Mixed Metal Oxides of the Type CoxZn1-xFe2O4 as Photocatalysts for Malachite Green Degradation Under UV Light Irradiation

Abstract

A combination of thermal and mechanical (high energy ball milling) treatment was applied in an attempt to obtain polycrystalline mixed metal binary and ternary oxides of the type Co_xZn_1-xFe₂O₄ (x=0; 0.25; 0.5; 0.75; 1). The synthetic procedure used successfully produced single-phased, homogeneous ZnFe₂O₄, CoFe₂O₄, and Co_0.75Zn_0.25Fe₂O₄, as well as mixed oxides, whose composition depended both on the duration of the high energy ball milling and the ratio Zn(II)/Co(II). The formation of spinel-like structures was proved by XRD, Mössbauer spectroscopy and Raman spectroscopy. For the characterization of the samples low-temperature N₂ adsorption, UV/Vis spectroscopy and transmission electron microscopy were applied. The energy band gap of the samples was calculated, suggesting they are promising photocatalysts. The decomposition of the Malachite Green in model water solutions under UV-light irradiation was successfully achieved in the presence of the samples as photocatalysts. The highest rate constant was obtained for the sample synthesized at longer milling time in combination with higher Zn(II)/Co(II) ratio. The photocatalytic activity of the ternary mixed oxides was compared with the pure hematite, α-Fe₂O₃, and the binary ZnFe₂O₄ and CoFe₂O₄ ferrites with spinel structure that were treated in the same way. A synergetic effect of α-Fe₂O₃ and the spinel-like structure on the photocatalytic properties of ternary mixed metal oxide was detected.