Photocatalytic H2O2 Production Over Photocatalysts Prepared By Phosphine-protected Au101 Nanoclusters on WO3
Photocatalytic H2O2 synthesis is an appealing and feasible strategy to replace the energy- intensive, tedious, and waste-generating anthraquinone process. Often, pure metal oxides show low activity in photocatalytic H2O2 production and therefore metal co-catalysts are required to improve the photoactivity. This work investigated photocatalytic H2O2 production using monodisperse gold nanoclusters Au101(PPh3)21Cl5 supported on WO3. From HRTEM imaging, the Au101 size in the uncalcined samples is in the cluster regime (<2 nm) and after calcination at 200 °C the size increases to ca. 4.5 nm. The roles of Au101 have been identified to reduce the charge carrier recombination and provide the active sites for O2 reduction which significantly enhances the photoactivity. Both uncalcined and calcined Au101/WO3 photocatalysts produce over 75 mM g-1 h-1 of H2O2 under UV light irradiation while the pure WO3 is inactive. At early times (up to 30 min), the production rate of H2O2 from calcined Au101/WO3 reaches 173 mM g-1 h-1 and is almost double the rate of the uncalcined catalyst (93 mM g-1 h-1). The higher photoactivity of calcined versus uncalcined Au101/WO3 can be attributed to the aggregated Au101 and removal of phosphine ligands from the Au core as verified by HRTEM and XPS. The reaction rate decreases over time which is attributed to the reverse reaction. Using a simple kinetic model, the rate constant of the H2O2 formation (kf) for uncalcined and calcined Au101/WO3 are 2.07 and 6.31 mM h-1, while the rate constant of the H2O2 decomposition (kd) for uncalcined and calcined Au101/WO3 are 0.49 and 2.93 h-1, respectively. This work highlights a simple preparation of highly active photocatalysts to produce H2O2 derived from Au101 clusters and WO3.