Kinetics of Ag/TiO2-photocatalyzed iodide ion oxidation

Abstract  

Ag-doped TiO₂ (anatase) samples (mass fraction w _Ag = 0.01 and w _Ag = 0.02) of 15.9 and 14.5 nm mean particle size and 11.46 and 10.14 m² g⁻¹ BET surface area were prepared by photodeposition. Doping results in surface plasmon resonance of the metallic silver nanoclusters at around 500 nm, but the absorption edge remains unaltered at 365 nm. Ag-doping remarkably enhances the photooxidation of iodide ion under UV light; iodine formation with Ag/TiO₂ with w _Ag = 0.01 is 16 times greater than with bare TiO₂. The reaction conforms to Langmuir–Hinshelwood kinetics with regard to both I⁻ and O₂. Increase of pH slows down iodine formation and sacrificial electron donors arrest the reaction. Pre-sonication of the catalyst slurry hinders the photocatalysis. Generation of iodine is much greater in acetonitrile than in water. Under the experimental conditions, Ag/TiO₂ with w _Ag = 0.01 is more efficient than Ag/TiO₂ with w _Ag = 0.02, and the enhanced photocatalysis is likely to be because of suppression of electron–hole pair recombination. Kinetic analysis reveals that increasing the Ag mass fraction from 0.01 to 0.02 enhances the surface pseudo-first-order rate constant but inhibits the adsorption of iodide ion and the oxygen molecule on the illuminated oxide surface.