Fig. 2.

Characterizations and thickness of ZIF-8 membranes. a The optical photographs of the Zn-based gel and the ZIF-8 powder. b N₂ adsorption isotherm and corresponding pore width distribution of the prepared ZIF-8. c XRD patterns of the simulated ZnO, the Zn-based gel layer and the calcinated Zn-based gel layer on PVDF hollow fibres. d XRD patterns of the simulated ZIF-8, the ZIF-8 membrane and the calcinated ZIF-8 membrane. The samples were prepared with sol concentration of 1 U, coating time of 2 s and vapour deposition time of 2 h. Thickness of ZIF-8 membranes prepared with different e coating time and f sol concentration. The thickness was measured at various locations to obtain the standard deviation. g Top and h cross-sectional view SEM images of the ZIF-8 membrane. Scale bar, 200 nm. AFM analysis of i the Zn-based gel layer and j the ZIF-8 membrane. R _q: i 3.6 nm and j 5.8 nm. R _a: i 2.8 nm and j 4.7 nm. Scale bar, 100 nm. k Grain size distribution of the Zn-based gel layer and the ZIF-8 membrane from AFM data. The samples were prepared with sol concentration of 0.1 U, coating time of 2 s and vapour deposition time of 2 h