Growth of ZnO self-converted 2D nanosheet zeolitic imidazolate framework membranes by an ammonia-assisted strategy

Shaping crystalline porous materials such as metal organic frameworks (MOFs) and zeolites into two-dimensional (2D) nanosheet forms is highly desirable for developing high-performance molecular sieving membranes. However, conventional exfoliation–deposition is complex and challenging for the large-scale fabrication of nanosheet MOF tubular membranes. Here, for the first time, we report a direct growth technique by ZnO self-conversion and ammonia assistance to fabricate zeolitic imidazolate framework (ZIF) membranes consisting of 2D nanosheets on porous hollow fiber substrates; the membranes are suitable for large-scale industrial gas separation processes. The proposed fabrication process for ZIF nanosheet membranes is based on the localized self-conversion of a pre-deposited thin layer of ZnO in a ligand solution containing ammonium hydroxide as a modulator. The resulting ZIF 2D nanosheet tubular membrane is highly oriented and only 50 nm in thickness. It exhibits excellent molecular sieving performance, with high H2 permeance and selectivity for H2/CO2 separation. This technique shows great promise in MOF nanosheet membrane fabrication for large-scale molecular sieving applications.