Sn and dual-oxygen-vacancy in the Z-scheme BiSnO/Sn/NiAl-layered double hydroxide heterojunction synergistically enhanced photocatalytic activity toward carbon dioxide reduction.

Photocatalytic conversion of carbon dioxide (CO) into high value-added chemicals is an attractive yet challenging process, primarily due to the readily recombination of hole-electron pairs in photocatalysts. Herein, dual-oxygen-vacancy mediated Z-scheme BiSnO/Sn/NiAl-layered double hydroxide (V-20BSL) heterojunctions were hydrothermally synthesized and subsequently modified with Sn monomers to enhance photocatalytic activity toward CO reduction. The abundance of oxygen vacancies endowed the V-20BSL with extended optical adsorption, enhanced charges separation, and superior CO adsorption and activation. The interfacial charges transfer of the V-20BSL was demonstrated to follow a Z-scheme mechanism via photochemical deposition of metal/metal oxide. Under visible light irradiation, the V-20BSL exhibited the highest yields of carbon monoxide (CO) and methane (CH), with values of 72.03 and 0.85 umol·g·h, respectively, which were 2.66 and 1.57 times higher than that of the V-NiAl-layered double hydroxide (V-1LDH). In situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) revealed that carboxylic acid groups (COOH*) and aldehyde groups (CHO*) were the predominant intermediates during CO reduction, and accordingly, possible CO reduction pathways and mechanism were proposed. This study presents a feasible approach to incorporate dual vacancies into Z-scheme heterojunctions for CO reduction.