Method for synergistically treating antibiotic wastewater by electro-fenton-electrocoagulation based on modified carbon nanotube composite cathode
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NORTHEAST NORMAL UNIVERSITY
- Filing Date
- 2026-05-26
- Publication Date
- 2026-08-07
AI Technical Summary
[0005]针对现有电芬顿耦合体系pH适用范围窄、阴极活性不足、抗生素矿化效率低的缺陷，本发明提供了一种基于改性碳纳米管复合阴极的电芬顿-电絮凝协同处理抗生素废水的方法
本发明通过优化酸改性多壁碳纳米管与粘结剂的配比制备复合阴极，有效增加阴极表面活性位点数量，降低界面电荷传递阻抗，提升两电子氧还原反应的过氧化氢原位生成效率，同时赋予阴极优异的过一硫酸盐非均相活化性能，有效解决了传统电芬顿体系普通阴极活性不足、电子传递效率低、过氧化氢生成量有限的缺陷。
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Figure CN122520186A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrochemical treatment technology for antibiotic wastewater, and in particular to a method for the synergistic treatment of antibiotic wastewater by electro-Fenton-electro-coagulation based on a modified carbon nanotube composite cathode. Background Technology
[0002] In recent years, the problem of antibiotic residues in the aquatic environment has become increasingly prominent. Among them, fluoroquinolone antibiotics, represented by ciprofloxacin, are difficult to remove effectively through natural photolysis and conventional biological treatment processes due to their stable molecular structure and strong biological inhibitory properties. Their residues can induce the spread of antibiotic resistance genes, threatening ecological security and public health. Developing efficient and stable deep treatment technologies for recalcitrant antibiotic wastewater is a core need in the current water treatment field.
[0003] Among existing technologies for treating recalcitrant organic wastewater, electro-Fenton technology is a widely used advanced electrochemical oxidation technology. It generates hydrogen peroxide by reducing oxygen in situ at the cathode, which then reacts with ferrous ions to produce hydroxyl radicals that oxidize and degrade pollutants. It has the advantages of controllable reaction, strong oxidation capacity, and no need to add large amounts of hydrogen peroxide. However, the traditional electro-Fenton system has obvious defects: ordinary cathode materials have insufficient active sites and low electron transfer efficiency, resulting in limited hydrogen peroxide generation; the system is highly dependent on strongly acidic conditions, and the treatment efficiency drops sharply under neutral and weakly alkaline conditions; the iron ion recycling efficiency is poor; and it relies only on the single oxidation pathway of hydroxyl radicals, which is insufficient for the mineralization of structurally stable antibiotics, and degradation intermediates are prone to remain.
[0004] Existing treatment systems that couple electro-Fenton and electrocoagulation can continuously release ferrous ions from the iron anode to replenish the Fenton reaction substrate, while the electrogenerated iron flocs can adsorb some pollutants and intermediate products, thus compensating for the shortcomings of single electro-Fenton to some extent. However, the existing coupling system still does not solve the problem of narrow pH application range, and has not achieved the synergistic generation of multiple active species. There is a lack of systematic development on the synergistic effect of persulfate activation, carbon-based cathode interface regulation and coupling system, resulting in poor adaptability of the system to complex water quality, low mineralization efficiency and insufficient cathode operation stability, making it difficult to meet the continuous treatment needs of actual antibiotic wastewater. Summary of the Invention
[0005] To address the shortcomings of existing electro-Fenton coupling systems, such as narrow pH range, insufficient cathode activity, and low antibiotic mineralization efficiency, this invention provides a method for the synergistic treatment of antibiotic wastewater using an electro-Fenton-electrocoagulation approach based on a modified carbon nanotube composite cathode.
[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for synergistic electro-Fenton-electro-coagulation treatment of antibiotic wastewater based on a modified carbon nanotube composite cathode includes the following steps: S1. Preparation of acid-modified multi-walled carbon nanotube / stainless steel composite cathode: Multi-walled carbon nanotubes are heated and stirred in a mixed acid of concentrated sulfuric acid and concentrated nitric acid for modification. The modified product is washed until neutral and then dried to obtain acid-modified multi-walled carbon nanotubes with oxygen-containing functional groups on the surface. The acid-modified multi-walled carbon nanotubes and binder are mixed and dispersed in an organic solvent at a mass ratio of 5:1 to obtain a uniform suspension. The suspension is coated on the surface of a pretreated stainless steel substrate, and after drying and compaction, a composite cathode is obtained. S2. Assemble the electrolysis reaction system: Use the composite cathode as the cathode and the pretreated iron plate as the sacrificial anode. Inject the antibiotic-containing wastewater to be treated into the electrolysis reactor, add sodium sulfate as the supporting electrolyte, and add persulfate at the same time to adjust the initial pH of the wastewater to 2-7. S3. Energize for coordinated processing: Apply a constant current, controlling the current density to be 2.86~8.57 mA / cm². 2 The process initiates an electro-Fenton-electro-coagulation synergistic reaction. During the reaction, the cathode generates hydrogen peroxide in situ through two-electron oxygen reduction. The iron anode continuously releases ferrous ions to trigger the Fenton reaction. At the same time, the ferrous ions and the composite cathode interface jointly activate persulfate and hydrogen peroxide generated in the system to produce reactive oxygen species. The iron flocs generated by the hydrolysis of iron ions simultaneously adsorb pollutants and degradation intermediates, achieving the degradation, removal and deep mineralization of antibiotics.
[0007] Furthermore, in S1, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1. The mixed acid modification reaction of multi-walled carbon nanotubes is carried out for 8 hours under constant temperature stirring conditions. After modification, the product is washed multiple times with acetone until the washing solution is neutral and then dried. The binder is polyvinylidene fluoride, the mass ratio of acid-modified multi-walled carbon nanotubes to polyvinylidene fluoride is 5:1, the organic solvent is N,N-dimethylacetamide, and the mixture is ultrasonically dispersed for 40 minutes to form a uniform suspension. The stainless steel substrate coated with the suspension is dried at 80°C for 12 hours and then compacted to obtain a composite cathode.
[0008] Furthermore, a uniformly entangled multi-walled carbon nanotube conductive network is formed on the surface of the composite cathode, which has mesoporous structure characteristics; when the mass ratio of acid-modified multi-walled carbon nanotubes to polyvinylidene fluoride is 5:1, the cathode has the highest cyclic voltammetric response and the lowest charge transfer impedance, and the interfacial electron transport performance and oxygen reduction activity reach the optimal balance.
[0009] Furthermore, the effective reaction area of both the composite cathode and the iron anode used in S2 is 70 cm². 2The dimensions are 5cm×7cm×0.1cm. During the pretreatment of the iron anode, it is first immersed in 1mol / L hydrochloric acid solution for 1min to remove surface oxides, then polished with sandpaper and rinsed with deionized water. During the pretreatment of the stainless steel substrate, it is first polished with sandpaper, then placed in acetone, ethanol and deionized water in sequence for ultrasonic cleaning.
[0010] Furthermore, in S2, the concentration range of sodium sulfate is 7~35mM, with an optimal concentration of 21mM; the concentration range of persulfate is 1~5mM, with an optimal concentration of 3mM; and the optimal current density in S3 is 5.71mA / cm³. 2 At this current density, the efficiency of reactive oxygen species generation and current utilization reaches the optimal balance, and the proportion of side reactions is minimized.
[0011] Furthermore, the optimal value for adjusting the initial pH of the wastewater in S2 is 3; through the heterogeneous activation effect of persulfate and hydrogen peroxide on the multi-walled carbon nanotube interface and the iron ions dissolved in the system, the applicable pH range of the system is effectively broadened, without relying on strongly acidic reaction conditions.
[0012] Furthermore, the reactive oxygen species generated in S3 are dominated by hydroxyl radicals. Quenching experiments have verified that the removal rate of antibiotics decreased significantly after the addition of tert-butanol, a hydroxyl radical quencher. The removal rate decreased further after the addition of methanol, a co-quencher of sulfate radicals and hydroxyl radicals. The removal rate continued to decrease after the addition of furfuryl alcohol, a singlet oxygen quencher. The three types of reactive species synergistically participate in the degradation of pollutants.
[0013] Furthermore, the iron flocs generated by the hydrolysis of iron ions in S3 are low-crystallinity amorphous iron gel structures with a surface rich in hydroxyl groups and adsorbed water. Compared with the crystalline iron oxide flocs generated under conditions without the addition of persulfate, they have a stronger adsorption and enrichment capacity for pollutants and degradation intermediates, which can further enhance the co-precipitation removal effect of pollutants.
[0014] Furthermore, the target pollutant in the antibiotic-containing wastewater to be treated is ciprofloxacin, with an initial concentration range of 10-100 mg / L. Under neutral pH conditions, the removal rate of ciprofloxacin by the system can still be maintained above 96%, and under optimal reaction conditions, the removal rate of ciprofloxacin can reach 99.68% within 30 minutes, while the total organic carbon removal rate can reach 74.19%. During the degradation of ciprofloxacin, the attack on adjacent sites of the piperazine ring and carboxyl group preferentially occurs, followed by hydroxylation, defluorination, ring opening, decarboxylation, and aromatic ring cleavage, ultimately achieving mineralization. The overall ecotoxicity of the degradation intermediates is lower than that of the original pollutant.
[0015] Furthermore, the composite cathode exhibits excellent cycle stability, maintaining a high removal efficiency for antibiotics even after five repeated uses; the carbon skeleton on the cathode surface is not significantly damaged before and after the reaction, the characteristic peaks of the D and G bands in the Raman spectrum are stable, only the oxygen-containing functional groups on the surface undergo limited reconstruction, and there is no obvious structural collapse or loss of active material.
[0016] The present invention has the following beneficial effects: This invention prepares a composite cathode by optimizing the ratio of acid-modified multi-walled carbon nanotubes to binder, which effectively increases the number of active sites on the cathode surface, reduces the interfacial charge transfer impedance, and improves the in-situ generation efficiency of hydrogen peroxide in the two-electron oxygen reduction reaction. At the same time, it endows the cathode with excellent heterogeneous activation performance of persulfate, effectively solving the defects of insufficient activity, low electron transfer efficiency and limited hydrogen peroxide generation of ordinary cathodes in the traditional electro-Fenton system.
[0017] This invention synergistically activates persulfate through the interface of ferrous ions and a composite cathode, simultaneously generating three types of reactive oxygen species: hydroxyl radicals, sulfate radicals, and singlet oxygen. Combined with the highly adsorbent amorphous iron flocs generated during the electrocoagulation process, it achieves a synergistic effect of multi-pathway oxidation degradation and adsorption co-precipitation, broadens the applicable pH range of the system, and does not require strong acid reaction conditions. It effectively solves the defects of existing coupled systems, such as narrow pH range, insufficient mineralization of antibiotics by a single oxidation pathway, and easy residue of degradation intermediates.
[0018] This invention uses an iron plate as a sacrificial anode, eliminating the need for additional large amounts of ferrous ions and oxidants, thus controlling operating costs. The composite cathode exhibits excellent cycle stability and can operate continuously for extended periods. It is suitable for treating antibiotic wastewater with different water quality characteristics and can be directly applied to scenarios such as advanced treatment of municipal wastewater effluent, upgrading of secondary effluent from the pharmaceutical industry, and advanced treatment of large-scale livestock wastewater. It can be integrated without large-scale modifications to existing water treatment facilities, demonstrating high engineering promotion value. Attached Figure Description
[0019] Figure 1 This is a flowchart of a method for synergistic treatment of antibiotic wastewater based on modified carbon nanotube composite cathode using electro-Fenton-electrocoagulation proposed in this invention. Figure 2 The following are performance characterization diagrams of the composite cathode proposed in this invention, where 1a is the cyclic voltammetry curve of cathodes with different mass ratios of PVDF to acid-modified multi-walled carbon nanotubes, and 1b is the electrochemical impedance Nyquist plot of cathodes with different ratios. Figure 3 This is a line graph showing the changes in ciprofloxacin removal rate under different initial pH conditions proposed in this invention. Figure 4The above are performance comparison charts of the system proposed in this invention and the traditional electro-Fenton-electrocoagulation system. 4a is a bar chart comparing the removal rates of ciprofloxacin at 30 min, and 4b is a bar chart comparing the removal rates of total organic carbon at 30 min. Figure 5 This is a bar chart showing the change in ciprofloxacin removal rate after five consecutive cycles of operation of the composite cathode proposed in this invention. Figure 6 These are Raman data images of the cathode before and after the reaction of the electrode plate proposed in this invention; Figure 7 The diagram shows the detection of reactive oxygen species proposed in this invention, where 7a is the electron paramagnetic resonance detection spectrum of hydroxyl radicals and sulfate radicals, 7b is the electron paramagnetic resonance detection spectrum of singlet oxygen, and 7c is a bar chart comparing the removal rates of ciprofloxacin in the quenching experiment. Figure 8 This is a schematic diagram of the degradation and transformation pathway of ciprofloxacin in the system of this invention. Figure 9 This is a scanning electron microscope image of the surface morphology of the composite cathode proposed in this invention; Figure 10 The image shows the pore size distribution curve of the composite cathode proposed in this invention. Figure 11 The Fourier transform infrared spectrum of the iron flocs generated after adding persulfate according to the present invention. Detailed Implementation
[0020] The following will refer to the appendices in the embodiments of the present invention. Figure 1-11 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0021] Example 1
[0022] S1. Preparation of acid-modified multi-walled carbon nanotube / stainless steel composite cathode: Multi-walled carbon nanotubes were placed in a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid at a volume ratio of 3:1. The mixture was stirred at 60°C for 8 hours. After the reaction, the mixture was cooled to room temperature, and the solid product was separated by filtration. The solid product was washed repeatedly with acetone until the washing solution was neutral. The solid product was then vacuum dried at 60°C for 12 hours to obtain acid-modified multi-walled carbon nanotubes with oxygen-containing functional groups on the surface. The acid-modified multi-walled carbon nanotubes and polyvinylidene fluoride were added to N,N-dimethylacetamide at a mass ratio of 5:1 and ultrasonically dispersed for 40 minutes to obtain a uniform suspension. A 304 stainless steel plate was polished with 800-grit sandpaper and then ultrasonically cleaned in acetone, ethanol, and deionized water for 10 minutes each. After drying, the suspension was evenly coated onto the stainless steel surface and dried in a forced-air dryer at 80°C for 12 hours. The composite cathode was then compacted under a pressure of 10 MPa.
[0023] A uniformly entangled multi-walled carbon nanotube conductive network is formed on the surface of the composite cathode, with a surface morphology as follows: Figure 9 As shown, multi-walled carbon nanotubes interlock to form a continuous conductive network, without obvious agglomeration or coating peeling defects; they possess mesoporous structure characteristics, and the pore structure characterization is as follows: Figure 10 As shown, the pore size is concentrated in the range of 2-50 nm, which is a typical mesoporous structure, allowing for full exposure of active sites for the oxygen reduction reaction. It exhibits the highest cyclic voltammetric response and the lowest charge transfer impedance, achieving an optimal balance between interfacial electron transport performance and oxygen reduction activity; as shown... Figure 2 As shown, when the mass ratio of PVDF to acid-modified multi-walled carbon nanotubes is 5:1, the cyclic voltammetric response current is the highest and the charge transfer impedance is the lowest, which is the optimal ratio.
[0024] S2. Assemble the electrolytic reaction system: Immerse the iron plate in a 1 mol / L hydrochloric acid solution for 1 minute to remove surface oxides, polish with 800-grit sandpaper, and rinse thoroughly with deionized water. This plate serves as the sacrificial anode. Both the composite cathode and the iron anode have an effective area of 70 cm². 2 The sample, measuring 5cm × 7cm × 0.1cm with an electrode spacing of 2cm, was placed in a single-chamber electrolytic reactor. 500mL of ciprofloxacin-simulated wastewater with an initial concentration of 50mg / L was injected. Sodium sulfate was added to bring the concentration to 21mM as the electrolyte, and persulfate was added to bring the concentration to 3mM. The initial pH of the wastewater was adjusted to 3 using a solution of 0.1mol / L sulfuric acid and 0.1mol / L sodium hydroxide.
[0025] S3. Energize for coordinated processing: Apply a constant current, controlling the current density to 5.71 mA / cm². 2The electro-Fenton-electrocoagulation synergistic reaction was initiated, with a reaction time of 30 minutes. During the reaction, hydrogen peroxide was generated in situ through the reduction of oxygen with two electrons at the cathode. The iron anode continuously released ferrous ions to trigger the Fenton reaction. At the same time, the ferrous ions and the composite cathode interface jointly activated persulfate to generate reactive oxygen species including hydroxyl radicals, sulfate radicals, and singlet oxygen. The low-crystallinity amorphous iron gel flocs generated by the hydrolysis of iron ions simultaneously adsorbed pollutants and degradation intermediates, achieving the degradation, removal, and deep mineralization of antibiotics.
[0026] After the reaction was completed, the sample was filtered through a 0.22 μm organic filter membrane, and the concentration of ciprofloxacin was determined by high performance liquid chromatography. The total organic carbon concentration was determined by a total organic carbon analyzer.
[0027] Under the conditions of this embodiment, the removal rate of ciprofloxacin reached 99.68% within 30 minutes, and the total organic carbon removal rate reached 74.19%. During ciprofloxacin degradation, the degradation preferentially involves attack on the piperazine ring and adjacent carboxyl groups, sequentially undergoing hydroxylation, defluorination, ring opening, decarboxylation, and aromatic ring cleavage, ultimately mineralizing into carbon dioxide, water, and small-molecule inorganic salts. The overall ecotoxicity of the degradation intermediates is lower than that of the original pollutant. The degradation pathway of ciprofloxacin is as follows: Figure 8 As shown, the pollutants undergo a series of processes including hydroxylation, ring opening, and bond breaking to achieve deep mineralization, without the accumulation of highly toxic intermediate products.
[0028] Example 2
[0029] S1. Preparation of acid-modified multi-walled carbon nanotube / stainless steel composite cathode: Multi-walled carbon nanotubes were placed in a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid at a volume ratio of 3:1. The mixture was stirred at 60°C for 8 hours. After the reaction, the mixture was cooled to room temperature, and the solid product was separated by filtration. The solid product was washed repeatedly with acetone until the washing solution was neutral. The solid product was then vacuum dried at 60°C for 12 hours to obtain acid-modified multi-walled carbon nanotubes with oxygen-containing functional groups on the surface. The acid-modified multi-walled carbon nanotubes and polyvinylidene fluoride were added to N,N-dimethylacetamide at a mass ratio of 5:1 and ultrasonically dispersed for 40 minutes to obtain a uniform suspension. A 304 stainless steel plate was polished with 800-grit sandpaper and then ultrasonically cleaned in acetone, ethanol, and deionized water for 10 minutes each. After drying, the suspension was evenly coated onto the stainless steel surface and dried in a forced-air dryer at 80°C for 12 hours. The composite cathode was then compacted under a pressure of 10 MPa.
[0030] S2. Assemble the electrolytic reaction system: Immerse the iron plate in a 1 mol / L hydrochloric acid solution for 1 minute to remove surface oxides, polish with 800-grit sandpaper, and rinse thoroughly with deionized water. This plate serves as the sacrificial anode. Both the composite cathode and the iron anode have an effective area of 70 cm². 2The sample, measuring 5cm × 7cm × 0.1cm with an electrode spacing of 2cm, was placed in a single-chamber electrolytic reactor. 500mL of ciprofloxacin-simulated wastewater with an initial concentration of 50mg / L was injected. Sodium sulfate was added to bring the concentration to 21mM as the electrolyte, and persulfate was added to bring the concentration to 3mM. The initial pH of the wastewater was adjusted to 7 using a solution of 0.1mol / L sulfuric acid and 0.1mol / L sodium hydroxide.
[0031] S3. Energize for coordinated processing: Apply a constant current, controlling the current density to 5.71 mA / cm². 2 The electro-Fenton-electrocoagulation synergistic reaction was initiated, with a reaction time of 30 minutes. In this embodiment, under neutral conditions at pH 7, the ciprofloxacin removal rate remained at 96.17% within 30 minutes. The heterogeneous activation of persulfate by the multi-walled carbon nanotube interface effectively broadened the pH range of the system, eliminating the need for strongly acidic reaction conditions. The pH range of the system is as follows: Figure 3 As shown, the removal rate of ciprofloxacin is higher than 96% within the pH range of 2 to 7, which is suitable for the pH fluctuation requirements of actual wastewater.
[0032] In this embodiment, the reactive oxygen species generated are dominated by hydroxyl radicals. Quenching experiments verified that the removal rate of ciprofloxacin decreased by 42% after adding 100mM hydroxyl radical quencher tert-butanol; by 67% after adding 100mM sulfate and hydroxyl radical co-quencher methanol; and by 79% after adding 50mM singlet oxygen quencher furfuryl alcohol. These three types of reactive oxygen species synergistically participate in pollutant degradation. The detection results of reactive oxygen species are as follows: Figure 7 As shown, electron paramagnetic resonance and quenching experiments jointly verified the coexistence and synergistic effect of the three types of active species. The iron flocs generated in the reaction were collected, freeze-dried, and characterized by X-ray diffraction. The results showed no obvious crystalline phase diffraction peaks, indicating a low-crystallinity amorphous iron gel structure with a surface rich in hydroxyl groups and adsorbed water, such as... Figure 11 As shown, 3400cm -1 The presence of strong hydroxyl stretching vibration peaks nearby indicates the presence of abundant active hydroxyl groups and bound water on the floc surface, resulting in higher adsorption activity. Compared to crystalline iron oxide flocs generated without the addition of monosulfate, the adsorption and enrichment capacity for pollutants and degradation intermediates is increased by more than 45%. Figure 6 As shown, after adding PMS, the flocs showed no obvious diffraction peaks, indicating a low-crystallinity amorphous structure with higher adsorption activity.
[0033] Example 3
[0034] S1. Preparation of acid-modified multi-walled carbon nanotube / stainless steel composite cathode: Multi-walled carbon nanotubes were placed in a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid at a volume ratio of 3:1. The mixture was stirred at 60°C for 8 hours. After the reaction, the mixture was cooled to room temperature, and the solid product was separated by filtration. The solid product was washed repeatedly with acetone until the washing solution was neutral. The solid product was then vacuum dried at 60°C for 12 hours to obtain acid-modified multi-walled carbon nanotubes with oxygen-containing functional groups on the surface. The acid-modified multi-walled carbon nanotubes and polyvinylidene fluoride were added to N,N-dimethylacetamide at a mass ratio of 5:1 and ultrasonically dispersed for 40 minutes to obtain a uniform suspension. A 304 stainless steel plate was polished with 800-grit sandpaper and then ultrasonically cleaned in acetone, ethanol, and deionized water for 10 minutes each. After drying, the suspension was evenly coated onto the stainless steel surface and dried in a forced-air dryer at 80°C for 12 hours. The composite cathode was then compacted under a pressure of 10 MPa.
[0035] S2. Assemble the electrolytic reaction system: Immerse the iron plate in a 1 mol / L hydrochloric acid solution for 1 minute to remove surface oxides, polish with 800-grit sandpaper, and rinse thoroughly with deionized water. This plate serves as the sacrificial anode. Both the composite cathode and the iron anode have an effective area of 70 cm². 2 The sample, measuring 5cm × 7cm × 0.1cm with an electrode spacing of 2cm, was placed in a single-chamber electrolytic reactor. 500mL of ciprofloxacin-simulated wastewater with an initial concentration of 100mg / L was injected. Sodium sulfate was added to bring the concentration to 21mM as the electrolyte, and persulfate was added to bring the concentration to 3mM. The initial pH of the wastewater was adjusted to 3 using a solution of 0.1mol / L sulfuric acid and 0.1mol / L sodium hydroxide.
[0036] S3. Energize for coordinated processing: Apply a constant current, controlling the current density to 5.71 mA / cm². 2 The electro-Fenton-electrocoagulation synergistic reaction was initiated, with a reaction time of 30 minutes. In this embodiment, for high-concentration ciprofloxacin wastewater with an initial concentration of 100 mg / L, the ciprofloxacin removal rate was 82.30% and the total organic carbon removal rate was 57.46% within 30 minutes, demonstrating the system's good treatment potential for high-concentration antibiotic wastewater.
[0037] Example 4
[0038] S1. Preparation of acid-modified multi-walled carbon nanotube / stainless steel composite cathode: Multi-walled carbon nanotubes were placed in a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid at a volume ratio of 3:1. The mixture was stirred at 60°C for 8 hours. After the reaction, the mixture was cooled to room temperature, and the solid product was separated by filtration. The solid product was washed repeatedly with acetone until the washing solution was neutral. The solid product was then vacuum dried at 60°C for 12 hours to obtain acid-modified multi-walled carbon nanotubes with oxygen-containing functional groups on the surface. The acid-modified multi-walled carbon nanotubes and polyvinylidene fluoride were added to N,N-dimethylacetamide at a mass ratio of 5:1 and ultrasonically dispersed for 40 minutes to obtain a uniform suspension. A 304 stainless steel plate was polished with 800-grit sandpaper and then ultrasonically cleaned in acetone, ethanol, and deionized water for 10 minutes each. After drying, the suspension was evenly coated onto the stainless steel surface and dried in a forced-air dryer at 80°C for 12 hours. The composite cathode was then compacted under a pressure of 10 MPa.
[0039] S2. Assemble the electrolytic reaction system: Immerse the iron plate in a 1 mol / L hydrochloric acid solution for 1 minute to remove surface oxides, polish with 800-grit sandpaper, and rinse thoroughly with deionized water. This plate serves as the sacrificial anode. Both the composite cathode and the iron anode have an effective area of 70 cm². 2 The sample, measuring 5cm × 7cm × 0.1cm with an electrode spacing of 2cm, was placed in a single-chamber electrolytic reactor. 500mL of ciprofloxacin-simulated wastewater with an initial concentration of 50mg / L was injected. Sodium sulfate was added to bring the concentration to 21mM as the electrolyte, and persulfate was added to bring the concentration to 3mM. The initial pH of the wastewater was adjusted to 3 using a solution of 0.1mol / L sulfuric acid and 0.1mol / L sodium hydroxide.
[0040] S3. Energize for coordinated processing: Apply a constant current, controlling the current density to 5.71 mA / cm². 2 The electro-Fenton-electrocoagulation synergistic reaction was initiated, with a reaction time of 30 minutes. After each reaction, the cathode was removed and rinsed three times with deionized water, without additional activation treatment. Freshly prepared simulated wastewater was then injected, and this process was repeated five times. After five cycles, the composite cathode still achieved a 98.79% removal rate of ciprofloxacin within 30 minutes, and a 70.22% removal rate of total organic carbon. The intensity ratio of the characteristic peaks in the D and G bands of the cathode Raman spectrum before and after the reaction showed no significant change, indicating no significant damage to the carbon framework structure. The Raman spectra of the cathode before and after the reaction are as follows: Figure 6 As shown, the intensity ratio of the D-band to the G-band only fluctuated slightly, proving that the cathode carbon structure showed no significant oxidation damage and excellent stability; only the surface oxygen-containing functional groups underwent limited reconstruction, without any active material shedding or structural collapse, demonstrating excellent long-term operational stability; the cycle performance of the composite cathode is as follows... Figure 5 As shown, the removal rate did not decrease significantly after 5 cycles, meeting the requirements for long-term operation.
[0041] Example 5
[0042] S1. Preparation of acid-modified multi-walled carbon nanotube / stainless steel composite cathode: Multi-walled carbon nanotubes were placed in a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid at a volume ratio of 3:1. The mixture was stirred at 60°C for 8 hours. After the reaction, the mixture was cooled to room temperature, and the solid product was separated by filtration. The solid product was washed repeatedly with acetone until the washing solution was neutral. The solid product was then vacuum dried at 60°C for 12 hours to obtain acid-modified multi-walled carbon nanotubes with oxygen-containing functional groups on the surface. The acid-modified multi-walled carbon nanotubes and polyvinylidene fluoride were added to N,N-dimethylacetamide at a mass ratio of 5:1 and ultrasonically dispersed for 40 minutes to obtain a uniform suspension. A 304 stainless steel plate was polished with 800-grit sandpaper and then ultrasonically cleaned in acetone, ethanol, and deionized water for 10 minutes each. After drying, the suspension was evenly coated onto the stainless steel surface and dried in a forced-air dryer at 80°C for 12 hours. The composite cathode was then compacted under a pressure of 10 MPa.
[0043] S2. Assemble the electrolytic reaction system: Immerse the iron plate in a 1 mol / L hydrochloric acid solution for 1 minute to remove surface oxides, polish with 800-grit sandpaper, and rinse thoroughly with deionized water. This plate serves as the sacrificial anode. Both the composite cathode and the iron anode have an effective area of 70 cm². 2 The sample, measuring 5cm × 7cm × 0.1cm with an electrode spacing of 2cm, was placed in a single-chamber electrolytic reactor. 500mL of ciprofloxacin-simulated wastewater with an initial concentration of 50mg / L was injected. Sodium sulfate was added to a concentration of 7mM as the electrolyte, and persulfate was added to a concentration of 1mM. The initial pH of the wastewater was adjusted to 3 using a solution of 0.1mol / L sulfuric acid and 0.1mol / L sodium hydroxide.
[0044] S3. Energize for coordinated processing: Apply a constant current, controlling the current density to 2.86 mA / cm². 2 The electro-Fenton-electrocoagulation synergistic reaction was initiated, with a reaction time of 30 minutes. After the reaction, samples were taken for testing. Within 30 minutes, the removal rate of ciprofloxacin was 98.21%, and the removal rate of total organic carbon was 68.34%.
[0045] Example 6
[0046] S1. Preparation of acid-modified multi-walled carbon nanotube / stainless steel composite cathode: Multi-walled carbon nanotubes were placed in a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid at a volume ratio of 3:1. The mixture was stirred at 60°C for 8 hours. After the reaction, the mixture was cooled to room temperature, and the solid product was separated by filtration. The solid product was washed repeatedly with acetone until the washing solution was neutral. The solid product was then vacuum dried at 60°C for 12 hours to obtain acid-modified multi-walled carbon nanotubes with oxygen-containing functional groups on the surface. The acid-modified multi-walled carbon nanotubes and polyvinylidene fluoride were added to N,N-dimethylacetamide at a mass ratio of 5:1 and ultrasonically dispersed for 40 minutes to obtain a uniform suspension. A 304 stainless steel plate was polished with 800-grit sandpaper and then ultrasonically cleaned in acetone, ethanol, and deionized water for 10 minutes each. After drying, the suspension was evenly coated onto the stainless steel surface and dried in a forced-air dryer at 80°C for 12 hours. The composite cathode was then compacted under a pressure of 10 MPa.
[0047] S2. Assemble the electrolytic reaction system: Immerse the iron plate in a 1 mol / L hydrochloric acid solution for 1 minute to remove surface oxides, polish with 800-grit sandpaper, and rinse thoroughly with deionized water. This plate serves as the sacrificial anode. Both the composite cathode and the iron anode have an effective area of 70 cm². 2 The sample, measuring 5cm × 7cm × 0.1cm with an electrode spacing of 2cm, was placed in a single-chamber electrolytic reactor. 500mL of ciprofloxacin-simulated wastewater with an initial concentration of 50mg / L was injected. Sodium sulfate was added to bring the concentration to 35mM as the electrolyte, and persulfate was added to bring the concentration to 5mM. The initial pH of the wastewater was adjusted to 3 using a solution of 0.1mol / L sulfuric acid and 0.1mol / L sodium hydroxide.
[0048] S3. Energize for coordinated processing: Apply a constant current, controlling the current density to 8.57 mA / cm². 2 The electro-Fenton-electro-coagulation synergistic reaction was initiated, with a reaction time of 30 minutes. After the reaction, samples were taken for testing, and the removal rate of ciprofloxacin was 98.75% and the removal rate of total organic carbon was 69.52% within 30 minutes.
[0049] Comparative Example S1. Cathode preparation: After polishing the 304 stainless steel plate with 800-grit sandpaper, it is ultrasonically cleaned in acetone, ethanol and deionized water for 10 minutes each, and then dried and used directly as the cathode.
[0050] S2. Assemble the electrolytic reaction system: Immerse the iron plate in a 1 mol / L hydrochloric acid solution for 1 minute to remove surface oxides, polish it with 800-grit sandpaper, and rinse it thoroughly with deionized water. This plate will serve as the sacrificial anode. The effective area of both the cathode and the iron anode is 70 cm². 2The sample, measuring 5cm × 7cm × 0.1cm with an electrode spacing of 2cm, was placed in a single-chamber electrolytic reactor. 500mL of ciprofloxacin-simulated wastewater with an initial concentration of 50mg / L was injected, and sodium sulfate was added to bring its concentration to 21mM as the electrolyte. Persulfate was not added. The initial pH of the wastewater was adjusted to 3 using a solution of 0.1mol / L sulfuric acid and 0.1mol / L sodium hydroxide.
[0051] S3. Co-treatment with electricity: A constant current was applied, with a current density controlled at 5.71 mA / cm, and the reaction time was 30 min. This comparative example corresponds to a traditional electro-Fenton-electro-flocculation coupling system without persulfate activation. After the reaction, samples were taken for testing. Within 30 min, the removal rate of ciprofloxacin was 72.45%, and the removal rate of total organic carbon was 41.26%. Performance comparison between the system of this invention and the traditional system is as follows: Figure 4 As shown, the removal rates of ciprofloxacin and total organic carbon in the system of this invention are increased by more than 37% and 80% respectively compared with the traditional system, demonstrating significant synergistic advantages.
[0052] Table 1 Comparison of processing effects between each embodiment and the comparative example As shown in the table above, the system of this invention exhibits excellent pollutant degradation and mineralization effects within all parameter ranges specified in the technical requirements, outperforming the traditional electro-Fenton-electrocoagulation system without persulfate activation. Example 1 represents the optimal parameter conditions, achieving most of the removal and deep mineralization of ciprofloxacin; Example 2 verifies that the system maintains high treatment efficiency under neutral pH conditions, eliminating the need for additional acid or alkali adjustments to strongly acidic wastewater, thus reducing reagent costs in practical applications; Example 3 verifies the system's suitability for high-concentration antibiotic wastewater; Example 4 verifies the long-term cyclic stability of the composite cathode, reducing cathode replacement frequency and further compressing operating costs; Examples 5 and 6 correspond to the upper and lower limits of the parameter ranges specified in the technical requirements, respectively, without the risk of excessively wide ranges.
[0053] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for synergistic treatment of antibiotic wastewater using an electro-Fenton-electrocoagulation approach based on a modified carbon nanotube composite cathode, characterized in that, Includes the following steps: S1. Preparation of acid-modified multi-walled carbon nanotube / stainless steel composite cathode: Multi-walled carbon nanotubes are heated and stirred in a mixed acid of concentrated sulfuric acid and concentrated nitric acid for modification. The modified product is washed until neutral and then dried to obtain acid-modified multi-walled carbon nanotubes with oxygen-containing functional groups on the surface. Acid-modified multi-walled carbon nanotubes and binder were mixed and dispersed in an organic solvent at a mass ratio of 5:1 to obtain a uniform suspension. The suspension was coated on the surface of a pretreated stainless steel substrate, and after drying and compaction, a composite cathode was obtained. S2. Assemble the electrolysis reaction system: Use the composite cathode as the cathode and the pretreated iron plate as the sacrificial anode. Inject the antibiotic-containing wastewater to be treated into the electrolysis reactor, add sodium sulfate as the supporting electrolyte, and add persulfate at the same time to adjust the initial pH of the wastewater to 2-7. S3. Energize for coordinated processing: Apply a constant current, controlling the current density to be 2.86~8.57 mA / cm². 2 The electro-Fenton-electro-coagulation synergistic reaction is initiated, hydrogen peroxide is generated in situ at the cathode, ferrous ions are released at the iron anode, and the ferrous ions and the composite cathode interface jointly activate persulfate and hydrogen peroxide generated in the system to produce reactive oxygen species. Iron ions are hydrolyzed to generate iron flocs that adsorb pollutants and degrade intermediate products.
2. The method for synergistic treatment of antibiotic wastewater based on modified carbon nanotube composite cathode using electro-Fenton-electrocoagulation according to claim 1, characterized in that, The volume ratio of concentrated sulfuric acid to concentrated nitric acid used in S1 is 3:
1. The mixed acid modification reaction of multi-walled carbon nanotubes is carried out for 8 hours under constant temperature stirring. The modified product is washed multiple times with acetone until the washing solution is neutral and then dried. The binder is polyvinylidene fluoride, the mass ratio of acid-modified multi-walled carbon nanotubes to polyvinylidene fluoride is 5:1, the organic solvent is N,N-dimethylacetamide, the mixture is ultrasonically dispersed for 40 minutes to form a uniform suspension, the stainless steel substrate coated with the suspension is dried at 80°C for 12 hours, and then compacted to obtain the composite cathode.
3. The method for synergistic treatment of antibiotic wastewater based on modified carbon nanotube composite cathode using electro-Fenton-electrocoagulation according to claim 2, characterized in that, The composite cathode surface forms a uniformly entangled multi-walled carbon nanotube conductive network with mesoporous structure characteristics; when the mass ratio of acid-modified multi-walled carbon nanotubes to polyvinylidene fluoride is 5:1, the cathode exhibits corresponding cyclic voltammetric response and charge transfer impedance characteristics.
4. The method for synergistic treatment of antibiotic wastewater based on modified carbon nanotube composite cathode using electro-Fenton-electrocoagulation according to claim 1, characterized in that, The effective reaction area of both the composite cathode and the iron anode used in S2 is 70 cm². 2 The dimensions are 5cm×7cm×0.1cm; during the pretreatment of the iron anode, it is first immersed in a 1mol / L hydrochloric acid solution for 1 minute, then polished with sandpaper and rinsed with deionized water. The stainless steel substrate is first polished with sandpaper, and then ultrasonically cleaned in acetone, ethanol, and deionized water in sequence.
5. The method for synergistic treatment of antibiotic wastewater based on modified carbon nanotube composite cathode using electro-Fenton-electrocoagulation according to claim 1, characterized in that, The concentration range of sodium sulfate added in S2 is 7~35mM; the concentration range of persulfate added is 1~5mM.
6. The method for synergistic treatment of antibiotic wastewater based on modified carbon nanotube composite cathode using electro-Fenton-electrocoagulation according to claim 1, characterized in that, In S2, the initial pH of the wastewater is adjusted to 3. Through the heterogeneous activation of persulfate and hydrogen peroxide by the interface of multi-walled carbon nanotubes and the iron ions dissolved in the system, ciprofloxacin is removed in the pH range of 2 to 7.
7. The method for synergistic treatment of antibiotic wastewater based on modified carbon nanotube composite cathode using electro-Fenton-electrocoagulation according to claim 1, characterized in that, The reactive oxygen species generated in S3 include hydroxyl radicals, sulfate radicals and singlet oxygen, with hydroxyl radicals being the main reactive oxygen species.
8. The method for synergistic treatment of antibiotic wastewater based on modified carbon nanotube composite cathode using electro-Fenton-electrocoagulation according to claim 1, characterized in that, The iron flocs generated by the hydrolysis of iron ions in S3 are low-crystallinity amorphous iron gel structures with rich hydroxyl groups and adsorbed water on their surface.
9. The method for synergistic treatment of antibiotic wastewater based on modified carbon nanotube composite cathode using electro-Fenton-electrocoagulation according to claim 1, characterized in that, The target pollutant in the antibiotic-containing wastewater to be treated is ciprofloxacin, with an initial concentration range of 10~100 mg / L. Under neutral pH conditions, the removal rate of ciprofloxacin by the system remains above 96%. Under the set reaction conditions, the removal rate of ciprofloxacin reaches 99.68% within 30 minutes, and the removal rate of total organic carbon reaches 74.19%.
10. The method for synergistic treatment of antibiotic wastewater based on modified carbon nanotube composite cathode using electro-Fenton-electrocoagulation according to claim 2, characterized in that, The composite cathode still achieved ciprofloxacin removal after being reused five times; the characteristic peaks of the D and G bands of the cathode Raman spectrum were stable before and after the reaction, the carbon skeleton structure was intact, and the oxygen-containing functional groups on the surface underwent limited reconstruction.