Synergistic Photocatalytic Decomposition of a Volatile Organic Compound Mixture: High Efficiency, Reaction Mechanism, and Long-Term Stability

Photocatalysis technology has been extensively applied for the treatment of volatile organic compounds (VOCs) commonly based on the performance evaluation against a single target component. However, in real situations, a multitude of VOCs are present simultaneously. Other than the studies with photocatalyst design, the mechanisms of mutual effects between different VOCs and the complex reactions at the pollutants/photocatalyst interface are highly delicate to seek for the optimal routes for their decomposition and mineralization. In this work, a comprehensive analysis was made for the destruction of the formaldehyde (CH2O) and toluene (C7H8) mixture. The synergistic efficiency in the decomposition of the CH2O/C7H8 mixture was first established relative to its individual component. The photocatalytic efficiency was maintained for 8 h on the SnO2 photocatalyst, and the durability of the proposed photocatalyst was stable enough even after 30 days of exposure to air. Direct evidence for the synergistic effect on the destruction of the CH2O/C7H8 mixture composition is hypothesized. Most likely, the addition of CH2O into C7H8 turns out to be the rate-determining step in the ring-opening process to promote the decomposition reaction rates for the mixture. It was revealed by gas chromatography–mass spectrometry and density functional theory calculations that the CH2O addition leads to the generation of o-tolualdehyde as key intermediates, which elevated the adsorption and activation of the aromatic ring. This work may offer better insights into the practicality of photocatalysis technology in decomposition of key gaseous pollutants by endowing the "conventional" SnO2 photocatalyst with novel applications.