Synthesis of titanium dioxide in O 2/Ar/SO 2/TiCl 4 microwave torch plasma and its band gap narrowing

Abstract

Titanium dioxide (TiO 2) nanoparticles were synthesized directly by injecting gas-phase titanium tetrachloride (TiCl 4) bubbled with a mixture of Ar and SO 2 into a 2.45 GHz microwave torch plasma operated in O 2 gas at atmospheric pressure. The absorption edge of the as-produced TiO 2 powders in the UV–Visible spectrum shifted from 457 nm to 483 nm as the SO 2 gas content in the mixture gas carrying the TiCl 4 was increased. According to X-ray photoelectron spectroscopy (XPS) and UV–Visible spectroscopy, the band gap narrowing was due to the incorporation of sulphur (S) species from the Ar and SO 2 mixture in the oxygen microwave torch plasma into the O site of TiO 2.