Construction Of CuFeO₂-based Heterogeneous Fenton Catalyst And Its Degradation Performances For Ofloxacin In Wastewater

Ofloxacin（OFX）,a common quinolone antibiotic,has been widely applied in medicine,animal husbandry,aquaculture and other production fields.Due to its poor bioaccumulation,chemical stability and biodegradability,the widespread production and excessive abuse of OFX pose a potential threat to the ecological environment and human health.Heterogeneous Fenton process is considered to be one of the most commonly used treatment technologies for the removal of quinolone antibiotic wastewater owing to its low cost and high efficiency.However,the traditional Fe-based heterogeneous Fenton catalysts have some problems such as slow Fe²⁺generation,high risk and high cost of H₂O₂transportation and management,which greatly limits its application in wastewater treatment.Based on that,this paper takes CuFeO₂with bimetallic active sites as the research object.In view of its easy agglomeration and the need for additional organic solvents in the preparation process,the heterogeneous photo-electric Fenton system was gradually constructed through oxygen vacancy regulation and system optimization;the key factors and mechanisms affecting the performance of OFX degradation in each system were revealed.The main research results are as follows:（1）In order to solve the problem that the traditional hydrothermal synthesis of CuFeO₂requires the addition of organic reducing agent,the CuFeO₂catalyst was synthesized by a simple one-step hydrothermal method with glucose as reducing agent.A series of characterization techniques confirmed that the prepared CuFeO₂catalyst possessed pure 3R phase,trapezoidal hexahedral structure,and CuFeO₂particles were agglomerated.With OFX as the target pollutant,the CuFeO₂/H₂O₂system was constructed.The effect of CuFeO₂loads,H₂O₂concentration and solution p H on OFX degradation were studied to optimize the degradation parameters.The cycling stability results confirmed that the CuFeO₂catalyst owned good stability after five successive degradation experiments.The free radical capture experiment and electron spin resonance（ESR）spectra displayed that^·OH was the main active radical in CuFeO₂/H₂O₂system.The X-ray photoelectron spectroscopy（XPS）analysis before and after reaction confirmed that bimetallic sites on the surface of CuFeO₂played a key role in the catalytic process.The possible degradation paths were proposed based on the mass spectrum results.Toxicity prediction results showed that the deep oxidative degradation of OFX could weaken the developmental toxicity and mutagenicity of OFX,thus reducing its potential environmental risk.（2）In order to solve the problems of slow Fe²⁺generation and long catalytic reaction time,visible light was introduced into CuFeO₂/H₂O₂system to enhance the oxidative degradation ability of OFX.The light response performances of CuFeO₂were analyzed by UV-Vis diffuse reflectance spectrum and XPS valence band spectrum.The degradation parameters were optimized by a series of single-factor experiments.Under the optimum conditions,namely CuFeO₂dosage of 0.6 g/L,concentration of H₂O₂of 6 m M and p H=3.6,the degradation rate of visible light/CuFeO₂/H₂O₂system was up to 85.3%after 2 h reaction.In addition,the rate constants of OFX degradation by CuFeO₂catalyst activated by H₂O₂under visible light were 774.9 times and 7.8 times higher than that of pure H₂O₂oxidation and pure CuFeO₂adsorption,respectively.The cycle stability results showed that the pure 3R phase CuFeO₂catalyst had good stability after five successive degradation experiments.The free radical capture experiment,ESR and XPS test results displayed that^·OH was the main free radical in visible light/CuFeO₂/H₂O₂system.The possible degradation mechanism was deduced,revealing that the synergistic interaction between bimetallic sites and e^-was the key to the degradation of OFX in the visible light/CuFeO₂/H₂O₂system,and the synergistic interaction between them could accelerate the interfacial cycle of Fe³⁺/Fe²⁺and Cu⁺/Cu²⁺,increase the concentration of reactive radicals in the system,and greatly accelerate the degradation of OFX.Based on theoretical calculation and experimental results,the possible degradation path was proposed.The toxicity prediction results showed that the comprehensive toxicity of OFX was relieved after degradation by visible light/CuFeO₂/H₂O₂system.（3）In order to solve the problems of agglomeration and insufficient catalytic activity in CuFeO₂,PVP/CFO heterogeneous catalyst with rich OVs was successfully prepared by PVP-assisted hydrothermal method.A series of characterizations suggested that PVP modification could not only reduce the agglomeration of CuFeO₂particles,but also produce rich OVs on the surface of CuFeO₂.Photochemical characterization exhibited that PVP/CFO-4 possessed better visible light absorption activity and faster photogenerated carrier separation efficiency than CuFeO₂.Under the optimum reaction conditions,namely,PVP addition of 4 g,PVP/CFO-4 dosage of 0.4 g/L,H₂O₂concentration of 2 m M,and the p H=3.6.After 60 min reaction,PVP/CFO-4 showed excellent OFX degradation performance in visible light+PVP/CFO-4+H₂O₂system,and the degradation efficiency was 94.2%.The results of the cyclic stability experiments showed that the removal rate of OFX by the visible light+PVP/CFO-4+H₂O₂system was only decayed by 11.3%after 10 h continuous reaction.The active substance capture experiment and ESR test results exhibited that^·OH and^·O₂^-were main active radicals in visible light+PVP/CFO-4+H₂O₂system.The proposed degradation mechanism revealed that the OVs in the surface of PVP/CFO-4 and e^-produced under visible light could accelerate the interfacial cycling of Fe³⁺/Fe²⁺and Cu⁺/Cu²⁺to promote the activation of H₂O₂and thus accelerate the degradation of OFX.Based on HPLC/MS analysis and Fukui function calculation results,the degradation intermediates of OFX in visible light+PVP/CFO-4+H₂O₂system were identified,and their possible degradation paths were proposed.The toxicity prediction results showed that the comprehensive toxicity of OFX was relieved after degradation by visible light+PVP/CFO-4+H₂O₂system.（4）In order to further accelerate the regeneration of Fe²⁺and solve the problem of the high cost and high explosion risk of H₂O₂in storage and transportation,the heterogeneous photo-electric Fenton system was constructed by coupling the prepared PVP/CFO-4 catalyst with the carbon felt cathode.The effects of different carbon felt materials,current density,solution p H value and other parameters on the production of H₂O₂at the cathode were discussed systematically.By optimizing the experimental parameters,under the conditions of catalyst dosage of 0.4 g/L,current density of 4 m A/cm²,and initial p H of 3.6,the OFX removal rate of OFX in heterogeneous photo-electric Fenton system reached 94.3%at 120min.The results of cyclic stability showed that the PVP/CFO-4 catalyst exhibited good stability,and the OFX efficiency decreased by 12.3%after five successive degradations.The free radical capture experiment and ESR test results showed that^·OH was the main active free radical in the heterogeneous photo-electric Fenton system;XPS spectra before and after the degradation reaction displayed that H₂O₂produced by carbon felt cathode could produce a large number of active radicals under the action of PVP/CFO-4,photogenerated electrons and electric field;The introduction of abundant OVs,visible light and electric field could accelerate the redox cycle of Fe³⁺/Fe²⁺and Cu⁺/Cu^2+-on the surface of PVP/CFO-4,and thus promote the degradation of OFX.The possible degradation paths were proposed based on the mass spectrogram results.The results of toxicity prediction analysis suggested that the comprehensive toxicity of OFX was relieved after the degradation of the system.