TiO2 nanoparticles : Traditional and novel synthetic methods for photocatalytic paint formulations

This review chapter is focused on the physico-chemical features and the related semiconductor activity of nanometric TiO2 both pure and formulated as photocatalytic paint. First the synthesis of the particles, with controlled structural and morphological aspects, is discussed on the grounds of both literature and original research data. Different synthetic approaches are presented: combustion, precipitation and solvothermal routes, sol-gel synthesis, and also more innovative methods like those assisted by ultrasound and microwaves. The photocatalytic activity with respect to the degradation of both water (organic dyes, chlorophenols, etc.) and air pollutants (nitrogen oxides, NOx, volatile organic compounds, VOC, etc.) is analyzed. Literature, commercial and home made samples are considered both in the case of pure and doped TiO2 The second part of the chapter concerns the formulation of photoactive paints. Liquid coating paint formulations are complex, multicomponent systems including resins as film forming agents, binders, additives, solvents and extenders. The possibility to incorporate nanoactive semiconductor materials (such as nano-TiO2 ) in order to obtain photocatalytic paints leads to several problems also due to the possible simultaneous photodegradation of the desired air pollutants and of the organic matrix of the coating. The few data, present in the literature concerning this latter points, are compared also with original laboratory results.