Deficient Bi24O31Br10 as a highly efficient photocatalyst for selective oxidation of benzyl alcohol into benzaldehyde under blue LED irradiation

摘要

The selective oxidation of benzyl alcohol (BA) into benzaldehyde (BAD) is an attractive model reaction for organic synthesis. Using a microwave-calcination route, a novel flower-like Bi24O31Br10 with surface oxygen vacancies and bromine vacancies was successfully synthesized. In the construction of Bi24O31Br10, glucose acts as a complexing, reducing, and structure-directing agent. The as-synthesized Bi24O31Br10 exhibits excellent activity for the photocatalytic aerobic oxidation of BA into BAD, with 99% conversion and 99% selectivity under blue LED irradiation at ambient conditions, which is 3.3-, 4.7-, and 27.8-fold higher than that of TiO2, Bi4O5Br2, and Bi12O17Cl2, respectively. The high selectivity is due to the suitable energy band of the as-synthesized Bi24O31Br10 (E-g = 2.51 eV, valence band potential = +2.38 V), while the high conversion rate is largely due to the efficient separation of photogenerated carriers, surface defects, positively charge surface, and 3D micro/nano-architecture. The primary active species, including h(+), e(-), center dot O-2(-), and center dot OH, are all involved in the photoreaction. On the basis of experimental results and quantum-chemistry calculations, a direct hole oxidative mechanism with two-step dehydrogenation pathway was suggested. In addition, the as-synthesized Bi24O31Br10 catalyst remains stable during the photocatalytic process, indicating its potential for practical applications.