Gas separation with mixed matrix membranes obtained from MOF UiO-66-graphite oxide hybrids

UiO-66-GO hybrids were obtained by hydrothermal synthesis of MOF UiO-66 (a Zr terephthalate) on graphite oxide (GO). These hybrids with appropriate texture and presence of nanosized MOF particles (in the ca. 30–100 nm range) have been used as fillers to prepare mixed matrix membranes (MMMs) with two different polymers, polysulfone (PSF) and polyimide (PI), as the matrixes, with contents varying between 0 and 32 wt%. The MMMs were applied to the separation of H2/CH4 and CO2/CH4 mixtures at different temperatures (35, 60 and 90 °C). Besides finding a good filler-polymer interaction, in the particular case of the hybrid filler, the barrier effect of the GO and the microporosity of the MOF dominated the separation properties of the MMMs. In all cases (different MMMs and separation mixtures) the effect of the temperature was to increase the permeability with a simultaneous decrease in the corresponding selectivity. In terms of permselectivity, the best H2/CH4 separation results were obtained (at 35 °C) with a PI based MMM containing only UiO-66 as filler (H2 permeability of 73 Barrer and H2/CH4 selectivity of 151), while a hybrid UiO-66-GO filler produced the best CO2/CH4 performance (CO2/CH4 selectivity value of 51 at 21 Barrer of CO2), also using a PI polymer

Synthesis of nanoparticles of zeolitic imidazolate framework ZIF-94 using inorganic deprotonators

A novel synthesis process of ZIF-94 (also known as SIM-1) is developed for particle size tuning, using either NaOH or NH4OH as a deprotonator. ZIF-94 originate from MOFs and have several advantages over traditional porous materials, in terms of their chemistry, structure and applications as catalysts, adsorbents, biocides and membrane materials. The existing synthesis process for ZIF-94 at a scale-up level produces particles of approximately 250 nm in size; an even smaller size is expected to result in an even better gas separation performance and catalytic activity. In this study, it was found that NaOH results in ZIF-94 particles with well-defined crystal structures, while in the case of NH4OH, the particles agglomerate to produce random shaped bigger particles. The optimum base to metal ratio was found to be 2 : 1 (NaOH : Zn), which shows a compromise between the particle size (114 +/- 3 nm) and BET specific surface area (254 +/- 4 m(2) g(-1)). Furthermore, the synthesized nanoparticles underwent thorough characterization by XRD, TGA, N-2 adsorption and electron microscopy revealing the lowest SEM average particle size of 84 +/- 3 nm

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)

Solventless synthesis of ZIF-L and ZIF-8 with hydraulic press and high temperature

In recent years, alternative methods to conventional synthesis of MOFs (metal-organic frameworks) have emerged due to the problematic use of solvents for both the environment and human health. Here we present the synthesis of ZIFs (zeolitic imidazolate frameworks) at high pressure by means of a hydraulic press provided with a heating mechanism. By the optimization of parameters such as temperature, time and the addition of promotor NH4NO3, a considerable increase in the reaction yield was achieved in products, neither washed nor activated, obtained since the first minute of reaction. Depending on the operation conditions, ZIF-L appeared as competing phase with ZIF-8. Upon transformation of ZIF-L into ZIF-8 in presence of ethanol, a reaction yield of 58.2% was achieved to highly crystalline ZIF-8 with a BET specific surface area of 947 m2/g. This green, fast, versatile and improved method suggests a possible way to future synthesis of other MOFs and the possibility of their industrial implementation

NH2-MIL-53(Al) and NH2-MIL-101(Al) in sulfur-containing copolyimide mixed matrix membranes for gas separation

Amino functionalized MOFs (NH2-MIL-53(Al) or NH2-MIL-101(Al)) were used as dispersed phase in the fabrication of mixed matrix membranes (MMMs) with a polymer matrix of sulfur-containing copolyimides (6FDA:DSDA/4MPD:4,4’-SDA 1:1 (polymer P1) or 6FDA/4MPD:4,4’-SDA 1:1 (polymer P2)). The gas separation properties of the MMMs obtained were tested for permeation of H2, CH4 and CO2. Membranes comprising polymer P1 showed better interaction with the fillers used than polymer P2, and therefore better separation properties, especially for NH2-MIL-101(Al). Upon NH2-MIL-101(Al) loading the performance of pure polymer was improved approaching the Robeson 1991 H2/CH4 and CO2/CH4 upper bound limits with high permeabilities, e.g. 114, 71 and 1.7 Barrer for H2, CO2 and CH4, respectively, using 10 wt.% NH2-MIL-101(Al)@P1. These improvements are related to the pore size of the filler, the flexibility and functional groups of sulfone-containing DSDA, and polymer rigidification

Insight into the reversible structural crystalline-state transformation from MIL-53(Al) to MIL-68(Al)

The reversible crystalline transformation between MIL-53(Al) and MIL-68(Al) is described. This followed a uniform conversion model with cleavage and formation of metal-ligand bonds after exchange or removal of guest molecules. MIL-68(Al) materials produced during the transformations had higher thermal stability and crystallinity than the as-synthesized MIL-68(Al)

Analysis of Solar Passive Techniques and Natural Ventilation Concepts in a Residential Building Including CFD Simulation

The European residential building sector accounts for over 40% of final energy consumption in the European Union member states. Therefore, an improvement of buildings energy efficiency represents a great instrument to reduce CO2 emissions. The first step to increase energy performance in buildings is to use passive strategies, such as orientation, natural ventilation or envelope optimisation. This paper presents an analysis of solar passive techniques and natural ventilation concepts in a case study: La Clota residential building, located near Barcelona (Spain). It has been carried out a comparative analysis of La Clota building in order to evaluate its energy and environmental performance with respect to a conventional building and also with respect to another hypothetic building with improved performance with respect to La Clota. Main tools used are energy dynamic simulation and, when necessary, CFD analysis in order to go into the effect of specific measures in depth. Accordingly, conclusions about the most effective energy measures are drawn, not only for this particular building, but also for other Mediterranean climate locations

Synthesis of layered titanosilicate JDF-L1 for fabrication of composite polyamide 6 film

In clay polymer nanocomposite technology, nowadays there is concern about the safety and environmental effects of the nanometric materials. In this work, sheets of layered titanosilicate JDF-L1 were synthesized with a size of 5.3 µmand thickness of 115 nm and used to fabricate composite polyamide 6 (PA6) films. The JDF-L1 synthesis was scaled in one pot and the rosette-like particles obtained were disaggregated using a simple process with NaOH solution. The composite with 2 wt.% of disaggregated JDF-L1, characterized by X-ray diffraction and electron microscopy, showed parallel orientation (with respect to the film itself) and good dispersion of the sheets. The composite had a similar barrier effect as the PA6 and its mechanical properties did not deteriorate. This opens up the use of this composite as a packing material providing other properties, such as a biocidal effect and synergy effect in combination with other additives

Thin supported MOF based mixed matrix membranes of Pebax® 1657 for biogas upgrade

This work shows the preparation of thin mixed matrix membranes (MMMs) with a 2-3 µm thick Pebax® 1657 layer on two different supports: a porous asymmetric polyimide P84® and dense polytrimethylsilylpropyne (PTMSP). Nanoparticles of metal-organic frameworks (MOFs) ZIF-8, MIL-101(Cr), UiO-66 and ZIF-7/8 core-shells were selected as fillers for the Pebax® 1657 based MMMs, all of them being MOFs with high CO2 adsorption capacity but different pore size distribution. All the membranes were characterized by SEM, FTIR, Raman, TGA and XRD analyses, showing in all cases a perfect compatibility of the Pebax® layer with both supports and also a good dispersion of the fillers in the polymeric matrix. These membranes were applied for the separation of equimolar CO2/CH4 mixtures at 35 °C under feed pressures between 3 and 5 bar, where an improvement in the gas separation performance with increasing pressure was noticed, thanks to the favored solubility of CO2. The synergistic compatibility between Pebax® 1657 and P84® gave rise to a 470% enhancement in CO2/CH4 selectivity, reaching a maximum value of 114 while the CO2 permeance increased by 40% up to 7.5 GPU. The addition of fillers in the Pebax® polymeric phase produced an improvement in the gas separation performance of the membranes, especially in terms of permeance, where the MMMs containing a 10 wt% loading of UiO-66 reached the optimum value of 11.5 GPU of CO2 (together with a CO2/CH4 selectivity of 55.6)

Enhancement of growth of MOF MIL-68(Al) thin films on porous alumina tubes using different linking agents

The preparation of MIL-68(Al) films on the inner surface of alumina tubes is reported. As the direct deposition of the MOF on bare alumina gives poor adhesion results, three different linking agents are employed to achieve a good MOF–support interaction. Colloidal silica LUDOX®, zeolite silicalite-1, and natural polysaccharide chitosan are chosen as binders, because they contain potential functional groups (hydroxy, amino, ether), which can establish hydrogen bonds. While colloidal silica leads to noncontinuous MOF layers, silicalite-1 and chitosan give rise to uniform and well-anchored films, as confirmed by the different characterization techniques used to study the MOF layer. Single-gas permeation experiments are carried out to determine the quality and ideal efficiency of the membranes prepared with silicalite-1 and chitosan. The results for the MIL-68(Al)/silicalite-1 membranes evidence the existence of macrodefects. However, no cracks are found when chitosan is used as a linking agent, and the gas flow through the MIL-68(Al)/chitosan membranes clearly follows Knudsen diffusion