Biogas upgrading involves CO2 removal from raw biogas to produce biomethane, a sustainable biofuel well aligned with international climate goals. Therefore, the development of efficient and cost-effective CO2 separation technologies to scale-up the production of biomethane is imperative.[1] In this context, an appealing candidate is F4_MIL-140A(Ce), an ultramicroporous Metal-Organic Framework based on Ce(IV) and tetrafluoroterephthalic acid as organic linker (Figure 1). This system exhibits a non-hysteretic step-shaped CO2 adsorption isotherm whose molecular origin is attributed to a cooperative CO2 mechanism that involves the concerted rotation of fluorinated aromatic rings.[2,3] To better understand the influence of fluorination of ligands on the absorption behaviour, we herein report a ligand engineering approach targeting the MIL-140A(Ce) topology and involving terephthalic linkers with different degree of fluorination and isomerism (Figure 1). To this end, we synthesised novel Fx-MIL_140A(Ce) MOFs by means of both an acetonitrile-based solvothermal synthesis and a milder methanol/water mixed solvent approach. The former route led to highly crystalline MOFs having unreacted linkers and fluoride ions trapped in the pores, while the latter allowed to obtain clean materials, although with lower crystallinity. The MOFs were characterized by solid-state NMR techniques that shed light on their local structure, as well as gas adsorption measurements. No step-shaped CO2 isotherm was observed, unravelling a strong relationship between the fluorination degree of the linker and the adsorption behaviour of the resulting materials. These results open the way to deeper experimental and computational investigations into structure-property relationship which will guide the design of such advanced materials and rationalize their separation performance. Figure 1. Linkers with different degree of fluorination and isomerism used in this work. [1] R. Murano, et al. Energies, 2021, 2431, 1-14 [2] R. D'Amato, et al. ACS Sustainable Chem. Eng. 2019, 7, 394-402 [3] M. Cavallo, et al. J. Mater Chem. A. 2023, 11, 5568-5583
Ligand engineering in MIL-140A(Ce) Metal- Organic Frameworks for biogas upgrading
Francesca Nardelli;Lucia Calucci;
2023
Abstract
Biogas upgrading involves CO2 removal from raw biogas to produce biomethane, a sustainable biofuel well aligned with international climate goals. Therefore, the development of efficient and cost-effective CO2 separation technologies to scale-up the production of biomethane is imperative.[1] In this context, an appealing candidate is F4_MIL-140A(Ce), an ultramicroporous Metal-Organic Framework based on Ce(IV) and tetrafluoroterephthalic acid as organic linker (Figure 1). This system exhibits a non-hysteretic step-shaped CO2 adsorption isotherm whose molecular origin is attributed to a cooperative CO2 mechanism that involves the concerted rotation of fluorinated aromatic rings.[2,3] To better understand the influence of fluorination of ligands on the absorption behaviour, we herein report a ligand engineering approach targeting the MIL-140A(Ce) topology and involving terephthalic linkers with different degree of fluorination and isomerism (Figure 1). To this end, we synthesised novel Fx-MIL_140A(Ce) MOFs by means of both an acetonitrile-based solvothermal synthesis and a milder methanol/water mixed solvent approach. The former route led to highly crystalline MOFs having unreacted linkers and fluoride ions trapped in the pores, while the latter allowed to obtain clean materials, although with lower crystallinity. The MOFs were characterized by solid-state NMR techniques that shed light on their local structure, as well as gas adsorption measurements. No step-shaped CO2 isotherm was observed, unravelling a strong relationship between the fluorination degree of the linker and the adsorption behaviour of the resulting materials. These results open the way to deeper experimental and computational investigations into structure-property relationship which will guide the design of such advanced materials and rationalize their separation performance. Figure 1. Linkers with different degree of fluorination and isomerism used in this work. [1] R. Murano, et al. Energies, 2021, 2431, 1-14 [2] R. D'Amato, et al. ACS Sustainable Chem. Eng. 2019, 7, 394-402 [3] M. Cavallo, et al. J. Mater Chem. A. 2023, 11, 5568-5583I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
