Engineering ZnSn(OH)6 with ternary active sites-directed hydroxyl vacancies for robust deep C6H6 photo-oxidation: Experiment and DFT calculations

Abstract

The removal mechanisms of low concentration benzene series VOCs over photocatalysts are often ascribed to the surface interface charge transfer or hydroxyl radical (OH) oxidation. Typically, reactive oxygen species (ROSs) contribute to the enhanced photoactivity, however, it remains ambiguous at this stage. Herein, ZnSn(OH)6 with hydroxyl vacancies (ZHS160) is examined to identify the specific ROSs for C6H6 photo-oxidation, namely holes, electrons, H2O and O2/O2− except OH. The well-designed ZHS160 possesses ternary active sites: hydroxyl vacancies for localizing electrons and adsorbing H2O molecules, exposed Zn and Sn sites for adsorbing/activating molecular C6H6 and O2, respectively. Therefore, ZHS160 exemplifies an exceptional photo-oxidation rate of low concentration C6H6 reaching 86%, far exceeding that of pristine ZnSn(OH)6 (22%). Impressively, the formed intermediates are confirmed to gain insights into their formation, chemical and electronic features as empowered by the in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), gas chromatography-mass spectrometry (GC–MS) and density functional theory (DFT) simulations. Accordingly, a distinguishing reaction path based on the pristine ZnSn(OH)6 and ZHS160 is elucidated. As such, these results advance the mechanistic understanding of deep photo-oxidation of C6H6 to CO2 over ZnSn(OH)6 with hydroxyl vacancies.