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

Abstract

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