Polyamide/MOF bilayered thin film composite hollow fiber membranes with tuned MOF thickness for water nanofiltration

A bilayered polyamide-MOF membrane was synthesized on the inner surface of a hollow fiber support (200/350 mm ID/OD). The continuous MOF layer was prepared by liquid phase crystallization, and after that a polyamide layer was formed by interfacial polymerization on the top of the MOF. Firstly, the influence of time in the crystal growth of the MOF layer (from 15 to 120 min) was studied. The main characteristics of such MOF layer were tested (gas permeance and selectivity, and layer thickness measurements by SEM) to decide which of them were the optimum to support the polyamide thin film. The final bilayered membranes were characterized by SEM imaging and XPS and their performance was established in the nanofiltration of a solution of sunset yellow (450 Da) in water. Both permeance and selectivity were improved compared to a conventional TFC membrane (without the MOF layer): water permeance from 0.06 ± 0.01 to 0.24 ± 0.09 L·m⁻²·h⁻¹·bar⁻¹, and dye rejection from 88 ± 2 to 98 ± 1%).