Impact of Chemical Primers on the Growth, Structure, and Functional Properties of ZIF-8 Films

Abstract

ZIF-8 (zeolitic imidazolate framework) metal-organic framework (MOF) thin films have been studied extensively given their possible applications in separation membranes and sensors and even for microelectronics. The wide variety of substrates and synthetic strategies used for ZIF-8 film formation causes a dispersion in the properties observed, and elucidation of the influence of each step in such processes is a much-desired goal that remains partially unexplored. Therefore, we herein focused on a thorough characterization of the effect of substrate surface chemistry given by chemical primers on the resulting films. Specifically, we used self-assembled monolayers (SAMs) of 3-mercapto-1-propanesulfonic acid (MPSA) and (3-aminopropyl)triethoxysilane (APTES). We have analyzed and evaluated its influence on growth progression, thickness, crystallinity, surface roughness, compactness, and porosity on ZIF-8 films grown via a one-pot liquid-phase epitaxy approach and the overall impact of those properties on molecular transport of different probes. We observed significant differences regarding transport properties, and thus available porosity, even for films featuring similar thickness, a parameter widely employed for film comparison. While MPSA renders more compact films and permselectivity, the same synthesis procedure applied to APTES-primed substrates yields lower compactness and lower selectivity on molecular transport. Altogether, our results demonstrate that surface chemical modification of substrates plays a fundamental role in the resulting MOF film structure and thus can be used to modulate crucial properties for prospective use in technological devices.