Oxygen Vacancy-Mediated Z-Scheme Charge Transfer in a 2D/1D B-Doped g-C3N4/rGO/TiO2 Heterojunction Visible Light-Driven Photocatalyst for Simultaneous/Efficient Oxygen Reduction Reaction and Alcohol Oxidation.

Abstract

Hydrogen peroxide (H2O2) is a powerful oxidant that directly or indirectly oxidizes many organic and inorganic contaminants. The photocatalytic generation of H2O2 is achieved by using a semiconductor photocatalyst in the presence of alcohol as a proton source. Herein, we have synthesized oxygen vacancy (Ov)-mediated TiO2/B-doped g-C3N4/rGO (TBCN@rGO) ternary heterostructures by a simple hydrothermal technique. Several characterization techniques were employed to explore the existence of oxygen vacancies in the crystal structure and investigate their impact on the optoelectronic properties of the catalyst. Oxygen vacancies offered additional sites for adsorbing molecular oxygen, activating alcohols, and facilitating electron migration from TBCN@rGO to the surface-adsorbed O2. The defect creation (oxygen vacancy) and Z-scheme mechanistic pathways create a suitable platform for generating H2O2 by two-electron reduction processes. The optimized catalyst showed the highest photocatalytic H2O2 evolution rate of 172 μmol/h, which is 1.9 and 2.5 times greater than that of TBCN and BCN, respectively. The photocatalytic oxidation of various lignocellulose-derived alcohols (such as furfural alcohol and vanillyl alcohol) and benzyl alcohol was also achieved. Photocatalytic activity data, physicochemical and optoelectronic features, and trapping experiments were conducted to elucidate the structure-activity relationships. The TBCN@rGO acts as a multifunctional Z-scheme photocatalyst having an oxygen vacancy, modulates surface acidity-basicity required for the adsorption and activation of the reactant molecules, and displays excellent photocatalytic performance due to the formation of a large number of active surface sites, increased electrical conductivity, improved charge transfer properties, outstanding photostability, and reusability. The present study establishes a unique strategy for improving H2O2 generation and alcohol oxidation activity and also provides insights into the significance of a surface vacancy in the semiconductor photocatalyst.