Mechanisms of iopamidol transformation catalyzed by a copper corrosion product (c-Cu2O) during peroxymonosulfate disinfection

Peroxymonosulfate (PMS) is an alternative disinfectant for drinking water. This study aimed to investigate the transformation of iopamidol (IPM) catalyzed by a main copper corrosion product (c-Cu2O) with PMS as a disinfectant. The observed pseudo-first-order constant (kobs) for the IPM degradation in the c-Cu2O/PMS system (0.033 min- 1) was 3 times that in the CuO/PMS system (0.011 min- 1). The quenching tests and the electron paramagnetic resonance (EPR) experiments indicate that O2 center dot- and 1O2 contributed to IPM degradation in the cCu2O/ PMS system. The complexation of metastable Cu(II) with a PMS molecule polarized the O-O bond and then facilitated the electron transfer from the PMS molecule to other PMS and O2 molecules, which directly and indirectly promoted the yield of O2 center dot- and 1O2. The iodine balance indicated that 26.0% of initial TOI was converted to IO3- , and CHI3 only accounted for 0.6% of the residual TOI. In the c-Cu2O/PMS system, IPM conversion was started with amide C-N bond breakage, deiodination reaction and hydrogen abstraction. This study helps to better understand the conversion mechanisms of iodine-containing organic micropollutants when PMS is deployed as a disinfectant in copper pipes.