Elucidating the impact of porous organic cage on thin film nanocomposite membranes for elevated nanofiltration

Abstract

Porous organic cages (POCs) have triggered significant interest in the design of molecule/ion sieving membranes owing to the high porosity, distinct window-cavity structure, and distinguished solution processability. In this study, the porous organic cage CC19 was explored as functional porous fillers to regulate the surface properties of thin film nanocomposite (TFN) membranes via interfacial polymerization (IP). The addition of CC19 was found to effectively heighten the porosity of membranes while giving rise to a decline in the crosslinking density of the polyamide film. The cage molecules present in the polyamide layer further are likely to pack in a window-to-window mode, forming interconnected 3D porous networks that serve as channels for efficient separation and rapid water molecule transport. Under the synergy effect of CC19 filler and the polyamide matrix, the composite membrane demonstrated a significantly improved permeability and efficient separation of mono−/divalent salts. As the CC19 content was 0.03 w/v%, the as-prepared CC19-TFN-0.03 membrane evinced an outstanding water permeability of 32.0 L m−2 h−1 bar−1, with comparably high rejection of Na2SO4 (96.4 %). This POC-modulated IP approach offers a guidance for designing high-permeable NF membranes for ion separation.