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

Deep mineralization of C7H8 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 C7H8 and C3H6O 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 (C7H8:C3H6O = 50:20 ppm), with a 97.8% degradation rate for C7H8 and a 100% degradation rate for C3H6O. The molecular O2 is the main active species for the photocatalytic oxidation of C7H8 and C3H6O. Especially, activated C7H8 and C3H6O undergo direct dehydrogenative cross-coupling in a radical state to produce the key intermediate C10H12O. Compared with the primary intermediate benzyl alcohol (ΔG = +1.52 eV), C10H12O (ΔG = −0.47 eV) displays a lower ring-opening energy barrier under •O2– attack, thereby facilitating the selectivity of the photocatalytic oxidation ring-opening reaction of C7H8 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 C7H8, thereby shedding light on innovative strategies for the efficient treatment of mixed polluted gases under real-world conditions.