TiO₂-NiO p-n nanocomposite with enhanced sonophotocatalytic activity under diffused sunlight

TiO₂-NiO composites with p-n junction were developed by assembling p-type NiO on n-type TiO₂ using ultrasound assisted wet impregnation method. The sonophotocatalytic efficiencies of pure TiO₂ and TiO₂-NiO composites were evaluated under diffused sunlight using methyl orange (MO) as a model pollutant. The impregnation of NiO nanoparticles on TiO₂ considerably enhanced the optical absorption in visible region (500-800nm) due to the formation of p-n junctions at the interface between TiO₂ and NiO. The internal electric field induced by the p-n junction led to effective separation of electron-hole pairs and thereby generating a large amount of reactive species for the degradation of MO. The individual effect of ultrasound and diffused sunlight for the degradation of MO was found to be 30% and 6%, respectively. A synergy of 4.8 fold was achieved when ultrasound was combined with photocatalytic degradation process in the presence of diffused sunlight. The sonophotocatalytic activity of TiO₂-NiO photocatalysts with different NiO loading was also evaluated and 10wt% NiO loading was found to be optimal. Moreover, 66% of Total Organic Carbon (TOC) removal was achieved with the optimized TiO₂-NiO composite in 140min. In addition, the TiO₂-NiO composite exhibited an enhanced photocurrent response under visible light illumination.