Structure and thermodynamics of water adsorption in NU-1500-Cr

Ching-Hwa Ho; Mason L Valentine; Zhijie Chen; Haomiao Xie; Omar Farha; Wei Xiong; Francesco Paesani

doi:10.1038/s42004-023-00870-0

Structure and thermodynamics of water adsorption in NU-1500-Cr

Commun Chem. 2023 Apr 15;6(1):70. doi: 10.1038/s42004-023-00870-0.

Authors

Ching-Hwa Ho¹, Mason L Valentine², Zhijie Chen³, Haomiao Xie³, Omar Farha³, Wei Xiong^{4

5}, Francesco Paesani^{6

7

8}

Affiliations

¹ Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, 92093, USA. c9ho@ucsd.edu.
² Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, 92093, USA.
³ Department of Chemistry and International Institute of Nanotechnology, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
⁴ Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, 92093, USA. w2xiong@ucsd.edu.
⁵ Materials Science and Engineering, University of California San Diego, La Jolla, CA, 92093, USA. w2xiong@ucsd.edu.
⁶ Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, 92093, USA. fpaesani@ucsd.edu.
⁷ Materials Science and Engineering, University of California San Diego, La Jolla, CA, 92093, USA. fpaesani@ucsd.edu.
⁸ San Diego Supercomputer Center, University of California San Diego, La Jolla, CA, 92093, USA. fpaesani@ucsd.edu.

Abstract

Metal-organic frameworks (MOFs) are a class of materials with diverse chemical and structural properties, and have been shown to effectively adsorb various types of guest molecules. The mechanism of water adsorption in NU-1500-Cr, a high-performance atmospheric water harvesting MOF, is investigated using a combination of molecular dynamics simulations and infrared spectroscopy. Calculations of thermodynamic and dynamical properties of water as a function of relative humidity allow for following the adsorption process from the initial hydration stage to complete filling of the MOF pores. Initial hydration begins at the water molecules that saturate the open Cr³⁺ sites of the framework, which is then followed by the formation of water chains that extend along the channels connecting the hexagonal pores of the framework. Water present in these channels gradually coalesces and fills the hexagonal pores sequentially after the channels are completely hydrated. The development of hydrogen-bond networks inside the MOF pores as a function of relative humidity is characterized at the molecular level using experimental and computational infrared spectroscopy. A detailed analysis of the OH-stretch vibrational band indicates that the low-frequency tail stems from strongly polarized hydrogen-bonded water molecules, suggesting the presence of some structural disorder in the experimental samples. Strategies for designing efficient water harvesting MOFs are also proposed based on the mechanism of water adsorption in NU-1500-Cr.

Abstract

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