Ammonia-assisted ZnO support-induced conversion approach to prepare oriented Zn2(bIm)4 membrane for hydrogen separation

Abstract

The construction of oriented two-dimensional MOF membrane is highly desirable for gas separation. At present, the most commonly used method is top-down exfoliation-deposition, but this method is complex, time-consuming, arduous, and difficult to prepare on a large-scale. The relatively simple and scalable direct growth approach is more attractive but still a major challenge. In this contribution, an ammonia-assisted ZnO support-induced strategy was developed to prepare highly oriented Zn2(bIm)4 membranes via in-situ solvothermal growth just in one cycle. This proposed approach is on the basis of the self-conversion of ZnO-support in ligand solutions containing ammonia modulators. The effects of ZnO-support calcination temperature, ammonia concentration, growth time and temperature on the formation of Zn2(bIm)4 membrane and gas separation performance were studied in detail. The prepared Zn2(bIm)4 membrane exhibited good stability in the mixed-gas test with H2/CO2 selectivity of 15.3 and hydrogen permeance of 1.25 × 10−8 mol· m−2·s−1·Pa−1, which is better than the upper-bound in 2008. The excellent membrane stability was due to the fact that ZnO support as the nucleation and anchoring sites to make the Zn2(bIm)4 membrane and support integrate. The preparation of Zn2(bIm)4 membrane by support-induced technology has the advantages of relatively simple preparation process, outstanding membrane stability and high gas separation property, which provides a very promising H2/CO2 separation membrane material. This method also provides a new way for the scaling-up 2D MOF membranes and their industrial applications.