A study into the self-cleaning surface properties—The photocatalytic decomposition of oleic acid

Abstract

Thin films of TiO 2 exhibiting developed mesoporosity with large surface area and pores ca 10 nm in size were shown efficient photocatalyst in the decomposition of thin layers of oleic acid deposited on their surface. The pore walls of these films were composed of small anatase nanocrystals (ca 40–60%) and some amorphous phase. As major intermediates of the oleic acid decomposition, nonanal and 9-oxononanoic acid were identified. Azelaic and nonanoic acid were detected as well, representing minor intermediates. These compounds have been shown to correspond with the products of a simulated oxidative degradation of cis-3-hexenoic acid computed by means of quantum chemistry. Cis-3-hexenoic acid was chosen as a simplified model of oleic acid having similar but reduced structure. It enabled to perform the theoretical study with a reasonable consumption of computation time. The simulated oxidative degradation of cis-3-hexenoic acid was induced by an attack of hydroxyl radical on the C C double bond. The main reaction pathway led to propanal, 3-oxopropanoic acid, and also hydroxyl radical. The organic products are analogous to the main degradation intermediates of oleic acid, nonanal and 9-oxononanoic acid. The prediction of hydroxyl radical elimination in the final step of the major reaction sequence would mean that it may act as a catalyst causing accelerated degradation of unsaturated compound including fatty acids.