Beatriz Seoane

Metal–organic framework nanosheets in polymer composite materials for gas separation

Composites incorporating two-dimensional nanostructures within polymeric matrices hold potential as functional components for several technologies, including gas separation. Prospectively, employing metal-organic-frameworks (MOFs) as versatile nanofillers would notably broaden the scope of functionalities. However, synthesizing MOFs in the form of free standing nanosheets has proven challenging. We present a bottom-up synthesis strategy for dispersible copper 1,4-benzenedicarboxylate MOF lamellae of micrometer lateral dimensions and nanometer thickness. Incorporating MOF nanosheets into polymer matrices endows the resultant composites with outstanding CO2 separation performance from CO2/CH4 gas mixtures, together with an unusual and highly desired increment in the separation selectivity with pressure. As revealed by tomographic focused-ion-beam scanning-electron-microscopy, the unique separation behaviour stems from a superior occupation of the membrane cross-section by the MOF nanosheets as compared to isotropic crystals, which improves the efficiency of molecular discrimination and eliminates unselective permeation pathways. This approach opens the door to ultrathin MOF-polymer composites for various applications.

Combination of MOFs and Zeolites for Mixed-Matrix Membranes

Mixed-matrix membranes (MMMs) were prepared by combinations of two different kinds of porous fillers [metal-organic frameworks (MOFs) HKUST-1 and ZIF-8, and zeolite silicalite-1] and polysulfone. In the search for filler synergy, the MMMs were applied to the separation of CO(2)/N(2), CO(2)/CH(4), O(2)/N(2), and H(2)/CH(4) mixtures and we found important selectivity improvements with the HKUST-1-silicalite-1 system (CO(2)/CH(4) and CO(2)/N(2) separation factors of 22.4 and 38.0 with CO(2) permeabilities of 8.9 and 8.4 Barrer, respectively).

Metal Organic Framework Crystals in Mixed-Matrix Membranes: Impact of the Filler Morphology on the Gas Separation Performance

Mixed-matrix membranes (MMMs) comprising NH2-MIL-53(Al) and Matrimid® or 6FDA-DAM have been investigated. The MOF loading has been varied between 5 and 20 wt%, while NH2-MIL-53(Al) with three different morphologies: nanoparticles, nanorods and microneedles have been dispersed in Matrimid®. The synthesized membranes have been tested in the separation of CO2 from CH4 in an equimolar mixture. At 3 bar and 298 K for 8 wt% MOF loading, incorporation of NH2-MIL-53(Al) nanoparticles leads to the largest improvement compared to nanorods and microneedles. The incorporation of the best performing filler, i.e. NH2-MIL-53(Al) nanoparticles, to the highly permeable 6FDA-DAM has a larger effect, and the CO2 permeability increased up to 85 % with slightly lower selectivities for 20 wt% MOF loading. Specifically, these membranes have a permeability of 660 Barrer with CO2/CH4 separation factor of 28, leading to a performance very close to the Robeson limit of 2008. Furthermore, a new non-destructive technique based on Raman spectroscopy mapping is introduced to assess the homogeneity of the filler dispersion in the polymer matrix. The MOF contribution can be calculated by modelling the spectra. The determined homogeneity of the MOF filler distribution in the polymer is confirmed by FIB-SEM analysis.

Sonocrystallization of zeolitic imidazolate frameworks (ZIF-7, ZIF-8, ZIF-11 and ZIF-20)

Zeolitic imidazolate frameworks ZIF-7, ZIF-8, ZIF-11 and ZIF-20 have been synthesized by sonocrystallization. In general, crystals obtained at lower temperatures and shorter times are smaller and have a narrower size distribution than those achieved by conventional solvothermal synthesis. Moreover, crystallization curves have been calculated from the XRD patterns and the Gualtieris model has been applied to simulate the extent of crystallization as a function of time. According to the parameters calculated, for ZIF-8 the nucleation rate controls the synthesis reaction, while for ZIF-11 and ZIF-20 both growth and nucleation rates are similar.

Accelerating the Controlled Synthesis of Metal–Organic Frameworks by a Microfluidic Approach: A Nanoliter Continuous Reactor

Segmented microfluidics was applied to the ultrafast crystallization of dicarboxylate based MIL-88B type metal-organic frameworks (MOFs; Fe-MIL-88B-NH2, Fe-MIL-88B, and Fe-MIL-88B-Br). Particular attention was paid to the influence of the temperature, residence time, and slug volume on the size and crystal size distribution of the MOFs. Average sizes in the 90-900 nm range with relatively narrow crystal size distributions were obtained with residence times as short as 20 s depending on the MOF type and synthesis conditions.

Insight into the crystal synthesis, activation and application of ZIF-20

The crystallization of the zeolitic imidazolate framework ZIF-20 has been tuned from the point of view of crystal size and aggregation by using rotation and seeding with a previously prepared material. In addition, the activation of ZIF-20 by solvent extraction has been found to be in correlation with the relative permittivity of the solvent. High permittivity solvents (acetone and methanol) extract more guest dimethylformamide but amorphize the structure, while those with low permittivity (n-pentane and chloroform) preserve the crystallinity of ZIF-20. The dispersion in commercial polysulfone of the small synthesized ZIF-20 particles obtained with low aggregation results in an improved O2-selective mixed matrix membrane (O2 permeability and O2/N2 selectivity being 1.0 (±0.0) Barrer and 6.7 (±0.5), respectively).

Azine‐Linked Covalent Organic Framework (COF)‐Based Mixed‐Matrix Membranes for CO2/CH4 Separation

Mixed-matrix membranes (MMMs) comprising Matrimid and a microporous azine-linked covalent organic frameworks (ACOF-1) were prepared and tested in the separation of CO2 from an equimolar CO2 /CH4 mixture. The COF-based MMMs show a more than doubling of the CO2 permeability upon 16 wt % ACOF-1 loading together with a slight increase in selectivity compared to the bare polymer. These results show the potential of COFs in the preparation of MMMs.

Metal organic framework synthesis in the presence of surfactants : Towards hierarchical MOFs?

We report the effect of synthesis parameters on the textural properties of Al based MOFs synthesized in the presence CTAB.

Crystallization in THF: the possibility of one-pot synthesis of mixed matrix membranes containing MOF MIL-68(Al)

A new methodology has been developed consisting of the use of the same solvent (tetrahydrofuran, THF) for both nanosized MOF MIL-68(Al) crystallization and polysulfone (PSF) mixed matrix membrane (MMM) casting, using this MOF as filler. The usual solvent for MIL-68 is dimethylformamide. However, the synthesis of this MOF has been studied here in THF (a solvent almost never used for MOFs) which makes possible the one-pot processability of both MOF and PSF, without the stages of crystal separation and drying from the mother liquor. The 8 wt% MIL-68(Al)@PSF MMMs were superior to the pure PSF membrane in the separation of both H2/CH4 and CO2/CH4 mixtures.

Shaping Covalent Triazine Frameworks for the Hydrogenation of Carbon Dioxide to Formic Acid

A facile one‐step method to shape covalent triazine frameworks (CTFs) for catalytic applications is reported. Phase inversion of the CTF powder by using a polyimide as a binder in a microfluidic device results in the formation of composite spheres with accessible CTF porosity and a high mechanical and thermal stability. The fabricated spheres can be used to host organometallic complexes. The obtained shaped catalysts, Ir@CTF spheres, are active and fully recyclable in the direct hydrogenation of carbon dioxide into formic acid under mild reaction conditions (20 bar and 50–90 °C) and in the dehydrogenation of formic acid.