Infiltration of 3D-macrocycles to integrally skinned asymmetric P84 co-polyimide membranes for boron removal

Abstract

We have molecularly designed negatively charged nanofiltration (NF) membranes by chemical modification of P84 flat membranes with hyperbranched polyethylenimine (HPEI) polymers and then infiltration of sulfocalix[4]arene (SCA4) to enhance their chemical stability and molecular sieving capability. The high molecular weight HPEI polymers developed a strong cross-linked network of P84 polymer chains with extraordinary chemical stability in solvents like N-methyl-2-pyrrolidone (NMP). In addition, the amine groups of HPEI ionically bonded with the electron-accepting sulfonic acid groups of SCA4, resulting in the cross-linked membranes with a proper pore dimension and enhanced size sieving capability. The NF membrane infiltrated with SCA4 in a 0.03 wt% SCA4 solution consisting of 50/50 (wt%) water and methanol for 8 h has boron rejections of 55.37 %, 67.23 %, 87.45 %, 89.95 %, and 98.24 % at pH = 4, 7, 8, 9 and 10, respectively. These performances are comparable with or superior to literature results for membranes made from thin-film interfacial polymerization. The unique SCA4 closed-loop structure not only enhances molecular sieving capability but also achieves negatively charged NF membranes that maximize the potential for removal of toxic ions. This study may provide useful insights to design NF membranes with the aid of supramolecular macrocycles for water reuse and removal of toxic ions.