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

•Synthesis of NiO assembled TiO2 composites using ultrasound assisted wet impregnation method•Coupling of wide band-gap NiO with TiO2 enhances the absorption to visible region•A synergistic of 4.8 fold is achieved when ultrasound is combined with photocatalysis under diffused sunlight•The reduction of TOC confirms the mineralization of MO dye•TiO2–NiO composite shows higher photocurrent response than bare TiO2 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.