An ambient temperature aqueous sol–gel processing of efficient nanocrystalline doped TiO2-based photocatalysts for the degradation of organic pollutants

An environmentally-friendly aqueous sol–gel process for producing undoped and Cu2+, Ni2+, Zn2+ or Pb2+-doped TiO2 photocatalysts exhibiting a remarkably high photocatalytic activity without requiring any calcination step has been developed. The physicochemical properties of the catalysts were characterized by ICP-AES, XRD, UV–Vis spectroscopy and nitrogen adsorption–desorption. It has been found that the catalysts are composed of nanocrystallites of anatase with a size of 6–7 nm and a specific surface area varying from 184 to 275 m2 g−1. A screening of the photocatalytic activity of the undoped and doped photocatalysts has been performed by evaluating the degradation of 4-nitrophenol under artificial light (330 nm < λ < 800 nm) after 7 h of illumination using a custom-designed multisample photoreactor. The activity measured for the TiO2-Undoped catalyst was found to be five times higher than the activity measured for uncalcined TiO2 catalysts produced by other sol–gel methods. We propose that this interesting result is due to the particular morphology of the xerogels obtained. It has also been demonstrated that the presence of the dopant leads to an enhancement of the photocatalytic activity in all cases. The role of particular dopants in modulating the photocatalytic activity will be discussed. Finally, the possibility of producing undoped and Zn2+-doped films presenting a higher activity than the commercial photocatalytic coating (Saint Gobain Glass Bioclean®) without requiring any calcination step has been demonstrated. These preliminary results constitute an important step forward in the development of photocatalytic films using a sol–gel process compatible with the constraints associated with large-scale industrial processing.