Biomass components toward H2 and value-added products by sunlight-driven photocatalysis with electronically integrated Auδ−-TiO2: concurrent utilization of electrons and holes

Abstract

While the progress of photocatalytic overall water splitting is hindered mainly by sluggish oxygen evolution kinetics, photocatalytic hydrogen generation using biomass components, such as glycerol as a sacrificial reagent, is a prudent way to efficient hydrogen production. Can we also utilize holes effectively to oxidize the sacrificial agent to value-added products (VAPs)? Towards answering this question of concurrent utilization of electrons and holes, a successful attempt has been made. Herein, we report a facile photo-deposition method to prepare well-dispersed plasmonic Au integrated with P25-TiO2. XPS studies show the nature of gold to be electron-rich or anionic, demonstrating strong electronic integration with titania and possible charge transfer from oxygen-vacancy sites to gold, which in turn helps the simultaneous production of large amounts of H2 (18 mmol h−1 g−1) and VAPs (glycolaldehyde, dihydroxyacetone, and formic acid) formation from glycerol. Elemental mapping and HRTEM images demonstrate a uniform distribution of Au on TiO2, leading to strong Au-TiO2 nano-heterojunctions, and hence a high photocatalytic activity. H2 yield decreases by 4 and 18-fold with glucose and cellulose, respectively, compared to glycerol. A systematic photocatalytic study was carried out under aerobic and anaerobic conditions to understand the glycerol oxidation products. In addition to H2, 4-10% of glycerol in 5 h was oxidized to VAPs in direct sunlight underscoring the high activity associated with Au@TiO2. Further, the C-C cleavage of glycerol also occurs to a significant extent. Hence, significantly prolonged irradiation is expected to result in improved results with longer-chain biomass components to VAPs. It is worth exploring the current approach with other metal-integrated semiconductors with different redox potentials and various biomass components towards H2 and VAP formation.