Adjusting Nitrogen Doping Level in Titanium Dioxide by Codoping with Tungsten: Properties and Band Structure of the Resulting Materials

Abstract

For a systematic study of the material, samples of W/N-codoped titania with different concentrations of the dopants were prepared. The physicochemical properties and in particular their band structure were subsequently evaluated experimentally to elucidate the effect of W-doping, N-doping, and W/N-codoping on the band structure of TiO2. For this purpose, a combined approach of optical spectroscopy and electrochemical impedance spectroscopy was chosen. The doped samples featured both a reduced band gap and a positively shifted conduction band edge. Both conduction band edge and band gap followed a linear dependence on the nitrogen content. They also demonstrate visible light absorption capability, which is associated with interstitial nitrogen doping. Tungsten doping did not influence the band structure of TiO2 directly. It did, however, facilitate nitrogen uptake and stabilize it at higher temperatures. These higher nitrogen doping levels then in turn reduced the band gap and lowered the conduction band edge. Codoping with tungsten therefore offers an excellent way to precisely adjust the nitrogen content and correspondingly the conduction band position of titanium dioxide.