Mechanical Properties of Microcrystalline Metal-Organic Frameworks (MOFs) Measured by Bimodal Amplitude Modulated-Frequency Modulated Atomic Force Microscopy

Yao Sun; Zhigang Hu; Dan Zhao; Kaiyang Zeng

doi:10.1021/acsami.7b06809

Mechanical Properties of Microcrystalline Metal-Organic Frameworks (MOFs) Measured by Bimodal Amplitude Modulated-Frequency Modulated Atomic Force Microscopy

ACS Appl Mater Interfaces. 2017 Sep 20;9(37):32202-32210. doi: 10.1021/acsami.7b06809. Epub 2017 Sep 8.

Authors

Yao Sun¹, Zhigang Hu², Dan Zhao², Kaiyang Zeng¹

Affiliations

¹ Department of Mechanical Engineering, National University of Singapore , 9 Engineering Drive 1, 117576 Singapore.
² Department of Chemical and Biomolecular Engineering, National University of Singapore , 4 Engineering Drive 4, 117585 Singapore.

PMID: 28849914
DOI: 10.1021/acsami.7b06809

Abstract

Direct measurement of the mechanical properties of microcrystalline metal-organic framework (MOF) nanoparticles is challenging and rarely explored. In this work, we apply an effective method to realize elastic modulus mapping of a series of isostructural single MOF nanoparticles (100-500 nm) via bimodal amplitude modulated-frequency modulated atomic force microscopy. By probing five types of zirconium (Zr) and hafnium (Hf) isostructural UiO-66-type MOFs, we experimentally found that UiO-66(Hf)-type MOFs possess the higher elastic modulus (46-104 GPa) than that of UiO-66(Zr)-type MOFs (34-100 GPa), both of which are higher than that of reported zinc/copper based MOFs (3-10 GPa). We also experimentally demonstrate that the mechanical properties of MOFs can be tuned by adjusting the chemical functionalities of the ligands or using different metal nodes. In detail, the sterically bulky functional groups increase the mechanical properties of the resultant UiO-66-type MOFs, possibly due to the increased atomic density. These results pave a way to the direct measurement of mechanical properties of MOFs crystalline particles and provide an incisive perspective to the design of MOFs with high mechanical properties.

Keywords: bimodal amplitude modulated-frequency modulated atomic force microscopy; elastic modulus mapping; mechanical properties; metal−organic frameworks.