ORIGINAL PAPER Kinetics of Ag/TiO 2 -photocatalyzed iodide ion oxidation Chockalingam Karunakaran • Premkumar Anilkumar • Paramasivan Gomathisankar Received: 4 December 2009 / Accepted: 25 February 2010 / Published online: 2 April 2010 Ó Springer-Verlag 2010 Abstract Ag-doped TiO 2 (anatase) samples (mass frac- tion 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 m 2 g -1 BET sur- face area were prepared by photodeposition. Doping results in surface plasmon resonance of the metallic silver na- noclusters 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/TiO 2 with w Ag = 0.01 is 16 times greater than with bare TiO 2 . The reaction conforms to Langmuir–Hinshelwood kinetics with regard to both I - and O 2 . Increase of pH slows down iodine formation and sacrificial electron donors arrest the reaction. Pre-sonica- tion of the catalyst slurry hinders the photocatalysis. Generation of iodine is much greater in acetonitrile than in water. Under the experimental conditions, Ag/TiO 2 with w Ag = 0.01 is more efficient than Ag/TiO 2 with w Ag = 0.02, and the enhanced photocatalysis is likely to be because of suppression of electron–hole pair recombina- tion. 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. Keywords Ag-doped TiO 2  Photochemistry  Catalysis  Surface  Nanoparticles Introduction Shining semiconductors with light of energy equal to or larger than the band gap creates electron-hole pairs, holes in the valence band and electrons in the conduction band. Whereas a fraction of these pairs reach the crystal surface and react with adsorbed substrates, leading to photocatal- ysis, the rest recombine resulting in low photocatalytic efficiency [1]. TiO 2 is a promising candidate for photo- catalytic material application because of its exceptional optical and electronic properties, chemical stability, non- toxicity, and low cost [2, 3]. Also, water is adsorbed on TiO 2 , both molecularly and dissociatively [4, 5], and hole trapping by either the surface hydroxyl groups or the adsorbed water molecules generates short-lived HO radicals, which are the primary oxidizing agents in the photomineralization of organics [6–9]. The high density of surface hydroxyl groups on the TiO 2 particle may also be the reason for the observed high photocatalytic activity of TiO 2 [10]. However, the high degree of recombination between the photogenerated electrons and holes is a major factor reducing photocatalytic efficiency. The photocata- lytic efficiency of TiO 2 can be improved by doping it with a noble metal such as silver [11–18]. The metal particles deposited on the surface of TiO 2 may act as sink for the photogenerated electrons and thus reduce electron–hole recombination. This migration of the conductance-band electrons to metal particles increases the lifetime of the holes and thus the photocatalytic efficiency. Investigations with Ag-doped TiO 2 as photocatalyst are many but they are on the degradation of organics [11–18]. Moreover, there is no report on the kinetics of Ag–TiO 2 photocatalysis and hence this study was conducted. Generation of energy- bearing chemicals by nonspontaneous reactions is the objective of solar energy conversion and storage, and C. Karunakaran (&)  P. Anilkumar  P. Gomathisankar Department of Chemistry, Annamalai University, Annamalainagar 608002, Tamilnadu, India e-mail: karunakaranc@rediffmail.com 123 Monatsh Chem (2010) 141:529–537 DOI 10.1007/s00706-010-0288-2