The influence of nitrogen partial pressure on visible-light-driven photocatalytic activity of sputtered titanium oxynitride thin films

Abstract

Using a reactive direct current magnetron sputtering method in an Ar, O2 and N2 atmosphere, titanium oxynitride (TiOxNy) thin films were deposited on silicon and glass substrates and then annealed in air at 500 °C for 1 h. X-ray diffraction analysis indicated that the thin films displayed only a rutile titanium dioxide (TiO2) phase when oxygen was used as the reactive gas. When the nitrogen was injected into the sputtering chamber, the thin films displayed a mixture of anatase and rutile phases of TiO2. The surface morphology, characterized by a field-emission scanning electron microscope, showed growth of grain size and formation of nano-pores with increased nitrogen partial pressure. The optical bandgaps of the thin films, evaluated from Tauc plots, were in a range from 2.90 to 3.17 eV. The photocatalytic activity of the thin films was examined under visible light using methylene blue (MB) as a dye model. The experimental results indicated that nitrogen content affected photocatalytic effectiveness during MB degradation. After irradiation with white light from an LED lamp for 120 min, the highest value of the pseudo-first-order reaction rate constant was 8.93 × 10−3 min−1, obtained from the TiOxNy thin film that contained the highest nitrogen content of 3.90 at.%.