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.
Understanding the
dynamic structural transformation of subnanometric
metal species is a key to the establishment of the structure–function
relationship for heterogeneous catalysts composed of single atoms
and subnanometric clusters. Unlike noble metal catalysts, the evolution
of non-noble metal catalysts containing singly dispersed atoms and
clusters during redox treatments and under reaction conditions has
not been well understood yet. In this work, with spectroscopic techniques
and aberration-corrected electron microscopy, the control of dynamic
structural transformations of supported CuO
x
species (from single ions to nanoclusters and nanoparticles)
by the combination of the redox and water treatment has been systematically
studied. Furthermore, their catalytic properties for two deNO
x
reactions (NO + CO, NH3 + NO
+ O2) have also been demonstrated to be strongly related
to the dispersion of Cu2+ species, providing insights into
the active sites in these model reactions for deNO
x
applications.
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