Activation Of Peroxymonosulfate By Mn-Based Composite Catalysts For The Degradation Of PPCPs

As three typical pharmaceutical and personal care products(PPCPs),sulfadiazine(SDZ),sulfamethoxazole(SMX)and carbamazepine(CBZ)are widely used in the medicine field and have been frequently detected in the effluent of sewage treatment plant,surface runoff and groundwater.Their potential hazards on environment and human health have attracted wide attention.However,the conventional water treatment processes are unable to remove the three drugs effectively.Therefore,New technologies and materials are needed to degrade such kinds of typical micro-organic matter to reduce the environmental pollution.Sulfate-based advanced oxidation process is a new kind of water treatment technology for the refractory organic pollutants.Manganese based catalysts have the advantages of high catalytic performance,low toxicity and low cost.In this study,three manganese based heterogeneous composite catalysts were fabricated through different methods and utilized for the degradation of sulfadiazine,sulfamethoxazole and carbamazepine via peroxymonosulfate(PMS)activation,respectively.The physical and chemical features of the as-synthesized samples,catalytic performance,structural stability,degradation mechanisms and the toxicity of intermediates were evaluated.Firstly,the magnetic MnFe2O4/δ-MnO2 catalyst was prepared by a two-step hydrothermal method.The crystal phase of MnO2 was determined to be δ type by XRD.The large specific surface area of the composite can provide lots of active sites to promote the degradation efficiency.The SEM analysis confirmed that the magnetic MnFe2O4 particles were coated on the surface of flower-ball like δ-MnO2.The results of VSM analysis proved that the material could be quickly separated by an external magnetic field from the aqueous phase.The results showed that the catalyst with an 20%MnFe2O4 loading displayed the best catalytic efficiency for SDZ degradation.The synergistic effect between MnFe2O4 and δ-MnO2 can effectively promote the degradation of SDZ.The MnFe2O4/δ-MnO2+PMS system exhibited high catalytic ability in a pH range of 3.0-11.0,and 10 mg/L(50 mg/L)of SDZ could be totally removed in 30 min.The apparent activation energy was calculated for 42.7 kJ/mol,which indicated that the degradation reaction was endothermic and the degradation process was mainly ruled by the chemical reaction rate on the catalyst surface.The quenching experiments and EPR analysis showed that SO4·-and ·OH were produced during the redox reactions of manganese and iron ions with different valences,while SO4·-was the main active substances for the degradation of SDZ.According to the nine degradation products obtained by HPLC-MS/MS,four possible degradation pathways of SDZ were proposed.The ecotoxicity of SDZ and intermediate products were compared and the results demonstrated that degradation of SDZ could reduce the pollution threat to water environment.After four times of recycling,the catalyst still maintained a high catalytic capacity.The leaking concentrations of metal ions were lower than the limits of relevant emission standards,which proved the structural stability of the catalyst.Secondly,the g-C3N4 nanosheets were prepared by calcining melamine and MnFe2O4 particles were loaded on the surface of the g-C3N4 nanosheets by a reflux stirring method.The as-synthesized catalyst were used for the degradation of SMX with PMS activation.The SEM results confirmed the successful loading of MnFe2O4 and the BET results indicated the mesoporous structure of catalyst,which could provide more active sites for reaction.The results of comparative experiments showed that the composite catalyst exhibited better catalytic capacity than bare MnFe2O4.The synergistic coefficient between MnFe2O4 and g-C3N4 was calculated for 60.53%,which revealed that the enhancement of catalytic performance was related to the synergistic effect between MnFe2O4 and g-C3N4.The results of factor experiments suggested that the catalyst with 30%MnFe2O4 loading displayed the best catalytic efficiency.In the pH range of 3.0-11.0,the degradation efficiency was increased and then decreased and the catalyst exhibited the best catalytic performance in the neutral environment.HA in water environment showed negligible impact on both degradation efficiencies and reaction rate constants.The quenching experiments and EPR analysis implied that both SO4·-and ·OH were produced during the degradation course with SO4·-played a dominant role.The enhanced catalytic efficiency of the composite was mainly attributed to the g-C3N4 nanosheets acted as the electron bridge between the catalyst and PMS to accelerated the electron transfer rate.Based on the seven degradation products obtained by HPLC-MS/MS analysis,SMX was degraded by S-N bond breaking,hydroxylation of functional groups and oxidation.The ecotoxicity of most intermediates were lower than the ecotoxicity of SMX to the indicator organisms.After three times of recycling,the catalyst still maintained a high catalytic capacity,which proved the structural stability of the catalyst.Thirdly,the bare Mn3O4 was fabricated by hydrothermal method.Then the EGCG coated Mn3O4(E@MO)was synthesized by an ultrasonic mixing method.The SEM results showed that the Mn3O4 particles are regular octahedron with smooth surface and clear edges.The spectra of XRD and FTIR presented that the loading of EGCG had not change the structure of Mn3O4.The E@MO was used to activate PMS for the degradation of CBZ.The comparative experiment proved that the composite catalyst exhibited higher catalytic efficiency(99%)in 30 min,which was 10%higher than the bare Mn3O4(89%).The corresponding reaction rate constant was 1.75 times of the monomer.EGCG coated on the surface of Mn3O4 could reduce the high valence manganese into low valence manganese,then the low valence manganese ions could continue reacted with PMS to generate to SO4·-and kept the high catalytic capacity.In the pH range of 3.0-11.0,the degradation efficiency of CBZ was decreased after an initially increase with increasing of the initial pH.The catalyst displayed the best catalytic performance in the partial neutral(5.8)and neutral environment.The apparent activation energy calculated by Arrhenius equation was proved to be 26.83 kJ/mol,which suggested that increasing temperature could effectively promote the intermolecular movement and accelerate the reaction rate.Cl-in the water exhibited dual effect on CBZ degradation while HCO3-exhibited inhibition on CBZ degradation.The results of quenching experiments and EPR analysis detected that SO4·-and ·OH were the main active components for the degradation of CBZ.As the reaction proceeds,the peak intensity of SO4·-decreased while the peak intensity of ·OH increased.After three times of recycling,the catalyst still maintained a high catalytic capacity and the spectra of XRD and FTIR did not change after the reaction,which suggested the stability of the catalyst.