Mechanism studies on methyl orange dye degradation by perovskite-type LaNiO3-δ under dark ambient conditions

•Methyl orange (MO), a probe compound of the azo dye, was degraded by LaNiO3-δ (LNO) even under dark ambient conditions at a fast rate and high degradation efficiency, compared to the catalysts with similar structures.•The intermediates formed during MO degradation by LNO were identified. MO was shown to degrade via main intermediates, sulfanilic acid anion and N,N-dimethyl-p-phenylenediamine (DPD), by ESI/MS and HPLC.•The mechanism behind MO degradation by LNO under dark ambient conditions was unraveled for the first time. It is a fundamental information on perovskite for dye degradation, especially for lanthanum series of perovskite.