Unveiling the unconventional roles of methyl number on the ring-opening barrier in photocatalytic decomposition of benzene, toluene and o-xylene

The ring-opening reaction is the rate-determining step for photocatalytic decomposition of aromatic VOCs with different methyl number. However, as a key challenge, the intrinsic relationship between the methyl number and ring-opening reaction efficiency has not been revealed. In order to clarify the ring-opening barriers and enhance the photocatalytic efficiency, the photocatalytic degradation pathway was systematically investigated aiming to elucidate the pivotal roles of methyl number on ring-opening mechanisms. The SnO2 is chosen as a photocatalyst to achieve highly efficient and stable photocatalytic degradation of benzene, toluene, and o-xylene respectively. It is unexpected to discover that the photocatalytic degradation performance and quantum efficiency are significantly elevated along with the increase of methyl number, reaching the highest efficiency for o-xylene with two methyl groups. The photocatalytic degradation efficiency of o-xylene on SnO2 is as high as 78.2 %, much higher than that of toluene (63.4 %) and benzene (55.9 %). The introduction of methyl groups could exert great influence on the distribution of electrons on the phenyl ring, enhance the adsorption and activation of benzene rings, and finally reduce the energy barrier of ring-opening reaction. The methyl number in the benzene ring is dominantly responsible for the elevated decomposition efficiency. This work proposes a new concept in mechanistic understanding of VOCs decomposition and propels the application of photocatalytic technology for efficient degradation of aromatic VOCs.