Photocatalytic degradation of VOCs on various commercial titanium dioxides: Impact of operating parameters on removal efficiency and by-products generation

Ultraviolet photocatalytic oxidation (UVPCO) is regarded as one of the promising technologies for indoor air remediation. The present study examines the photocatalytic activity of four commercialized titanium dioxide photocatalysts (P25, PC500, UV100, and S5-300A) in a small-scale single-pass continuous flow reactor. Challenge compounds have been chosen from two prevalent VOC families in indoor environment: toluene (aromatics) and methyl ethyl ketone (ketones). The influence of key experimental conditions including concentration (100-1000 ppb), relative humidity (0-50% at 23 °C), light intensity (1.25-5 W m−2), and residence time (0.02-0.1 s) on removal efficiency are evaluated. Due to the fact that one of the main shortcomings of PCO air purifiers is by-products generation, a special emphasis is put on identification and quantification of gaseous by-products using HPLC and GC-MS methods. The obtained efficiencies on various photocatalysts are explained considering crystalinity, crystalline phase, crystal size, surface area, and population of surface hydroxyl groups. Despite possessing lower crystalinity, PC500, UV100 and S5-300A outperformed P25 in toluene and MEK removal efficiency, primarily owed to their larger surface area, smaller crystal size, and higher concentration of surface hydroxyl groups. Acetone, acetaldehyde, and formaldehyde were identified as the main gaseous by-products in PCO of toluene and MEK.