Singlet-oxygen-driven photocatalytic degradation of gaseous formaldehyde and its mechanistic study

Conventional studies on photocatalytic oxidation reaction have focused primarily on hydroxyl radical (•OH) as a major reactive oxygen species (ROS). This perspective may not be suitable for gaseous HCHO photodegradation due to the short lifetime and diffusion length of •OH. Identification of divergent ROS and understanding their characteristics for the gas-phase photocatalytic oxidation are further required. Here, we report a BiOI/TiO2 p-n junction photocatalyst, which uses mobile singlet oxygen (1O2) as the main ROS for gaseous HCHO photooxidation. The introduction of p-n heterojunctions causes a charge transfer that prefers mobile 1O2 generation rather than •OH due to an energetically favorable desorption free energy, accelerating HCHO oxidation. Finally, we demonstrated the photocatalytic filter performance of HCHO-to-CO2 conversion for 150 h with a conversion efficiency of 87 ± 1.3 % in a single-pass reactor. Our systematic study reveals the potential of the overlooked 1O2-driven gaseous HCHO photocatalytic degradation process.