Selective oxidation of benzyl alcohol into benzaldehyde over semiconductors under visible light: The case of Bi12O17Cl2 nanobelts

In this study we propose several criteria for semiconductor photocatalysts suitable for visible light driven selective oxidation of BA to BAD by employing several literature-reported photocatalysts (P25, g-C3N4, In(OH)xSy, Bi3O4Br, BiOBr and Cu2O) to oxidize BA under visible light, and then demonstrate that the selectivity of photocatalytic oxidation of benzyl alcohol is highly depended on the position of valence band of semiconductors and Bi12O17Cl2 nanobelts could efficiently and selectively oxidize benzyl alcohol into benzaldehyde under visible light via direct hole oxidation. Although the presence of molecular oxygen and the generation of superoxide radicals are important for the selective oxidation of benzyl alcohol, the exact role of molecular oxygen is merely to trap photogenerated electrons to produce superoxide radicals during Bi12O17Cl2 photocatalysis, which could inhibit the recombination of photogenerated charge carries, but might not be involved in the alcohol oxidation directly. The role of molecular oxygen during Bi12O17Cl2 photocatalysis was found to be different from those of TiO2 and g-C3N4 previously reported. This study provides new physical insights for the roles of active species during selective oxidation of alcohol under visible light and the design of novel visible light active photocatalysts for selective oxidation of alcohol.