Photocatalytic Mineralization Of Indoor Toluene, Deactivation And Regeneration Of TiO₂-Based

Indoor air pollution has attracted much attention in recent years. Photocatalytic oxidation (PCO) method, as a new and effective air purification technique, has a promising application in indoor air purification. In this research, different TiO2-based photocatalysts were prepared using commercial P25 as a precursor. And they were noble metal-loaded photocatalyst Pt/TiO2, titania nanotubes (TNT) and heteroj unction photocatalyst SnO2/TiO2, respectively. X-ray diffraction (XRD), transmission electron microscopy (TEM) equipped with energy dispersive X-ray spectrometer (EDX), and electrochemical characterization methods were used to analyize the physical-chemical performance of the photocatalysts. Toluene was served as the target pollutant, the photocatalytic performance of different TiO2-based photocatalysts were analyzed by detecting the concentration of toluene, CO and CO2 using gas chromatography-flame ionization detector (GC-FID). The mineralization processes of toluene with different photocatalysts under different lights irradiation were investigated from several aspects.The study showed that bare P25 exhibited unsatisfactory photocatalytic activity. All the TiO2-based photocatalysts increased the toluene degradation ratio, complete mineralization rate and photocatalyst degradation rate. Among which, SnO2/TiO2 had the best photocatalytic activity. The toluene degradation ratio and the complete mineralization rate were increased to 100% and 52.1%, respectively. On the other hand, the 254+185 nm vacuum ultraviolet light (VUV) irradiation significantly enhanced the photodegradation of toluene relative to 254 nm ultraviolet light (UV) alone. The improvement of photocatalytic efficiency was owned to the combined effect of VUV and photocatalytic technology which could produce more reactive oxygen species.The deactivation and regeneration characteristics of P25 and SnO2/TiO2 were investigated under UV and VUV sources. The results revealed that after 5 rounds of toluene photodegradation activity test, P25 became deactivated under UV or VUV irradiation. It is worth noting that VUV irradiation can mineralize portion of the intermediate products, adsorbed on the phtotcatalyst surface, much more thoroughly. For SnO2/TiO2, the CO2 formation rate in toluene degradation process declined nearly half after 20 h UV irradiation, and the photocatalysts was deactivated. VUV irradiation was employed to regenerate deactivated SnO2/Tio2, the reactive species such as OH, O2-, O(1D), O(3p), and O3 could be generated, which maked rapid degradation of intermediates on the photocatalyst surface, and then SnO2/TiO2 photocatalytic activity recovered completely. Therefore, UV photodegradation combined with VUV regeneration can be a feasible photocatalytic process, which attributed to the synergistic effect of UV and VUV.