Oxygen vacancies mediated enhanced photocatalytic activity of band gap engineered BaSn_1−<i>x</i>Cu_<i>x</i>O₃ towards methylene blue degradation under visible and sunlight

Photocatalysis, an advanced oxidation process (AOP), has been well explored as a promising and sustainable technology for tackling environmental pollution. This method involves semiconductors which generate powerful reactive oxygen species, capable of breaking down organic pollutants, on excitation with appropriate light energy. Among the diverse range of oxide semiconductors explored, perovskite oxides are an important family. While BaSnO₃ is a known perovskite photocatalyst, its intrinsic photocatalytic efficiency is limited by poor separation of charge carriers. To overcome this, a proven strategy is to create oxygen vacancies. These defects suppress electron-hole recombination leading to enhanced photocatalytic degradation. Hence, we have synthesized the system BaSn_1-<i>x</i> Cu _<i>x</i> O₃ (<i>x</i> = 0.0 to 0.2) and characterized well. Synthesis of the BaSn_1-<i>x</i> Cu _<i>x</i> O₃ series was successfully carried out <i>via</i> a facile solid-state reaction route. Powder X-ray diffraction (XRD) confirms the phase purity and cubic crystal structure. Fourier transform infrared spectroscopy (FT-IR) confirms the Ba-O, Sn-O, Cu-O vibrations. The surface morphology and particle size distribution examined using field emission scanning electron microscopy (FE-SEM) reveal that the particles are cubic in shape. The optical properties investigated using ultraviolet diffuse reflectance spectroscopy (UV-DRS) indicate the band gaps to be in the range of 3.15-2.42 eV. Photoluminescence study confirms the effective charge carrier separation on doping with Cu. Its photocatalytic activity under visible and sunlight using methylene blue (MB) as a model pollutant has been studied. Indeed, we could enhance the photocatalytic activity of BaSnO₃ and Cu doping at the Sn site (<i>x</i> = 0.2) exhibits 8 times higher rate constant than the parent phase under visible light and 60 times higher under sunlight respectively. The degradation percentages of MB are more than 95% in the doped phase in 30 min in both visible & sunlight whereas the parent phase exhibits it in 3 h. The significantly enhanced activity can be attributed to the oxygen vacancies created due to the substitution of Sn⁴⁺ by Cu²⁺. We have also proposed a possible degradation pathway. This study constitutes the first documentation of the photocatalytic activity of BaSn_1-<i>x</i> Cu _<i>x</i> O_3, thereby opening new avenues for its potential applications in environmental remediation.