratio of 0.75:1.5 to obtain a bio-based nitrogen-doped carbon material.

[0080] The bio-based carbon material prepared above was used to prepare a carbon cathode in the same way as in Example 1, and was used in an electrocoagulation coupled electrochemical oxidation system to treat indigo dyeing wastewater. The treatment conditions were exactly the same as in Example 1, and will not be repeated here.

[0081] The bio-based nitrogen-doped carbon powder obtained above was subjected to BET analysis, and its specific surface area was 32.81 m². 2 / g, mesopore volume 0.2632cm³ 3 / g.

[0082] The treated indigo dyeing wastewater was tested, and the COD removal rate was 67.62%, the decolorization rate was 87.73%, and the energy consumption during the experiment was 22.34 kWh / cm³. 3 The pH rose to 7.4.

[0083] Comparative Example 7 This comparative example provides a method for preparing nitrogen-doped carbon materials, which differs from Example 1 only in that the carbon source, purslane, is replaced with carbon black, and the nitrogen source, silkworm pupa shell, is replaced with melamine. The specific steps are as follows: Carbon black and melamine were mixed evenly at a mass ratio of 10:1 and added to a tube furnace under a nitrogen atmosphere. The temperature was increased to 550°C at a rate of 10°C / min, and carbonized for 50 min. After cooling, the mixture was washed with deionized water until the pH reached 7.0 and then dried in a forced-air drying oven at 100°C to obtain nitrogen-doped carbon material.

[0084] The nitrogen-doped carbon material prepared above was used to prepare a carbon cathode in the same way as in Example 1, and was used in an electrocoagulation coupled electrochemical oxidation system to treat indigo dyeing wastewater. The treatment conditions were exactly the same as in Example 1, and will not be repeated here.

[0085] The nitrogen-doped carbon material obtained above was subjected to BET analysis, and its specific surface area was 36.79 m². 2 / g, mesopore volume 0.3252cm³ 3 / g.

[0086] The treated indigo dyeing wastewater was tested, and the COD removal rate was 53.58%, the decolorization rate was 86.77%, and the energy consumption during the experiment was 16.83 kWh / cm³. 3 The pH rose to 7.5.

[0087] Comparative Example 8 This comparative example provides a method for preparing nitrogen-doped carbon materials, which differs from Example 1 only in that the carbon source, purslane, is replaced with carbon nanotubes, and the nitrogen source, silkworm pupa shell, is replaced with urea. The specific steps are as follows: Carbon nanotubes and urea were mixed evenly at a mass ratio of 10:1 and added to a tube furnace under a nitrogen atmosphere. The temperature was increased to 550°C at a rate of 10°C / min, and carbonized for 50 min. After cooling, the mixture was washed with deionized water until the pH reached 7.0 and then dried in a forced-air drying oven at 100°C to obtain nitrogen-doped carbon material.

[0088] The nitrogen-doped carbon material prepared above was used to prepare a carbon cathode in the same way as in Example 1, and was used in an electrocoagulation coupled electrochemical oxidation system to treat indigo dyeing wastewater. The treatment conditions were exactly the same as in Example 1, and will not be repeated here.

[0089] The nitrogen-doped carbon material obtained above was subjected to BET analysis, and its specific surface area was 32.24 m². 2 / g, mesopore volume 0.4049cm³ 3 / g.

[0090] The treated indigo dyeing wastewater was tested, and the COD removal rate was 54.24%, the decolorization rate was 86.53%, and the energy consumption during the experiment was 15.43 kWh / cm³. 3 The pH rose to 7.1.

[0091] Comparative Example 9 This comparative example provides a method for preparing bio-based nitrogen-doped carbon materials. The only difference from Example 1 is that the carbon source, purslane, is replaced with Jerusalem artichoke vine, and the nitrogen source, silkworm pupa shells, is replaced with carrot residue. The specific steps are as follows: Step a: Use an ultrasonic cleaner to ultrasonically clean Jerusalem artichoke vines and carrot residue for 30 minutes, then put them in a forced-air drying oven at 100°C to dry, and let them cool naturally to room temperature. Grind and pulverize them separately to obtain Jerusalem artichoke vine powder and carrot residue powder. Step b: Under a nitrogen atmosphere, the Jerusalem artichoke vine powder is heated to 150°C at a rate of 10°C / min and carbonized for 30 min to obtain Jerusalem artichoke vine carbonized powder. Step c: Mix Jerusalem artichoke vine powder and carrot residue powder evenly at a mass ratio of 10:1, add to a tube furnace under nitrogen atmosphere, heat to 550℃ at a rate of 10℃ / min, carbonize for 50min, cool, wash with deionized water until pH is 7.0, and dry in a forced-air drying oven at 100℃ to obtain carbon-nitrogen mixed powder. Step d: The Jerusalem artichoke carbonized powder and carbon-nitrogen mixed powder are mixed evenly at a mass ratio of 0.75:1.5 to obtain bio-based nitrogen-doped carbon material.

[0092] The bio-based carbon material prepared above was used to prepare a carbon cathode in the same way as in Example 1, and was used in an electrocoagulation coupled electrochemical oxidation system to treat indigo dyeing wastewater. The treatment conditions were exactly the same as in Example 1, and will not be repeated here.

[0093] The bio-based nitrogen-doped carbon powder obtained above was subjected to BET analysis, and its specific surface area was 24.33 m². 2 / g, mesopore volume 0.3042cm³ 3 / g.

[0094] The treated indigo dyeing wastewater was tested, and the COD removal rate was 75.52%, the decolorization rate was 99.10%, and the energy consumption during the experiment was 13.71 kWh / cm³. 3 The pH rose to 7.2.

[0095] In summary, the carboxyl and hydroxyl groups abundant on the surface of purslane carbonized powder can neutralize the OH groups generated during electrolysis in situ. - Maintaining a near-neutral environment ensures the continuous adsorption of pollutants by the aluminum-based flocs and provides suitable conditions for the catalytic reaction. Its conductive structure also facilitates electron transport channels. The abundant mesoporous structure formed through carbonization provides rapid mass transfer channels for oxygen, pollutants, and reactive species. Furthermore, the pyridine N and pyrrole N active sites transformed from silkworm pupa shells promote efficient two-electron reduction reactions of oxygen, generating large amounts of H₂O₂ and ·OH, thus fully oxidizing S₂O₄. 2- The material effectively removes reducing pollutants and controls the ratio of purslane carbonized powder to carbon-nitrogen mixed powder, ensuring a balance between catalytic site density, mass transfer efficiency, and pH regulation capability. Ultimately, the material simultaneously achieves adsorption, catalytic oxidation, and environmental stabilization functions, resulting in a COD removal rate of over 80% and a decolorization rate of over 98% for indigo dyeing wastewater. This successfully achieves efficient purification and stable treatment of indigo dyeing wastewater, providing a practical and feasible technical solution for the in-depth treatment of industrial dyeing and printing wastewater.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a bio-based nitrogen-doped carbon material, characterized in that, Includes the following steps: Step a: Under an inert atmosphere, carbonize purslane powder at 140℃~160℃ to obtain carbonized purslane powder; Step b: Mix purslane powder and silkworm pupa shell powder evenly at a mass ratio of 5:1 to 15:1, and carbonize at 500℃ to 600℃ in an inert atmosphere to obtain carbon-nitrogen mixed powder. Step c: Mix the purslane carbonized powder and carbon-nitrogen mixed powder evenly to obtain a bio-based nitrogen-doped carbon material.

2. The method for preparing bio-based nitrogen-doped carbon materials as described in claim 1, characterized in that, In step a, the carbonization is carried out by a programmed temperature increase to 140℃~160℃, with a heating rate of 5℃ / min~15℃ / min.

3. The method for preparing bio-based nitrogen-doped carbon materials as described in claim 1, characterized in that, In step a, the carbonization time is 20 min to 40 min.

4. The method for preparing bio-based nitrogen-doped carbon materials as described in claim 1, characterized in that, In step b, the carbonization is carried out by a programmed temperature rise to 500℃~600℃, with a heating rate of 5℃ / min~15℃ / min.

5. The method for preparing bio-based nitrogen-doped carbon materials as described in claim 1, characterized in that, In step b, the carbonization time is 40 min to 60 min.

6. The method for preparing bio-based nitrogen-doped carbon materials as described in claim 1, characterized in that, In step c, the mass ratio of the purslane carbonized powder to the carbon-nitrogen mixed powder is (0.5~1):(1.5~2).

7. A bio-based nitrogen-doped carbon material, characterized in that, It is prepared by the method for preparing bio-based nitrogen-doped carbon materials according to any one of claims 1 to 6.

8. A bio-based nitrogen-doped carbon cathode, characterized in that, Including the bio-based nitrogen-doped carbon material as described in claim 7.

9. The application of the bio-based nitrogen-doped carbon cathode as described in claim 8 in the electrocoagulation coupled electrochemical oxidation treatment of dyeing and printing wastewater.

10. A method for treating dyeing and printing wastewater by electrocoagulation coupled with electrochemical oxidation, characterized in that, Includes the following steps: S1, adjust the pH value of the dyeing and printing wastewater to be treated to acidic; S2, using aluminum as the anode and the bio-based nitrogen-doped carbon cathode as described in claim 8 as the cathode, electrolyzes the dyeing and printing wastewater, while simultaneously introducing oxygen into the cathode region, allowing the electrolyzed wastewater to settle and separate solids and liquids to obtain treated wastewater.

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