Insights into the Structure and Adsorption Properties of a Novel Aluminum L-Aspartate Metal-Organic Frame-work

Herein we report on the green synthesis of the novel aluminum-based metal organic framework (MOF) Al(OH)( L -Asp) (L-H2Asp = L-aspartic acid; Al-L-Asp) isostructural to Al-fumarate. The synthesis was performed in mild conditions by using GVL (GVL = γ-valero lactone), a solvent derived from biomasses valorization. The MOF structure, modelled through DFT calculations, is consti-tuted of 1D-infinite Al-hydroxo chains connected by the carboxylic groups of L-aspartic acid with a framework topology similar to that of Al-MIL-53. Al-L-Asp displays thermal stability up to 240 °C and no breathing effects are observed upon thermal activa-tion. SS-NMR was used to investigate the activation process and chemical details of the pore structure and of the activation dy-namics. The activated MOF has been exploited in carbon dioxide adsorption. The BET surface area is about 600 m2g-1 and the MOF CO2 capture capacity reaches 3.2 mmol∙g-1 at T = 0° C and pCO2 = 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 30 kJ∙mol-1, proving the beneficial effect of the pres-ence of an amino-group on the linker skeleton on the CO2-MOF interaction. CO2/N2 IAST selectivity is relatively high, ranging from 60 to more than 80 at increasing pressure range (from 0.1 to 1 bar). These values overcome those measured for the analogue fumarate MOF and they are comparable to the benchmark compounds for CO2 in post-combustion adsorption applications.