| With increasingly strict effluent standard across the world,ozonation has become a conventional technology for advanced wastewater treatment.To meet the discharge and reuse water requirement,enhancing the mineralization of organic pollutants in ozonation has raised concerns from both academia and industry.Heterogeneous catalytic ozonation is a clean technology and attracts extensive attention worldwide due to efficient performance in water treatment.However,most reported catalysts for ozonation are of micro/nanometer size in powder form and are thus difficult to separate from water,which remarkably limited their practical application in full-scale wastewater treatment.Bubble column is the most commonly used reactor for ozonation in water treatment,and millimetric catalysts with spherical shape are particularly desired due to the hydrodynamic considerations.The common industrial catalysts in large particle size usually have insufficient pore structure,specific surface area and active sites for ozonation.Well developed porosity is necessary for catalysts to promote mass transfer in catalytic ozonation.In this study,a mesoporous Ce-Ti-Zr ternary oxide(CTZO)millisphere of large size(0.8-1.0 mm in diameter)and high surface area(180 m2·g-1)was synthesized by impregnation method using Ti-Zr binary oxide(TZO)millisphere as the host.N2 adsorption/desorption,XRD,SEM-EDS,TEM,STEM-EDS,H2-TPR,and XPS were employed to characterize the composite catalyst.Oxalic acid(OA),a typical short-chain#12 pollutant to evaluate the catalytic activity of CTZO.The catalytic mechanism was revealed and catalytic performance of CTZO for degradation of toxic contaminants was then evaluated.The new spacing(0.336 nm)suggested the possible intercalation of CeO2 into the lattice structure of TZO during the calcination step.The mechanical strength of CTZO millisphere was reflected by its compressive load(7.6 N),which fulfilled the hydrodynamic requirement for practical application in column reactors.The fraction of Ce(?)is much higher on the surface of CTZO(49.2%)than CeO2(27.5%),resulting in its high catalytic activity in ozone decomposition and mineralization of OA.The most favorable catalytic ozonation of OA was observed at pH 3.0 and the FTIR analysis proved that the adsorption of OA by CTZO via surface complexation is a requisite step for its ozonation.The EPR analysis and radical scavenging experiment confirmed that·OH was the dominating reactive species in catalytic ozonation of OA by CTZO.XPS revealed that the oxidation of OA was mediated by the Ce(?)/Ce(?)redox cycle,which continously accepts the electron supplied from OA ligand and meanwhile donates electron to activate O3 into·OH.The formation of more Ce(?)and active sites on the surface of CTZO could be due to the mesoporous microenvironment confined by the TZO framework,which could lead to insufficient contact of the impregnated Ce precursor with O2 during the calcination step.Therefore more Ce(?)was retained and incorporated into the TZO framework to form the efficient CTZO millisphere catalyst.The catalytic ozonation of OA by CTZO was enhanced in the presence of sulfate,and EPR analysis revealed that under acidic conditions,·OH radicals were partially converted into sulfate radicals(SO4-·)with longer lifetime over·OH.Eight cyclic runs demonstrated that the CTZO millispheres exhibited high stability for sustainable catalytic ozonation of OA in bubble column reactor without noticeable release of Ce or change of Ce valence state.CTZO was used for degradation of 4-chlorophenol,chloroxylenol,ibuprofen,diclofenac,norfloxacin,and sulfamethoxazole.The removal of TOC was promoted by CTZO to different extents(22.3-42.5%)compared to sole ozonation,which proved the potential of CTZO as a promising catalyst for ozonation of toxic contaminants.This study will provide methodology and technology for the development of efficient ozonation catalysts towards practical application in advanced water treatment. |
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