Efficient activation of persulfate by copper-coated nano zero-valent iron for degradation of nitrogenous disinfection by-products: The key role of Cu

The essential shortcoming of rapid passivation deactivation limits the efficient application of nano zero-valent iron (nZVI) in eliminating disinfection byproducts from drinking water. Copper-coated nano zero-valent iron (Cu-nZVI) bimetallic composites were synthesized to efficiently activate persulfate (PS) to remove nitrosopyrrolidine (NPYR). By introducing Cu-coated coatings, nZVI is protected from direct contact with PS; thus, Cu-nZVI appears to activate PS efficiently and stably without rapid deactivation. Compared with plain nZVI, the constructed Cu-nZVI/PS system significantly increased the removal efficiency for NPYR from 76.3 % to 94.3 % at a pH of 7.0. The Cu-nZVI composites achieved a synergetic effect on the degradation of NPYR by regulating PS activation and reactive oxygen species (ROS) formation, promoting Fe2+/Fe3+ cycling with the Cu-nZVI surface and accelerating the electron transport capacity. The bursting tests and electron paramagnetic resonance (EPR) tests confirmed that multiple types of ROS coexisted in the Cu-nZVI/PS system. Furthermore, vulnerable sites and degradation pathways on the NPYR molecule were predicted by density functional theory (DFT) calculations. Toxicity predictions revealed decreased biotoxicity of NPYR and its intermediates. The NPYR removal efficiency decreased slightly to 81.1 % after 30 days of ageing, which demonstrates the excellent potential of the composites for realistic applications.