Solar active heterojunction of p-CaFe2O4/n-ZnO for photoredox reactions

Abstract

Abstract In order to enable the solar activity of ZnO and to reduce the rate of recombination of the electron–hole in the use of Ca ferrite for photoredox reaction, heterojunction composite of these two semiconductors was prepared and characterized. The solar activity of the heterojunction was determined in two separate synthetic waste waters containing Rhodamine B (RhB) and Cr (VI). The underlying mechanisms of the RhB decolourization/mineralization and Cr (VI) reduction to Cr (III) were elucidated. Within the calcination temperature and precursors combination ratios (i.e. Ca Ferrite and ZnO ratio) studied, the optimum photoredox efficiency was achieved at 500 °C and precursors combination ratio of 1:1. The SEM analysis and elemental mapping showed an even dispersion of the precursors mix. The presence of Ca Ferrite conferred solar activity and narrowed the band gap of the heterojunction. The photoluminescence spectra and electro impedance spectra showed that the recombination rate of the heterojunction was lowered than that of any of the precursors. The fitting of the time–concentration profiles of the RhB decolourization/mineralization and Cr(VI) reduction to the pseudo first order kinetic equation showed that the values of the rate constants greatly depended on the initial pollutant concentrations. While all the generated reactive species were found to be responsible for the decolourization/mineralization of RhB, the superoxide was the sole reactive species ascertained for the Cr (VI) reduction to Cr (III).