Trace Amount of SnO2-Decorated ZnSn(OH)6 as Highly Efficient Photocatalyst for Decomposition of Gaseous Benzene: Synthesis, Photocatalytic Activity, and the Unrevealed Synergistic Effect between ZnSn(OH)6 and SnO2

It is still a challenge to develop a high-performance photocatalyst for the abatement of aromatic compounds like benzene (C6H6), which has been regarded as a priority hazardous volatile organic compound substance in the indoor atmosphere. Zinc hydroxystannate (ZnSn(OH)(6), ZHS) is a promising material for this application. However, the key structural features that are responsible for the high activity are still ambiguous. To address this issue, a series of ZHS with different surface properties were hydrothermally synthesized by varying the treatment temperature and the solution pH. Although ZHS can be readily synthesized under a mild reaction condition (temp 90-120 degrees C, pH 4-10), most of the samples were contaminated by a trace amount of low-crystallized SnO2. Pristine ZHS can only be produced in a strong alkaline solution (pH 13). The sample prepared at 120 degrees C in a pH 10 solution shows the highest activity for the degradation of gaseous C6H6 and an efficiency almost 6 times higher than P25 (TiO2). More importantly, no obvious deactivation of the sample and the formation of stable deposits were observed in a long-term reaction for 48 h. Although the SnO2 amount is quite small and bare ZHS shows almost no activity, both of them are indispensable for the degradation of C6H6. SnO2 and ZHS can be understood as photoactive sites to produce charge carriers and preferential sites for the adsorption of O-2, H2O, and C6H6, respectively. A synergistic effect between SnO2 and ZHS in the formation of active radicals and the degradation of C6H6 accounts for the high performance of the SnO2-decorated ZHS.