Oxygen vacancy-mediated BaSn1-x Ni x O3 perovskite as a round-the-clock catalyst for dark and ambient degradation of azo dyes and crystal violet.

The advanced oxidation process involving reactive oxygen species (ROS) is considered a potential method for the degradation of pollutants in water. However, this process requires the application of semiconductors which, upon excitation with light generate electrons and holes on the surfaces that react with oxygen and water respectively to result in reactive oxygen species. There is a need for materials that generate ROS even in the absence of light (dark), so that the process is round the clock and economical. Towards this purpose, we have designed Ni doped BaSnO3 perovskite to show that this system degrades many azo dyes and crystal violet in the dark and under ambient conditions. This study involves the strategic engineering of oxygen vacancies in BaSnO3 perovskites through the controlled aliovalent substitution of Sn4+ with Ni2+ to enable continuous 24-hours environmental remediation. The successful incorporation of Ni into the lattice and the subsequent formation of electron-rich oxygen vacancies were confirmed by X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR), and were supported by a comprehensive suite of analytical techniques, including XRD, FE-SEM/EDS, and FT-IR. These vacancies serve as active catalytic centres, facilitating the generation of ROS in aqueous media under both dark and ambient light conditions, a mechanism further validated by comparative Nb5+ doping. Notably, Congo red dye achieved 98.4% degradation within 15 minutes with a high-rate constant of 30.7 × 10-2 min-1 in the dark. The optimised catalyst, BaSn1-x Ni x O3 where x = 0.2, exhibits exceptional performance, achieving ultrafast degradation. Significant mineralization efficiency, up to 82.6%, is observed for crystal violet as confirmed by total organic carbon (TOC) removal. Identification of intermediates via HR-MS coupled with ECOSAR toxicity modelling, demonstrate that the process effectively yields non-toxic products. Furthermore, ECOSAR toxicity predictions confirm that the degradation process significantly reduces the ecotoxicity of the resulting byproducts. This shift from toxic dyes to less harmful intermediates ensures the safety of the treated waste water for safe aquatic ecosystems.