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

•MOF layer synthesis time has a direct influence on its thickness.•As the metal/ligand ratio in the MOF synthesis decreases the MOF layer thickness and H2/CH4 selectivity decrease.•The bilayered polyamide (PA)-ZIF-93 membrane enhances both water permeance and dye rejection compared to the TFC membrane.•The ZIF-93 layer decreases the PA film cross-linking, but the superposition of both layers increases the membrane rejection.