Solar Degradation of Methyl Orange over La(Mn,Co)O3 Nano-perovskites and Thin Films

Abstract

The substantial release of azo dyes presents an environmental and public health challenge due to their mutagenic, light-absorbing properties and their long life time. Photocatalytic degradation of these dyes could support regular wastewater treatment in purifying the process effluents of the textile industry. In this work, LaCoO3, LaMnO3 and La2CoMnO6 nanoparticles were synthesized using a citrate sol-gel method, and characterized using X-ray diffraction, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy and bright-field transmission electron microscopy. Using methyl orange as a model compound, and following the photobleaching process using in-situ UV-Vis spectroscopy, the as-synthesized LaCoO3 and La2CoMnO6 nanoparticles were demonstrated to be capable of photocatalytic degradation under visible light, although not unassisted: the degradation proceeded only at a pH of 3, or with the addition of the electron acceptor K2S2O8. Moreover, the La2CoMnO6 nanoparticles showed greater catalytic activity than LaCoO3. Additionally, LaCoO3 and La2CoMnO6 thin films were deposited on Nb–SrTiO3 by means of pulsed laser deposition and studied by in-situ reflection high-energy electron diffraction, high-resolution X-ray diffraction, atomic force microscopy and X-ray absorption spectroscopy. While these films were intended as model surfaces for mechanistic analysis of the nanoparticle catalysts, their tensile strain, as a result of lattice mismatch to the substrate, resulted in electronic states diverging from bulk.