N-doped TiO₂ nanothin films: photocatalytic and hydrophilicity properties

¹ Department of Physics, Central Tehran Branch, Islamic Azad University, Tehran, Iran
² Superconductivity Research Laboratory (SRL), Department of Physics, University of Tehran, 14399-55961 Tehran, Iran

^a e-mail: kimia@khayam.ut.ac.ir

Received: 26 July 2012
Revised: 22 October 2012
Accepted: 17 December 2012
Published online: 25 January 2013

Abstract

Nitrogen-doped TiO₂ nanothin films were synthesized by spray pyrolysis method using TiCl₄ as a precursor. Five samples including 0.0, 0.1, 0.2, 0.3 and 0.4 molar urea (as a nitrogen source) were fabricated. XRD spectra of the samples confirm that increasing the nitrogen doping initiates anatase to rutile-phase transformation and narrows band gap from 3.60 to 3.46 eV. This means that doping nitrogen increases the rate of the anatase to rutile-phase transformation. UV-vis spectrophotometer of the thin films showed 85–90% transmission in the visible region. AFM images indicate the increase of roughness and the grain size of the samples by increasing nitrogen doping. Optical band gaps were calculated by Tauc plot with values larger than those reported for bulk samples. The larger band gap might be due to the strain from lattice distortion. High hydrophilicity and photocatalytic properties were observed in thin films during UV illumination that persists for 210 min. It was found that the sample with the largest amount of N doping shows the best hydrophilicity activity and photocatalytic property.