Health issues concerning carbon-TiO2 nanomaterials produced by flame synthesis

Titanium dioxide TiO2 is one of the most important and most used materials in the modern era. Because of its properties it is suitable for a large number of applications in several different fields. In the bulk phase, it is primarily used as a white pigment. As nanomaterial, it is a component in dye-sensitized and organic solar cells as well as in food and personal care products. In the last years personal care applications are increasing; for example nano-powdered TiO2 is extensively employed as physical filter in commercial sunscreens, since it is capable to adsorb and scatter both UVA and UVB radiations and to eliminate the natural opacity typical of microsized sunscreens. However, together with its physical and chemical properties, it is important to assess health implications that the use of TiO2 powder in the nanometer scale might have in personal care applications. A possible way to reduce health implications, especially when related to the formation of freeradicals, is given by coating and doping of TiO2 nanoparticles with organic and inorganic additives. Different efficiencies in preventing the release of free radicals can be achieved, depending on the nature of coating and doping. In this work, the formation of pure TiO2 nanoparticles and carbon-titania nanocomposite by flame synthesis is presented. The procedure is based on the injection of Ti precursor solutions inside hydrocarbon flames with different equivalent ratios. This allows us to synthesize nano-sized particles (1-10 nm), with specific crystallinity phase and carbon content. Chemical and physical properties, composition and dimension of flame-synthesized nanoparticles are characterized by Raman spectroscopy, UV-visible light absorption and Atomic Force Microscopy. Analysis of Reactive Oxygen Species in human keratinocytes cellular lines is used to select the operating conditions of the synthesis process leading to the production of TiO2-carbon nanopowder with reduced adverse health effect.