Effects of surface fluorination of TiO2 on photocatalytic oxidation of gaseous acetaldehyde

Surface fluorinated TiO2 (F-TiO2) shows interesting photocatalytic behaviors that are distinguished from bare TiO2 in many ways. The effects of surface fluorination of TiO2 on the photocatalytic oxidation (PCO) of acetaldehyde under the ambient air conditions were investigated in this study. Both bare TiO2 and F-TiO2 films were compared for the adsorption and degradation of acetaldehyde. The surface fluorination of TiO2 markedly inhibited the adsorption of acetaldehyde and the total amount of CH3CHO adsorbed on F-TiO2 was as low as 30% of that on bare TiO2. However, the PCO rate constant for CO2 production was highly enhanced with F-TiO2 on the contrary. The total amount of CH3CHO adsorbed on the photocatalyst films could be quantitatively converted into CO2. The first-order rate constant for the photocatalytic generation of CO2 increased by 2.5 times upon the surface fluorination of TiO2. The effects of surface fluorination on the dark adsorption of acetaldehyde and the PCO kinetics were compared and discussed in detail. The present study demonstrates that the enhanced PCO activity with F-TiO2 is also observed at the F-TiO2/air interface while the similar phenomenon was previously observed at the F-TiO2/water interface. The enhanced PCO activities of F-TiO2 might be apparently masked by the hindered adsorption of substrates on F-TiO2 but the PCO kinetics on F-TiO2 is indeed much faster than that on bare TiO2.