Enhanced performance of Fe(III)/persulfate for the degradation of DEET: Working mechanism of ascorbic acid

The introduction of ascorbic acid (AA) into Fe(III)/PS system exhibited extremely high activity on the removal of N,N-diethyl- meta -toluamide (DEET) and other pollutants. The removal efficiency of DEET within 30 min reached 90.13%, its dynamic curve obeyed second-order kinetic model and the k obs was calculated to be 0.150 L·mg −1 ·min −1 . Compared with other reducing agents, AA was tested to be the most suitable. The optimal dosages of Fe(III), PS and AA were tested to be 0.1, 1.0 and 0.5 mM, respectively. Furthermore, the introduction of AA extended the working pH to 2.5–9.3. Common anions posed different degrees of inhibition on DEET degradation at relatively high concentration, while a small dosage of HCO 3 − (<1 mM) abnormally exerted a positive role. In terms of reaction mechanism, scavenger experiment and EPR observation illustrated that ·OH and ·SO 4 − dominated DEET degradation, yet slight Fe(Ⅳ) was also found during the reaction, which indicated that Fe(Ⅳ) may also contribute to DEET removal. Different from the rapid consumption of Fe(II) in Fe(II)/PS system, Fe(II) in Fe(III)/PS/AA system entered a dynamic equilibrium state in the later stage of the reaction, which can decompose PS to form ·SO 4 − continuously. Furthermore, the reduction and chelation ability of AA both functioned a key role. According to the degradation intermediates identified by LC-MS analysis, the degradation pathways of DEET could be divided into two directions, which covered opening benzene ring and removing side chain.