Degradation of diethyl phthalate (DEP) by UV/persulfate: An experiment and simulation study of contributions by hydroxyl and sulfate radicals

Abstract

Degradation of diethyl phthalate (DEP) by ultraviolet/persulfate (UV/PS) process at different reaction conditions was evaluated. DEP can be degraded effectively via this process. Both tert-butyl (TBA) and methanol (MeOH) inhibited the degradation of DEP with MeOH having a stronger impact than TBA, suggesting sulfate radical (▪) and hydroxyl radical (HO) both existed in the reaction systems studied. The second-order rate constants of DEP reacting with ▪ and HO were calculated to be (6.4±0.3)×107 M−1s−1 and (3.7±0.1)×109 M−1s−1, respectively. To further access the potential degradation mechanism in this system, the pseudo-first-order rate constants (ko) and the radical contributions were modeled using a simple steady-state kinetic model involving ▪ and HO. Generally, HO had a greater contribution to DEP degradation than ▪. The ko of DEP increased as PS dosages increased when PS dosages were below 1.9 mM. However, it decreased with increasing initial DEP concentrations, which might be due to the radical scavenging effect of DEP. The ko values in acidic conditions were higher than those in alkaline solutions, which was probably caused by the increasing concentration of hydrogen phosphate (with higher scavenging effects than dihydrogen phosphate) from the phosphate buffer as pH values rose. Natural organic matter and bicarbonate dramatically suppressed the degradation of DEP by scavenging ▪ and HO. Additionally, the presence of chloride ion (Cl−) promoted the degradation of DEP at low Cl− concentrations (0.25–1 mM). Finally, the proposed degradation pathways were illustrated.