title: Photocatalytic reactivities of Nafion-coated TiO2 for the degradation of charged organic compounds under UV or visible light.
abstract: Nafion (perfluorinated polymer with sulfonate groups)-coated TiO2 particles (Nf/TiO2) were prepared and their reactivities for the photocatalytic degradation (PCD) of charged organic substrates were investigated. The presence of Nafion adlayers drastically changed the positive TiO2 surface charge to a negative one over the entire pH range and significantly influenced the PCD kinetics and mechanisms. The UV-induced PCD of tetramethylammonium (TMA; cationic substrate) was greatly enhanced in the presence of Nafion adlayers on TiO2 because the ion-exchange sites within the Nafion can hold cationic substrates. On the other hand, despite the unfavorable electrostatic interaction between the Nf/TiO2 and anionic substrates, the PCD of dichloroacetate (DCA) and acid orange 7 (AO7) with Nf/TiO2 was not significantly inhibited. The visible-light-sensitized degradation of dyes was enhanced with Nf/TiO2 not only for cationic dyes (methylene blue (MB) and rhodamine B (RhB)) whose uptake on Nf/TiO2 is enhanced, but also for an anionic dye (AO7) that is less adsorbed on Nf/TiO2. The unexpected behavior in AO7 degradation seems to be related to the role of the Nafion layer in retarding the charge recombination. These observations indicate that Nf/TiO2 can enhance the PCD reactivity for cationic substrates without sacrificing the PCD reactivity for anionic substrates. In addition, it was found that the sensitized degradation of RhB followed a different path when the surface of TiO2 was coated with Nafion. The N-de-ethylation of RhB that leads to the generation of rhodamine-110 was a prevailing path with Nf/TiO2, whereas the cleavage of the chromophoric ring structure was dominant with pure TiO2. The effects of Nafion adlayers on the photoinduced electron transfer and PCD kinetics and mechanisms are discussed.
authors.affiliation: School of Environmental Science and Engineering and Department of Chemistry, Pohang University of Science and Technology, Pohang 790-794, Korea.
authors.forename: Hyunwoong
authors.initials: H
authors.lastname: Park
authors.forename: Wonyong
authors.initials: W
authors.lastname: Choi
mesh_terms: D002384:Catalysis; D004396:Coloring Agents / Q000737:chemistry*; D004579:Electron Transport; D005465:Fluorocarbon Polymers / Q000737:chemistry / Q000528:radiation effects*; D008027:Light; D009930:Organic Chemicals / Q000737:chemistry*; D010782:Photolysis; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D004396:Coloring Agents; D005465:Fluorocarbon Polymers; D009930:Organic Chemicals; C009495:titanium dioxide; C040402:perfluorosulfonic acid; D014025:Titanium