Facile synthesis of MOFs with uncoordinated carboxyl groups for selective CO₂ capture via postsynthetic covalent modification

Abstract

A postsynthetic covalent strategy involving dual-acyl chloride has been developed to introduce uncoordinated carboxyl groups into amine containing metal-organic frameworks (MOFs). The carboxyl group functionalized MOFs have been characterized by various techniques, including X-ray diffraction patterning, scanning electron microscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance, thermal gravimetric analysis, and gas adsorption. Results clearly indicated uncoordinated carboxyl groups were successfully grafted to the MIL-101(Cr)-NH 2 framework. In addition, most of the amine groups (>80%) were grafted with carboxyl groups, which indicates this method is very effective.The thermal stability and adsorption selectivity of CO 2 /N 2 were substantially enhanced, albeit the BET surface areas and total pore volumes were reduced. These observations could be explained by the effect of elimination of macropores in the framework due to the projecting of new functional groups in pore apertures. Here the successful fabrication of a MOF with uncoordinated carboxyl groups provides the possibility of efficiently modifying other MOFs.

Hierarchical Porous and Zinc‐Ion‐Crosslinked PIM‐1 Nanocomposite as a CO2 Cycloaddition Catalyst with High Efficiency

“…[15] The results for PIM-1, PIM-COONa, and PIM-COONa-Zna re shown in Figure 6b-d. PIM-COONa-Zn achieves the highest CO 2 /N 2 selectivity,w hich is stable at 55 for flue gas and at 52 for ideal gas at 0.1 MPa. [24] After metalation,t he positively charged Zn 2 + of PIM-COONa-Zn can further generated ipole-dipole interactions with CO 2 through electrostatic interactions. [35] The increasing CO 2 adsorption with pressure is caused by the increased interaction of COO À with CO 2 .F irst, the carboxyl groups increase the interaction enthalpy between the ligand framework and CO 2 molecules and, simultaneously,m itigate the entropyl oss upon CO 2 adsorption through the formation of multiple configurations for the interactionsb etween carboxyl groupsa nd CO 2 molecules.…”

“…[35] The increasing CO 2 adsorption with pressure is caused by the increased interaction of COO À with CO 2 .F irst, the carboxyl groups increase the interaction enthalpy between the ligand framework and CO 2 molecules and, simultaneously,m itigate the entropyl oss upon CO 2 adsorption through the formation of multiple configurations for the interactionsb etween carboxyl groupsa nd CO 2 molecules. [24] After metalation,t he positively charged Zn 2 + of PIM-COONa-Zn can further generated ipole-dipole interactions with CO 2 through electrostatic interactions.…”

“…The pendant nitrile groups can be converted into carboxyl groups by one-step hydrolysis in basic solution. [24] Therefore, introducing COOH should be af easible approach for enhancing bondingi nteractions. [23] In addition to diverse coordination modelsg enerated from the COOH group, the negatively charged COO À can further form strong electrostatic interactions with positively charged metal ions through strong ionicb onds, compared with the single-coordination effect.…”

“…In addition to this stable complexation, COOH is an ucleophilic reagent that promotes the ring-opening of the epoxidea nd then the cycloaddition of CO 2 .F urthermore, COOH-based ligandsh ave relatively high adsorption capacity for CO 2 because of the strong interaction and high adsorptionh eat. [24] Therefore, introducing COOH should be af easible approach for enhancing bondingi nteractions. The high surfacea rea of the PIM backbone promotest he highly active metal-ion sites, and the ionic bond plays ap ositive role to improve the bonding structure stability.I ti sw orth mentioning that the hierarchical porous structure promotes mass transport, but most current hierarchicalp orous polymers are prepared by template methods.…”

Exfoliated Molybdenum Disulfide Encapsulated in a Metal Organic Framework for Enhanced Photocatalytic Hydrogen Evolution

“…Previous studies have mostly focused on MOFs for sensing, drug delivery, batteries and selective catalysis. Their application as photocatalysts, however, has not been thoroughly reported, and their photocatalytic ability is limited as MOFs lack the capacity to absorb visible light [15,16]. While it is well known that bulk MoS 2 is unsuitable for photocatalytic applications owing to its inadequate reduction and oxidation capabilities, exfoliated MoS 2 shows a direct band gap of 1.9~3.9 eV due to quantum confinement.…”