Sulfated CeO2-TiO2 as H2 evolution photocatalyst: Synergic effects of heterojunction and sulfation on catalyst performance

SO42−/CeO2/TiO2 composite oxides are successfully fabricated via sol-gel method and impregnation process for photocatalytic H2 production. The characterization results from XRD, FTIR and TEM revealed that the heterojunctions were formed by the formation of Ti-O-Ce bond across the SO42−/CeO2/TiO2 interface, which was contributed significantly to separation of photo-generated carriers. Py-FTIR spectra and XPS results indicated that Lewis acid and Brønsted acid sites were formed over the surface of SO42−/CeO2/TiO2 composite, which was owing to SO42− coordinated to the metal on the sample surface. The induced Lewis acid sites could enhance the separation of photogenerated carriers, and Brønsted acid sites could provide protons for photocatalytic H2 production. In addition, the Lewis acidity could facilitate the shift of conduction band minimum to a more negative value, which improves the photocatalytic H2 production capacity of SO42−/CeO2/TiO2. The results of photocatalytic H2 production revealed that SO42−/CeO2/TiO2 composite exhibits superior photocatalytic activity compared to bare CeO2, TiO2 and CeO2-TiO2 composite. Notably, it achieves the average H2 yield rate of 6295.2 μmol·g−1 h−1 over a period of 5 h. Combine the results of spectra analysis and photocatalytic activity H2 evolution, it can be concluded that the synergetic effects of heterojunction structure of CeO2/TiO2 composite and acid impregnation promoted the photocatalyst activity.