Conversion of membrane surface charge property via post-crosslinking for heavy metal ions removal

The heavy metal ions pollution aggravates the clean water shortage crisis. The polyamide nanofiltration membranes fabricated via interfacial polymerization are potential for removal of heavy metal ions, but their negatively charge surface renders low rejection efficiency. To solve the issue, we proposed a surface charge conversion method by chemical crosslinking the positively charged polyethyleneimine (PEI) on the thin polyamide nanofiltration membrane. The such prepared positively charged nanofiltration membrane presents enhanced rejection to heavy metal ions while maintaining the high water permeance. After optimization of the membrane fabrication conditions, the PEI-modified membrane demonstrates a pure water permeance of 7.2 L^.m⁻².h^−1.bar⁻¹ with >95 % rejection to Cu²⁺ and other heavy metal ions. Moreover, the membrane could maintain the high performance to mixed metal ion aqueous solutions. Combined with its remarkable stability under high pressure and long-term running, the positively charged membrane has great potential to be deployed for treatment of practical wastewater towards sustainable development via cleaning water and precious metals recovery.