Preparation method and application of iron-doped biochar catalyst and cathode

Abstract

This invention discloses a method for preparing and applying an iron-doped biochar catalyst and cathode, relating to the field of wastewater treatment technology. The catalyst preparation includes: pyrolysis purification of BC; introduction of Fe ions into CMC to obtain a homogeneous mixture; addition of purified BC, mixing to adjust pH, washing, and freeze-drying to obtain the catalyst. The cathode preparation method includes: activation by carbon cloth soaking, rinsing and calcining, acetone soaking, rinsing and drying for later use; sequential addition of anhydrous ethanol, water, and Nafion solution to the catalyst, mixing, ultrasonication, drop-coating onto prepared carbon cloth, and drying to obtain the electrode. The invention also includes the application of the cathode in activating H2O2 to treat SQX under an electric field. The composite cathode disclosed in this invention can efficiently activate H2O2 and react with exposed iron active sites to generate highly oxidizing and non-selective hydroxyl radicals, activating the Fenton reaction.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to the electrochemically enhanced heterogeneous catalytic hydrogen peroxide system for the degradation of antibiotic wastewater, specifically a method for preparing and applying an iron-doped biochar catalyst and cathode. Background Technology

[0002] Antibiotics, as highly effective antibacterial agents and growth promoters, are widely used in animal husbandry, aquaculture, and the prevention and treatment of human and animal diseases. After entering an organism, a small portion of antibiotics can be directly absorbed and utilized, while the majority is excreted in the form of the original drug or metabolites. These antibiotics then enter the aquatic ecosystem through various pathways, inducing the formation of drug-resistant bacteria and the lateral transfer of resistance genes, thereby harming human health and ecological balance.

[0003] Sulfonamides (SAs) are a class of synthetic antibiotics containing the p-aminobenzenesulfonamide structure. They possess broad-spectrum antibacterial properties and are therefore widely used as veterinary drugs and feed additives in animal husbandry and aquaculture. Sulfaquinoxaline (SQX), a type of sulfonamide antibiotic, is widely used to treat coccidiosis in poultry and livestock. Its quinoxaline group also exhibits mutagenic and carcinogenic properties. Low concentrations of sulfaquinoxaline, typically in the ng / L-μg / L range, can be detected in rivers, sewage treatment plants, and other water bodies. Current methods for treating sulfonamide antibiotics mainly include physical, chemical, and biological methods. While a single method can effectively degrade sulfonamide antibiotics, its low cost-effectiveness limits its widespread use.

[0004] Electro-Fenton (EF) technology is a novel electrochemical advanced oxidation technique (AOP) developed in recent decades. The electro-Fenton reaction occurs through the generation of H₂O₂ and Fe near the cathode. 2+ The reaction rapidly generates •OH, which acts on pollutants. However, the oxygen reduction process in the electro-Fenton reaction is slow, requiring cathode materials to reduce the overpotential and accelerate the reaction rate. Therefore, a catalyst with good catalytic activity is needed. However, heterogeneous catalysts have some drawbacks, such as the difficulty in recovering powdered catalysts from the reaction system, which increases the cost of use, and the decrease in catalytic efficiency due to agglomeration or leaching during the reaction. Summary of the Invention

[0005] To address the problem that the oxygen reduction process in the electro-Fenton system is slow when degrading antibiotics in wastewater, requiring a catalyst with good catalytic activity, and that existing heterogeneous catalysts suffer from a series of problems such as difficulty in recovery, high cost, and continuous decline in catalytic efficiency, this invention provides a method for preparing an iron-doped biochar catalyst and cathode, as well as its application.

[0006] This invention is achieved using the following techniques:

[0007] The present invention provides a method for preparing an iron-doped biochar catalyst, comprising the following steps:

[0008] a. BC (Biochar) Purification

[0009] BC (biochar) is a carrier for iron oxide-catalyzed Fenton. BC made from coconut shells was selected and pyrolyzed in a tube furnace at 400℃ for 5 hours under argon atmosphere with a heating rate of 10℃ / min. The resulting solid powder was transferred to a 1M dilute hydrochloric acid solution and continuously stirred at 60℃ for 6 hours. The solution was washed with deionized water until the final pH of the filtrate was 6.5-7. It was then washed three times with ethanol and dried overnight to obtain purified BC.

[0010] b. CMC (Sodium Carboxymethyl Cellulose) Pretreatment

[0011] CMC (sodium carboxymethyl cellulose) is a suitable carrier for metal oxide nanomaterials. CMC was dissolved in N2-treated deionized water, and FeCl3•6H2O and FeSO4•7H2O were added. The FeCl3•6H2O and FeSO4•7H2O were then added according to the Fe... 2+ Fe 3+ A homogeneous mixture was obtained by adding ingredients at a 1:2 ratio and sonicating for 20 minutes.

[0012] c. Preparation of CMC-Fe3O4 / BC

[0013] The purified BC prepared in step a was added to the homogeneous mixture. After mixing for 20 min, the mixture was stirred at 200 r / min at 50 °C. The pH was adjusted to 12 with 5 M NaOH to promote the deposition of Fe3O4 on the BC surface. The resulting mixture was left to stand at room temperature overnight. The precipitate was washed three times with deionized water and then three times with ethanol. The mixture was then freeze-dried at -60 °C for 24 h to obtain the CMC-Fe3O4 / BC catalyst.

[0014] The present invention provides an iron-doped biochar cathode, comprising a carbon cloth substrate and a CMC-Fe3O4 / BC catalyst supported on the surface of the carbon cloth.

[0015] The present invention provides a method for preparing an iron-doped biochar cathode, comprising the following steps:

[0016] a. Carbon cloth pretreatment

[0017] Cut the carbon cloth into 5cm×3cm pieces. Soak the cut carbon cloth in an acid solution for 24 hours to activate it. The acid solution consists of 3 parts of 10% nitric acid and 1 part of 10% sulfuric acid. Rinse with deionized water until neutral. Place it in a muffle furnace and bake at 400℃ for 1 hour. Soak in acetone to clean impurities. After sonication for 30 minutes, rinse with deionized water and air dry at room temperature for later use.

[0018] b. Catalyst treatment

[0019] Take 30 parts by mass of CMC-Fe3O4 / BC catalyst powder and place it in a beaker. The CMC-Fe3O4 / BC catalyst is prepared by the method provided in this invention. Add 2.64 parts by volume of anhydrous ethanol, 3 parts by volume of water, and 0.36 parts by volume of 30% Nafion solution in sequence. After mixing, sonicate for 60 minutes to make it uniformly dispersed to obtain a mixed solution.

[0020] c, load

[0021] The mixed solution prepared in step b was drop-coated onto the pretreated carbon cloth, giving full play to the high electrochemical activity of the carbon cloth, which provided favorable conditions for the two-electron reduction of oxygen at the cathode to generate H2O2. After drying at 40℃ for 5h, the CMC-Fe3O4 / BC electrode was obtained.

[0022] The present invention provides an application of an iron-doped biochar cathode, including the application of a CMC-Fe3O4 / BC cathode in a three-electrode system, specifically the CMC-Fe3O4 / BC cathode activating H2O2 to treat sulfaquinoxaline (SQX) under the action of an electric field.

[0023] Furthermore, the electric field is provided by a single-chamber electrolytic cell, which includes a cell body with a volume of 200 mL. The cell body is equipped with a knob-operated top cover, which has electrode holes and aeration head holes. An anode, a cathode, and a reference electrode are installed in the electrode holes. The anode is a carbon brush with a length of 60 mm and a diameter of 50 mm. The cathode is a CMC-Fe3O4 / BC cathode. The reference electrode is a saturated calomel electrode. The CMC-Fe3O4 / BC cathode is placed vertically through a titanium wire passing through carbon cloth. The carbon cloth is parallel to the carbon brush and the distance between them is 3 cm.

[0024] The aeration head has an opening for insertion, and an aeration tube is inserted into the opening. The aeration tube is located next to the cathode electrode and controls the aeration rate to be 0.3 L / min. During the reaction, it provides sufficient dissolved oxygen near the cathode to accelerate the reaction.

[0025] The pool contains an electrolyte, which is 50mM Na2SO4. Before the electrocatalytic reaction, sulfaquinoxaline is added to the electrolyte as a pollutant with a concentration of 10mg / L. An anode, a cathode, and a reference electrode are immersed in the electrolyte.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This invention discloses a method for preparing and applying an iron-doped biochar catalyst and cathode. Biochar (BC) is suitable as a support for iron oxide catalytic Fenton-like catalysts, and sodium carboxymethyl cellulose (CMC) is considered a suitable support for metal oxide nanomaterials due to its biodegradability and other properties. The two are combined as a support for supporting iron oxide to synthesize a CMC-Fe3O4 / BC catalyst. The CMC-Fe3O4 / BC is then loaded onto carbon cloth as a cathode, which is used to activate hydrogen peroxide in an electro-Fenton system to degrade sulfaquinoxaline.

[0028] The composite cathode CMC-Fe3O4 / BC provided in this invention is used as an iron-based catalyst electrode for the cathode of a heterogeneous electro-Fenton system. It uses carbon cloth as the substrate electrode, which fully utilizes its high electrochemical activity and provides favorable conditions for the two-electron reduction of oxygen at the cathode to generate H2O2.

[0029] Compared to the conventional method of separating powdered catalysts from solution and performing steps such as washing, centrifugation, and drying, which is time-consuming and has a low recovery rate, this invention uses a carbon cloth-supported CMC-Fe3O4 / BC method. This method only requires washing and drying the carbon cloth after use, and it can be reused. The recovery is simple and has less loss.

[0030] In the closed loop, the experimental group using CMC-Fe3O4 / BC as the cathode catalyst achieved a degradation rate of 92.65% for sulfaquinoxaline within 5 hours, which was 14.81% and 23.95% higher than the other control groups, respectively. Attached Figure Description

[0031] Figure 1 Scanning electron microscope images of BC and CMC-Fe3O4 / BC catalysts.

[0032] Figure 2 Elemental distribution diagram of CMC-Fe3O4 / BC catalyst.

[0033] Figure 3 The effect of different degradation systems on the degradation rate of sulfaquinoxaline. Detailed Implementation

[0034] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Example 1

[0035] An iron-doped biochar cathode is used to activate H2O2 treatment of SQX under an electric field, comprising the following steps:

[0036] a. Carbon cloth pretreatment

[0037] Cut the carbon cloth into 5cm×3cm pieces. Soak the cut carbon cloth in an acid solution for 24 hours to activate it. The acid solution consists of 3 parts of 10% nitric acid and 1 part of 10% sulfuric acid. Rinse with deionized water until neutral. Place it in a muffle furnace and bake at 400℃ for 1 hour. Soak in acetone to clean impurities. After sonication for 30 minutes, rinse with deionized water and air dry at room temperature for later use.

[0038] b, BC purification

[0039] BC was pyrolyzed under argon atmosphere, and the resulting solid powder was transferred to dilute hydrochloric acid solution. The solution was stirred continuously at 60°C for 6 hours, washed with deionized water until the final pH of the filtrate was 6.5-7, washed three times with ethanol, and dried overnight to obtain purified BC.

[0040] c. CMC preprocessing

[0041] CMC was dissolved in deionized water treated with N2, and FeCl3•6H2O and FeSO4•7H2O were added. The mixture was sonicated for 20 minutes to obtain a homogeneous solution.

[0042] d. Preparation of CMC-Fe3O4 / BC

[0043] The purified BC prepared in step a was added to the homogeneous mixture and mixed for 20 min. The mixture was then stirred at 200 r / min at 50 °C. The pH was adjusted to 12 with NaOH. The resulting mixture was left to stand at room temperature overnight. The precipitate was washed three times with deionized water and then three times with ethanol. Finally, it was freeze-dried at -60 °C for 24 h to obtain the CMC-Fe3O4 / BC catalyst.

[0044] The CMC-Fe3O4 / BC catalyst was tested, and the results are as follows:

[0045] Electron microscopy was used to scan the raw material BC and the CMC-Fe3O4 / BC catalyst, and the results are as follows: Figure 1 As shown, the top is BC and the bottom is CMC-Fe3O4 / BC catalyst. The raw material BC has an irregular surface morphology, and the surface is covered with irregular fine particles, and the overall surface is relatively smooth; while the surface of CMC-Fe3O4 / BC has a more porous structure and a loose internal structure, which may have a larger specific surface area and more active sites.

[0046] The elemental distribution of the CMC-Fe3O4 / BC catalyst is as follows: Figure 2 As shown, C, O, and Fe are confirmed to be the main constituent elements in the CMC-Fe3O4 / BC catalyst, and they are uniformly dispersed.

[0047] e. Catalyst treatment

[0048] Take 30 mg of CMC-Fe3O4 / BC catalyst powder and place it in a beaker. The CMC-Fe3O4 / BC catalyst was prepared using the method provided in this invention. Add 2.64 mL of anhydrous ethanol, 3 mL of water, and 360 μL of 30% Nafion solution in sequence. After mixing, sonicate for 60 min to disperse it evenly and obtain a mixed solution.

[0049] f, load

[0050] The mixed solution prepared in step e was drop-coated onto the pretreated carbon cloth and dried at 40°C for 5 hours to obtain the CMC-Fe3O4 / BC electrode, which is a carbon cloth composite cathode co-modified with iron-based / biomass char, and can be used in heterogeneous electric Fenton systems.

[0051] g, using a CMC-Fe3O4 / BC electrode for electrocatalytic reduction degradation of sulfaquinoxaline

[0052] In a single-chamber electrolytic cell with a reactor volume of 200 ml, a carbon cloth-supported CMC-Fe3O4 / BC electrode was used as the functional cathode, a 60 mm long and 50 mm diameter carbon brush was used as the anode, and a saturated calomel electrode was used as the reference electrode. The CMC-Fe3O4 / BC cathode was placed vertically through a titanium wire passing through the carbon cloth, which was parallel to the carbon brush and spaced 3 cm apart. During the electrocatalytic reduction and degradation of sulfaquinoxaline, aeration and oxygenation were carried out, and 2e⁻ was used as the oxygen source. - The oxygen reduction reaction generates H2O2, and the composite cathode can efficiently activate H2O2 on its surface and combine with the exposed iron active sites to activate the Fenton reaction, thereby generating hydroxyl radicals (·OH) with strong oxidizing power and non-selectivity, which improves the degradation rate of antibiotics.

[0053] The electrolyte was 50 mM Na2SO4. Sulfaquinoxaline was added as a pollutant before the electrocatalytic reaction, with a pollutant concentration of 10 mg / L. The pH of the reaction system was adjusted to 3 using H2SO4. The working voltage was -0.8 V, the electrolysis time was 5 h, and continuous aeration was carried out during the reaction at a rate of 0.3 L / min. Sufficient dissolved oxygen was provided near the cathode during the reaction to accelerate the reaction. Comparative Example 1

[0054] The treatment of sulfaquinoxaline in wastewater using catalyst-free carbon cloth as electrodes in a closed loop includes the following steps:

[0055] In Example 1, the cathode electrode was replaced with carbon cloth without catalyst support. The pretreatment of the carbon cloth without catalyst support was the same as in step a, and steps b to f were omitted. The remaining electrocatalytic reduction degradation of sulfaquinoxaline was the same as in step g. Comparative Example 2

[0056] The treatment of sulfaquinoxaline in wastewater using CMC-Fe3O4 / BC supported carbon cloth as an electrode under open-circuit conditions includes the following steps:

[0057] Steps a to f are the same as in Example 1. In step g, there is no need to connect a circuit to supply working voltage, nor is a saturated calomel electrode installed as a reference electrode. The sulfaquinoxaline is degraded only by the adsorption of the electrode. The remaining operations are the same as in Example 1.

[0058] The electrolytes in Example 1 and Comparative Examples 1 and 2 were sampled every 1 hour. Excess tert-butanol was added to quench free radicals, and the concentration of antibiotics in the reaction solution was detected by high performance liquid chromatography (HPLC). Finally, the degradation rate of sulfaquinoxaline was obtained.

[0059] Within 5 hours, the test results are as follows: Figure 3 As shown, in Example 1, under the conditions of working voltage -0.8V, reaction system pH of 3, aeration rate of 0.3L / min, and sulfaquinoxaline concentration of 10mg / L, the degradation rate of sulfaquinoxaline reached a maximum of 92.65%, while in Comparative Example 1, the degradation rate of sulfaquinoxaline reached a maximum of 77.84%, and in Comparative Example 2, the degradation rate of sulfaquinoxaline reached a maximum of 68.7%.

[0060] In summary, the experimental data under the three conditions show that CMC-Fe3O4 / BC as the cathode can achieve a degradation rate of 92.65% within 5 hours, which is significantly better than Comparative Example 1 and Comparative Example 2. This demonstrates the importance of the catalyst in the heterogeneous catalytic degradation of antibiotics by H2O2. Electrochemical activation of H2O2 is limited, while the hydroxyl radicals generated after the catalyst activates H2O2 can efficiently degrade antibiotic wastewater.

[0061] The scope of protection claimed by this invention is not limited to the specific embodiments described above. Moreover, for those skilled in the art, this invention can have various modifications and alterations. Any modifications, improvements, and equivalent substitutions made within the concept and principles of this invention should be included within the scope of protection of this invention.

Claims

1. An application of an iron-doped biochar cathode, characterized in that: The application of CMC-Fe3O4 / BC cathode in a three-electrode system involves the CMC-Fe3O4 / BC cathode activating H2O2 to treat sulfaquinoxaline SQX under the action of an electric field. The CMC-Fe3O4 / BC cathode includes a carbon cloth substrate and a CMC-Fe3O4 / BC catalyst supported on the surface of the carbon cloth. Preparation method of the CMC-Fe3O4 / BC catalyst Includes the following steps: a) Biochar BC purification Biochar BC was pyrolyzed under argon atmosphere, and the resulting solid powder was transferred to dilute hydrochloric acid solution. The solution was stirred continuously at 60°C for 6 hours, washed with deionized water until the final pH of the filtrate was 6.5-7, washed three times with ethanol, and dried overnight to obtain purified biochar BC. b. Sodium carboxymethyl cellulose (CMC) pretreatment Sodium carboxymethyl cellulose (CMC) was dissolved in N2-treated deionized water, and FeCl3•6H2O and FeSO4•7H2O were added. The mixture was ultrasonicated for 20 minutes to obtain a homogeneous solution. c. Preparation of CMC-Fe3O4 / BC The purified BC prepared in step a was added to the homogeneous mixture. After mixing for 20 min, the mixture was stirred at 200 r / min at 50 °C. The pH was adjusted to 12 with NaOH. The resulting mixture was left to stand at room temperature overnight. The precipitate was washed three times with deionized water and then three times with ethanol. The mixture was then freeze-dried at -60 °C for 24 h to obtain the CMC-Fe3O4 / BC catalyst.

2. The application of the iron-doped biochar cathode according to claim 1, characterized in that: The electric field is provided by a single-chamber electrolytic cell, which includes a cell body containing an electrolyte. The electrolyte contains an anode, a cathode, and a reference electrode. The anode is a carbon brush, the cathode is a CMC-Fe3O4 / BC cathode, and the reference electrode is a saturated calomel electrode.

3. The application of an iron-doped biochar cathode according to claim 2, characterized in that: The pool body is equipped with a knob-operated top cover, which has electrode holes and aeration head holes; an aeration pipe is inserted into the aeration head holes, and the aeration pipe controls the aeration rate to be 0.3L / min. The CMC-Fe3O4 / BC cathode is placed vertically through a titanium wire passing through carbon cloth, with the carbon cloth parallel to the carbon brush and spaced 3 cm apart.

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