MOF-in-COF molecular sieving membrane for selective hydrogen separation

Hongwei Fan,Alexander Mundstock,Hong Meng,Manhua Peng,Ina Strauss,Jürgen Caro

doi:10.1038/s41467-020-20298-7

Abstract

Covalent organic frameworks (COFs) are promising materials for advanced molecular-separation membranes, but their wide nanometer-sized pores prevent selective gas separation through molecular sieving. Herein, we propose a MOF-in-COF concept for the confined growth of metal-organic framework (MOFs) inside a supported COF layer to prepare MOF-in-COF membranes. These membranes feature a unique MOF-in-COF micro/nanopore network, presumably due to the formation of MOFs as a pearl string-like chain of unit cells in the 1D channel of 2D COFs. The MOF-in-COF membranes exhibit an excellent hydrogen permeance (>3000 GPU) together with a significant enhancement of separation selectivity of hydrogen over other gases. The superior separation performance for H2/CO2 and H2/CH4 surpasses the Robeson upper bounds, benefiting from the synergy combining precise size sieving and fast molecular transport through the MOF-in-COF channels. The synthesis of different combinations of MOFs and COFs in robust MOF-in-COF membranes demonstrates the versatility of our design strategy.

Highlights

Covalent organic frameworks (COFs) are promising materials for advanced molecularseparation membranes, but their wide nanometer-sized pores prevent selective gas separation through molecular sieving
Before the preparation of metal–organic frameworks (MOFs)-in-COF membrane, a continuous TpPa-1 layer was grown onto a porous α-Al2O3 substrate surface via an in situ solvothermal synthesis method, with the aim to provide the nanoconfined template for the subsequent MOF growth
It is expected that one SOD cage as a unit cell of ZIF-67 is formed inside the 1D pore channels of TpPa-1 to give the ZIF-67-in-TpPa-1 membrane

Summary

Introduction

Covalent organic frameworks (COFs) are promising materials for advanced molecularseparation membranes, but their wide nanometer-sized pores prevent selective gas separation through molecular sieving. Molecular sieving membranes with abundant and uniform pore structures that can break the Robeson limit are desirable for energy-efficient gas separation[4] To this end, typical porous materials, such as zeolites[5,6,7], metal–organic frameworks (MOFs)[8,9,10,11,12,13], microporous organic materials[14,15,16,17,18], or two-dimensional (2D) layered materials[19,20,21,22,23] as sieving membranes have been extensively investigated over the past decade. COF family, possess inherent properties like high porosity, versatile and tunable pore size, well-defined pore structure and readily tailored functionalities, but have superior thermochemical stability in comparison with the coordination-based MOFs26,27 These fascinating features make COFs excellent candidates for constructing new-generation molecular sieving membranes for advanced separation[28,29,30,31,32,33]. To date there is no concept to exploit the MOF-in-COF materials as membranes for separation applications

Methods

Results

Conclusion