Amphibian-inspired amino acid ionic liquid functionalized nanofiltration membranes with high water permeability and ion selectivity for pigment wastewater treatment

Inspired by the amphibian skin of Bombina orientalis, which is a kind of ancient toad species, amino acid ionic liquid (AAIL) is employed to functionalize interfacial polymerized nanofiltration membrane. AAIL offers the membranes with (1) higher hydrophilicity leading to pure water permeability of 12.2 L·h⁻¹·m⁻²·bar⁻¹, which is 63% higher than conventional NF membranes; (2) more negatively charged surface and slightly larger pore size, which results in a high Na₂SO₄/NaCl selectivity of 973.9, which is 43 times increased from conventional NF membrane and effective for resource recovery from pigment wastewater. Furthermore, the amino acid end groups (glycine) of AAIL, similar to the epidermal secretion of Bombina orientalis, act as humectant that prevents pore shrinkage during heat-treatment, which is important for membrane storage and transport. The AAIL functionalized membrane may provide an effective strategy to design high performance nanofiltration membranes for small molecular separations in pigment and other industries.