Charge separation manipulation in lead-free Cs3Sb2Br9/WO3 heterojunction for efficient green-light-driven oxidation of benzyl alcohol and mechanistic insights

Abstract

Herein, we report an effective strategy to suppress charge recombination in Cs3Sb2Br9 (CSB) photocatalyst by integrating it with electron storing semiconductor, WO3. The resulting Cs3Sb2Br9/WO3 (CSBW) heterojunction is investigated for its charge carrier dynamics and photocatalytic activity via the selective oxidation of benzyl alcohol (BA) to benzaldehyde. The CSBW heterojunction exhibits nearly three-fold enhancement in the BA conversion rate (7,995 μmol g-1 h-1) compared to the pristine CSB (2,892 μmol g-1 h-1), while WO3 shows negligible activity. By selectively using green light to mainly activate the CSB component, we clearly isolated the electron-accepting ability of the WO3 from its self-photoactivation, uncovering the role of WO3 in the CSBW composite. Both experimental and theoretical studies reveal that electrons, transferred from the CSB component, are trapped at the reduced W5+ site within the WO3, thereby verifying an electron sink function of WO3 which effectively suppresses the undesirable charge carrier recombination in the CSBW photocatalyst. Through this electron transfer and trapping mechanism presumably via Sb–O and Cs–O bonds, the photoinduced holes remaining on the CSB are efficiently isolated and participates in the selective oxidation, promoting the overall photocatalytic activity of the CSBW heterostructure. Mechanistic studies employing Hammett plot analysis, radical trapping and scavenger tests, and DFT calculations indicate that BA oxidation proceeds predominantly via carbon-centered radical intermediate (PhCH•OH), where photoinduced hole serves as the key active species. This work demonstrates an alternative approach to efficiently suppress the rapid electron hole recombination which is a critical bottleneck in low-dimensional, lead-free halide perovskites, thereby advancing their utilization in visible-light driven photocatalysis and related applications.