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PRINCIPAL PUBLICATION AND AUTHORS

CO2 adsorption in a robust iron(III) pyrazolate-based MOF: molecular-level details and frameworks dynamics from powder X-ray diffraction adsorption isotherms, R. Vismara (a,b), S. Terruzzi (c), A. Maspero (a), T. Grell (c), F. Bossola (d), A. Sironi (c), S. Galli (a,e), J.A.R. Navarro (b), V. Colombo (c,d,e), Adv. Mater. 2209907 (2023); https:/doi.org/10.1002/adma.202209907 (a) Università degli Studi dell Insubria, Como (Italy) (b) Universidad de Granada, Granada (Spain) (c) Università degli Studi di Milano, Milano (Italy) (d) CNR - Istituto di Scienze e Tecnologie Chimiche Giulio Natta , Milano (Italy) (e) Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali, Firenze (Italy)

REFERENCES

[1] Z. Ji et al., Adv. Funct. Mater. 30, 2000238 (2020). [2] C. Gropp et al., ACS Cent. Sci. 6, 1255 (2020). [3] D.E. Jaramillo et al., Nat. Mater. 19, 517 (2020). J. Oktawiec et al., Nat. Commun. 11, 3087 (2020). [4] D. Lenzen et al., Chem. Commun. 56, 9628 (2020). J. Lill et al., J. Phys. Chem. C 126, 2214 (2022). [5] Z.R. Herm et al., Science 340, 960 (2013).

pressure range P = 0-8 bar (Figure 51b). A glass capillary containing pre-activated Fe2(BDP)3 was connected to the gas handling system, which allows accurate dosing of the gas probe (Figure 52).

Ab-initio structure determination followed by Rietveld refinement made it possible to i) unveil the framework response to the gas entrance, ii) localise the CO2 primary adsorption sites and iii) quantify the amount of gas adsorbed. The host framework favours the adsorption process, as CO2 entrance is accompanied by a rotation of the ligand central ring. The three independent CO2 molecules, occupying the same primary adsorption sites irrespective of temperature and pressure (Figure 51c), were found to be involved in both host-guest and guest- guest interactions. Of higher relevance, highly reliable HR-PXRD adsorption isotherms were built for both temperatures (Figure 51d) by calculating the moles of adsorbed CO2 at each pressure point from the pertinent occupancy factors. The Freundlich-Langmuir model was successfully applied to the HR-PXRD adsorption isotherms, enabling, for the first time, the straightforward calculation of the isosteric heat of adsorption (Qst) by

applying the Clausius-Clapeyron equation (Figure 51e). Notably, the absolute values of Qst, which are in very good agreement with those obtained from conventional adsorption isotherms (Figure 51e), monotonically increase with increasing guest loading.

Overall, HR-PXRD adsorption isotherms enabled the extraction of detailed crystallographic features such as the host-guest interactions triggering/favouring the adsorption of the guest, and also revealed the thermodynamics of the adsorption process, which, for this case study, was indicative of a cooperative adsorption behaviour. This is thought to be the first time that such a detailed PXRD analysis has been performed for porous materials, showing that it is possible to go beyond the crystallochemistry and dynamics of the adsorption process to extract fundamental thermodynamic information. Notably, this work shows a very encouraging agreement between the results obtained from conventional volumetric adsorption experiments and HR-PXRD adsorption isotherms, opening the way to an increasing level of comprehension of adsorption processes through diffraction experiments.

Fig. 52: Illustration of the in-situ CO2 adsorption measurement setup at ID22.