Remarkably efficient removal of toxic bromate from drinking water by porphyrin-viologen covalent organic framework
Presence of carcinogenic bromate (BrO3–) in drinking water became a global concern and efforts of its removal mainly focused on addressing the source. Herein, we rationally designed porphyrin-based covalent organic framework (PV-COF) with a cationic surface to render electrostatic interactions and porphyrin core to induce hydrogen bonding interactions for the efficient removal of BrO3– from water. Through H-bonding and electrostatic interactions, PV-COF exhibited an exceptional bromate removal efficiency (maximum adsorption capacity, Qmax: 203.8 mg g–1) with the fastest uptake rate (Kabs) of 191.45 g mg–1 min–1. The bromate concentration was reduced to far below the allowed concentration in drinking water (10 ppb) within 20 minutes. We studied the relationship between bromate adsorption and COF surface modification by metalation of the porphyrinic core or neutralization of the viologen linkers by chemical reduction. Bromate adsorption mechanism was studied by EDAX mapping and molecular simulations, and it was found that ion exchange and hydrogen bonding formation drive the adsorption. Importantly, PV-COF could be easily recycled several times without compromising its adsorption efficiency.