Important role of open copper sites on adsorption of various molecules in Cu-BTC metal organic framework

Authors: Iuliia Mikulska (Diamond Light Source) , Roberto Boada (Diamond Light Source; Universitat Autònoma de Barcelona) , Shusaku Hayama (Diamond Light Source) , Matteo Aramini (Diamond Light Source) , Luke Keenan (Diamond Light Source) , Monica Amboage (Diamond Light Source) , Sofia Diaz-Moreno (Diamond Light Source)
Co-authored by industrial partner: No

Type: Conference Paper
Conference: XAFS2021
Peer Reviewed: No

State: Published (Approved)
Published: July 2021

Abstract: Cu-BTC metal-organic framework (MOF) has been found to be a promising candidate for removing hazardous substances from air via adsorption1. To understand the role that the copper sites in Cu-BTC play in the adsorption process, we have performed a detailed X-ray absorption spectroscopy (XAS) study. Conventional XAS and high energy resolution fluorescence detection XAS (HERFD-XAS) were collected on degassed Cu-BTC, and after being exposed to CO2, water and benzene. The EXAFS analysis reveals that, although the local environment around the copper centers in all samples is similar, differences can be found in the first and second coordination shells. We have found that the Cu-O distance in the first coordination shell is slightly larger when the sample is immersed in water and benzene than in the degassed sample, while it does not change for the sample exposed to CO2. Small differences are also observed in the Cu-Cu distance, gradually increasing from 2.49 Å in the degassed sample, to 2.52 Å, 2.58 Å and 2.63 Å upon adsorption of CO2, benzene and water, respectively. HERFD-XAS has been used to obtain information about the electronic and geometric structure around the copper metal centers, as the use of high energy resolution enhances the features in the XANES spectrum enabling the detection of subtle changes2. We have observed differences in the intensity and the energy position of some of the XANES spectral features upon adsorption of different adsorbates that can be attributed to changes in the local environment around the copper centers, as detected in the EXAFS analysis. In this study we show that XAS is a powerful and very sensitive tool for studying host-guest interactions in MOFs, providing atomic-level insights into adsorption mechanisms.

Subject Areas: Materials, Chemistry

Instruments: I20-EDE-Energy Dispersive EXAFS (EDE)

Added On: 09/08/2021 13:16

Discipline Tags:

Chemistry Materials Science Metal-Organic Frameworks Metallurgy Organometallic Chemistry

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) High Energy Resolution Fluorescence Detected XAS (HERFD-XAS)