Exploring the photocatalytic conversion mechanism of gaseous formaldehyde degradation on TiO2–x-OV surface

To understand the conversion mechanism of photocatalytic gaseous formaldehyde (HCHO) degradation, strontium (Sr)-doped TiO 2– x –OV catalysts was designed and synthesized in this study, with comparable HCHO removal performance. Our results proved that foreign-element doping reduced Ti 4+ to the lower oxidation state Ti (4– x )+ , and that the internal charge kinetics was largely facilitated by the unbalanced electron distribution . Oxygen vacancies (OVs) were developed spontaneously to realize an electron-localized phenomenon in TiO 2– x –OV, thereby boosting O 2 adsorption and activation for the enhanced generation of reactive oxygen species (ROS). At the chemisorption stage, in-situ DRIFTS spectra and density functional theory calculation results revealed that surface adsorbed O 2 (O ads ) and lattice O (O lat ) engaged in the isomerisation of HCHO to dioxymethylene (DOM) on TiO 2– x –OV and TiO 2 , respectively. Time-resolved DRIFTS spectra under light irradiation revealed that the DOM was then converted to formate and thoroughly oxidized to CO 2 and H 2 O in TiO 2– x –OV. While bicarbonate byproducts were detected from DOM hydroxylation or possible side conversion of CO 2 in TiO 2 , owing to insufficient consumption of surface hydroxyl. Our study enhances the understanding on the photocatalytic oxidation of HCHO, thereby promoting the practical application in indoor air purification .