Photocatalytic destruction of volatile aromatic compounds by platinized titanium dioxide in relation to the relative effect of the number of methyl groups on the benzene ring

Abstract

The photocatalytic destruction (PCD) of volatile organic compounds (VOC) into environmentally benign compounds is one of the most ideal routes for the management of indoor air quality. It is nevertheless not easy to achieve the mineralization of aromatic VOC through PCD technology because of their recalcitrant structures (i.e., conjugated π benzene ring). In this research, the PCD potential against three model aromatic hydrocarbons (i.e., benzene (B), toluene (T), and m-xylene (X): namely, BTX) has been explored using a titanium dioxide (TiO2) supported platinum (Pt) catalyst after the high-temperature hydrogen (H2)-based reduction (R) pre-treatment (i.e., Pt/TiO2-R). The effects of the key process variables (e.g., relative humidity (RH), oxygen (O2) content, flow rate, VOC concentration, and the co-presence of VOC) on the PCD efficiency and related mechanisms were also assessed in detail. The PCD efficiency is seen to increase with the rise in the increasing number of methyl groups on the benzene ring (in the order of benzene (46.5%), toluene (68.2%), and m-xylene (95.9%)), as the adsorption and activation of the VOC molecule on the photocatalyst surface are promoted by the increased distribution of electrons on the benzene ring. The BTX were oxidated subsequently by the photogenerated reactive oxygen species (ROS), i.e., the hydroxyl radicals (•OH) and superoxide anion radicals (•O2−). The overall results of this study are expected to help expand the applicability of photocatalysis towards air quality management by offering detailed insights into the factors and processes governing the photocatalytic decomposition of aromatic VOCs.