Primary Events in the Photocatalytic Deposition of Silver on Nanoparticulate TiO₂

Abstract

The photocatalytic deposition of silver from ethanol solution on TiO2 nanoparticles prepared with a chemisorbed surface alkoxide layer has been examined in real time by picosecond-resolved transient absorption spectroscopy. This photocatalyst formation of surface-trapped photoelectron states, hypothesized to be Ti(III), can be followed on the time scale of the experiment (≤10 ns). Loss of these electrons to recombination is inconsequential, presumably owing to sacrificial hole trapping by the surface alkoxide states. Silver deposition occurs on the same time scale, and the pseudo-first-order rate constant for growth of the silver(0) transient absorption is the same as for the disappearance of the Ti(III) states under these conditions. We infer that one-electron, inner sphere reduction of Ag(I) by Ti(III) is rate determining in the formation of the colloidal silver deposit. These particles must accordingly grow by a sequence of alternating electronic and ionic events analogous to those hypothesized to be involved in latent image formation in silver halide photography. The quantum yield for silver deposition under our conditions was estimated as ca. 0.8, much higher than that reported by other authors (refs , , and 6).

Photo‐induced processes in heterogeneous nanosystems. From photoexcitation to interfacial chemical transformations

“…Our conclusion of competition between the physical recombination pathway through surface active centers and surface chemical reaction was supported by the time-resolved spectroscopic data for the photocatalytic deposition of silver on nanoparticulate TiO 2 in a solid/liquid heterogeneous system consisting of TiO 2 particles and silver acetate as reported by Sahyun and Serpone [7]. The system was excited by picosecond laser pulses in the presence of high concentrations of alcohol pre-adsorbed on the particle surface.…”

“…For example, in the original state before laser pulse excitation, there exist only anion and cation vacancies, and consequently only processes of charge carrier trapping by these vacancies is possible. This means that any faster process (either electron or hole trapping) occurs first with a probability dictated by the trapping crosssection of the corresponding type of vacancy and by the (2), and in the presence of dihydrogen (3) [7] {Copyright by the American Chemical Society}.…”

Research on photodegradation of formaldehyde by nanocrystalline N-TiO2 powders under visible light irradiation

“…However, the relatively wide band gap (3.2 eV) of anatase TiO 2 limits its applications under irradiation by visible light. Many methods have been carried out to improve the visible light photocatalytic activity of TiO 2 [11][12][13][14][15][16][17], and doping with nitrogen is one promising option [18]. There have been few systematic studies of photocatalytic degradation of HCHO by TiO 2 powders under visible light irradiation.…”

Studies on photocatalytic activity of Ag/TiO2 films

“…There are two main obstacles for the practical application of TiO 2 photocatalyst: low quantum efficiency and restriction to short wavelength excitation. A common way to enhance the quantum efficiency is to load a noble metal on the surface of TiO 2 powder or thin film by photochemical deposition method [12][13][14][15][16][17][18][19][20][21][22][23]. Especially, the deposition of silver has attracted much attention [17][18][19][20][21][22][23].…”