Modulator-Mediated Functionalization of MOF-808 as a Platform Tool to Create High-Performance Mixed-Matrix Membranes

Abstract

Modulator mediated functionalization (MoFu) is introduced as a new and versatile platform tool to improve the separation performance of MOF-based membranes, exemplified here by the creation of mixed-matrix membranes (MMMs) with enhanced CO2 separation efficiency. The unique structure of MOF-808 allows incorporation of CO2-philic modulators in the MOF framework during a one-pot synthesis procedure in water, thus creating a straightforward way to functionalize both MOF and corresponding MMM. As a proof of concept, a series of fluorinated carboxylic acids (trifluoroacetic acid (TFA), pentafluoropropionic acid (PFPA) and heptafluorobutyric acid (HFBA)) and non-fluorinated alkyl carboxylic acids (acetic acid (AA), propionic acid (PA) and butyric acid (BA)) were used as modulator during MOF-808 synthesis.Two of the best MMMs prepared with 30 wt% MOF-TFA (100% increase in CO2/CH4 separation factor, 350% increase in CO2 permeability) and 10 wt% MOF-PFPA (140% increase in CO2/CH4 separation factor, 100% increase in CO2 permeability) scored very close to or even crossed the 2008 and 2018 upperbound limits for CO2/CH4. Due to its facile functionalization (and its subsequent excellent performance), MOF-808 is proposed as an alternative for widely used UiO-66, which is, from a functionalization point-of-view and despite its widespread use, a rather limited MOF.

Monodispersed MOF-808 Nanocrystals Synthesized via a Scalable Room-Temperature Approach for Efficient Heterogeneous Peptide Bond Hydrolysis

“…For example, one very recent effort with MOF-808 produced nanoparticles with low BET surface area (622 m 2 /g) and poor crystallinity. 49 In our case, we control the crystal size via a concentration-induced method (illustrated in Figure 2a), where the volume of water and formic acid are kept constant and the concentration of Zr 6 oxoclusters and BTC linker simultaneously tuned. The MOF-808-RT synthesized with BTC concentration of 18.75 mg/ mL exhibits a uniform crystal size of 850 (±10) nm (labeled "850 nm MOF-808" in the following) according to scanning electron microscopy (SEM) images (Figure 2b).…”

S,O-Functionalized Metal–Organic Frameworks as Heterogeneous Single-Site Catalysts for the Oxidative Alkenylation of Arenes via C–H activation

“…MOF-808 ([Zr6(µ3-O)4(µ3-OH)4(btc)2(CH3COO)6]; btc 3− = 1,3,5-benzenetricarboxylate) was chosen as a support to attach L1 for several reasons: (1) the modulator ligands (formate, acetate, etc.) on the Zr6-clusters can readily be exchanged by other ligands with carboxylic acid groups via solvent-assisted ligand exchange (SALE); [66][67][68] (2) the large adamantane cages with an internal pore diameter of 18.4 Å can accommodate the ligands without limiting the diffusion of reactants and products; 69,70 (3) the high oxidation state of Zr IV ensures a strong bond between the Zr6-cluster and the carboxylate group of the ligand, yielding chemically and thermally stable functionalized materials; 71,72 (4) MOF-808 can be produced cheaply on a large scale via a facile "green" synthesis route. 73 Methanol was chosen as the solvent for the SALE since it increases the mobility of the modulators on the Zr6-clusters.…”

Modulated synthesis of thiol-functionalized fcu and hcp UiO-66(Zr) for the removal of silver(i) ions from water

“…The thiophilic character of silver and mercury metal cations is well-known inliterature and can be explained by the HSAB concept (HSAB = hard and soft acids and bases) where interactions of soft Lewis bases (like thiol or thiolate) and soft Lewis acids are preferred. 43 It is well established that the addition of monocarboxylic acid modulators, like benzoic acid or acetic acid, 3 can enhance the formation of defects in UiO-MOFs, 44,45 which in turn can improve porosity, 46 stability 47 and even catalytic activity. 6a In this work we used mercaptoacetic acid (HMAc, Scheme 1) to modulate the synthesis of UiO-66, opening the potential of an easy and low-cost method for the introduction of thiol groups into the UiO-66 framework while preserving general UiO-66 properties like porosity and stability.…”