Multivariate metal-organic framework MTV-MIL-101 via post-synthetic cation exchange: is it truly achievable?

Multivariate metal-organic frameworks generated through post-synthetic modification: impact and future directions

Reticular chemistry has proven to be invaluable over time, thanks to the structural versatility, and tailored porosity observed in structures like metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and metal-organic polyhedra (MOPs). Despite the wide array of ligands and metals available for synthesizing MOFs, they are still somewhat constrained by the reliance on de novo conditions and the focus on generating MOFs with single ligand and metal. To surpass these limitations, researchers have established strategies to generate multivariate (MTV) MOF structures incorporating more than one ligand/metal into the crystal lattice. MTV-MOFs have demonstrated enhanced properties by virtue of the additional functionalities incorporated within their structures. One approach to developing MTV-MOFs is through post-synthetic modification (PSM), where new functionalities are introduced after the initial synthesis, thereby achieving the enhanced properties of MTV-MOFs even in cases where the new functionalities are incompatible with MOF synthesis.

Pebax® 2533/PVDF thin film mixed matrix membranes containing MIL-101 (Fe)/GO composite for CO2 capture

MIL-101 (Fe) and MIL-GO composites were successfully synthesized and used as fillers for the preparation of Pebax® 2533/PVDF thin film MMMs for CO₂/N₂ separation. The defect-free Pebax® 2533/PVDF thin film MMMs were fabricated by casting the Pebax solution containing fillers on the PVDF support. The presence of GO nanosheets in the reaction solution did not destroy the crystal structure of MIL-101 (Fe). However, the BET surface area and total pore volume of MIL-GO decreased dramatically, comparing with MIL-101 (Fe). The incorporation of MIL-GO-2 into Pebax matrix simultaneously increased the CO₂ permeability and the CO₂/N₂ ideal selectivity of Pebax® 2533/PVDF thin film MMMs mainly owing to the porous structure of MIL-GO-2, and the tortuous diffusion pathways created by GO nanosheets. MMMs containing 9.1 wt% MIL-GO-2 exhibited the highest CO₂ permeability equal to 303 barrer (1 barrer = 10⁻¹⁰ cm³ (STP) cm cm⁻² s⁻¹ cmHg⁻¹) and the highest CO₂/N₂ ideal selectivity equal to 24. Pebax-based MMMs containing composite fillers showed higher gas separation performance than the Pebax-based MMMs containing single filler (GO or MOFs). Therefore, the synthesis and utilization of 3D@2D composite filler demonstrated great potential in the preparation of high-performance MMMs for gas separation processes.

MIL-101 (Fe) and MIL-GO composites were successfully synthesized and used as fillers for the preparation of Pebax® 2533/PVDF thin film MMMs for CO₂/N₂ separation.