Abstract
Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) is commonly used as an antibacterial agent in various industrial products and is often detected in wastewater effluent. Comparison was made for triclosan degradation by photolysis and TiO2 photocatalysis (under UV irradiation (125 W)) based on analysis of transformation products, together with ecotoxicity evaluation. The morphology of the TiO2 was characterized by X-ray diffractometry (XRD) and field emission gun-scanning electron microscopy (FEG-SEM). Triclosan quantitation was performed by high performance liquid chromatography (HPLC). The optimal condition was obtained using a response surface model and desirability profile. The initial concentration of triclosan used in all the experiments was 10 mg L-1 to achieve comprehensive identification of transformation products. The optimal experimental condition was 30 mg L-1 TiO2 at pH 10. The photocatalytic system achieved > 99% triclosan degradation at 30 min of reaction. The mineralization rates by photolysis and photocatalysis were 25 and 90%, respectively. A total of 27 transformation products were identified using liquid chromatography quadrupole time of flight mass spectrometry (QTOF MS), being that 25 were new structures, not previously reported in the literature. Ecotoxicity assays demonstrated that triclosan and some of the major transformation products did not cause deleterious effects towards Lactuca sativa and Daphnia magna after 16 h of treatment.
Highlights
Triclosan (TCS, 5-chloro-2-(2,4-dichlorophenoxy) phenol) is an antimicrobial and fungicidal compound that is widely used in personal care products, textiles, soaps, and first aid products
Both photolysis and UV/TiO2 photocatalysis were highly effective in degrading TCS
A significant difference between the two processes was observed for TCS mineralization, with photocatalysis being 50% more efficient than photolysis, at 180 min of reaction, confirming the importance of use of the catalyst
Summary
The mobile phase was acetonitrile:water (70:30 v v-1), at a flow rate of 1 mL min-1, and the detector wavelength was 280 nm These conditions resulted in a linear response, with R2 (correlation coefficient) of 0.99, limits of detection (LOD) and quantification (LOQ) of 0.1 and 1.0 mg L-1, respectively, and relative standard deviation (RSD) of 4.2%. The degradation and mineralization assays employed an initial TCS concentration of 10.0 mg L-1, prepared in ultrapure water. This concentration was higher than found in the environment, its use enabled identification of TPs without the need of extraction procedures (such as solid phase extraction (SPE)), as well as evaluation of the mineralization capacity of the system by total organic carbon (TOC) analysis.
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