N-doped TiO2 visible light photocatalyst films via a sol–gel route using TMEDA as the nitrogen source

N-doped TiO2 thin films were successfully prepared using N,N,N′,N′-tetramethylethane-1,2-diamine (TMEDA) via a single step sol–gel synthesis. Characterisation by X-ray diffraction and Raman spectroscopy confirmed that the anatase crystal type of TiO2 was present in all samples. UV/Vis spectroscopy was used to determine the absorbance and band-gap of the materials. Stearic acid and resazurin dye Photo-degradation measurements were used to show the enhanced photocatalytic properties of the materials. Both of these methods are well known for the assessment of photocatalytic films for self cleaning applications with stearic acid being the preferred model for bacteria. The N-doped films showed superhydrophilicity under filtered white light conditions, whereas the undoped films did not show any photo-induced superhydrophilicity. The N-doped TiO2 films show interstitial nitrogen content rather than substitutional and a substantial red-shift of the band-gap. They were shown to be superior visible light photocatalysts when compared to similar non-doped films. The nature of the chelating ligand, TMEDA, has a profound effect on the oxidation state of the Ti centres, with low concentrations of TMEDA promoting the formation of Ti3+ centres giving a superior photocatalyst. This method is to the best of our knowledge the easiest, reliable and most reproducible one step route to achieve N-doped TiO2 films for photocatalytic applications. These N-doped TiO2 films could have potential applications; as self-cleaning surfaces in healthcare, water sterilisation, and solar energy harvesting.