Ozonation Of Nitrobenzene From Water Using Cerium Loaded Silicon-based Catalysts:Efficiencies And Mechanisms

Cerium(Ce)oxides loaded three silicon-based(Ce/Si)catalysts,silicon spherule(Ce/SS),white carbon black(Ce/WCB)and MCM-41 zeolite(Ce/MCM),were prepared and characterized.Their efficiencies and mechanisms in catalytic ozonation processes(COP)of nitrobenzene removal from water were investigated in the present study.The loadings of Ce oxides increased the catalytic activity relative to silicon-based supports alone.The Ce-O-Si and Si-O(H)-Al structures as well as abundant surface hydroxyl groups(-OH)are the composite active sites for Ce/Si catalysts.The Ce/Si catalysts aided COP(Ce/Si-COP)treatments all doubled the total organic carbon(TOC)removals compared to single ozonation treatment.The different support materials exhibited different chemical processes during the removal of nitrobenzene from water.Ce/SS owns more Ce-O-Si active sites and Ce/MCM has strong adsorption,promoting their catalytic activity.Therefore,Ce/SS-COP(96.77%)and Ce/MCM-COP(92.84%)showed high TOC removals in comparision with Ce/WCB-COP(86.64%),in 60 minute-reaction.The hydroxyl radicals(·OH)mediated oxidation dominates the Ce/Si-COP.Additionally,superoxide radicals(·O2-)and single-line oxygen radicals(1O2)involve in the oxidation.The nitrobenzene first converts to polyhydroxy compounds and benzoquinone under attacks of radicals.And then small molecule intermediates are formed and finally mineralized to CO2 and H2O.This study shows the potential application of silicon-based materials as catalysts in COP that efficiently treat refractory chemical wastewaters.