《Oxygen Isotope Tracing Study to Directly Reveal the Role of O₂ and H₂O in the Photocatalytic Oxidation Mechanism of Gaseous Monoaromatics》

Graphical Abstract:

Website: https://doi.org/10.1021/acs.est.1c05134

Abstract：

O₂ and H₂O influence photocatalytic oxidation mechanism of gaseous monoaromatics, but still in unclear manner, due to lack of direct evidence. Tracing oxygen atom from ¹⁶O₂ and H₂¹⁸O to intermediate can clarify their roles. Low H₂¹⁸O content suppressed formation of benzenedicarboxaldehydes during oxidation of xylenes and ¹⁶O₂ more affected yield of total intermediates, while neither of them altered amount percentage order of products. Methylbenzaldehydes, methylbenzyl alcohols and benzenedicarboxaldehydes possessed dominant ¹⁶O percentage (≥69.49%), while higher ¹⁸O distribution was observed in methylbenzoic acids and phthalide (≥59.51%). Together with interconversion results of products revealed ¹⁶O₂ determining transformation of xylenes initially to methylbenzaldehydes and then to methylbenzyl alcohols or benzenedicarboxaldehydes, while H₂¹⁸O mainly contributed for conversion of methylbenzaldehydes to methylbenzoic acids or phthalide. Further interaction sites of xylene and its product with H₂O and O₂ were confirmed by molecular dynamic calculations. Same roles of ¹⁶O₂ and H₂¹⁸O in degradation of toluene, ethylbenzene, 1,2,4-trimethylbenzene and 1,3,5-trimethylbenzene were also verified. This is the first time to provide the direct evidence to reveal role of O₂ and H₂O in photocatalytic oxidation mechanism of gaseous monoaromatics. The findings are helpful to achieve controllable product formation from oxidation of monoaromatics and predict their migration process in atmospheric environment.