Preparation Of Manganese-Based Oxygen/Sulfide Composites And Study On The Efficiency And Mechanism Of Photocatalytic Degradation Of Ciprofloxacin

With the extensive use of antibiotics by humans,antibiotics continue to accumulate in the aquatic environment.Many kinds of antibiotics,such as macrolides,sulfonamides,fluoroquinolones and tetracyclines,are commonly found in pharmaceutical wastewater,medical wastewater,aquaculture wastewater,domestic sewage and surface water.The continuous accumulation of antibiotics can induce the production,spread and proliferation of drug-resistant bacteria and genes,which seriously threatens the safety of the water ecological environment and the health of humans.Ciprofloxacin（CFX）is one of the most representative quinolone antibiotics,which is frequently detected in the water environment because it is widely used for its broad antibacterial spectrum and strong antibacterial activity.The degradation efficiency of ciprofloxacin by traditional physical/biological methods is limited,therefore it is urgent to develop cost-effective materials and methods to achieve the deep degradation of ciprofloxacin.In recent years,photocatalytic or photoassisted catalytic processes have attracted extensive attention in the field of antibiotics degradation.Numerous studies have shown that semiconducting metal oxides/sulfides could be used as photocatalysts or activators for antibiotic degradation.However,the high recombination rates of photogenerated electron-hole pairs,the limited response ranges to sunlight and the difficult collection of powder materials limit the wide application of photo-oxidation processes.Therefore,in this study,manganese oxides/sulfides immobilized composite catalysts were developed and applied as photocatalysts or peroxymonosulfate（PMS）activators for ciprofloxacin degradation.The results would provide theoretical basis and technical guidance for the practical application of photocatalytic degradation of ciprofloxacin.The main research contents and conclusions are summarized as follows:1.Photocatalytic degradation of ciprofloxacin in water by PS@r GO@MnO₂materialsFirstly,three kinds ofα-MnO₂ with different sizes were prepared by hydrothermal method,and a novel pumice-supported photocatalyst PS@r GO@MnO₂ was further prepared by a two-step hydrothermal method.The XRD,SEM,FT-IR and Raman results showed that the PS@r GO@MnO₂ was successfully synthesized,in which the MnO₂ is flower-shaped and intertwines withγ-type nano-branched chains.Considering the photocatalytic degradation efficiency of CFX and its operating cost,the optimal dosage of PS@r GO@MnO₂ was determined to be 10 g/L,and the initial concentration of CFX was 5 mg/L.And the PS@r GO@MnO₂ was used in a wide p H range,which could effectively degrade CFX under weak acid/base conditions.In addition,the catalyst was easy to recover,and the degradation efficiency of PS@r GO@MnO₂ to CFX could still maintain more than 60%after being recycled three times.Moreover,its good photocatalytic degradation efficiency for CFX in real water bodies were also observed,such as the removal rates of CFX were 73.24%,62.15%,68.33%,67.63%and 61.08%for tap water,secondary effluent,lake water,Fu River water and Xijiang River water,respectively.UV-Vis test showed that the PS@r GO@MnO₂with a band gap of 2.16 e V performed a wider light utilization range than PS@r GO and PS@MnO₂.Photoluminescence,photocurrent response and charge transfer resistance tests demonstrated the fast separation and migration of photogenerated carriers and the reduced recombination rate of electron-hole pairs in the photocatalytic process of PS@r GO@MnO₂.Holes（h⁺）and superoxide radicals（·O₂^-）played the main role in the catalytic degradation of PS@r GO@MnO₂to CFX.Six main degradation products were detected by LC-MS,and degradation pathways were speculated to include the removal of F^-by hydroxylation of the quinoline ring and the cleavage of the piperazine ring.The ecotoxicity of these products was evaluated by ECOSAR software,and results showed that the ecotoxicity of CFX to the water environment was greatly reduced after photocatalytic degradation by PS@r GO@MnO₂.2.Photocatalytic degradation of ciprofloxacin in water by visible light-responsive GF@PPy@MnS materialsTo broaden the photoresponse range of manganese-based catalysts,the conductive polymers polypyrrole（PPy）and MnS were in situ grown on the graphite felt by an ice bath-hydrothermal two-step method to prepare GF@PPy@MnS composite catalyst.The results of XRD,FT-IR and Raman showed the successful preparation of the GF@PPy@MnS.SEM images indicated that PPy is composed of a large number of nanoparticles and MnS is an urchin-shaped nanoflower.EDS test showed that the GF@PPy@MnS is mainly composed of elements such as C,N,O,Mnand S.The effects of PPy loading rates,MnS morphologies,catalyst dosages,initial CFX concentrations and p H values on the photocatalytic efficiencies were all conducted.Under the optimal conditions,the removal rate of CFX under simulated sunlight for 5 h could reach 87%,and the degradation rate of CFX could still reach 78.5%after three cycles.Besides,the CFX degradation rates of GF@PPy@MnS in tap water,secondary effluent,lake water and Fu River water were60.00%,51.00%,54.50%and 58.30%,respectively.UV-Vis tests showed that GF@PPy@MnS could absorb ultraviolet and visible light from 450 to 800 nm.The relatively lower band gap of GF@PPy@MnS（2.31e V）than PPy and MnS could enhance its photocatalytic activity.Free radical quenching experiments showed that the main active species were holes（h⁺）and singlet oxygen（¹O₂）.3.The performance of GF@PPy@MnS based photo-assisted PMS activation process for ciprofloxacin degradation in waterTo further improve the mineralization of GF@PPy@MnS for CFX,the GF@PPy@MnSbased photo-assisted PMS activation process was performed to degrade CFX.When the reaction time was 1 h,the photocatalytic degradation rate of CFX by GF@PPy@MnS was only 48%.And the degradation rate of CFX in PMS activation by xenon lamp irradiation was 62%.Notably,GF@PPy@MnS-based photo-assisted PMS activation could significantly improve the CFX degradation rate to 83%.Under the conditions of catalyst dosage of 1.6 g/L,PMS concentration of 0.6 g/L and xenon lamp irradiation for 1 h,the removal rate of 2 mg/L CFX was about 99.9%.The degradation efficiency of CFX in the GF@PPy@MnS-based photo-assisted PMS activation process was stable in the p H range of 5-9,which was also stable（～89.1%）after recycling 5 times.The degradation rates of CFX in tap water,secondary effluent,lake water and river water were as high as 87.91%,97.41%,89.21%and 81.15%,respectively.The free radical quenching experiments showed that the main active species of the system were singlet oxygen（¹O₂）and holes（h⁺）.Based on the above,two novel immobilized manganese-based photocatalysts were developed in this study to achieve the efficient recovery of catalysts.The photoresponse ranges of the catalysts were improved by material compounding.And PMS activation by photocatalytic reactions was conducted to improve the deep mineralization of CFX.This research would provide technical and theoretical guidance for the application of photocatalytic degradation of antibiotics.