Mechanism of heterogeneous catalytic ozonation of p-chloronitrobenzene in aqueous solution with iron silicate dried at different temperatures

Abstract

The degradation efficiencies of p-chloronitrobenzene (pCNB) in aqueous solution by processes employing ozone alone and ozone/iron silicates based on iron silicates dried at 60, 250, 600, or 800°C were investigated. The results demonstrated that iron silicate dried at 60°C possessed better catalytic capacity for the ozonation of pCNB than that dried at higher temperatures owing to increased concentrations of hydrogen peroxide (H2O2) and the formation of hydroxyl radicals (⋅OH). Adsorption of pCNB on the surface of iron silicate exhibited no remarkable influence on the degradation efficiency of pCNB. An increase in the drying temperature was found to slightly increase the adsorption ability and significantly reduce the catalytic activity of the iron silicate. Because of the formation of a new crystalline phase, the catalytic activity of iron silicate dried at 800°C was the lowest. The results of the mechanism analysis suggest that Fe2O3, FeOOH, and silicato-iron(III) surface complexes are the dominant components of catalytic activity in the iron silicate catalytic ozonation of pCNB. Moreover, the surface hydroxyl groups of the iron silicate determine the initiation of ⋅OH from ozone decomposition.