Heterojunctions have been verified to be effective for separation of photogenerated electrons and holes, therefore improving the photocatalytic efficiency. Meanwhile, cerium oxide (CeO2) is an ideal semiconductor for studying the influence of different exposed crystal facets on regulation of electron transport pathways over heterojunctions. Herein, various kinds of crystal facet-dependent CeO2/g-C3N4 (graphitic carbon nitride) heterojunctions have been successfully engineered as representative model catalysts, and their critical role in regulating charge transfer pathways has been confirmed by systemic characterizations. It was found that facet-dependent heterojunctions followed different charge transport pathways, leading to different H2 evolution activities. In detail, heterojunctions with (100) and (110) exposed surfaces followed the Z-scheme transport pathways, while heterojunction with (111) exposed surface followed the type-II pathway. The H2 evolution rates via these three kinds of heterojunctions were determined to be 3.084, 1.925, and 1.128 mmol·g-1·h-1, respectively, which were 13.3, 7.9, 4.2 times that of bare g-C3N4. It's revealed that the different exposed crystal facets of CeO2 with different Fermi levels determine the transport pathways of photogenerated carriers. This work shows an example of controlling photocatalytic activity by facet-dependent heterojunctions and reveals the importance role of crystal-facet engineering toward heterojunction construction, which is expected to provide an important guidance for the design of new photocatalytic systems.
Keywords: Crystal-facet engineering; Hydrogen evolution; Photocatalysis; Type-II; Z-scheme.
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