Engineering the TiO2-Graphene Interface to Enhance Photocatalytic H2 Production

In this work, TiO2-graphene nanocomposites are synthesized with tunable TiO2 crystal facets ({100}, {101}, and {001} facets) through an anion-assisted method. These three TiO2-graphene nanocomposites have similar particle sizes and surface areas; the only difference between them is the crystal facet exposed in TiO2 nanocrystals. UV/Vis spectra show that band structures of TiO2 nanocrystals and TiO2-graphene nanocomposites are dependent on the crystal facets. Time-resolved photoluminescence spectra suggest that the charge-transfer rate between {100} facets and graphene is approximately 1.4 times of that between {001} facets and graphene. Photoelectrochemical measurements also confirm that the charge-separation efficiency between TiO2 and graphene is greatly dependent on the crystal facets. X-ray photoelectron spectroscopy reveals that Ti-C bonds are formed between {100} facets and graphene, while {101} facets and {001} facets are connected with graphene mainly through Ti-O-C bonds. With Ti-C bonds between TiO2 and graphene, TiO2-100-G shows the fastest charge-transfer rate, leading to higher activity in photocatalytic H-2 production from methanol solution. TiO2-101-G with more reductive electrons and medium interfacial charge-transfer rate also shows good H-2 evolution rate. As a result of its disadvantageous electronic structure and interfacial connections, TiO2-001-G shows the lowest H-2 evolution rate. These results suggest that engineering the structures of the TiO2-graphene interface can be an effective strategy to achieve excellent photocatalytic performances.