Doping TiO2 films with carbon nanotubes to simultaneously optimise antistatic, photocatalytic and superhydrophilic properties

Abstract

Pure and multiwall carbon nanotube (MWCNT)-doped titanium dioxide (TiO2) films, synthesised from two sol–gel routes (alcoholic and aqueous) and deposited by dip-coating on glass, have been developed as conductive, photocatalytic and superhydrophilic materials. While already crystallised in anatase structure at low temperature when synthesised in water, samples prepared in alcohol are amorphous. Their crystallisation in air has been studied at increasing temperatures. Effective incorporation of functionalised MWCNTs is confirmed in both aqueous and alcoholic samples with a closer interaction with TiO2 particles in the case of aqueous synthesis. In alcoholic samples, 400 °C seems to be an optimised calcination temperature since 300 °C does not allow crystallisation into anatase and 500 °C removes MWCNTs through burning. The purpose of MWCNT doping is to obtain coatings that exhibit easy-to-clean or self-cleaning properties. This can be achieved through an optimised combination of electrical conductivity (for antistatic property), photoactivity and superhydrophilicity. These three properties require the crystallisation of TiO2 into anatase. MWCNT doping dramatically increases both conductivity and photocatalytic activity, especially in alcoholic samples for the former and in aqueous samples for the latter. On the other hand, MWCNT introduction does not significantly affect the (super)hydrophilicity of films, which depends solely on the crystallinity of TiO2.