17O-1H correlation NMR spectroscopy provides accessible and direct insights into CO2 capture chemistry

Abstract

17O NMR spectroscopy is emerging as a powerful probe of the chemistry of CO2 capture and storage materials. However, the technique is currently underutilised, owing to (i) challenging spectral interpretation of quadrupolar nuclei (I = 5/2), especially when multiple oxygen environments are present, and (ii) the restricted access to ultra-high magnetic fields that are often required to obtain high signal-to-noise spectra. In this work, we demonstrate and expand the use of 17O-1H NMR correlation methods for application to CO2 capture materials. Utilising the robust and accessible nature of PRESTO and D-RINEPT sequences, we provide insights into CO2 binding sites in hydroxide-based metal-organic frameworks, MFU-4l-OH and CFA-1-OH. We report results readily obtained at accessible field strengths down to 9.4 T, highlighting the pros and cons compared to ultra-high field acquisition, and provide a refined model for the binding mechanism in CFA-1-OH, through uniquely accessible information of the zinc hydroxide binding sites. Finally, we include a brief Additional Information section at the end of this article detailing practical considerations for new 17O-1H correlation pulse sequence users.