Molecular-Level Insight into CO2 Adsorption on the Zirconium-Based Metal-Organic Framework, UiO-66: A Combined Spectroscopic and Computational Approach

Carbon dioxide (CO2) capture and separation in sorbent materials relies on the interactions that take place between guest molecules and topological or chemical features of the sorbent. Although researchers have developed an immense library of metal-organic framework (MOP) designs, which range in shape, size, and chemical functionality, a molecular-level understanding of how MOF structure and functionality affect capture and transport has yet to be fully achieved. In this work, in situ infrared spectroscopic techniques, coupled with density functional theory, were used to provide insights into the binding locations and energetics of CO2 on the zirconium-based MOF, UiO-66. Two unique CO2 binding motifs in UiO-66 were identified through differing vibrational frequencies of the asymmetric OCO stretching mode. One configuration is established through hydrogen bonding with mu(3)-OH groups on the MOF nodes, and a second binding mode exists where CO2 is stabilized through dispersive interactions. Variable temperature infrared spectroscopy revealed adsorption enthalpies of -38.0 1.5 and -30.2 +/- 1.3 kJ/mol for the hydrogen-bonded and dispersion-stabilized complexes, respectively. The techniques and results from this study can be extended to other gas-MOF systems to reveal how topological features affect gas sorption and to provide insight into the next-generation sorbent material designs.