The role of CO2 on climate change is motivating the development of new technologies for CO2 capture. In particular, adsorbents capable of direct air capture (DAC) of CO2 are highly sought since this process is not constrained to point sources. In addition, CO2 removal from confined environments such as NASA spacecraft requires highly selective and efficient adsorbents. Our group has been investigating metal-organic frameworks (MOFs) containing transition metal hydroxide (M–OH) groups as selective adsorbents for CO2 DAC. For example, CFA-1-ZnOH (Zn(ZnOH)4(bibta)3, bibta2– = 5,5’-bibenzotriazolate) adsorbs large amounts of CO2 at very low partial pressures (&gt;2 mmol g-1 at ≤ 5 mbar) via a reversible M–OH + CO2 = M–O2COH chemisorption process and can be regenerated with relatively mild heating. Short intercluster Zn-Zn distances (~7.7 A) between the secondary building units (SBUs) of this MOF result in synergistic hydrogen-bonding interactions that lead to its outstanding low-pressure CO2 adsorption performance. This presentation will discuss the synthesis and characterization of a novel Zn benzotriazolate MOF, Zn9(bbtCO)6(O2CCH3)6 (bbtCO2– = bis(1H-benzo[d][1,2,3]triazolate-5-yl)methanone). The structure of this new framework has been determined using a combination of electron and X-ray diffraction analysis, revealing the presence of Zn9 SBUs and short intercluster Zn–Zn distances of ~6 Å. Postsynthetic OAc–/OH– ligand exchange yields Zn9(bbtCO)6(OH)6, which shows good CO2 adsorption at very low pressures. Diffuse reflectance infrared Fourier transform spectroscopy confirms the formation of zinc bicarbonate groups upon adsorption CO2. Thermal swing adsorption/desorption experiments show that the MOF requires high temperatures for regeneration, indicating that the shortened intercluster Zn–Zn distance has a profound influence on CO2 adsorption.

Zinc benzotriazolate MOFs: Synthesis, characterization, and application for CO2 capture.

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