Degradation of orange II dye under dark ambient conditions by MeSrCuO (Me = Mg and Ce) metal oxides

This work investigates the catalytic performance and materials property of ternary metal oxides as Me0.25Sr0.25Cu0.5O (Me = Mg and Ce). The catalysts were tested for the heterogeneous degradation of orange II (OII) azo dye in aqueous solution in the dark at room temperature without any other reagents or energy/light irradiation. The MeSrCuO degraded more than 97% OII in the first 30 min, higher than that of binary metal oxides SrCuO (90.5%) or single metal oxides CeO2 (23.6%) and MgO (23.3%). The degradation pathway predominantly occurred by OII contacting the catalyst surface and resulting in the breakdown of azo bonds and the generation of electrons. Partial mineralization of OII dye occurred thus confirming the generation of radical species. Hence, electrons reacted with dissolved O-2 in the OII aqueous solution, leading to the consecutive formation of reactive radical species (e.g., O-2(center dot-), HO2 center dot, H2O2, (OH)-O-center dot). Radical trapping experiment confirmed the presence of radical species. XPS analysis revealed part of Cu2+ underwent irreversible reduction after reaction due to the electron donation from OII with the accompanied increase in Cu+ species in the spent samples. Cycling tests confirmed the reduction of the catalytic activity, clearly indicating that Cu2+ was the active phase in MeSrCuO for the degradation of OII dye.