Metal-organic Frameworks Loading Research Articles

Metal–Organic Frameworks Encapsulated in Photocleavable Capsules for UV-Light Triggered Catalysis

A smart catalyst that can be activated by UV-light was prepared by encapsulating metal–organic framework (MOF) particles in microcapsules with a photocleavable polyurea shell. Addition of palmitic acid as a modulator during the synthesis of the Fe-terephthalate MOF MIL-88B(Fe) yields MOF particles with a hydrophobic surface. These particles can be successfully encapsulated via interfacial polymerization, as proven by a combination of powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) techniques. By the incorporation of photolabile groups in the polymer shell, UV light can be employed to trigger degradation of the capsules, releasing the catalytic load. Catalyst activation triggered by UV light was monitored by recording the rates for catalytic tetramethylbenzidine (TMB) oxidation with H2O2. The reactivity could be controlled by tuning irradiation time, UV intensity, or MOF loading. The activity of the capsules was up to 90 times higher after irradiation.

Fabrication of ultrathin films containing the metal organic framework Fe-MIL-88B-NH 2 by the Langmuir–Blodgett technique

Abstract In this work, the fabrication of ultrathin films containing the metal organic framework (MOF) Fe-MIL-88B-NH 2 by the Langmuir–Blodgett (LB) technique has been explored. MOF crystals of two different sizes (1.5 ± 0.3 and 0.07 ± 0.01 μm) have been synthesized and assembled at the air–liquid interface by the LB method. The effect of the subphase pH and particle size on the film formation process has been studied. Moreover, for the first time, mixed MOF + polymer (the commercial soluble polyimide Matrimid ® ) LB films containing different MOF loadings have been fabricated. These experiments show that it is possible to obtain ultrathin MOF + polymer films with a controlled MOF density. Furthermore, MOF particles are homogeneously distributed in the polymer matrix, even with very large amounts of MOF (up to 95 wt%). LB films have been incorporated into materials of different nature, including glass and mica substrates and also polymeric membranes based on polysulfone Udel ® and PIM-1 (polymer of intrinsic microporosity), and the modification of water contact angle after LB film deposition has been analyzed.

Mixed matrix membranes incorporated with amine-functionalized titanium-based metal-organic framework for CO2/CH4 separation

High performance mixed matrix membranes arise from a targeted selection of constituent materials, especially the choice of fillers. An amine-functionalized metal-organic framework (MOF), NH2-MIL-125(Ti), was used in this work to prepare polysulfone-based mixed matrix membranes (MMMs). Permeation measurements on CO2/CH4 gas mixture demonstrate that the incorporation of NH2-MIL-125(Ti) particles can significantly improve the CO2 permeability compared to the pure polymer membrane, along with slightly enhanced CO2/CH4 separation factor. This work also shows that the separation factor at high pressures can remain almost unchanged for the prepared MMMs with the MOF loadings up to 20wt%. The obtained results may provide useful information in facilitating the applications of promising MOF-containing MMMs for the practical membrane-based natural gas purification.

Post-treatment effect on gas separation property of mixed matrix membranes containing metal organic frameworks

In this work a series of mixed matrix membranes (MMMs) containing metal organic frameworks (MOFs) were fabricated to investigate the influence of post-treatment on their gas separation properties. It was revealed that gas permeabilities increased considerably as treatment temperature increased from 150°C to 180°C and remained almost unchanged after 200°C; gas permeability of MMMs from 200°C treatment was about 3 times higher when compared with MMMs treated at 150°C. From results of physical characterization including TGA, XRD, SEM, ATR-FTIR and nitrogen absorption it was inferred that higher temperature treatment induced gas permeability increase should be mainly attributed to more effective removal of residual solvent in micro-pores of MOFs; and gas permeation properties of MMMs with different treatment durations from 24h to 96h further confirmed our conclusion. This heat treatment induced permeability increase phenomenon was further verified by varying the polymer and MOF combinations. At the end Cu3(BTC)2/ODPA–TMPDA MMMs with different MOF loadings were prepared and the one with best performance appeared at 40wt% loading: a dramatic increase of CO2 permeability from 47.7Barrer to 260.7Barrer with almost unchanged CO2/CH4 selectivity from 29.26 to 27.75.

Highly Adsorptive, MOF‐Functionalized Nonwoven Fiber Mats for Hazardous Gas Capture Enabled by Atomic Layer Deposition

While metal‐organic frameworks (MOFs) show great potential for gas adsorption and storage, their powder form limits deployment opportunities. Integration of MOFs on polymeric fibrous scaffolds will enable new applications in gas adsorption, membrane separation, catalysis, and toxic gas sensing. Here, we demonstrate a new synthesis route for growing MOFs on fibrous materials that achieves high MOF loadings, large surface areas and high adsorptive capacities. We find that a nanoscale coating of Al2O3 formed by atomic layer deposition (ALD) on the surface of nonwoven fiber mats facilitates nucleation of MOFs on the fibers throughout the mat. Functionality of MOFs is fully maintained after integration, and MOF crystals are well attached to the fibers. Breakthrough tests for HKUST‐1 MOFs [Cu3(BTC)2] on ALD‐coated polypropylene fibers reveal NH3 dynamic loadings up to 5.93 ± 0.20 mol/kg(MOF+fiber). Most importantly, this synthetic approach is generally applicable to a wide range of polymer fibers (e.g., PP, PET, cotton) and MOFs (e.g., HKUST‐1, MOF‐74, and UiO‐66).

High Flux Thin Film Nanocomposite Membranes Based on Metal–Organic Frameworks for Organic Solvent Nanofiltration

Thin-film nanocomposite membranes containing a range of 50-150 nm metal-organic framework (MOF) nanoparticles [ZIF-8, MIL-53(Al), NH2-MIL-53(Al) and MIL-101(Cr)] in a polyamide (PA) thin film layer were synthesized via in situ interfacial polymerization on top of cross-linked polyimide porous supports. MOF nanoparticles were homogeneously dispersed in the organic phase containing trimesoyl chloride prior to the interfacial reaction, and their subsequent presence in the PA layer formed was inferred by a combination of contact angle measurements, FT-IR spectroscopy, SEM, EDX, XPS, and TEM. Membrane performance in organic solvent nanofiltration was evaluated on the basis of methanol (MeOH) and tetrahydrofuran (THF) permeances and rejection of styrene oligomers (PS). The effect of different post-treatments and MOF loadings on the membrane performance was also investigated. MeOH and THF permeance increased when MOFs were embedded into the PA layer, whereas the rejection remained higher than 90% (molecular weight cutoff of less than 232 and 295 g·mol(-1) for MeOH and THF, respectively) in all membranes. Moreover, permeance enhancement increased with increasing pore size and porosity of the MOF used as filler. The incorporation of nanosized MIL-101(Cr), with the largest pore size of 3.4 nm, led to an exceptional increase in permeance, from 1.5 to 3.9 and from 1.7 to 11.1 L·m(-2)·h(-1)·bar(-1) for MeOH/PS and THF/PS, respectively.

Visualizing MOF Mixed Matrix Membranes at the Nanoscale: Towards Structure‐Performance Relationships in CO2/CH4 Separation Over NH2‐MIL‐53(Al)@PI

Mixed matrix membranes (MMMs) composed of metal organic framework (MOF) fillers embedded in a polymeric matrix represent a promising alternative for CO2 removal from natural gas and biogas. Here, MMMs based on NH2‐MIL‐53(Al) MOF and polyimide are successfully synthesized with MOF loadings up to 25 wt% and different thicknesses. At 308 K and ΔP = 3 bar, the incorporation of the MOF filler enhances CO2 permeability with respect to membranes based on the neat polymer, while preserving the relatively high separation factor. The rate of solvent evaporation after membrane casting proves key for the final configuration and dispersion of the MOF in the membrane. Fast solvent removal favours the contraction of the MOF structure to its narrow pore framework configuration, resulting in enhanced separation factor and, particularly, CO2 permeability. The study reveals an excellent filler‐polymer contact, with ca. 0.11% void volume fraction, for membranes based on the amino‐functionalized MOF, even at high filler loadings (25 wt%). By providing precise and quantitative insight into key structural features at the nanoscale range, the approach provides feedback to the membrane casting process and therefore it represents an important advancement towards the rational design of mixed matrix membranes with enhanced structural features and separation performance.

Optimization of continuous phase in amino-functionalized metal–organic framework (MIL-53) based co-polyimide mixed matrix membranes for CO2/CH4 separation

Nano-size non- and amino-functionalized flexible crystalline metal-organic frameworks (MOFs) MIL-53(Al) and NH2-MIL-53(Al), two co-polyimides 6FDA/ODA-DAM (1 : 1 and 1 : 4) and cross-linked co-polyimide 6FDA-ODA-DAM (1 : 1, 2% agent cross-linking APTMDS) were used to prepare mixed matrix membranes (MMMs) whilst membranes consisting of MIL-53(Al) and commercial polyimides (Matrimid 5218 and Ultem 1000) were also fabricated for comparison. Pure gases and blends of CO2 and CH4 permeation tests showed enhanced separation performance of MMMs with relatively high NH2-MIL-53(Al) loadings (CO2 permeability up to 65 Barrer, ideal selectivity up to 36.5). A detailed study of the relation between MMM properties and their morphology as affected by the nature of continuous polyimide phase was performed. The separation factor increased with MOF loading. Furthermore, these materials showed stable CO2/CH4 selectivity at increasing feed pressure, in contrast to the traditional polymer membranes. The separation performances as functions of operation temperature and composition of gas mixture were also studied. Experimental permeation data of MMMs with 6FDA-ODA-DAM (1 : 1, 2% agent cross-linking APTMDS) and up to 35 wt% NH2-MIL-53(Al) loading are in excellent agreement with the modeling predictions by both the Maxwell model and the modified Maxwell model. An approximately ideal morphology was reached when preparing MMMs. A computational optimized process was proposed in order to estimate simultaneously three independent parameters, including gas permeability of dispersed filler, interphase thickness and polymer chain rigidification factors, which would be applied for non-ideal MMM systems.

Amine-Functionalized MIL-53 Metal–Organic Framework in Polyimide Mixed Matrix Membranes for CO2/CH4 Separation

Flexible crystalline metal–organic framework (MOF) of nanosize particles (Al-MIL-53) and 6FDA-ODA polyimides were used to produce mixed matrix membranes (MMM). These MMM display excellent CO2/CH4 separation properties even without any compatibilization (amine grafting). The ideal selectivity and separation factor were found to increase with increasing MOF loading. Furthermore, these materials have an improved CO2/CH4 separation factor with increasing pressure, in contrast to traditional polymer membranes.

Macro-/microporous MOF composite beads

We have prepared a series of metal–organic framework (MOF) composite materials by depositing crystalline MOFs into mm-sized macroporous polyacrylamide (PAM), oxide or oxide–PAM beads using solvothermal methods or immersion in mother solutions. The facile nature of the composite preparation is in part due to the inherent hydrophilicity and processability of the PAM, which bears suitable functionality to interact with the MOF. The resulting composites display hierarchical porosity across the macro- and microporous length scales; the MOF loading level, and hence degree of microporosity in the composites, can be tuned by modulating the concentration of the reactants in the MOF synthesis. The MOF@PAM beads display enhanced mechanical stability and handling over bulk MOF phases in heterogeneous reaction systems, clearly indicating that such materials can improve recovery and recyclability of crystalline MOFs. This is an important step for future applications.