Structure and Carbon Dioxide Adsorption Properties of a Nanosized Aluminum l -Aspartate Metal–Organic Framework

Herein, we report on the green synthesis of a nanosized (40 nm average size platelet crystals) aluminum-based metal−organic framework (MOF) [Al(OH)(L-Asp)(HNO3)0.31]·1.5H2O (L-H2Asp = L-aspartic acid; Al-L-Asp), composed of nanometric crystals and isostructural to Al-fumarate. The synthesis was performed under mild conditions using γ-valerolactone (GVL), a solvent derived from biomass valorization. The MOF structure, modeled through DFT calculations, is constituted of 1D- infinite Al-hydroxochains connected by the carboxyl icgroups of L-aspartic acid with the same framework topology as that of Al- MIL-53. Al-L-Asp displays thermal stability up to 240 °C , and no breathing effects are observed up on thermal activation. Solid-state NMRwasusedtoinvestigatetheactivationprocessandchemicaldetailsoftheporestructureandactivationdynamics.Theactivated MOF has been exploited in carbon dioxide adsorption. The BET surface area is about 600 m2·g−1 , and the MOF CO2 capture capacity reaches 3.2 mmol·g−1 at T = 0 °C and pCO 2 = 1 bar. Remarkably, compared to the Al-fumarate analogue, the CO2 heat of adsorption is increased from about 20 kJ·mol−1 to a value of 30kJ·mol−1 , proving the beneficial effect of the presence of an amino group on the linkers keleton on the CO2-MOF interaction. CO2/N2IAST selectivity is relatively high, ranging from 60 to more than 80 at increasing pressure range (from 0.1 to 1bar). These values overcome those measured for the analogue fumarate MOF, and they are comparable to the benchmark compounds for CO2 in postcombustion adsorption applications.