Sn and dual-oxygen-vacancy in the Z-scheme Bi2Sn2O7/Sn/NiAl-layered double hydroxide heterojunction synergistically enhanced photocatalytic activity toward carbon dioxide reduction

Photocatalytic conversion of carbon dioxide (CO 2 ) 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 Bi 2 Sn 2 O 7 /Sn/NiAl-layered double hydroxide (V O,O -20BSL) heterojunctions were hydrothermally synthesized and subsequently modified with Sn monomers to enhance photocatalytic activity toward CO 2 reduction. The abundance of oxygen vacancies endowed the V O,O -20BSL with extended optical adsorption, enhanced charges separation, and superior CO 2 adsorption and activation. The interfacial charges transfer of the V O,O -20BSL was demonstrated to follow a Z-scheme mechanism via photochemical deposition of metal/metal oxide. Under visible light irradiation, the V O,O -20BSL exhibited the highest yields of carbon monoxide (CO) and methane (CH 4 ), with values of 72.03 and 0.85 umol·g −1 ·h −1 , respectively, which were 2.66 and 1.57 times higher than that of the V O -NiAl-layered double hydroxide (V O -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 2 reduction, and accordingly, possible CO 2 reduction pathways and mechanism were proposed. This study presents a feasible approach to incorporate dual vacancies into Z-scheme heterojunctions for CO 2 reduction.