| 초록 |
The formation of surface fluorides on TiO2 (F-TiO2) uniquely affects both photocatalytic reactions and photoelectrochemical behaviors. The fluoride adsorption is favored at acidic pH and greatly reduces the positive charge on TiO2 by replacing ≡Ti-OH by ≡Ti-F species. Effects of surface fluorination on the photocatalytic reactivities are very different depending on the kind of substrates to be degraded. The photocurrents collected in TiO2 suspensions, which are mediated by electron shuttles, and short-circuit photocurrents are also markedly reduced in the presence of F-. It is proposed that fluorination enhances OH radical-mediated oxidation rate and inhibits hole-transfer mediated oxidation rate due to the hindered adsorption (or complexation) of substrates on F-TiO2. In addition, ≡Ti-F group seems to act as an electron-trapping site and to reduce interfacial electron transfer rates by tightly holding trapped electrons due to the strong electronegativity of the fluorine. Finally, elementary charge transfer processes on F-TiO2 and their implications to photocatalytic reaction pathways are discussed. |
