Bio-base Metal Organic Frameworks as Potential CO₂ Adsorbents

Environmental friendliness and high adsorption capacity are important properties of CO₂ adsorbents. Bio-based metal–organic framework (bioMOFs) materials offer notable benefits for CO₂ capture. Amino acids like l-glutamic acid (Glu) and L-aspartate (Asp) are employed as ligands for the synthesis of bioMOFs, Asp-Cu and Glu-Cu. Characterization results confirmed that Asp-Cu and Glu-Cu possessed tertiary amine and secondary amine structures, respectively. The adsorption capacities of Glu-Cu and Asp-Cu were up to 253 mg·g⁻¹ and 277 mg·g⁻¹ at 1 bar CO₂ pressure and 190 mg·g⁻¹ and 223 mg·g⁻¹ at 0.15 bar CO₂ pressure. The CO₂ adsorption properties of bioMOFs were comprehensively evaluated under various conditions, including temperature, water content, SO₂ concentration, and other compositions. Adsorption data were fitted well with the pseudo-first-order kinetics and Weber-Morris intraparticle diffusion model. The kinetic studies revealed that a small amount of water significantly accelerated the pseudo-first-order kinetic constants, whereas excess water vapor greatly hindered the intra-diffusion constants of CO₂. The presence of SO₂ led to a decrease in the adsorption capacity of both MOFs due to rapid reactions occurring with active sites on the MOF surface. Furthermore, these bioMOFs were easily recovered and regenerated for at least 20 cycles. The primary CO₂ adsorption mechanism involved catalytic hydration reactions on Asp-Cu, while chemical adsorption occurred on Glu-Cu. Both mechanisms were accompanied by physical adsorption.