Enhanced d–d transitions in HKUST/Bi2WO6 nanocomposite mediated visible-light driven selective conversion of benzyl alcohol to benzaldehyde

Abstract

Enhanced solar absorption mediated by the direct involvement of the d–d transition in a suitably selected HKUST/Bi₂WO₆ photocatalyst is reported towards the efficient and selective conversion of benzyl alcohol to benzaldehyde. The selected catalyst possesses a suitable band alignment with a filled d band (2.21 V and 0.65 V) perfectly placed between the valence band (1.77 eV) and conduction band (−1.04 eV) of Bi₂WO₆. This ideal band alignment mediates facile charge mobility from HKUST to Bi₂WO₆ and effects an enhancement in the otherwise Laporte forbidden d–d transitions besides suitably red shifting the existing LMCT (ligand to metal charge transfer) band from 3.4 eV to 2.7 eV. The enhanced d–d transitions along with the redshifted LMCT in the HKUST/Bi₂WO₆ composite effect an efficient oxidative photoconversion of benzyl alcohol to benzaldehyde with a conversion efficiency of 85% and selectivity of 95%. The photocatalytic performance thus achieved is far superior to the performance of the individual HKUST (conversion = 17%; selectivity = 99%) and Bi₂WO₆ (conversion = 29%; selectivity = 90). The performance of HKUST/Bi₂WO₆ is found to be comparable with that of the best catalysts reported in the literature for this conversion.