Boosting the CO2 adsorption performance by defect-rich hierarchical porous Mg-MOF-74

[Display omitted] •Hierarchical porous Mg-MOF-74 was synthesized by weak coordination of Cl−.•The mesoporous content of hierarchical porous Mg-MOF-74 reached 34.90%.•The CO2 saturated adsorption capacity increased by 15% at ambient pressure.•The IAST selective adsorption performance of CO2/N2 increased by 20 times.•The adsorption capacity and rate of low pressure were improved. Adsorbents with high adsorption capacity and high selectivity are crucial for carbon capture, utilization and storage (CCUS) technology applied to industrial flue gas to reduce carbon emissions. In this paper, a defect-rich hierarchical porous Mg-MOF-74 was synthesized successfully with MgCl2·6H2O used as a metal source considering that the weak coordination of Cl− may interfere with the normal coordination process of metal centers and organic ligands, which causes the formation of crystal defects. Through the analysis of a series of characterizations, ligand deletion of Mg-MOF-74 prepared with MgCl2·6H2O was confirmed, and the deleted ligand was estimated to be approximately 20% compared with the traditional Mg-MOF-74 prepared with Mg(NO3)2·6H2O, which led to mesopores accounting for 36.9%, and the width of mesopores reached 13.1 nm. Compared with traditional Mg-MOF-74, the adsorption heat of CO2 at zero load of the defect-rich hierarchical porous Mg-MOF-74 increased from 36 kJ·mol−1 to 46 kJ·mol−1, and the saturated adsorption capacity of CO2 under ambient pressure was improved by 15%. Interestingly, the IAST selective adsorption performance of CO2/N2 was increased by 20 times. Compared with the saturated adsorption capacity for traditional Mg-MOF-74, the equivalent adsorption capacity of hierarchical porous Mg-MOF-74 only needs 17 kPa, indicating that it is suitable for carbon capture operation in a real flue environment. Calculations of density functional theory (DFT) confirmed that the active site of the hierarchical porous Mg-MOF-74 has a lower adsorption energy with CO2 due to the presence of defects, which is regarded to play a key role in improving the CO2 capture performance.