K⁺ and CeO₂ nanoparticles modified OMS-2 nanorods for enhanced activity and stability of photocatalytic toluene oxidation: K⁺ charge modulation and mechanistic investigation

For photocatalytic toluene oxidation, available photo-generated charges and active oxygen species are of great importance. Due to the advantages of K+ and CeO2, CeO2/K-OMS-2 (Ce/KM) were prepared for photocatalytic toluene oxidation, which exhibited better activity and stability than that of Ce/0M (no K+) and K-OMS-2. The band structures and DFT calculations revealed that K+ in the K-OMS-2 tunnels changing Fermi levels led to Z-scheme heterojunction formation, and acting as charge modulation kinetically promoted photo-charge transfer. Meanwhile, the charge balance of K+ increased the proportion of Mn3+, leading to the generation of hydroxyl groups for toluene adsorption via strong OH-pi interactions. In addition, oxygen adsorbed on Ce3+ and square-Ce3+-O-Ce4+, and enhanced oxygen migration were observed on Ce/KM, which further interacted with photo-generated charges to generate radicals. In situ DRIFTS and GC-MS suggested the degradation pathway, i.e., the oxidizing radicals on Ce/KM attacked methyl of toluene, formed benzaldehyde, benzoic acid intermediates, opened benzene ring and finally mineralized into carbon dioxide and water. Notably, benzyl alcohol intermediate deposited and poisoned only K-OMS-2, not Ce/KM, confirming the excellent stability of Ce/KM. Furthermore, the effects of the humidity on reaction process were revealed.