Materials Stability and Toxicology - Safety Issues

The presence of titania particles in sunscreens was the main reason for the investigation of its dermal penetration properties, and a study suggested that fine particles (10-50 nm) can penetrate the skin, although the sample size was too small to 

Another specific and important aspect to consider is the possibility that an environmentally heterogeneous photocatalyst can lead to the undesirable formation of reaction intermediates which are more toxic than the starting reagents. For instance, the Ti02-based photodegradation of ethanol, a relatively innocuous air pollutant, occurs through its transformation into the more toxic acetaldehyde. Condensation reactions can also lead to the formation of traces of methyl formate, ethyl formate, or methyl acetate. Catalyst design is therefore important to increase the overall oxidation rate to ensure complete mineralization (formation of C02 and H20). 

In addition, problems related to leaching of photocatalysts into the environment must be considered as metals are generally toxic, especially when present as reduced micro- or nanoparticles. 

2 Mills, A. and Le Hunte, S. (1997) An overview of semiconductor photocatalysis. Journal of Photochemistry and Photobiology A Chemistry, 108 (1), 1-35. 

3 Carp, O., Huisman, C.L., and Reller, A. (2004) Photoinduced reactivity of titanium dioxide. Progress in Solid State Chemistry, 32 (1-2), 33-177. 

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