Peroxydisulfate Activation By ZnFe₂O₄-N-BC Under Visible Light For Degradation Of Antibiotics

Nowadays,the water pollution caused by antibiotics has become increasingly serious.And the advanced oxidation processes（AOPs）are the most fast and cost effective methods of treating antibiotics in wastewater.AOPs based on visible light（Vis）and peroxydisulfate（PDS）show strong degradation ability to refractory antibiotic wastewater.It is important to explore high efficiency activation materials for them application.In this study,visible light responsive ZnFe₂O₄ catalyst was supported on nitrogen-doped wheat straw biochar（N-BC）to improve the stability,recycling and catalytic performance of Vis and PDS.The catalytic properties of Vis,PDS and VIS-PDS systems were investigated respectively.And the relevant activation and degradation mechanisms were elucidated.In addition,the synergistic coefficient and mechanism of Vis-PDS coupling system were analyzed.The specific study findings are as follows:（1）Used wheat straw biochar as the main material,magnetically recyclable ZnFe₂O₄ and N codoped biochar was synthesized by the impregnation-pyrolysis method.Furthermore,the material was characterized by XRD,FTIR,SEM-EDS,BET,VSM,XPS.The results showed that ZnFe₂O₄-N-BC had obvious layered structure and abundant functional groups,which provided sufficient active sites for catalytic reaction.And biochar can improve the photogenerated electron-hole separation efficiency,inhibit the charge recombination,and prolong the charge carriers recombination time.Moreover,the composite material has superparamagnetism,and can still be separated quickly under the external magnetic field.This was convenient for recycling and reuse,and met the application requirements.（2）The results shown that ZnFe₂O₄-N-BC has excellent Vis catalytic performance.The tetracycline（20 mg/L）degradation efficiency reached 91.5%within 90 min under the optimized condition.Further,through the quenching experiments and electron paramagnetic resonance（EPR）tests,the main active substance in the system was h⁺（h⁺>O₂^-·>·OH）.In addition,the main degradation intermediates were investigated by HPLC-MS and the possible transformation pathways were proposed.（3）A series of degradation experiments indicated that ZnFe₂O₄-N-BC has high catalytic performance for PDS.And 99.0%oxytetracycline（50 mg/L）was degraded within 90 min under the optimal conditions.The radical quenching experiment and EPR analysis indicated that the main active substance in ZnFe₂O₄-N-BC/PDS system was measured to be ¹O₂（¹O₂>SO₄^-·>·OH）.Furthermore,the main degradation intermediates were investigated by HPLC-MS and the possible transformation pathways were proposed.（4）By combining Vis with PDS,the synergism and degradation mechanism of ZnFe₂O₄-N-BC bifunctional catalyst in VIS-PDS coupling system were elucidated.Under the same reaction conditions,reaction time and antibiotic,the degradation rate of ZnFe₂O₄-N-BC/Vis system was 36.1%,that of ZnFe₂O₄-N-BC/PDS was 41.9%,and that of ZnFe₂O₄-N-BC/Vis-PDS system was up to 98.5%.In addition,the degradation rate constants of the ZnFe₂O₄-N-BC/Vis-PDS coupling system were 22.7 and 17.4 times higher than those of the ZnFe₂O₄-N-BC/Vis and ZnFe₂O₄-N-BC/PDS systems,respectively.The synergistic efficiencyη_syn was26.3%,and the synergistic coefficient Sc was 9.845.More importantly,the the coupled system showed a wider p H adaptation range,and required less PDS for the same antibiotic concentration compared to the other two single systems.Furthermore,the radical quenching experiment and EPR analysis indicated that such as h⁺,SO₄^-·,·OH,¹O₂ and O₂^-·played an important role,and contribution rate was ranked according to ¹O₂>SO₄^-·>O₂^-·>·OH>h⁺.Finally,the main degradation intermediates were investigated by HPLC-MS and the possible transformation pathways were proposed.