Synthesis and characterization of novel bimetallic Mg-Ca/DOBDC metal–organic frameworks as a high stability CO2 adsorbent

In this work, novel bimetallic Mg-Ca/DOBDC MOFs (a MOFs built of Mg(OAc)2·4H2O and Ca(OAc)2·H2O linked by 2,5-dioxido-1,4-benzenedicarboxylate (DOBDC) ligands) were prepared for the first time using Mg2+ as the major metal and Ca2+ as the second metal. The dynamic CO2 adsorption performance of the novel synthesized bimetallic MOFs was comprehensively tested and discussed, including the second metal content, inlet gas flow rate and adsorption temperature. The influence of the second metal Ca on the structure and morphology of original Mg/DOBDC MOF was intensively studied. Furthermore, CO2 penetration curve model and adsorption mechanism of the bimetallic MOFs in the adsorption–desorption cycle were also discussed. The results showed that the introduction of the second metal Ca creates unsaturated vacancies and increases the metal active sites, thus improving the gas adsorption performance and structural stability of the material. The Mg-Ca3.0/DOBDC MOFs with Ca doping of 3.0 mmol showed a maximum CO2 uptake of 10.92 mmol g−1 at 0.1 MPa and 25 °C. Compared with the parent Mg/DOBDC MOF, it was improved by about 151.16%, and its cyclic stability was also greatly improved.