Self-cleaning properties of TiO₂-coated glass : Degradation, under simulated solar light, of palmitic (hexadecanoic) acid and fluoranthene layers deposited on the glass surface

Abstract
The self-cleaning property of glass arises from a thin transparent TiO₂ coating. Under solar UV light, TiO₂ becomes capable of degrading organics at its surface. Our objectives were : to assess the self-cleaning efficiency with respect to the removal of compounds representative of organic deposits ; to identify and, if possible, quantify the intermediate products formed during the destruction of these organic layers both to complete the data concerning the self-cleaning properties and to have an insight into the photocatalytic degradation pathways. Our target compounds were palmitic (hexadecanoic) acid and fluoranthene : both are present in the atmospheric solid particles and come from various sources. The removal rates of layers of these compounds sprayed on the self-cleaning glass were found to be sufficient for the expected application. The identified intermediates (about 40 for each compound) show the gradual splitting of the palmitic acid chain and the oxidative openings of the aromatic rings of fluoranthene. In the case of palmitic acid the products give some indications about the photocatalytic mechanism. About 20 % of the organic carbon contained in the initial compounds was transformed into volatile carbonyl products. In the case of fluoranthene, this percentage was less than for the degradation on TiO₂-free glass.