Quantitative assessment on the contribution of direct photolysis and radical oxidation in photochemical degradation of 4-chlorophenol and oxytetracycline
2016
Liu, Yiqing | He, Xuexiang | Fu, Yongsheng | Dionysiou, Dionysios D.
In UV-254 nm/H₂O₂ advanced oxidation process (AOP), the potential degradation pathways for organic pollutants include (1) hydrolysis, (2) direct H₂O₂ oxidation, (3) UV direct photolysis, and (4) hydroxyl radical (HO•) reaction. In this study, the contribution of these pathways was quantitatively assessed in the photochemical destruction of 4-chlorophenol (4-CP), demonstrating pathways (3) and (4) to be predominantly responsible for the removal of 4-CP by UV/H₂O₂ in 50 mM phosphate buffer solution. Increasing reaction pH could significantly enhance the contribution of direct photolysis in UV/H₂O₂ process. The contribution of HO• oxidation was improved with increasing initial H₂O₂ concentration probably due to the increased formation of HO•. Presence of sodium carbonate (Na₂CO₃) as in UV/H₂O₂/Na₂CO₃ system promoted the degradation of 4-CP, with carbonate radical (CO₃ •⁻) reaction and direct photolysis identified to be the main contributing pathways. The trends in the contribution of each factor were further evaluated and validated on the degradation of the antibiotic compound oxytetracycline (OTC). This study provides valuable information on the relative importance of different reaction pathways on the photochemical degradation of organic contaminants such as 4-CP and OTC in the presence and absence of a CO₃ •⁻ precursor.
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