Quantitative assessment on the contribution of direct photolysis and radical oxidation in photochemical degradation of 4-chlorophenol and oxytetracycline

摘要

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 (HOaEuro cent) 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 center dot oxidation was improved with increasing initial H2O2 concentration probably due to the increased formation of HO center dot. Presence of sodium carbonate (Na2CO3) as in UV/H2O2/Na2CO3 system promoted the degradation of 4-CP, with carbonate radical (CO3 center dot-) 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 center dot- precursor.