TiO2 photocatalysts have great potential for environmentally friendly applications, such as pollution remediation, artificial photosynthesis and CO2 reduction. Photocatalysis is a green, solar-powered process, which relies on photocatalyst materials absorbing sunlight to create light-generated electrons and holes, which then kick-start a series of chemical reactions, such as CO2 reduction. However, the efficiency of TiO2 photocatalysts is limited because of two drawbacks: they can absorb only UV light, and their light-generated electrons and holes can rapidly recombine before having an opportunity to take part in chemical reactions. To mitigate these problems, a variety of TiO2-based composites have been investigated. Carbon nanomaterials, such as graphene, are some of the most effective materials that can be used form TiO2-based photocatalytic composites. However, the nature of their interaction and the origin of graphene's beneficial effect on the photocatalytic performance is still unclear.
A team of scientists from the University of Sheffield used state-of-the-art theoretical modelling to explore the nature of the interactions between graphene and TiO2. In particular, they went beyond the typical idealised model of perfect, defect-free TiO2/graphene interfaces, to include defects in graphene. Defects, such as carbon vacancies, can form during synthesis of graphene and are likely to be present in low concentrations. The study found that the presence of carbon vacancies dramatically changes the binding at TiO2/graphene interfaces: instead of weak physisorption interactions observed at idealised interfaces, strong covalent bonds are formed between TiO2 and carbon atoms at the defect site.
This change in the nature of binding has a significant effect on the electronic structure of the interfaces: while idealised defect-free interfaces have electronic states localised either only on TiO2 or only on graphene, covalently bonded interfaces form hybridised electronic states with contributions from both graphene and TiO2. "These hybridised states play a key role in the dynamics of light-generated electrons and holes: they are expected to facilitate charge transfer and hinder electron-hole recombination, so that more electrons and holes will be available to take part in photocatalytic reactions", said Natalia Martsinovich, senior author of the paper. "Therefore, defects are not detrimental; instead, they are instrumental in achieving high efficiencies of TiO2/graphene photocatalysts".
The research team expects that these results will encourage experimental researchers to use defect engineering to design graphene-based photocatalytic interfaces with desired defects, as a controllable route to achieving high photocatalytic efficiencies.
About Carbon Future
Carbon Future ( https://www.sciopen.com/journal/2960-0561 ) is an open access, peer-reviewed, and international interdisciplinary journal sponsored by Tsinghua University and published by Tsinghua University Press. It serves as a platform for researchers, scientists, and industry professionals to share their findings and insights on carbon-related materials and processes, including catalysis, energy storage and conversion, as well as low carbon emission process and engineering. It features cutting-edge research articles, insightful reviews, perspectives, highlights, and news and views in the field of carbon. It aims at being a leading journal in related fields. The article publishing charge is covered by the Tsinghua University Press.
