Figure 7. Interaction energy between NO3- and N atom of quaternary ammonium group at different relative positions (a). Nitrate positions during removal categorized by total interaction potential (b). Van der Waals and electrostatic interaction energy between nitrate and MHC (c). Number of H bonds between NO3- and coordinating water molecules during removal process (d). Snapshots of nitrate removal pathway by quaternary ammonium groups (e). O, red; N, dark blue; H, gray; C, green. Methyl group C atoms on quaternary ammonium N atoms in (a) were highlighted in light blue.