Performance of surface fluorinated P25-TiO2 on the photocatalytic degradation of volatile organic compounds in indoor environment

Abstract

Volatile organic compounds (VOCs) are considered as a major group of indoor air contaminants with several adverse health effects. Photocatalytic oxidation process (PCO) has been applied for the removal of indoor VOCs. In the PCO process, the adsorption extent of water molecules on the surface of photocatalysts is a decisive factor for PCO efficiency. Water molecules contribute in PCO process either as; a) the main hydroxyl radical’s source and enhance the removal efficiency, or b) compete with VOCs to adsorb on the super-hydrophilic surface of P25 and reduce the photodegradation efficiency. In this study, the effects of surface fluorination on the photoactivity and surface hydrophilicity of commercial P25 were investigated. The fluorinated P25 (F-P25) nanoparticles were synthesized to remove methyl ethyl ketone (MEK) from the indoor environment. Surface fluorination formed the surface ≡ Ti – F by an exchange reaction between the surface hydroxyl groups (OH) and fluoride ions (F−) and decreased the water vapor adsorption on the photocatalyst’s surface. Herein, the photocatalytic efficiency of F-P25 was compared to P25 under a continuous-flow condition with a small residence time (0.026 sec) at four different relative humidity levels (0, 20, 40, and 60%). Furthermore, the performances of F-P25 and P25 on the generation of by-products, including formaldehyde and acetaldehyde were also evaluated. The results revealed that the F-P25 enhanced the photodegradation of MEK compared to bare-P25 in all tested relative humidity levels; however, the generation of the by-products increased as relative humidity increased.