Surface and Electronic Structure of Titanium Dioxide Photocatalysts

Abstract

TiO 2 films prepared by sol-gel route are active photocatalysts for the oxidation of organics in photoelectrochemical cells. The as-grown films for photocatalysis applications and those exposed to Ar + or H 2 + +Ar + ion bombardment are characterized by different spectroscopic methods, such as X-ray diffraction (XRD), atomic force microscopy (AFM), UV-vis transmittance, photothermal deflection spectroscopy (PDS) and X-ray photoelectron spectroscopy (XPS), as well as by conductance. This material has defects associated with oxygen vacancies produced during the sample preparation which support nondissociative adsorption of O 2 when films are exposed to air. Charge transfer from reduced Ti species to adsorbed dioxygen leads to Ti-O 2surface complexes that are partially removed by heating at 200 °C, and fully removed after 30 min ion bombardment. By comparison with the relatively well-understood structural defects of bombarded TiO 2 we arise to a quite complete structural model of the as grown material which corresponds to an amorphous semiconductor possessing relative low disorder and density of states as compared with a pure amorphous material. These TiO 2 films are modeled as low size crystalline domain embedded in an amorphous matrix whose electronic structure exhibit exponential band tails and a narrow band close to the conduction band. The latter is fully or partially occupied depending on the presence of adsorbed electron scavengers such as dioxygen.

A comprehensive study of the influence of the stoichiometry on the physical properties of TiOx films prepared by ion beam deposition

“…The presence of adsorbed O 2 2− ͑peroxide͒ and O 2 − ͑superoxide͒ with maximum BE at ϳ531 eV and 532 eV, respectively predominant. 6,40 These species, as well as O − , are formed by adsorption of O 2 onto reduced surfaces. 41 Curves a and b, at lowest P O 2 can be assigned to physisorbed O 2 to a monolayer or less of chemisorbed O for which a lower BE is expected.…”

“…59 Once the sample thickness reaches ϳ100 nm, the observed pale yellow color is characteristic of TiO 2 . 6,60 A complete analysis of the optical properties of these films is currently being investigated and will be reported elsewhere.…”

“…[1][2][3][4][5][6][7][8][9][10] The use of TiO 2 powders or films is potentially important in the attempts to solve some environmental and energy problems. 11 Moreover, TiO 2 coatings improve surface hardness and wear resistance.…”

The effect of pH on the photonic efficiency of the destruction of methyl orange under controlled periodic illumination with UV-LED sources

“…The photogenerated h vb + and e cb -are highly reactive with standard redox potentials of +2.53 and -0.52 respectively and can directly take part in the oxidation or reduction of substrates or indirectly through less reactive intermediates [11]. During photocatalytic reactions, the TiO 2 catalyst surface is covered by adsorbed O 2 and OH -molecules which play significant roles in interfacial charge-transfer; O 2 is an efficient electron scavenger, while the adsorbed OH -provide efficient hole traps [12]. Degussa (Evonik) P25 TiO 2 catalyst, which exhibits a high activity in photocatalytic reactions has been widely investigated as a photocatalyst and has been accepted as the de-facto standard in the research community [13].…”

Enhanced Photophysical Properties of Nanopatterned Titania Nanodots/Nanowires upon Hybridization with Silica via Block Copolymer Templated Sol-Gel Process

“…Titanium dioxide (TiO 2 ) based nano materials has gained considerable attention due to its unique physicochemical properties, such as non-toxicity, insolubility, stability and high photoactivity, based on which widespread applications were accomplished [1][2][3][4]. Numerous routes to synthesize low dimensional TiO 2 in a controlled condition have been reported [5][6][7].…”