Direct Synthesis of Ultrathin Two-Dimensional Co-Based Metal–Organic Framework Membranes by the Conversion of Co(OH)₂ Sheets for Gas Separation

Abstract

Ultrathin two-dimensional (2D) metal–organic framework (MOF) nanosheet membranes have shown significant promise for gas separation application because of their excellent molecular transport characteristics. However, the preparation of oriented 2D MOF membranes by direct growth remains challenging, especially on tubular substrates. In this study, we propose a bottom-up strategy to prepare a highly oriented 2D Co2(bIm)4 (bIm = benzimidazole) membrane via the conversion of Co­(OH)2 sheets with assistance from graphene oxide (GO) in organic ligand synthetic solution. Both the introduced GO and Co­(OH)2 layers play important roles in inducing the highly oriented growth of stable 2D Co2(bIm)4 membranes. The obtained 2D Co2(bIm)4 membrane of around 210 nm in thickness displays outstanding separation properties. The permeance for H2 is 2.54 × 10–7 mol·m–2·s–1·Pa–1, and the ideal selectivities for H2/CO2, H2/N2, and H2/CH4 are as high as 23.1, 18.5, and 28.7, respectively. This approach opens up a new avenue via a direct growth method for preparing highly oriented MOF nanosheet tubular membranes for efficient gas separation.