TiO₂/WO₃/graphene for photocatalytic H₂ generation and benzene removal: Widely employed still an ambiguous system

Clean energy, as well as air and water pollution, have emerged as significant challenges in today's society. Photocatalysis offers a potential solution to address these issues. It is an advanced oxidation process that utilises light to activate a semiconductor. Among photocatalytically active materials, titanium dioxide (TiO2) semiconductors are widely recognised. However, the performance of TiO2 is hindered by its wide band gap (similar to 3.2 eV) and high recombination rate of photo-generated electron-hole (e(-)-h(+)) pairs. To overcome these limitations, TiO2 in heterojunction with tungsten trioxide (WO3) has gained substantial attention for various photocatalytic applications. However, the literature reports contradictory behaviours due to variations in synthesis techniques and photocatalytic applications.In this study, we extensively investigated the photocatalytic properties of the TiO2/WO3 system for the removal of gaseous benzene, and H-2 generation. To enhance the transport and lifetime of photo-generated excitons, graphene nanoplatelets were incorporated into the TiO2/WO3 system. We examined several parameters that influenced the photocatalytic activity of the synthesised materials, including the WO3 to TiO2 ratio, the presence of graphene, and the specific photocatalytic application. Interestingly, the position of the conduction bands played a crucial role in hydrogen generation. The TiO2/WO3 system exhibited a type-II heterojunction. While the hybridisation of TiO2 with WO3 was found to be detrimental to light-induced benzene removal and H-2 generation, the modification of TiO2/WO3 with graphene nanoplatelets significantly improved the photocatalytic hydrogen generation. Notably, the specimen with 15 mol% WO3 and 1 wt% graphene demonstrated a five-fold increase in yield compared to its counterpart without graphene. These findings provide valuable insights for data-driven catalysis research.