Defect Engineering of Low-Coordinated Metal-Organic Frameworks (MOFs) for Improved CO2 Access and Capture

Whilemetal-organic frameworks (MOFs) are promisinggasadsorbents, their tortuous microporous structures cause additionalresistance for gas diffusion, thus hindering the accessibility ofinterior active sites. Here, we present a practical strategy to incorporatemissing cluster defects into a representative low-coordinated MOFsstructure, Mg-MOF-74, while maintaining the stability of a defect-richstructure. In this proposed method, graphene oxide (GO) is employedas modulator, and crystallization time is varied to promote defectformation by altering the nucleation and crystal growth processes.The best performing GO-modified Mg-MOF-74 sample (MOF@GO 40 h) achieved18% and 15% improvement in surface area and total pore volume, respectively,over pristine Mg-MOF-74. The reduced diffusion resistance to gasflow translates to increased accessibility for gas molecules to activeMg adsorption sites inside the MOFs, leading to enhanced CO2 capture performance; the CO2 uptake quantity of MOF@GO40 h arrives at 6.06 mmol/g at 0.1 bar and at 9.17 mmol/g at 1 barand 25 & DEG;C, 19.29% and 16.37% higher, respectively, than thatof the pristine Mg-MOF-74, with a CO2/N-2 selectivityaround 17.36% greater than that of pristine Mg-MOF-74. Our study demonstratesa facile approach for incorporating defects into MOFs systems withlow coordination environments, thus expanding the library of defect-richMOFs beyond the current highly coordinated MOF systems.