Single-Step Synthesis of Al-Doped TiO2 Nanoparticles Using Non-Transferred Thermal Plasma Torch

Abstract

Al-doped TiO2 nanoparticles possessing visible-light photocatalytic activity were fabricated with an atmospheric-pressure thermal plasma system via a single-step direct combination of vaporized Ti, Al, and O-2. Pure Ti and Al2O3 powders and ultrahigh-purity O-2 were used as the precursors. The experimental results showed that the size of synthesized TiO2 was between 10 and 105 nm. Nevertheless, the nanoparticles with sizes smaller than 50 nm accounted for approximately 80% of the total number. The observed size reduction appeared to be the suppression on particle growth due to the introduction of Al species into TiO2 crystal. The largest specific surface area of the Al-doped TiO2 was 44 m(2).g(-1). The anatase phase was noticeably decreased with increasing the Al2O3 addition. The absorption spectra of Al-doped TiO2 shifted from UV to visible-light region with respect to an increase in Al2O3 addition. Oxygen in the formed TiO2 was found to be in TiO2 crystal lattice and in surface hydroxyl groups. Both Ti4+ and Ti3+ existed in the formed TiO2. However, the Ti3+ amount significantly increased with increasing Al2O3 addition due to Al/Ti substitution and the resulted oxygen vacancy. (C) 2012 The Japan Society of Applied Physics