Synthesis of zeolitic imidazolate framework-78 molecular-sieve membrane: defect formation and elimination

Abstract

Metal-organic frameworks (MOFs) are ideal micro-and mesoporous materials for molecular separation. A defect-free MOF membrane supported on a porous substrate is required for high separation performance, however it is rather difficult to eliminate the micro-defects or intercrystalline gaps in the membranes. In this work, a ZIF-78 membrane was synthesized on a porous ZnO support. The defect formation mechanism in the membrane was illustrated by in situ thermal expansion analysis. A novel strategy was proposed to eliminate not only the macroscopic defects but also the intercrystalline gaps in the membrane by controlling the diffusion of solvent molecules through the channels of the ZIF-78 crystal. The ZIF-78 membrane exhibited high performance in separating H 2 . The ideal selectivity and mixture separation factor of H 2 -CO 2 are 11.0 and 9.5, respectively. The approach reported in this paper offers an efficient and universal strategy for the facile synthesis of highquality MOF membranes on porous supports.

ZIF-8 membranes with improved reproducibility fabricated from sputter-coated ZnO/alumina supports

“…Following the same protocol, zinc-based MOF (ZIF-78) membranes were also successfully fabricated through the partial self-conversion of ZnO supports (Dong et al, 2012). However, low porosity of ZnO support, besides the brittle property, limits its application as support for membrane gas separation.…”

“…Partial self-conversion of inorganic support to metal-organic frameworks (MOFs) membrane can effectively promote the heterogeneous nucleation and enhance the binding strength between MOF grain and support, improving the reproducibility of as-synthesized membranes (Dong et al, 2012;Guo et al, 2009;Hu et al, 2011;Khaletskaya et al, 2014;Liu et al, 2014b;Marti et al, 2013;Zhang et al, 2013;Zhang et al, 2014). For example, Jin et al (Hu et al, 2011) prepared continuous MIL-53(Al) membranes on α-alumina supports, in which the α-alumina support acted as the inorganic source reacting with the organic ligand to grow a seeding layer.…”

Zeolite membranes – a review and comparison with MOFs

“…This method has been widely reported. [315][316][317][318] There is also much progress in the prediction of pore size and functionalities of MOFs. In the so-called isoreticular chemistry, 319 desired topologies can be achieved by design and isoreticular series of compounds with the same topology but different pore sizes can be prepared.…”

Zeolitic imidazolate framework membranes for gas separation: A review of synthesis methods and gas separation performance

“…H 2 , CO 2 , 42 N 2 , O 2 , SF 6 , Ar, and CO) and condensable organic gases (i.e. CH 4 , 43 C 2 H 4 , C 2 H 6 , C 3 H 6 , C 3 H 8 , C 4 H 10 ) to achieve a variety of separations, 44 including those of isomers, chiral, and bio-molecules. In addition, 45 membrane technology offers superior economics compared to 46 conventional separation techniques, and it is estimated that the 47 use of membranes can decrease energy costs by as much as 30% 48 when compared with conventional, energy intensive technologies 49 [1].…”

“…[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41], titania [23,42], YSC [43], ZnO [44], and SiO 2 [45]. Titania is 173 a substrate that promotes heterogeneous nucleation; however, it is 174 too expensive and brittle [25].…”