Disclosing the Role of Defect‐Engineered Metal–Organic Frameworks in Mixed Matrix Membranes for Efficient CO₂ Separation: A Joint Experimental‐Computational Exploration

Abstract

Incorporation of defects in metal-organic frameworks (MOFs) offers new opportunities for manipulating their microporosity and functionalities. The so-called "defect engineering" has great potential to tailor the mass transport properties in MOF/polymer mixed matrix membranes (MMMs) for challenging separation applications, for example, CO 2 capture. This study first investigates the impact of MOF defects on the membrane properties of the resultant MOF/polymer MMMs for CO 2 separation. Highly porous defect-engineered UiO-66 nanoparticles are successfully synthesized and incorporated into a CO 2 -philic crosslinked poly(ethylene glycol) diacrylate (PEGDA) matrix. A thorough joint experimental/simulation characterization reveals that defect-engineered UiO-66/PEGDA MMMs exhibit nearly identical filler-matrix interfacial properties regardless of the defect concentrations of their parental UiO-66 filler. In addition, nonequilibrium molecular dynamics simulations in tandem with gas transport studies disclose that the defects in MOFs provide the MMMs with ultrafast transport pathways mainly governed by diffusivity selectivity. Ultimately, MMMs containing the most defective UiO-66 show the most enhanced CO 2 /N 2 separation performance-CO 2 permeability = 470 Barrer (four times higher than pure PEGDA) and maintains CO 2 /N 2 selectivity = 41-which overcomes the trade-off limitation in pure polymers. The results emphasize that defect engineering in MOFs would mark a new milestone for the future development of optimized MMMs.

Mitigated Aging in a Defective Metal–Organic Framework Pillared Polymer of an Intrinsic Porosity Hybrid Membrane for Efficient Gas Separation

“…Defective UiO-66 nanoparticles can be fabricated using FA to create defects in the framework by replacing the original organic linkers (denoted as UiO-66-FA) . As shown in Figure a, the main powder X-ray diffraction (PXRD) peaks from UiO-66 and UiO-66-FA samples are in good agreement with the standard pattern of UiO-66, while the pattern of UiO-66-FA contains an obvious broad peak spanning a two theta range of 2–7° (Figure b), which can be thought of as the reo phase of UiO-66 with cluster missing defects by the competitive coordination of FA modulators. − Furthermore, N 2 sorption isotherms collected at 77 K reveal that N 2 sorption capacity was obviously increased (Figure c) with the corresponding Brunauer–Emmett–Teller (BET) surface areas increasing from 1328 m 2 /g for UiO-66 to 1741 m 2 /g for UiO-66-FA. Accordingly, pore size distributions estimated using the Horvath–Kawazoe (HK) method showed a higher accessible pore volume for UiO-66-FA than that of UiO-66 (inserted in Figure c).…”

Surface Modification of Matrimid® 5218 Polyimide Membrane with Fluorine-Containing Diamines for Efficient Gas Separation

“…The structural properties of diamine-modified Matrimid membranes were investigated to understand the observed gas separation performances. Evaluation of d-spacing offers useful information on chain packing modes in polymer membranes, which can be obtained by analyzing the X-ray diffraction (XRD) patterns [ 16 , 37 , 50 , 51 ], represented in Figure 7 a,b. The XRD pattern of the pristine Matrimid film shows two amorphous peaks at 2θ = 16.01° and 23.27°, which are assigned to the average distance between the closely packed chains (d-spacing = 5.54 Å) and the π–π stacking of the aromatic rings (3.81 Å), respectively [ 52 , 53 ].…”

“…In this regard, post-modification of existing polyimides has been explored as a simple and efficient strategy. Common post-treatment protocols can be classified into blending (e.g., polymer blends and mixed matrix membranes) [ 16 , 17 , 18 , 19 ], physical modification (e.g., surface coating, annealing, and ultraviolet (UV) beam irradiation) [ 20 , 21 , 22 , 23 ], and chemical modification (e.g., functionalization, grafting, and crosslinking) [ 2 , 11 , 15 ]. For polyimides, chemical modification is regarded as the most promising post-treatment process since it takes advantage of its well-known chemistry, simple processing, and corresponding desirable membrane performance such as improved selectivity as well as plasticization resistance [ 3 , 11 , 24 , 25 ].…”

Switching gas permeation through smart membranes by external stimuli: a review

“…[79][80][81] There are also organic-based membranes such as the covalent organic framework (COF), 82,83 carbon-based membranes including graphene [84][85][86] and graphene oxide (GO), [87][88][89] and hybrid membranes such as the metal-organic frameworks (MOF). [90][91][92][93][94][95][96][97] These various types of functional membranes have played an essential role in various elds. However, such membranes still have some disadvantages such as limited applicability.…”