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

Abstract

Clean energy, as well as air and water pollution, have become key challenges in today's society. Photocatalysis could be one of the ways to address them. It is considered as an advanced oxidation method that involves light to activate a semiconductor. Semiconductors based on titanium dioxide (TiO2) are widely regarded as photocatalytically active materials. However, the performance of TiO2 has limitations due to its wide band gap (~3.2 eV), and a high recombination rate of the photo-generated electron-hole (e−−h+) pair. To overcome these drawbacks, TiO2 in heterojunction with tungsten trioxide (WO3) is well recognized as one of the most explored systems for photocatalytic applications. Depending on the synthesis technique, and the photocatalytic application, various yet contrasting behaviour can be found in the literature. In this work, the photocatalytic properties of the TiO2/WO3 system were thoroughly examined in the removal of gaseous benzene, and generation of H2. Graphene nanoplatelets were included into the TiO2/WO3 system to increase transport and life-time of the photo-generated exciton. The investigation of various parameters that affected the photocatalytic activity of synthesised materials were carried out, including the ratio of WO3 to TiO2, the presence of graphene, and the nature of the photocatalytic application. It has been observed that the position of the conduction bands played indeed a key-role in case of hydrogen generation. A type II heterojunction was found in the TiO2/WO3 system. Modification of TiO2/WO3 with graphene nanoplatelets improved the photocatalytic hydrogen generation, which was particularly evident in samples with higher WO3 content. The most significant increase in hydrogen production was observed with the photocatalyst with 15 mol% WO3 and 1 wt% graphene − a five-fold increase in yield, compared to its counter-part with no graphene.