Catalytic Ozonation of Herbicide 2,4-D over Cobalt Oxide Supported on Mesoporous Zirconia

Abstract

Cobalt oxide was supported on ordered mesoporous zirconia (MZ) by wet impregnation, drying, water washing, and calcinations with cobalt acetate tetrahydrate as the metal precursor for the first time. The material (CoOx/MZIW) was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, temperature-programmed reduction, and UV−vis diffuse reflectance spectra measurement. The studies showed that the [Co(H2O)6]2+ interacted strongly with surface hydroxyls of mesoporous zirconia, leading to a highly dispersed CoOx layer. The CoOx existed mainly as Co3O4 phase. Furthermore, the catalyst was found to be highly effective for the mineralization of 2,4-dichlorophenoxyacetic acid (2,4-D) aqueous solution with ozone. The multivalence oxidation states and high dispersion of CoOx enhanced the interfacial electron transfer, causing the higher catalytic reactivity. On the basis of all information obtained under different experimental conditions, CoOx/MZIW enhanced the mineralization of 2,4-D by the formation of the hydroxyl radical (•OH) resulting from the catalytic decomposition of ozone.