Design, performance, and charge transfer insights into step-scheme zinc hydroxystannate/titanium dioxide heterostructures for enhanced photocatalytic oxidation of gaseous benzene

The design of a photocatalyst is crucial for the efficient photocatalytic oxidation (PCO) of indoor air pollutants like volatile organic compounds (VOCs). A highly effective strategy for enhancing photocatalytic activity is the construction of step (S)-scheme heterojunctions, which are engineered by coupling semiconductors such as n-type zinc hydroxystannate (ZnSn(OH)₆, ZS) with n-type titanium dioxide (TiO₂, T). The potential of the formed ZST photocatalyst is explored for the PCO of 1 ppm benzene under 1 W ultraviolet (UV) irradiation. It achieves a clean air delivery rate of 1.71 L min^-1 with a 10% removal efficiency rate of 21.9 µmol g^-1 h^-1 and a mass-normalized apparent quantum yield of 6.08 ×10^-4 molecule photon^-1 g^-1. The PCO activity of ZST is further assessed under several process variables. In situ DRIFTS analysis indicates that benzene mineralization proceeds through phenolate, acetate, maleate, and methylene reaction intermediates. Theoretical analyses (charge density difference and electron localization function) confirm an interfacial S-scheme electron transfer from ZnSn(OH)₆ to TiO₂. This mechanism effectively separates highly reactive carriers while promoting recombination of less active species for efficient benzene mineralization to carbon dioxide (CO₂) and water (H₂O). These findings provide valuable insights for designing high-performance catalytic systems against robust aromatic hydrocarbons.