Evaluation of oxygen carriers based on manganese-iron mixed oxides prepared from natural ores or industrial waste products for chemical looping processes

Manganese-iron mixed oxides have been identified as promising oxygen carrier materials in chemical looping processes. In this work, low-cost raw materials are considered for the production of this type of oxygen carrier. Four manganese based minerals from deposits of different locations – South Africa, Gabon(x2) and Brazil – and two iron based materials (Fe-ore from Spain and Redmud waste) were used to prepare suitable oxygen carriers through a new two-step production method: a mixing-grinding (about 5 µm) pre-treatment followed by pelletizing, crushing and sieving to produce particles of the desired size (100–300 µm). This method was required in order to form the MnFe mixed oxide and to provide permanent magnetic properties, which were not found when the oxygen carriers were prepared by the classical one-step method, i.e. crushing and sieving of raw materials to the desired particle size (100–300 µm). The oxygen uncoupling capability of the developed materials was extremely low and even completely lost after repeated redox cycles. However, they were reactive under chemical looping conditions with H2, CO and CH4. Reactivity varied with the raw materials used and with the redox cycles, being of crucial importance for its evolution the intensity of the chemical stress during hundreds of redox cycles. © 2022 The Author

Chemocatalysis of sugars to produce lactic acid derivatives on zeolitic imidazolate frameworks

Several research studies related to biorefining have focused on developing routes for biomass conversion into biomaterials or platform molecules. In this work, the zeolitic imidazolate frameworks (ZIFs) ZIF-8 and ZIF-67 have been tested as catalysts in the conversion of sugars (sucrose, glucose and fructose) into methyl lactate. ZIF-8 and ZIF-67 have the same sodalite type zeolite structure but behaved differently in the sugar conversion in methanol due to the respective presence of Zn and Co in their structures. ZIF-8 has been found to be the most active for the conversion of sugars into methyl lactate (yield 42%) and was reused in four catalytic cycles. The chemical and physical effects caused by these cycles on the catalysts have been studied by several techniques (X-ray diffraction, thermogravimetric analyses, infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electronic microscopy and nitrogen adsorption)

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)

Synthesis and gas adsorption properties of mesoporous silica-NH2-MIL-53(Al) core-shell spheres

Ordered mesoporous silica-NH2-MIL-53(Al) core-shell spheres of about 4 µm in diameter have been synthesized by seeding the corresponding mesoporous silica spheres (MSSs) with crystals of NH2-MIL-53(Al) and subsequent secondary crystal growth into a MOF shell. The morphology of the particles was analyzed by SEM, while TGA, EDX and XRD characterizations gave information on the composition and structure of this material and the activation of the MOF. N2 adsorption analysis revealed that the NH2-MIL-53(Al) shell controlled the access of guest molecules into the hydrophilic silica mesoporous structure, while the breathing behavior of the microporous NH2-MIL-53(Al) shell was confirmed by CO2 adsorption isotherms

Enhancement of CO2/CH4 separation performances of 6FDA-based co-polyimides mixed matrix membranes embedded with UiO-66 nanoparticles

Metal-organic frameworks (MOFs) incorporation into mixed matrix membranes (MMMs) is gaining more attention due to the combined advantages of high separation performance and easy processability. Nanoparticles (NPs) of CO2-philic MOF UiO-66 (Zr-BDC) were synthesized with high surface area and ca. 50 nm particle size (and also for comparison with 100 and 200 nm sizes). They were incorporated into three 6FDA-based co-polyimides (namely 6FDA-BisP, 6FDA-ODA, and 6FDA-DAM), forming MMMs with loadings in the 4–23 wt% range. The NPs and MMMs were characterized accordingly by XRD, BET, SEM, TEM, FTIR, and TGA. CO2 and CH4 isotherms on the NPs were measured by a static volumetric method at the pressure up to 10 bar. Fractional free volume (FFV) was calculated using solid density, measured by pycnometer. Gas separation performance was evaluated using a feed composition of 50%:50% CO2:CH4 binary mixture at 35 °C and a pressure difference of 2 bar. The presence of UiO-66 NPs in the continuous 6FDA-BisP and 6FDA-ODA co-polyimides improved both CO2 permeability and CO2/CH4 selectivity by 50–180% and 70–220%, respectively. In the case of 6FDA-DAM MMMs, the CO2 permeability was significantly improved by 92%, while maintaining the CO2/CH4 selectivity. The best results in terms of CO2/CH4 selectivity were 41.9 for 6FDA-BisP (17 wt% filler loading, 108 Barrer of CO2), 57.0 for 6FDA-ODA (7 wt% filler loading, 43.3 Barrer of CO2) and 32.0 for 6FDA-DAM (8 wt% filler loading, 1728 Barrer of CO2)

Nanosheets of MIL-53(Al) applied in membranes with improved CO 2 /N 2 and CO 2 /CH 4 selectivities

MIL-68(Al) and MIL-53(Al) are carboxylate-based metal-organic frameworks (MOFs) with the same chemical composition but different structures (polymorphs). In this study, MIL-53(Al) nanosheets of ca. 150 nm in size with an average thickness of 3.5 ± 0.9 nm were obtained after immersion of a sample composed of MIL-68(Al) and MIL-53(Al) in water under different conditions (ultrasound, stirring, reflux, 60 °C and room temperature). The disaggregated MIL-53(Al) nanosheets produced under more severe conditions were suspended in a PDMS solution and then deposited on asymmetric polyimide P84® supports under vacuum filtration to form supported mixed matrix membranes (MMMs). When applied to the separation of CO 2 /CH 4 and CO 2 /N 2 mixtures, the MMM with MIL-53(Al) nanosheets improved the CO 2 /CH 4 (28.4-28.7 vs. 22.4) and CO 2 /N 2 (19.9-23.2 vs. 17.5) selectivities of the conventional MIL-53(Al) MMM with higher CO 2 permeances (20.8-29.6 GPU vs. 9.5 GPU for CO 2 /CH 4 and 17.7-26.8 GPU vs. 11.2 GPU for CO 2 /N 2 )

Caffeine Encapsulation in Metal Organic Framework MIL-53(Al) at Pilot Plant Scale for Preparation of Polyamide Textile Fibers with Cosmetic Properties

Currently in the marketplace, we can find clothing items able to release skin-friendly ingredients while wearing them. These innovative products with high-added value are based on microencapsulation technology. In this work, due to its lightness, flexibility, porosity, chemical affinity and adsorption capacity, metal-organic framework (MOF) MIL-53(Al) was the selected microcapsule to be synthesized at a large scale and subsequent caffeine encapsulation. The synthesis conditions (molar ratio of reactants, solvents used, reaction time, temperature, pressure reached in the reactor and activation treatment to enhance the encapsulation capacity) were optimized by screening various scaling-up reactor volumes (from lab-scale of 40 mL to pilot plant production of 3.75 L). Two types of Al salts (Al(NO3)3·9H2O from the original recipe and Al2(SO4)3 as commercial SUFAL 8.2) were employed. The liporeductor cosmetic caffeine was selected as the active molecule for encapsulation. Caffeine (38 wt %) was incorporated in CAF@MIL-53(Al) microcapsules, as analyzed by TGA and corroborated by GC/MS and UV-vis after additive extraction. CAF@MIL-53(Al) microcapsules showed a controlled release of caffeine during 6 days at 25 °C (up to 22% of the initial caffeine). These capsules were incorporated through an industrial spinning process (with temperatures up to 260 °C) to manufacture PA-6 fibers with cosmetic properties. Up to 0.7 wt % of capsules were successfully incorporated into the fibers hosting 1700 ppm of caffeine. Fabrics were submitted to scouring, staining, and washing processes, detecting the presence of caffeine in the cosmetic fiber. © 2022 The Authors. Published by American Chemical Society

Measurement of the broadband complex permittivity of soils in the frequency domain with a low-cost Vector Network Analyzer and an Open-Ended coaxial probe

The performance of a handheld Vector Network Analyzer (VNA), the nanoVNA, a low-cost, open-source instrument, was evaluated. The instrument measures the complex permittivity of dielectric media from 1-port reflection parameters in the 1 – 900 MHz bandwidth. We manufactured an open-ended coaxial probe using a SMA-N coaxial adapter to perform dielectric measurements. The accuracy of the nanoVNA was comparable to that of a commercial VNA between 1 and 500 MHz according to tests in reference organic liquids, while a lack of stability was found beyond 700 MHz. The self-manufactured open-ended coaxial probe was subjected to a Finite Element Method (FEM) analysis and its electromagnetic (EM) field penetration depth was determined to be 1.5 mm at 100 MHz, being reduced to 1.3 at 900 MHz and thus demonstrating a frequency-dependent support volume. The broadband complex permittivity of three mineral soils of varied textures was obtained for a range of bulk densities and water contents from dry to water-saturated conditions. The dielectric response of the soils approximated the well-known Topp et al. (1980) equation at high frequencies. At lower frequency however, higher permittivities were exhibited due to dielectric dispersion, which emphasizes the importance of EM-based soil moisture sensor operating frequency when considering sensor calibration or comparing the response of different sensors.This research was funded by Agencia Estatal de Investigación (AEI), project numbers: AGL2016-77282-C3-3-R and PID2019-106226-C22 AEI/https:///https://doi.org/10.13039/501100011033 | Ministerio de Educación y Formación Profesional, grant numbers: FPU17/05155 and FPU19/00020. Funding for David A. Robinson was provided by a Natural Environment Research Council (NERC) award number NE/R016429/1 as part of the UK–ScaPE Programme Delivering National Capability. We also acknowledge funding from the Polish National Agency for Academic Exchange, grant number: PPI/APM/2018/1/00048/U/001. The authors wish to thank Agencia Estatal de Investigación (AEI), Ministerio de Educación y Formación Profesional, Natural Environment Research Council (NERC) and Polish National Agency for Academic Exchange (NAWA) for the funding provided. The authors also wish to thank Juan Antonio Albaladejo for his help in machining the experimental OE coaxial probe

Fabrication of ultrathin films containing the metal organic framework Fe-MIL-88B-NH2 by the Langmuir-Blodgett technique

In this work, the fabrication of ultrathin films containing the metal organic framework (MOF) Fe-MIL- 88B-NH2 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

Tuning the separation properties of zeolitic imidazolate framework core-shell structures via post-synthetic modification

The conversion of ZIF-8 into ZIF-7 via post-synthetic modification with benzimidazole has been monitored by quantifying the liberated 2-methylimidazole by chromatography. The reaction kinetics have been adjusted to the shrinking core model, providing the diffusion coefficient of bIm inside the pores and the reaction kinetic constant (2.86 × 10-7 cm2 s-1 and 1.36 × 10-4 cm s-1, respectively). A wide variety of ZIF-7/8 hybrid core-shell frameworks have been obtained during this reaction. The most promising have been characterized by SEM/TEM, TGA, N2 and CO2 adsorption, FTIR and 13C NMR, showing features of the coexistence of both phases inside the frameworks. Their structures have also been simulated, providing comparable XRD and adsorption results. The hybrid material has been used as a filler for PBI mixed matrix membranes (MMMs) applied to H2/CO2 separation, enhancing the performances of the bare PBI polymer and MMMs containing ZIF-8 or ZIF-7 as a filler, with a maximum H2 permeability value of 1921 Barrer and a H2/CO2 selectivity of 11.8