Influencing investigation of metal ions on heterogeneous catalytic ozonation by ceramic honeycomb for the degradation of nitrobenzene in aqueous solution with neutral pH

Abstract

Abstract Influence of metal ions on heterogeneous catalytic ozonation by ceramic honeycomb for degradation of nitrobenzene in aqueous solution was investigated through the semi-continuous batch experiments to compare apparent reaction rate constant (kapp) and hydroxyl radical ( OH) formation rate ( k · OH ) in the presence of different metal ions including monovalent (Na+, K+ and Ag+), divalent (Zn2+, Ni2+, Co2+, Mn2+, Ca2+, Fe2+, Cu2+ and Mg2+) and trivalent ions (Fe3+, Al3+ and Cr3+). Each metal ion can increase kapp and k · OH in the process of ozonation alone under the present experimental conditions. Except for the positive influence of Mn2+, the others all show the early enhancement effect and the latter inhibition effect on kapp and k · OH , namely existing a critical maximum concentration of metal ion for catalytic ozonation. The ratio of OH initiation from heterogeneous and homogeneous systems decreases with the increasing concentration of metal ion, indicating that the contribution of OH initiation derived from heterogeneous catalytic system decreases. Results confirm that the increasing concentration of metal ion causes the decrease in density of surface hydroxyl groups on ceramic honeycomb, and a novel correlation is established between the density decrease rates of surface hydroxyl group and the standard reduction potentials of metal ions.