Facile ZIF–8 nanocrystals interlayered solvent–resistant thin–film nanocomposite membranes for enhanced solvent permeance and rejection

Introduction of nanomaterials into thin–film nanocomposite (TFN) membranes can improve the solvent permeance for organic solvent reverse (OSRO) and forward osmosis (OSFO) processes. However, the severe nanomaterials aggregation and the formation of defects in membrane rejection layer, which decreased the rejection of membrane against various solutes. Herein, we proposed a novel strategy of thin–film nanocomposite (TFNi) membrane featuring an interlayer of metal–organic framework (MOF, ZIF–8) by one–step fabrication in the simultaneous phase–inversion and crosslinking process. This strategy integrates the precipitation of polyimide (PI) substrates, crosslinking between the PI and hexanediamine, and generated ZIF–8 nanocrystals through the interfacial diffusion. Furthermore, one–step strategy of ZIF–8 effectively mitigate its agglomeration in the surface of support layers by SEM characterization. A prepared polyamide (PA) rejection layer with high crosslinking and low thickness was characterized by XPS and TEM. The resulting TFNi membranes with ZIF–8 interlayer (OSFOISG–2.5) showed a molecular weight cut–off of ~500 Da, the remarkable DI water and THF permeances (9.73 and 1.62 L m–2 h–1 bar–1 under RO mode), and the higher ethanol fluxes (2.10 ± 0.11 LMH under FO mode and 2.97 ± 0.31 LMH under PRO mode). In addition, the solvents permeance of the OSFOISG–2.5 membrane was furtherly improved by 10 h DMF activation without loss of the polystyrene rejection in RO mode. This study also provides insight for the preparation of ZIF–8 on the polymer's matrix for large–scale production.