Comparison of the degradation of molecular and ionic ibuprofen in a UV/H2O2 system.

The advanced oxidation technologies based on •OH can effectively degrade the pharmaceutical and personal care products under operating conditions of normal temperature and pressure. In this study, direct photolysis of ibuprofen (IBU) is slow due to the relatively low molar extinction coefficient and quantum yield. Compared to direct photolysis, the degradation kinetics of IBU was significantly enhanced in the UV/H2O2 system, mainly by •OH radical mediated oxidation. In the UV/H2O2 system, the degradation rate of ionic IBU was slightly faster than that of the molecular form. Kinetic analysis showed that the second-order reaction rate constant of ionic IBU (5.51 × 109 M-1 s-1) was higher than that of the molecular form (3.43 × 109 M-1 s-1). The pseudo first-order rate constant for IBU degradation (kobs) increased with increasing H2O2 dosage. kobs can be significantly decreased in the presence of natural organic matter (NOM), which is due to (i) NOM radical scavenging effects (dominant role) and (ii) UV absorption. The degradation of IBU was inhibited by HCO3-, which was attributed to its scavenging effect. Interestingly, when NO3- was present in aqueous solution, a slight increase in the degradation rate was observed, which was due to NO3- absorbing photons to generate •OH at a low quantum yield. No obvious effects were observed when SO42 and Cl- were present.