Synergistic Activation of Small Molecules and Free Radicals for the Deep Mineralization of Mixed VOCs

Abstract

Deep mineralization of C 7 H 8 is often impeded by an ambiguous understanding of the key contributors to active species and the mechanism of benzene ring activation. Herein, the implementation of ZnSn(OH) 6 as a photocatalyst for the degradation of a mixture of C 7 H 8 and C 3 H 6 O aims to investigate the synergistic activation effects between small molecules and reactive free radicals. Upon irradiation, the catalyst exhibits a remarkable average decomposition efficiency of 98.42% toward the mixture (C 7 H 8 :C 3 H 6 O = 50:20 ppm), with a 97.8% degradation rate for C 7 H 8 and a 100% degradation rate for C 3 H 6 O. The molecular O 2 is the main active species for the photocatalytic oxidation of C 7 H 8 and C 3 H 6 O. Especially, activated C 7 H 8 and C 3 H 6 O undergo direct dehydrogenative cross-coupling in a radical state to produce the key intermediate C 10 H 12 O. Compared with the primary intermediate benzyl alcohol (ΔG = +1.52 eV), C 10 H 12 O (ΔG = −0.47 eV) displays a lower ring-opening energy barrier under • O 2− attack, thereby facilitating the selectivity of the photocatalytic oxidation ring-opening reaction of C 7 H 8 and the photodegradation of the mixture. The present research delves into the collaborative interplay between small molecules and reactive free radicals during the mineralization process of C 7 H 8 , thereby shedding light on innovative strategies for the efficient treatment of mixed polluted gases under real-world conditions.