Porous organic cage supramolecular membrane showing superior monovalent/divalent salts separation

Abstract

Nanofiltration process has been perceived as one of the promising approaches in desalination and separation of monovalent/divalent salts. Despite significant progresses has been made in permeability and salt rejection, the industrial separation for monovalent/divalent salts is limited by the insufficient selectivity for ions with different charges and sizes. This work firstly proposed a porous organic cage supramolecular membrane with topologically structured “window-to-window” channels for the fast transport of monovalent ions and water molecules. Specifically, porous organic cage (RCC3) molecule and nonpolar alkyl of dodecyltrimethylammonium bromide (DTAB) were assembled into supramolecular RCC3@DTAB through hydrophobic interaction by molecular recognition of polar cavity. Furthermore, terephthaloyl chloride (TPC) was employed as a crosslinker by interfacial polymerization to construct RCC3@DTAB-TPC supramolecular film onto the surface of polydopamine modified polysulfone (PSf) substrate. The results suggested that RCC3@DTAB-TPC membrane displayed a high permeability of 13.9 L m−2 h−1 bar−1, and attractive performance for monovalent/divalent salts separation and small molecule solutions desalination. The salt rejections to Na2SO4, MgSO4, NaCl and MgCl2 are 98.5%, 90.1%, 19.8% and 12.8%, and the selectivities of NaCl/Na2SO4 and NaCl/MgSO4 reached 42.6 and 7.8, respectively. Besides, the separation factors for NaCl/medicine and NaCl/dye mixtures are 95.5 of δNaCl/DG and 76.6 of δNaCl/CR, respectively. The excellent separation performance of RCC3@DTAB-TPC supramolecular membrane provides a new idea for developing high-efficiency membranes for monovalent/divalent salts separation.