Understanding the role of defective sites and pores functionalization in the adsorption properties of a robust pyrazolate-based Metal Organic Framework for CO2 capture

Fossil fuels are a major source of energy worldwide, accounting for more than 85% of global energy consumption, but their combustion releases significant amounts of CO2 into the environment. Until greener energy sources become practicable, CO2 sequestration remains the most viable option for reducing anthropogenic CO2 emissions. Lately, metal-organic frameworks (MOFs) have received considerable attention for CO2 capture and storage (CCS) applications. MOFs are crystalline open coordination networks formed via the self-assembly of metal cations or inorganic clusters and polydentate organic linkers. The adsorption behavior of porous materials is greatly impacted by their microstructural features, such as surface area, topology of the network, and the presence of defective sites.1 In this context, we selected a pyrazolate-based MOF, Fe2(BDP)3 [H2BDP = 1,4-bis(1H-pyrazol-4-yl)benzene],2 known for its exceptionally high thermal and chemical stability, to investigate the role of defective sites in the CO2 uptake process. To this aim, we synthesized a series of MOF samples with different amounts of acid modulator, to tune the concentration of defects within the framework. To further explore the effect of the pores functionalization, the amino-tagged derivatives, Fe2(BDP)1-x(BDP-NH2)x [H2BDP-NH2 = 2-amino-1,4-bis(pyrazol-4-yl)benzene; x = 0.5, 1], were also prepared. The materials were characterized through adsorption experiments and a combination of short- and long-range techniques: in situ XAS, PXRD, and PDF analysis. Moreover, the dynamic structure was investigated using in situ high-resolution powder X-ray diffraction (HR-PXRD) at variable temperature and gas pressure, which is an invaluable tool to gain insight into the localization of adsorption sites and thermodynamic information of the CO2 adsorption mechanism.3 1. E. López-Maya et al. Adv. Funct. Mater. 2014, 24, 6130. 2. Z.R. Herm et al. Science 2013, 340, 960. 3. R. Vismara et al. Adv. Mater. 2024, 36, 2209907.