Sara Sorribas

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.

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.

MOF nanoparticles of MIL-68(Al), MIL-101(Cr) and ZIF-11 for thin film nanocomposite organic solvent nanofiltration membranes

Nanoparticles (NPs) of MOFs MIL-101(Cr), MIL-68(Al) and ZIF-11 with sizes of 70, 103 and 79 nm, respectively, have been used in the development of thin film nanocomposite (TFN) membranes. Such membranes were synthesized with an ultrathin polyamide layer, in which NPs are embedded, about 100–150 nm thick on top of a polyimide P84® asymmetric support. Several important effects have been studied in the synthesis of the membranes for their application to organic solvent nanofiltration (OSN): the effect of the non-solvent bath, the chemical post-treatment, the concentration of precursors for interfacial polymerization and the polymerization time. The influence of different solvents (water, methanol, acetone and THF) and solutes (Acridine Orange, Sunset Yellow and Rose Bengal) on the OSN has also been studied. The hydrophilic character of the membrane and the solvent-membrane and solute–membrane interactions are shown to be the most important parameters affecting the performance of the composite membranes. A maximum permeance of 6.2 L m−2 h−1 bar−1 and a rejection above 90% was obtained from the combination of ZIF-11 and a post-treatment via filtration with dimethylformamide.

Langmuir-Blodgett Films of the Metal-Organic Framework MIL-101(Cr): Preparation, Characterization, and CO2 Adsorption Study Using a QCM-Based Setup

This work reports the fabrication and characterization of Langmuir-Blodgett films of nanoparticles (size 51 ± 10 nm) of the metal organic framework MIL-101(Cr). LB film characterization by SEM, UV-vis, GIXRD, and QCM has shown that the addition of 1 wt % of behenic acid to MOF dispersion allows obtaining dense monolayers at the air-water interface that can be deposited onto solid substrates of different nature with transfer ratios close to 1. Moreover, a QCM-based setup has been built and used for the first time to measure CO2 adsorption isotherms at 303 K on MOF LB films, proving that LB films with MOF masses between 1.2 (1 layer) and 2.3 (2 layers) μg can be used to obtain accurate adsorption values at 100 kPa, similar to those obtained by conventional adsorption methods that require much larger MOF quantities (tens of milligrams).

Insight into ETS-10 synthesis for the preparation of mixed matrix membranes for CO2/CH4 gas separation

An in-depth study into the synthesis of the titanosilicate ETS-10 has been carried out to obtain crystals with different particle sizes, roughness and porosity. The effect of these parameters on the CO2/CH4 gas separation performance using mixed matrix membranes (MMMs) has been studied. MMMs based on ETS-10 polycrystalline particles of 1–2 μm in size with high surface roughness and porosity gave rise to a good filler dispersion and filler–polymer interaction. The addition of 10 wt% ETS-10 polycrystalline particles into the polysulfone matrix increased the CO2 permeability from 6.1 to 7.8 Barrer and the CO2/CH4 selectivity from 31 to 38. When using the polyimide 6FDA-6FpDA, a glassy polymer with high gas permeability, the addition of 10 wt% ETS-10 polycrystalline particles increased the CO2 permeability from 96 to 125 Barrer, with a decrease in CO2/CH4 selectivity from 56 to 51.