Photocatalytic oxidation of cytostatic drugs via UV and visible light responsive TiO2 in the aqueous environment
Date Issued
2015
Date
2015
Author(s)
Lin, Hank Hui-Hsiang
Abstract
Cytostatic drugs are a class of pharmaceuticals that are increasingly used in cancer therapies. However, they have genotoxic, mutagenic, carcinogenic or teratogenic effects in non target organism. They have been detected in the both effluent of the municipal and hospital wastewater treatment plants due to their stability and persistency. 5-fluorouracil and cyclophosphamide are two of the most commonly used cytostatic (antineoplastic) drugs in the world. This study applied photocatalytic oxidation to remove 5-fluorouracil and cyclophosphamide. 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 (h_vb^+). 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. On the other hand. 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 MicrotoxR, it is suggested that the oxidation products of cyclophosphamide are even more recalcitrant and toxic. In order to apply photocatalytic oxidation system under visible light, visible light responsive TiO¬¬¬2 has been widely studied for several years. Among visible light responsive TiO2, N-doped TiO2 has been received much more attention because of its higher photoactivity and relatively simple manufacture process. Microwave has been considered as a promising and energy saving process as synthesis in the recent years. The microwave-treated N-doped TiO2 removed 5-fluorouracil with a higher degradation efficiency than N-doped TiO2 synthesized with the traditional thermal treatments. The most efficient N-doped TiO2 (N6) was synthesized using 1 M NH4OH pre-immersion and a 3 h 180°C microwave treatment, followed by 550°C calcination for 6 h. The photocatalytic degradation of 5-fluorouracil achieved 88.8% removal within 20 h of treatment by N6 under visible light, which is higher than that obtained by Degussa P25 TiO2 (61.5%). Higher concentrations of NH4OH and longer calcination times resulted in decreased 5-fluorouracil degradation; the particle size of the synthesized N-doped TiO2 increased after calcination. The surface area decreased while the pore volume and pore size increased after synthesis. Furthermore, the basicity of the sites on the synthesized N-doped TiO2 decreased after calcination. Photocatalytic oxidation was shown to be effective in decomposing 5-fluorouracil and cyclophosphamide, therefore, it has potential to apply to hospital wastewater treatment plants. However, the effects of water matrix, the relationship between toxicity changes and by-products, mineralization must be the important considerations and necessarily investigated before real application.
Subjects
5-fluorouracil
cyclophosphamide
cytostatic drugs
microwave
N-doped TiO2
photocatalytic oxidation
Type
thesis
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