Solar-driven photocatalytic transformation of toluene to benzoic acid over perovskite-type NiTiO3 decorated with reduced GO and g-C3N4 nanosheets

In this work, a perovskite-type nickel (II) titanate (NiTiO3; labeled as NTO) was synthesized and supported with reduced graphene oxide (rGO) and graphitic carbon nitride (CN: g-C3N4) nanosheets by ultrasound-assisted impregnation method. The solar-induced photocatalytic activity and selectivity of the prepared NTO-based perovskite catalysts were evaluated for toluene (TOL) oxidation to benzoic acid (B_COOH) under varying operating conditions. Results revealed that the NTO perovskite exhibited a higher selectivity (95-98%) for the photooxidation of TOL to B_COOH by 125-95 times higher than benzaldehyde (B_CHO) and benzyl alcohol (B_CH2OH) at 1 vol% H2O2 and O2 flow. At zero H2O2 level, the selective oxidation of TOL to B_CHO and B_CH2OH enhanced by 5.4 and 2.7 times as compared with the B_COOH production rate. Besides, NTO@CN (NTN) outperformed NTO@rGO (NTG) for the selective photocatalytic oxidation of TOL to B_COOH in solvent-free and water media under UV, visible, and sunlight irradiation. The production yield of B_COOH was 388.4, 491.2, and 455.6 mu mol/L over NTO, NTN, and NTG, respectively at 1 vol% H2O2 and O2 flow for 3 h of solar irradiation. In both composites, carbon sheets supported the photocatalytic stability of NTO and potential energy for H2O2 decomposition to center dot OH radicals. This is validated by the radical scavenger test and electron para-magnetic resonance (EPR) analysis, which verified the crucial role of hydroxyl (center dot OH) radicals in the photo-catalytic oxidation of TOL to B_COOH. These findings proved the effectiveness of NTN and NTG perovskite composites for solar-induced organic synthesis of benzoic acid from water contaminated with toluene using sunlight (as a renewable energy source).