Influence of mixed-phase TiO2 on the activity of adsorption-plasma photocatalysis for total oxidation of toluene

Herein, the effects of different crystalline phases of TiO2 on the adsorption-plasma photocatalytic oxidation of toluene were investigated. First, photocatalysts loaded on a molecular sieve (MS) were characterised and the catalytic performance of toluene abatement was evaluated in a plasma system. The COX yield of the pure anatase (An) sample outperformed other samples in the adsorption-plasma photocatalytic oxidation process, especially for CO2 yield (69.1%). It was revealed that the highest space-time-yield of 2.35 gco2/Lcat•h was also achieved using plasma-An/MS. However, the highest total toluene abatement (99.5%) was achieved in the plasma-P25/MS system. The plasma-generated UV flux only played a minor role in photocatalyst activation because of the very low UV flux of 2.7 μW/cm2 generated by discharge. For the degradation pathway, compared with the plasma-MS system, byproducts of 1,3-Butadiyne (C4H2), guanidine, methyl- (C2H7N3) did not exist in the TiO2-assisted system, indicating a difference in the toluene degradation pathway. There were no obvious effects of different TiO2 samples on organic byproducts generation, and almost a complete mineralisation of all byproducts was observed after 30 min of treatment, with the exception of ethylamine (C2H7N) and acetaldehyde (C2H4O). Finally, a cycled adsorption-plasma study was conducted to reveal the sustainability of the process. A partial deactivation of plasma-An/MS with less than 7% decrease in CO2 selectivity after 7 cycles was revealed, which is a promising result for use in possible industrial applications.