Highly (2 2 2)-oriented flexible hollow fiber-supported metal-organic framework membranes for ultra-permeable and selective H2/CO2 separation

Abstract

Metal-organic framework (MOF) membranes demonstrate enormous potential for energy-efficient gas separations, while the construction of flexible and oriented MOF-based membranes remains a significant challenge. Herein, we prepared an ultrathin and highly (222)-oriented ZIF-8 layer with unique honeycomb cellular structures on porous aminated polyethersulfone (PES) hollow fibers (HF) via UV radiation-induced surface amino-grafting followed by a homogeneous fluidic processing method, and the reaction conditions including amino-grafting density, radiation power, flow rate, and reaction time et al. were systematically investigated and optimized. The orientation of reflection originated from the difference in attachment energy of crystal planes induced by the surface amino groups. The coherent (222)-oriented NH2-ZIF-8@HF membrane exhibited distinguished H2/CO2 separation performance with a mixed-gas H2 permeance of 75711 ± 610 GPU, among the highest values of previously reported hollow fiber supported ZIF membranes, and the H2/CO2 selectivity of 21.2 ± 0.11 at 150 °C. Additionally, the NH2-ZIF-8@HF membrane displayed outstanding mechanical and thermal stability with negligible deterioration of gas separation performance after folding and unfolding at 180° for 20 times and several temperature-swing cycles. ZIF-7 and ZIF-67 composite membranes were also prepared with outstanding H2/CO2 separation performance following the same strategy. The facile membrane fabrication method and exceptional separation performance make NH2-ZIF@HF membranes attractive for important industrial energy-efficient H2 recovery from steam cracking and similar processes.