The prepared membrane was treated with PEI (5% w/v in water) in an oven for 48 h at 35 °C. The pH of the PEI solution was maintained at approximately 7.3 by HCl addition. The activated chloride (-Ph-CH2Cl) moieties of the membrane underwent nucleophilic substitution with PEI. Subsequently, the membrane was washed with deionised water to remove unbound PEI and stored in fresh deionised water.