Photocatalytic activity of mesoporous films based on N-doped TiO2nanoparticles

Abstract

TiO₂ based photocatalytic coatings are currently restricted to outdoor applications due to the requirement of UV light. Nitrogen doping of TiO₂ was used here to activate them in indoor conditions for self-cleaning applications. We developed an original process, allowing nitridation of anatase nanoparticles dispersed within a porous silica matrix, at high temperatures (up to 800 °C), with neither structural change, nor aggregation and growth of the nanoparticles. After chemical dissolution of the silica, N-doped TiO₂ particles were dispersed in water allowing the preparation of both concentrated colloidal aqueous dispersions and transparent sol–gel films in which N-doped particles are dispersed in a sol–gel silica binder with a controlled porosity. The N-doped TiO₂ nanoparticles present visible light photocatalytic activity due to the presence of bulk nitrogen species. We showed that the photocatalytic activity of the films can be improved by an additional oxidative thermal treatment suppressing the Ti³⁺ ions which act as recombination centers in TiO₂. We thus succeeded in preparing coatings twenty times more active than the reference under irradiation at 390 nm by monitoring the degradation of the Rhodamine 6G dye.