Photoinduced Electron Accumulation of Titanium Dioxide Nanoparticles Modified Electrodes

Abstract

Titanium dioxide ( TiO 2) nanoparticles (Nps) were prepared by the hydrolysis of titanium tetraisopropoxide ( TTIP ) in 2-propanol with different water contents (0.5 vol% to 7.2 vol%) at 45 °C. The diameter of the Nps was estimated to be 1.5±0.5 nm ( L - TiO 2) and 3.0±0.6 nm ( S - TiO 2) from the onset wavelength in the absorption spectra and by transmission electron microscopy (TEM). A modified Pt electrode with a three-layered sandwich structure was prepared; the outermost and innermost layers were composed of S - TiO 2 and L - TiO 2, respectively, and the middle layer contained 1, 1'-dimethyl-4,4'-bipyridyl ( MV 2+)/Nafion®. Irradiation by a 500 W superhigh-pressure mercury lamp produced electrons in the conduction band of TiO 2. An anodic current was observed after turning off the light. The mechanism by which anodic current is generated after turning off the radiation involves the reduction of MV 2+ to MV +. by photogenerated electrons on the Nps and the diffusion of MV +. in the middle layer. After turning off the irradiation, MV +. transferred an electron to the Pt electrode via holes in the innermost layer or the conduction band of S - TiO 2 coincidentally localized on the Pt electrode, resulting in the generation of the anodic current. The generation of MV +. was confirmed by the absorption spectra of MV +.. As a sacrificial reagent, 2-propanol (0.1 M) was used.