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

Abstract

While metal−organic frameworks (MOFs) are promising gas adsorbents, their tortuous microporous structures cause additional resistance for gas diffusion, thus hindering the accessibility of interior active sites. Here, we present a practical strategy to incorporate missing cluster defects into a representative low-coordinated MOFs structure, Mg-MOF-74, while maintaining the stability of a defect-rich structure. In this proposed method, graphene oxide (GO) is employed as modulator, and crystallization time is varied to promote defect formation by altering the nucleation and crystal growth processes. The best performing GOmodified Mg-MOF-74 sample (MOF@GO 40 h) achieved 18% and 15% improvement in surface area and total pore volume, respectively, over pristine Mg-MOF-74. The reduced diffusion resistance to gas flow translates to increased accessibility for gas molecules to active Mg adsorption sites inside the MOFs, leading to enhanced CO 2 capture performance; the CO 2 uptake quantity of MOF@GO 40 h arrives at 6.06 mmol/g at 0.1 bar and at 9.17 mmol/g at 1 bar and 25 °C, 19.29% and 16.37% higher, respectively, than that of the pristine Mg-MOF-74, with a CO 2 /N 2 selectivity around 17.36% greater than that of pristine Mg-MOF-74. Our study demonstrates a facile approach for incorporating defects into MOFs systems with low coordination environments, thus expanding the library of defect-rich MOFs beyond the current highly coordinated MOF systems.

Green, efficient and controllable synthesis of high-quality MOF-74 with high gravity technology

“…Acetic acid can partially replace the organic ligand (dhtp) and bind to the interior metal nodes of the framework structure, thereby blocking the connections between the metal sites and the organic ligands and creating defects in that region. 57,58 X-ray photoelectron spectroscopy (XPS) confirmed the presence of defects in MOF-74-Co-0.46 eq. HOAc (Fig.…”

Pore engineering of metal–organic frameworks for boosting low-pressure CO2 capture

“…Niu and co-workers found that graphene oxide could also be utilized as a modulator to alter the nucleation and growth of Mg-MOF-74 crystals, thus facilitating the formation of missing cluster defects. 119 At 298 K and 0.1 bar, the CO 2 uptake of the MOF@GO composite was enhanced by 19.29% due to the increased pore accessibility. Besides the modulator, changing the metal source has also been shown to introduce defects into MOFs.…”

Emerging porous materials for carbon dioxide adsorptive capture: progress and challenges

“…3B). In addition, defect control in porous materials could also influence the pore structure with enhancements to the pore volume and surface area, 35–37 giving rise to a further boost in capacity.…”