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 H2 production from methanol solution. TiO2 -101-G with more reductive electrons and medium interfacial charge-transfer rate also shows good H2 evolution rate. As a result of its disadvantageous electronic structure and interfacial connections, TiO2 -001-G shows the lowest H2 evolution rate. These results suggest that engineering the structures of the TiO2 -graphene interface can be an effective strategy to achieve excellent photocatalytic performances.
For photocatalytic CO 2 reduction, the synergistic effect of Lewis acidity and basicity on CO 2 activation is worthy of study. On the basis of a large number of oxygen defects (Lewis acidity) and hydroxyl groups (Lewis basicity) on the CeO 2 surface, CeO 2 {110} and CeO 2 {100} crystal planes were developed to investigate the synergistic effect on photocatalytic CO 2 reduction. Compared with CeO 2 {100}, the surface oxygen defects were prone to generate on CeO 2 {110}, leading to available visible light absorption and faster photogenerated charge transfer. The experimental results and DFT calculations showed that the OH species on the CeO 2 {110} surface were richer and provided more electron density, i.e., Lewis basicity. Furthermore, the possible adsorption intermediate was investigated and suggested that CeO 2 {110} was more beneficial for the adsorption and activation of CO 2 reactant than CeO 2 {100}, resulting in generation of carboxylate species and •CO 2 − radicals, instead of carbonate. Under the control of surface Lewis acidity and basicity, CeO 2 {110} had superior photocatalytic performance of CO 2 reduction than the {100} plane.
In this work, NiO/CeO2 catalysts were synthesized with tunable CeO2 crystal facets ({110}, {111} and {100} facets) to study the crystal-plane effects on the catalytic properties.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.