Defect engineering on zeolitic imidazolate framework membrane via thermal annealing for organic solvent nanofiltration

Abstract

Zeolitic imidazolate frameworks (ZIFs) have been attracting intensive attention in membrane separation fields because of their ultrahigh specific surface areas, well-defined apertures, and variable topological characteristics. However, the aperture sizes of ZIFs are smaller than the kinetic diameters of most organic solvent molecules, which impedes their applications in organic solvent separation. Herein, we develop a thermal annealing-derived methodology for defect engineering on the ZIF-67 membrane. This post-synthetic modification not only expanded the aperture size of ZIF-67 but also repaired intercrystalline cracks in the polycrystalline ZIF-67 layer. By controlling the thermal annealing conditions, the permeability of the polycrystalline ZIF-67 membrane toward organic solvent nanofiltration was enhanced by two times. Moreover, the annealed ZIF-67 membrane showed a high rejection of more than 99.6% for dyes (Evans blue) and pharmaceutical molecules (tetracycline, vitamin B12). This work provides an avenue for the controllable modification of ZIFs membranes to broaden their applications.