Synthesis of Si O-Bridged g-C3N4/WO3 2D-Heterojunctional Nanocomposites as Efficient Photocatalysts for Aerobic Alcohol Oxidation and Mechanism Insight

It is highly desired to promote the charge transfer and separation of WO3 for a highly efficient green process for photocatalytic aerobic selective alcohol oxidation. In this work, 2D WO3 nanoplates (2D WO) with enlarged surface area and favorable charge separation were successfully fabricated by the phase-separated hydrolysis-solvothermal method. The photoactivities of resulting 2D WO were improved by coupling with 2D g-C3N4 nanosheets (2D CN) to construct the 2D/2D type nanocomposites, and then, they were further enhanced by introducing silicate bridges between 2D WO and CN via a facile wet chemical method. The amount-optimized Si-O-bridged 2D/2D g-C3N4/WO3 nano composite exhibited excellent photoactivity and high selectivity for aerobic selective alcohol oxidation by a 5-fold enhancement compared to bare WO under full-light irradiation, which is attributed to the significantly improved charge separation by the Z-scheme between 2D WO and 2D CN and facilitated charge transfer through the silicate bridges. The Z-scheme charge transfer mechanism was clearly verified by the single-wavelength photocurrent action spectra and single-wavelength fluorescence spectra. Moreover, the subsequent charge-carrier-induced photocatalytic reaction mechanism was investigated by the scavenger trapping and O-18(2) isotope-labeled experiments. It is made evident that the photogenerated holes mainly dominate the selective alcohol oxidation. This present work has shown superior photocatalytic performance among all reported works on the WO3-based photocatalysts for aerobic selective alcohol oxidation to date. The research basis could be provided by this work for the synthesis of highly active WO3-based photocatalysts for aerobic selective organic oxidation.