Photocatalytic oxidation of 5-fluorouracil and cyclophosphamide via UV/TiO2 in an aqueous environment

Abstract

Cytostatic drugs are a class of pharmaceuticals that are increasingly used in cancer therapies; 5-fluorouracil is one of the most commonly used cytostatic (antineoplastic) drugs in the world. This study applied photocatalytic oxidation to remove 5-fluorouracil. Degussa P25 showed a higher photocatalytic degradation efficiency for 5-fluorouracil removal than Aldrich TiO2 and ZnO. Under optimal conditions (20 mg L−1 TiO2 at pH 5.8), 200 μg L−1 5-fluorouracil can be removed within 2 h (k = 0.0375 min−1). 5-fluorouracil was found to be decomposed by near-surface OHfree radicals produced from valence holes (hvb+). At a relatively high concentration, 5-fluorouracil (27.6 mg L−1) is >99.9% removed within 4 h by 300 mg L−1 Degussa P25, while 24 h is required to reach complete mineralization with 96.7% fluoride recovery. Cyclophosphamide is another widely used cancer drug that follows a similar decomposition pathway. Cyclophosphamide (27.6 mg L−1) was also >99.9% eliminated within 4 h, but dechlorination and mineralization reached only 79.9% and 55.1%, respectively, after 16 h of irradiation. Together with the results for Microtox®, it is suggested that the oxidation products of cyclophosphamide are even more recalcitrant and toxic. For engineering practices, despite the fact that photocatalytic oxidation can rapidly remove target antineoplastic, it is also important to further evaluate the treatment efficiency of the photoproducts.