Dye Degradation Activity and Stability of Perovskite-Type LaCoO_3−x (x=0∼0.075)

Abstract

Perovskite-type LaCoO_3−x(x=0∼0.075) porous powder was synthesized via citrate sol-gel method. With calcination temperature increasing, its crystal structure changed from LaCoO₃ to LaCoO_2.925 with the increase in oxygen vacancy. The synthesized LaCoO_3−x contains a large amount of adsorbed oxygen on its surface due to the existence of oxygen vacancy to some extent. Dye degradation activity of LaCoO_3−x in methyl orange solution was investigated both under the visible light irradiation (>400 nm) and in the dark. LaCoO_3−x exhibited dye degradation activity in the dark when being preserved in methyl orange solution for a long time caused by the reducibility of Co³⁺ in LaCoO_3−x, and then dye molecule was oxidized gradually and slowly. The degradation rate was improved under the visible light due to the optical property of LaCoO_3−x in visible light region. After degradation, methyl orange molecule may be decomposed to acetate group in a small amount. After use for a long time, some Co³⁺ was reduced to Co²⁺ accompanied by the formation of oxygen vacancy, and then LaCoO₃ transformed to LaCoO_2.925 gradually. For LaCoO_3−x calcined at 800°C, LaCoO_3−x perovskite skeleton structure was stable, and can be reused in recycle dye degradation.