Photocatalytic degradation of domoic acid using nanocrystalline TiO 2 thin films

Abstract

Domoic acid (DA) is a water-soluble marine neurotoxin produced and released by Pseudo-nitzschia species. It is remarkably pervasive in North American coastal waters, where it is a threat to public health and some marine life, and has resulted in severe economic losses in the shellfish and crustacean harvesting industry. In this paper we report on the development of nanocrystalline titania thin films that were used as photocatalyst in the UV photodegradation of DA. TiO 2 thin films produced by a sol–gel dip-coating method in the presence of polyethylene glycol (PEG) of different molecular weights (200, 400 and 600), were deposited on glass and fused quartz substrates, and crystallized at different temperatures (90, 500 and 900 °C). The films were characterized using UV–vis, FTIR, SEM, XRD, and Raman spectroscopy. For the photocatalytic activity measurements, the TiO 2 films were immersed in a DA solution (2500 ng/mL) and exposed for various times at room temperature to UV irradiation ( λ ∼ 350 nm). DA analysis was carried out by HPLC, and the photocatalytic activity was quantified as the rate of disappearance of DA. The photocatalytic activity of the TiO 2 thin films was studied as a function of their crystallization temperature, type of PEG content, and thickness. The films prepared at low temperature proved to be very efficient photocatalysts. They showed a higher photocatalytic activity than those produced at high temperature. Also, using PEG of higher molecular weight in the TiO 2 coating solutions increased the effectiveness of the degradation. When using UV irradiation alone, without photocatalyst, the degradation of DA was not significant. The presence, transformation, and degradation of various DA isomers were observed during the photodegradation process, and a photodegradation mechanism is proposed.