TiO2 supported-reduced graphene oxide co-doped with gallium and sulfur as an efficient heterogeneous catalyst for the selective photochemical oxidation of alcohols; DFT and mechanism insights

Abstract

Achieving organic transformation reactions using green synthesis methods under mild conditions is always an aspiration of scientists. In this study, Ga, S co-doped TiO2/reduced graphene oxide (GaxSy@TRG) nanocomposite was synthesized by an innovative surfactant-free ultrasonic-assisted solvothermal method and used to catalyze the selective photocatalytic oxidation of benzyl alcohol under visible light irradiation. The prepared photocatalyst was analyzed via XRD, FT-IR, Raman, N2 adsorption–desorption, SEM, TEM, EDX, ICP-MS, UV–Vis absorption, and electrochemical impedance spectroscopy (EIS) measurement. The characterization outcomes indicated the prepared co-doped TiO2 nanoparticles with anatase crystal structure possessed a mesoporous texture and were uniformly distributed on the RGO surface. The conversion of GO to RGO was confirmed through FT-IR and Raman spectra. The prepared nanocomposites were examined for their ability in artificial photocatalysis and displayed remarkable catalytic activity for the selective oxidation of alcohols into benzaldehyde. The co-doped catalysts showed significantly enhanced photocatalytic ability, due to improved photogenerated electrons transfer, enhanced charge carriers separation and extended optical absorption to the visible light range. Moreover, the synergistic effect of dopants that could act as electron trapping centers and RGO as a powerful acceptor material efficiently reduced photogenerated electron-hole recombination and promoted charge migration. A high conversion rate of 85% was obtained over the Ga5.0S10.0@TRG photocatalyst after 110 min under visible light irradiation. The results from density functional theory (DFT) calculations revealed that the hybridization of Ga 4s and S 3p orbitals with valance band can remarkably affect the decreasing of band gap energy. The mechanism of photocatalytic oxidation of benzyl alcohol under visible light irradiation was proposed using the combination of experimental and computational methods.