Synthesis of Polyam-N-Cu2+ Resin

A commercially available weak base anion exchanger (Purolite weak base anion, details in table S4) with primary amine functional groups was used as the parent polymer for preparing Polyam-N-Cu²⁺. The parent polyamine resin has an average particle size of 500 ± 50 μm and was conditioned by rinsing with distilled water (DI) for 1 hour before use. Similar products are likely to be available from other manufacturers; no endorsement is implied. To convert the parent polyamine resin into Polyam-N-Cu²⁺, a CuCl₂ solution (1000 mg/liter) at pH ≈ 4.0 was passed through the parent resin in a fixed-bed column. After loading the Cu, the resin beads were rinsed with DI to remove the residual chemicals, and the as-prepared Polyam-N-Cu²⁺ resin beads were used in this study after air drying. A chelating polymeric resin with iminodiacetate functionality (Amberlite IRC718; details in table S2) was treated through the same Cu(II)-loading protocol to prepare polyiminodiacetate-Cu and compare with Polyam-N-Cu²⁺.