Tuning the optical, electrical and photocatalytic properties of nanoparticulate TiO2 through anatase-coating on rutile

C Karunakaran, P Navamani and P Gomathisankar

Abstract

Nanocrystalline TiO₂, because of its unique electronic and optical properties, stability, nontoxicity, etc, finds a wide range of applications including pigments, sunscreen materials, photocatalysts and catalysts. Although numerous transition metal oxides and sulfides and their combinations are reported as photocatalysts, their stability, nontoxicity, etc, have not been assessed for adoption by industries. So is the case with metal or metal ion-doped TiO₂. Here we show that by coating anatase TiO₂ over rutile TiO₂ nanoparticles, without compromising the nontoxicity, stability, cost, etc, the charge transfer resistance, absorption edge, moisture-adsorption and photocatalytic activity are modified to suit different types of applications, such as UV light protection with moderation of photocatalytic activity to act as sunscreen materials and pollutant-degradation through photocatalysis. Anatase TiO₂-coated rutile TiO₂ nanoparticles were obtained by a particulate sol-gel technique. Coating of anatase over rutile blue-shifts the absorption edge, increases largely the charge transfer resistance and enhances the moisture-adsorption. Charge transfer resistance of anatase-coated rutile decreases under band gap illumination. The photocatalytic activity of the nanocrystalline anatase-rutile is less than that of pristine anatase but larger than that of pristine rutile. This study enables to adopt different phases of TiO₂ for divergent applications.