Electron-irradiation induced changes in the phases and photocatalytic activity of TiO2 nanoparticles

Abstract

Samples of TiO2 nanoparticles, with mixed anatase and rutile phases, were irradiated with 6.5MeV electrons at fluences, 1.5, 2.0, 2.5, 3.0, and 3.5×1015ecm−2 and characterized by several methods. With increasing electron fluence, a continuous decrease in the average particle size from ∼80nm to around 30nm were observed along with a decrease in the rutile and the anatase phases of TiO2, but at different rates, and growth of the TiO2 brookite phase at slow rate. The photocatalytic activities of different electron irradiated TiO2 samples, in the photodegradation of methylene blue, were studied by recording UV–Vis absorption spectra of the respective solutions. On electron irradiation, even though the rutile phase in the TiO2 was decreasing, the photocatalytic activity of the nanoparticles increased continuously with fluence up to ∼3.0×1015ecm−2, but decreased at 3.5×1015ecm−2. The energy levels introduced by the brookite phase and the electron induced defects in TiO2 could have effectively reduced the electron–hole recombination rate in the absence of the rutile phase. The observed enhancement in the photocatalytic activity of the irradiated TiO2 is attributed to the formation of small size particles, the introduction of the oxygen related vacancies and other defects, the growth of the brookite phase, and increased absorption of radiation over the ultraviolet and visible range.