Construction of high amine density polymer‑sodium alginate based gel: Efficient and selective Cu(II) removal enabled by optimization strategy of interfacial compatibility and three-dimensional mass transfer network

Traditional small-molecule amine-modified adsorbents suffer from insufficient free amine coordination sites, fragile 3D cross-linking networks and poor interfacial compatibility in Cu(II) wastewater treatment. Herein, a high-amine-density linear polymer polyethyleneimine (PEI) was incorporated into a graphene oxide/sodium alginate/montmorillonite (GO/SA/MMT) system via an induced self-assembly strategy to fabricate a composite gel PEI-GSM. PEI simultaneously supplies abundant free amine sites, promotes synergistic inter-chain cross-linking, and constructs a highly porous 3D interpenetrating network that provides ample mass transfer pathways and coordination sites for Cu(II). Our study provides an in-depth analysis of the structure-property relationship, interfacial regulation patterns and adsorption mechanisms of PEI-GSM gels, and compares their performance with that of small-molecule amine modification strategies in terms of enhancing Cu(II) coordination capacity, strengthening the cross-linked network and optimizing interfacial compatibility. PEI-GSM achieves 98.3% Cu(II) removal efficiency along with excellent reusability and anti-interference ability. Notably, the Cu(II)-loaded PEI-GSM serves as a visible-light photocatalyst for enrofloxacin degradation via ·OH and ·O₂^- radicals, realizing waste resource utilization and mitigating secondary pollution of spent adsorbents.