Layered homologous compounds (ZnO)kIn2O3 (k = 3, 5, and 7) as novel photocatalysts for visible-light-driven photocatalytic degradation of textile pollutants

Abstract

Homologous compounds (ZnO)kIn2O3 (hereafter IZO-k, where k = 3, 5, and 7) consist of a layered structure that features optically active and electrically conductive segments together. Herein, these compounds were synthesized using auto-combustion method to assess their photocatalytic performance against Methylene Blue (MB), Indigo Carmine (IC) dyes and an industrial effluent (IE). XRD analysis revealed the smallest crystallite size, while BET studies confirmed higher values of specific surface area (31.60 m2/g), pore diameter (3.42 nm) and pore volume (0.067 cm3/g) for IZO-5. UV-vis spectroscopy revealed the band gap widening with increasing 'k', while IZO-5 and IZO-7 exhibit lower PL emissions in the visible range. The existence of ZnO and In2O3 phases in the synthesized samples is confirmed by FT-IR and Raman analysis. Comparative studies between various exposure conditions revealed that MB degradation was primarily achieved through photocatalysis. With 0.2 g/L IZO-5 dosage, 97.4 % MB, 99 % IC, 82.3 % IE, and 61 % mix dye were degraded in 160 min of visible light exposure. The pH of MB solution was found to be a highly influential factor, with faster photocatalytic efficiency observed under basic conditions. Moreover, the catalyst demonstrated good stability by achieving 86 % MB degradation after three cycles. The experimental analysis followed first-order kinetics with a good fit (R2 > 0.97) for all reactions, as compared to zero- and second-order kinetics. The photocatalytic degradation was dominated by *OH and *O2-, as validated by quenching experiments. The formation of S-scheme heterojunction at the ZnO and In2O3 interface is credited with enabling effective separation of charge carriers, thereby enhancing pollutant degradation efficiency.