Synthesis and photocatalytic activity of ferrites under visible light: A review

This review presents the use of ferrites in photocatalytic conversion of visible solar energy to generate e(-)/h(+), which in turn produce reactive oxygen species through redox processes, for the degradation of the contaminants. Spinel ferrites have a relatively narrow band gap (similar to 2.0 eV) making them capable of such processes. Synthesis approaches of ferrites include thermal methods, sol-gel and citrate methods, co-precipitation, and solid-state reactions. Different techniques to characterize ferrites are X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning-electron microscopy (SEM), and transmission electron microscopy (TEM). Ferrites have been applied as photocatalysts alone, in composites with other photocatalysts, as well as with other oxidants such as H2O2. Ferrites are effective in each case, however when used as composite photocatalysts their degradation efficiency are enhanced. Combination of ferrites with H2O2 either under light irradiation or dark conditions, a Fenton-type system is created, which produces hydroxyl radicals to enhance the degradation processes. Examples are presented for applications of ferrites for the degradation and/or adsorption of a number of different contaminants for environmental purification including inorganics, bacteria, and large organic molecules such as dyes. (C) 2011 Elsevier B.V. All rights reserved.