Enhanced mineralization capacity for photocatalytic toluene degradation over Ag3PO4/TiO2: the critical role of oxygen vacancy

Mesoporous disk-like Ag3PO4/TiO2 heterojunctions with rich oxygen vacancies using MIL-125(Ti)-derived TiO2 as support were prepared for photocatalytic degradation toward toluene. The low amount of Ag3PO4 into Ag3PO4/TiO2-10 (1.7 wt% Ag3PO4) greatly improved the toluene mineralization capacity up to 95 %, which was much higher than that of the TiO2 alone (41.3 %). In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) directly verified that the benzene ring was opened rapidly by the Ag3PO4/TiO2-10, while intermediate (like benzaldehyde and benzoic acid) accumulation occurred using pristine TiO2 as photocatalyst. It was demonstrated that Z-scheme heterojunction was formed between Ag3PO4 and TiO2, in which the photo-induced electrons were transferred from conduction band (CB) of the Ag3PO4 to valence band (VB) of the TiO2 under photoexcitation, boosting the generation of reactive oxygen species and inhibiting the photocorrosion of Ag3PO4. Interestingly, quantitative structure-activity relationship suggested that oxygen vacancies as crucial active sites both activated molecular oxygen and captured the photo-induced electrons to form •O2− that dominated in toluene mineralization. This work proved that the construction of Z-scheme heterojunction between MIL-125(Ti)-derived TiO2 and Ag3PO4 solved the inactivation of TiO2 and photocorrosion of Ag3PO4 in photocatalysis, highlighting the role of oxygen vacancy in determining the active species and mineralization degree for photocatalytic toluene elimination.