Nitrogen-doped TiO2 thin films: photocatalytic applications for healthcare environments

N-doped TiO2 has for many years received interest as visible light photocatalytic materials. Here we give our perspective on the subject with special consideration towards the use of visible light photocatalysts in the field of antimicrobial materials with applications in healthcare environments. The subject is reviewed and critiqued from synthetic techniques to characterisation and assessment of functional properties. N-doped TiO2 has huge potential to form commercially viable antimicrobial surfaces that are easily implemented within the healthcare environment. We aim to shed light on the illusive nature of the mechanism of the different types of N-doping and comment on how these affect the properties of the catalysts themselves. Small concentrations of nitrogen doped under mild conditions lead to interstitial doping, which also promotes the creation of oxygen vacancies. Many believe that it is these oxygen vacancies that actually promote the formation of visible light photocatalysis and hence there is an indirect correlation between the interstitial doping and the photocatalysis. As the concentration of interstitial nitrogen increases the oxygen vacancies increase, however the presence of oxygen vacancies in turn encourages substitutional doping which then fills the oxygen vacancies. This cyclic relationship leads to photocatalysts that are very sensitive to changing nitrogen concentration.