High Surface Proton Conduction in Nanostructured ZIF-8
authors Munoz-Gil, D; Figueiredo, FML
nationality International
journal NANOMATERIALS
author keywords ZIF-8; nanostructure; surface; protonic conductivity
keywords METAL-ORGANIC FRAMEWORKS; ZEOLITIC IMIDAZOLATE FRAMEWORKS; EXTERNAL SURFACE; STABILITY; ADSORPTION; SEPARATION; XPS
abstract The zeolitic imidazolate framework-8 (ZIF-8) combines a significantly high microporosity with an excellent thermal, chemical, and hydrothermal stability. Here, we demonstrated that ZIF-8 can display significant levels of protonic conductivity through a water-mediated surface transport mechanism associated to the presence of di-coordinated Zn ions revealed by X-ray photoelectron spectroscopy. A set of powders with particle sizes from 2.8 mu m down to 80 nm studied by dynamic water vapour sorption analysis was used to demonstrate that water adsorbs predominantly in the micropore cavities of microcrystalline ZIF-8, whereas adsorption on the external surface becomes the dominant contribution for the nanostructured material. Impedance spectroscopy in turn revealed that the protonic conductivity of the nanocrystalline ZIF-8 was two orders of magnitude higher than that of the micron-sized powders, reaching approximately 0.5 mS.cm(-1) at 94 degrees C and 98% relative humidity. Simple relations were derived in order to estimate the potential gains in water uptake and conductivity as a function of the particle size. This new strategy combining particle nanostructuring with surface defects, demonstrated here for one of the most know metal organic framework, is of general application to potentially boost the conductivity of other materials avoiding chemical functionalization strategies that in most if not all cases compromise their chemical stability, particularly under high humidity and high temperature conditions.
publisher MDPI
year published 2019
volume 9
issue 10
digital object identifier (doi) 10.3390/nano9101369
web of science category Nanoscience & Nanotechnology; Materials Science, Multidisciplinary
subject category Science & Technology - Other Topics; Materials Science
unique article identifier WOS:000495666800024
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journal analysis (jcr 2017):
journal impact factor 3.504
5 year journal impact factor 3.811
category normalized journal impact factor percentile 66.708
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