Calcium-alginate/HKUST-1 interlayer-assisted interfacial polymerization reaction enhances performance of solvent-resistant nanofiltration membranes

This study aimed to further enhance the solvent stability and flux of organic solvent-resistant nanofiltration (OSN) membranes. Based on hexane diamine cross-linked polyetherimide (PEI) ultrafiltration membranes, in-situ calcium alginate (CaAlg) hydrogel doped with HKUST-1 was constructed as an interlayer, and then the OSN membrane with an integral covalent bond structure was constructed from interfacial polymerization reaction and NN dimethylformamide (DMF) activation. The membrane showed ultra-thinness (polyamide (PA) layer thickness reduced from 97 to 11 nm), large surface area (surface roughness increased from 75.6 to 113 nm), high hydrophilicity (water contact angle reduced from 60.1° to 54.45°), and negative charge. The CaAlg-HKUST-1 interlayer limited the piperazine diffusion rate by hydrogen bonding and covalent bonding, etc., reduced the thickness of the PA layer, and linked the base membrane and the PA layer by its internal integral covalent bonding, which effectively enhanced the structural stability of the OSN membrane. The PA/CaAlg-HKUST-16/PEI membrane achieved a flux of 29.4 L·m−2·h−1 in ethanol and a rejection of 94.7 % in 0.1 g·L-1 methyl blue. Different dye rejection tests, solvent flux tests, DMF and acetone immersion tests, fouling resistance tests, and continuous operation tests show PA/CaAlg-HKUST-16/PEI membrane has better solvent resistance, dye separation performance, and stable membrane flux. Hence, it has great application prospects in the fields of organic solvents and other types of wastewater treatment.