Block Ratio Optimized Cationic Polyacrylamides for Enhanced Nitrate Rejection Under Applied Potential

The integration of charged polymers and reverse osmosis membranes presents a promising approach to capture undesired ions and enhance water purification efficiency. In this paper, di-block cationic polyacrylamides (DCPAMs) as charged polymers are evaluated separately in bulk solution and within a reverse osmosis process to capture nitrite ions introduced by NaNO3. To achieve this, molecular dynamics simulations are conducted to systematically investigate the effects of polymer configuration, concentration, and salt concentration on ion adsorption and water purification performance. The results reveal that nitrate ions exhibit strong adsorption to the charged polymers, leading to the displacement of chloride ions into the bulk solution. The polymer conformations are found to play a critical role in the performance of the process. When an electric potential is applied, anions are strongly attracted to the electrode with a total positive charge, and nitrate ions remain closer to the electrode surface than other ions. The simultaneous application of RO membranes and DCPAMs achieves salt rejection efficiencies ranging from 78% to 100%, depending on DCPAM type and salt concentration. These findings pave the way for further computational studies on combined processes to advance water purification technologies.