Defect-Free MOF-Based Mixed-Matrix Membranes Obtained by Corona Cross-Linking

Abstract

Functionalized UiO-66 metal–organic frameworks (MOF) particles were covalently grafted with hydride-terminated poly­(dimethylsiloxane) (PDMS) via postsynthetic modification. These PDMS-coated MOF particles (termed here “corona-MOF”) were used in the preparation of mixed-matrix membranes (MMMs). Defect-free MMMs with weight loadings of 50% were achieved with corona-MOF particles, attributed to the improved dispersibility of the corona-MOF particles and covalent linkages between the corona-MOF particles and the polymer matrix. The PDMS MMMs showed distinct separation features in single gas permeation tests, displaying much higher CO2 gas permeation with no decrease in selectivity when compared to MMMs prepared with unmodified UiO-66 particles. Single gas separation tests with CO2, N2, and propane were performed to probe the separation mechanism of the corona-MOF MMMs, demonstrating that these MMMs avoid nonideal “sieve-in-a-cage” and “plugged sieves” scenarios. Additionally, due to covalent bond formation between both the MOF and the polymer matrix in corona-MOF MMMs, particle aggregation is negligible during film curing, allowing for the formation of flexible, self-standing MMMs of <1 μm in thickness. Low quantities of polymer covalently attached to the MOF surface (<5 wt %) are sufficient to fabricate thin, defect-free, high MOF-loading MMMs.

The surface chemistry of metal–organic frameworks and their applications

“…2a) for improved incorporation into poly (vinyl alcohol) membranes, 35 while UiO-66 containing pendant allyl groups has been modified with silane-terminated polydimethylsiloxane oligomers that allow enhanced incorporation and crosslinking into a PDMS matrix. 41 Direct polymerization from MOF surfaces is also being explored. Reacting UiO-66-NH 2 with a bulky dianhydride installs anhydrides at the MOF particle surfaces, which can be reacted with diamines and subsequently imidized to generate a polyimide-coated MOF hybrid capable of membrane formation at up to 88% w/w MOF.…”

Metal Organic Framework — Based Mixed Matrix Membranes for Carbon Dioxide Separation: Recent Advances and Future Directions

“…Based on the type and structure of the polymer matrix, a wide range of MOFs are available to be used as fillers with a variety of organic functionalities and chemical flexibility of the organic part of the framework. Besides, suitable post-synthetic modification of MOFs can significantly enhance the polymer-MOF interfacial interaction and increase the separation efficiency (Katayama et al, 2019 ). Recently, MMMs have also been developed in situ by growing MOFs within the polymer matrix followed by curing of the latter.…”

“…(F) Formation of corona-MOFs and the respective corona-MOF loaded PDMS MMM. Reproduced from Katayama et al ( 2019 ) with permission from ACS. (G) Formation of PDA@ZIF-8 and the possible CO 2 transport mechanism in Pebax/PDA@ZIF-8 MMMs.…”

“…50 wt. % of corona-MOF particles were subsequently incorporated to the PDMS matrix to fabricate a defect-free MMM (Katayama et al, 2019 ). Corona-MOF based MMMs possess a robust covalent interaction between both MOF and the polymer phases leading to negligible particle aggregation during the film curing and resulting in free-standing, flexible MMMs of <1 μm thickness ( Figure 5F ).…”

Improved gas transport properties of polyurethane–urea membranes through incorporating a cadmium‐based metal organic framework

“…39 Among these fillers, MOFs have shown a great potential for use in the fabrication of MMMs for CO 2 capture due to their high porosity, diversity in synthesis and modification, and selectivity toward a specific gas. 40,41 Additionally, high surface area and excellent dispersibility of MOFs in the most polymers have led to an improvement in the gas permeability, selectivity, or both. [42][43][44][45] PIM-UiO66 membranes with different ligands and particle sizes were developed.…”