Ligand Defect Density Regulation in Metal–Organic Frameworks by Functional Group Engineering on Linkers

Abstract

Defects in solid materials vitally determine their physicochemical properties; however, facile regulation of the defect density is still a challenge. Herein, we demonstrate that the ligand defect density of metal–organic frameworks (MOFs) with a UiO-66 structural prototype is precisely regulated by tuning the linker groups (X = OMe, Me, H, F). Detailed analyses reveal that the ligand defect concentration is positively correlated with the electronegativity of linker groups, and Ce-UiO-66-F, constructed by F-containing ligands and Ce-oxo nodes, possesses the superior ligand defect density (>25%) and identifiable irregular periodicity. The increase in ligand defect density results in the reduction of the valence state and the coordination number of Ce sites in Ce-UiO-66-X, and this merit further validates the relationship between the defective structure and catalytic performance of CO2 cycloaddition reaction. This facile, efficient, and reliable strategy may also be applicable to precisely constructing the defect density of porous materials in the future.

Tethering Effects in Oligomer-Based Metal–Organic Frameworks

“…FTIR bands in molecular IRMOF-1 associated with the −COO – asymmetric stretch (1610 cm –1 , 1508 cm –1 ) and −COO – symmetric stretch (1393 cm –1 ) of the bdc 2– ligand are shifted to lower frequencies in oligoIRMOF-1 samples (1607–1605, 1498–1496, and 1387–1385 cm –1 , respectively; Figure ). These modest shifts are attributed to electron donation of the alkoxy side groups in the bdc 2– oligomers . There is no evidence of large populations of uncoordinated linker −COOH groups, which can be generally identified by a band at ∼1650 cm –1 , although a shallow stretch at this energy is visible in some of the oligoIRMOF-1 samples (Figure S20).…”

Strategies for induced defects in metal–organic frameworks for enhancing adsorption and catalytic performance

“…The synthesis of MOFs, including isoreticular ligand series, which can manage the pore size with different lengths, is possible to induce defects. 45 The final MOF binds a mixture of organic ligands and shows an odd breathing behavior by reversibly losing the long-range crystalline order by evacuation. Therefore, this method of synthesis can be applied as a strategy to introduce the defect structure into the MOFs.…”

Advanced Transmission Electron Microscopy for Identification of Atomic‐Scale Configurations of Zeolite‐Supported Metal Catalysts

“…[ 9 ] The effective means to obtain ultrathin imaging area (< 5 nm is the best) and enhance the contrast of the metal species that could be differentiated with the zeolite framework atoms are the key points. Our recently developed iDPC‐assisted HAADF‐STEM imaging approach [ 10 ] may provide an alternative that the iDPC‐STEM is first used for the sample searching and adjustment under ultra‐low beam current and HAADF‐STEM is then collected only one shot after increasing the beam current for quantitative analysis based on Z 2 contrast. This method that not only minimizes the electron dose but also enhances the contrast for low atomic number metal species is valid in revealing the intrinsic structures of electron beam‐sensitive materials.…”