Co@NC@ZIF-8-hybridized carbon molecular sieve membranes for highly efficient gas separation

Abstract

Carbon molecular sieve (CMS) membranes are widely used for the separation of similar molecular kinetic diameter gas. However, their performance is limited by a large amount of discontinuous porous structures and a few adsorption affinity sites. Herein, we first prepared magnetic Co@NC@ZIF-8 nanoparticles, followed by introducing it into the polyimides matrix to design precursor membrane with vertical nanochain-like particle distribution by magnetic field induction. Afterwards, hybrid carbon molecular sieve (HCMS) membranes were prepared by pyrolyzing precursor with high-temperature under N2 atmosphere, which had ordered microporous architecture and Co-N-C structure. Resultant HCMS membranes prepared by magnetic field induction had excellent gas separation performance, whose CO2, N2 and CH4 permeabilities were 27,050, 2614 and 622 Barrer, with CO2/N2, CO2/CH4 and N2/CH4 selectivities of 10.4, 43.5 and 4.2 respectively. These values far exceeded 2019 CO2/CH4 and 2008 N2/CH4 upper bounds as well as approached 2008 CO2/N2 upper bound. The superior performance resulted from the vertically ordered nanochain-like channels for gas transport, which dramatically shortens the transport path of gas molecules to intensify shape sieving potential. Moreover, the Co-N-C structure on the wall of channels could facilitate CO2 transport due to the π complexation. Additionally, a large quantity of nitrogen sites in the carbonized Co@NC@ZIF-8 enhance CO2 adsorption selectivity owing to the acid-base interaction. More remarkably, after 30-day aging testing, it was found that HCMS membranes prepared by magnetic field induction had exceptional aging resistance compared to the pristine CMS membranes and one without magnetic field induction under the same aging environments.