Enhanced photocatalytic activity under visible light in N-doped TiO2 thin films produced by APCVD preparations using t-butylamine as a nitrogen source and their potential for antibacterial films

Atmospheric pressure chemical vapour deposition (APCVD) of N-doped titania thin films has been achieved from titanium (IV) chloride, ethyl acetate and t-butylamine at a deposition temperature of 500 °C and the films characterised by XRD, Raman spectroscopy, XPS, SEM, UV–visible–NIR spectroscopy, contact angle measurements and stearic acid degradation. The films were compared to two industrial self-cleaning products: Activ™ and BIOCLEAN™ and shown to be significantly better in both photocatalysis and superhydrophilicity, two preferential properties of effective self-cleaning coatings. X-ray diffraction showed the films have the anatase TiO2 structure. High resolution X-ray photoelectron spectroscopy was consistent with small quantities of nitrogen (0.15–0.7 at.%) occupying an interstitial site (N 1s ionisation at ∼400 eV). This work sheds light on the current confusion within the literature as to the role of nitrogen in the enhancement of the photocatalytic properties of thin films with direct evidence that selective doping at the interstitial site (ionisation ∼400 eV by XPS) has a pronounced effect on enhancing photocatalysis. Surprisingly in the majority of films no XPS peak for N for O substitution was observed (ionisation ∼396 eV by XPS). This is to our knowledge the first example of an N-doped titania film with only interstitial doping. These films showed significant photocatalysis with visible light. The best films were tested for their antimicrobial properties and found to be an effective agent for the destruction of Escherichia coli using lighting conditions commonly found in UK hospitals.