S,N co-doped nanocrystalline TiO2. Synthesis, Characterizations and Photocatalytic Activity.

TiO2, also known as titania, is very strong, light, refractory (mp 1800 °C) and resistant to corrosion and drastic chemical conditions; it has high photocatalytic activity (PCA), a relatively low cost and it is non toxic . Titanium dioxide pigment is the single greatest use of titanium worldwide: almost 95% of the total production is consumed with this purpose. However, TiO2 is commonly used also in papers, cements, plastics, cosmetics and food industry. In recent years TiO2 has also played a major role in fine photocatalytic applications. Possible uses of TiO2 as photocatalyzer are innumerable. Among these purification of wastewaters, protective coatings of ancient marbles and materials, degradation of organic pollutants, sterilization and self–cleaning materials. These range from paints to cements, from glasses to ceramics and asphalts. Unfortunately TiO2 has a low quantum yield for the photochemical conversion of solar energy.
However, for all the mentioned purposes it is necessary to realize innovative synthetic routes that permit to get specific phases, controlled surface area and crystals dimensions. This Thesis was performed in the context of these studies. The main aims of the work were the synthesis of nanocrystalline titanium dioxide (sol–gel reaction) with controlled properties (phase content, crystals dimensions, morphological aspects) exploring the possibility to extend the absorption to the visible light by means of nitrogen doping and testing the PCA against the conversion of NOx (one of the main pollutant in Milan metropolitan area). The thesis focused on the role of the ions SO42– and NH4+ as a promoter of the anatase phase and as a visible light shifter respectively. The coupled behaviour of the ions was also investigated. Other parameters like the ratio of Ti/H2O or H2O/IPA used during the synthesis were not investigated since data are available in the literature22. Characterizations of the structure of the home–made samples were performed through different analytical techniques including XRPD, XPS, BET, UV–reflectance and TEM.
It was also outlined a method to produce an efficient photocatalytic paint. It was hoped that a final outcome of the thesis would have been the discovery of a way to formulate an efficient photocatalytic paint (optimization of chemicals, mixing ratio, mixing of nanocrystalline photocatalytic TiO2 and testing of the photocatalytic activity). In this, we have succeeded exploiting several commercial samples and tracing a future path to be followed to get the best catalytic activity under visible (solar) irradiation.