Journal of Molecular Catalysis A-Chemical, Vol.378, 221-226, 2013
Effect of valence band energy on the photocatalytic performance of N-doped TiO2 for the production of O-2 via the oxidation of water by visible light
Five types of N-doped TiO2 (TiO2-xNx, x=0, 0.005, 0.015, 0.03, and 0.06) nanoparticles were prepared and evaluated for use as a catalyst for production of 02 via the oxidation of water by irradiation with visible light. The resulting materials were characterized using ultraviolet diffuse reflectance spectroscopy (UV-DRS), electrochemical impedance spectroscopy (EIS), and photoluminescence (PL) techniques. The results indicate that a change in band gap energy (E-g) as a function of N-doping level in the materials resulted in a change in the valence band (VB) level, but not the conduction band (CB) level. The very small upward shift in VB enhanced the photocatalytic formation of OH center dot radicals produced by irradiation with visible light. In addition, the small amount N-dopant (up to 3 at%) incorporated into the samples accelerated the evolution of O-2, rather than the formation of OH center dot species. The incorporation of larger amounts of N-dopant in the TiO2-xNx reduced the rates of both O-2 evolution and OH center dot formation, due to the small energy level of VB and the short life time of the photo-generated charges. The performance of TiO1.97N0.03 nanoparticles with an E-g value of 2.8 eV was outstanding for the evolution of O-2 from the water under the experimental conditions used. (c) 2013 Elsevier B.V. All rights reserved.