A 24/7 perovskite catalyst through oxygen vacancy engineering for the rapid catalytic degradation of azo dyes under dark and ambient light conditions

Abstract

Oxygen vacancies are introduced into the perovskite BaSnO₃ through the controlled substitution of Sn⁴⁺ by Cu²⁺, and their presence is confirmed by X-ray photoelectron spectroscopy and electron spin resonance. These electron-rich vacancies actively generate reactive oxygen species (ROS) in the dark (in the absence of light) and under ambient light conditions in an aqueous medium, as verified through scavenger studies and terephthalic acid and nitroblue tetrazolium assays. The role of oxygen vacancies in ROS formation is further validated by comparative substitution of Cu²⁺ and Nb⁵⁺ at the Sn site. Notably, BaSn_1.8Cu_0.2O₃ exhibits ultrafast catalytic degradation of four different toxic azo dyes, achieving more than 90% degradation within 20–60 minutes under both dark and ambient light conditions, surpassing many reported catalysts. In particular, amaranth dye showed 91.1% degradation within 20 minutes, with a high rate constant of 14.5 × 10⁻² min⁻¹ under dark conditions. TOC removal efficiencies of 43.9% and 59.6% for methyl orange and acid orange II, respectively, confirm the substantial mineralisation of the dyes to CO₂ and H₂O. HRMS analysis enables the identification of intermediates and the elucidation of possible degradation pathways, while ECOSAR toxicity predictions indicate that the degradation process reduces the ecotoxicity of the products. Overall, these results highlight the exceptional potential of this system for round-the-clock environmental remediation.