Search results for "Frame"
showing 10 items of 1767 documents
The structural, phonon and optical properties of [CH3NH3]M0.5CrxAl0.5−x(HCOO)3 (M = Na, K; x = 0, 0.025, 0.5) metal–organic framework perovskites for…
2019
We report the structural, phonon and luminescence studies of six heterometallic perovskite-type metal–organic frameworks (MOFs) templated by methylammonium cations (CH3NH3+ and MeA+) with the following formulae: [MeA]Na0.5Cr0.5(HCOO)3 (MeANaCr), [MeA]K0.5Cr0.5(HCOO)3 (MeAKCr), [MeA]Na0.5Al0.5(HCOO)3 (MeANaAl), [MeA]K0.5Al0.5(HCOO)3 (MeAKAl), [MeA]Na0.5Cr0.025Al0.475(HCOO)3 (MeANaAlCr, 5 mol% of Cr3+ ions) and [MeA]K0.5Cr0.025Al0.475(HCOO)3 (MeAKAlCr, 5 mol% of Cr3+ ions). All of them crystallise in a monoclinic system (P21/n space group) with one MeA+ cation in an asymmetric unit forming four medium-strength hydrogen bonds (HBs) with a metal-formate framework. The DSC measurements and XRD s…
Reprocessing and restabilization of greenhouse films
2002
From the ecological and economical points of view, reprocessing of polyethylene greenhouse films is a promising solution to reduce discarded materials and to produce useful, or potentially useful, objects for service. Films exposed outdoors, however, show inferior mechanical properties and the melt processing worsens these properties. The addition of stabilizers and antioxidants to recycled plastic products prevents inherent thermal instabilities from occurring within the time frame of proper processing. In this study, we attempt to explore ways for improving product performance by the addition of four different additives when the recycled films undergo intensive shear processing. The proce…
Recent Progress in the Development of Composite Membranes Based on Polybenzimidazole for High Temperature Proton Exchange Membrane (PEM) Fuel Cell Ap…
2020
[EN] The rapid increasing of the population in combination with the emergence of new energy-consuming technologies has risen worldwide total energy consumption towards unprecedent values. Furthermore, fossil fuel reserves are running out very quickly and the polluting greenhouse gases emitted during their utilization need to be reduced. In this scenario, a few alternative energy sources have been proposed and, among these, proton exchange membrane (PEM) fuel cells are promising. Recently, polybenzimidazole-based polymers, featuring high chemical and thermal stability, in combination with fillers that can regulate the proton mobility, have attracted tremendous attention for their roles as PE…
Exploiting Reaction-Diffusion Conditions to Trigger Pathway Complexity in the Growth of a MOF.
2021
Coordination polymers (CPs), including metal–organic frameworks (MOFs), are crystalline materials with promising applications in electronics, magnetism, catalysis, and gas storage/separation. However, the mechanisms and pathways underlying their formation remain largely undisclosed. Herein, we demonstrate that diffusion-controlled mixing of reagents at the very early stages of the crystallization process (i.e., within ≈40 ms), achieved by using continuous-flow microfluidic devices, can be used to enable novel crystallization pathways of a prototypical spin-crossover MOF towards its thermodynamic product. In particular, two distinct and unprecedented nucleation-growth pathways were experimen…
Ab initio studies on the lattice thermal conductivity of silicon clathrate frameworks II and VIII
2016
The lattice thermal conductivities of silicon clathrate frameworks II and VIII are investigated by using ab initio lattice dynamics and iterative solution of the linearized Boltzmann transport equation(BTE) for phonons. Within the temperature range 100-350 K, the clathrate structures II and VIII were found to have lower lattice thermal conductivity values than silicon diamond structure (d-Si) by factors of 1/2 and 1/5, respectively. The main reason for the lower lattice thermal conductivity of the clathrate structure II in comparison to d-Si was found to be the harmonic phonon spectra, while in the case of the clathrate structure VIII, the difference is mainly due to the harmonic phonon spe…
Cation influence in adsorptive propane/propylene separation in ZIF-8 (SOD) topology
2019
Separation of propylene/propane is one of the most challenging and energy consuming processes in the chemical industry. Propylene demand is increasing and a 99.5% purity is required for industrial purposes. Adsorption based solutions are the most promising alternatives to improve the economical/energetic efficiency of the process. Zeolitic Imidazolate Frameworks (ZIFs) combine the desired characteristics from both MOFs and zeolites: tunability and flexibility from metal organic frameworks, and exceptional thermal and chemical stability from zeolites. In order to enlighten the role of the cation in the sodalite ZIF-8 framework for propane/propylene separation, dynamic breakthrough measuremen…
Spin Crossover Metal-Organic Frameworks with Inserted Photoactive Guests: On the Quest to Control the Spin State by Photoisomerization
2021
International audience; Three Hofmann-like metal-organic frameworks {Fe(bpac)[Pt(CN)4]}•G (bpac=1,2-bis(4-pyridyl)acetylene) were synthesized with photoisomerizable guest molecules (G = trans-azobenzene, trans-stilbene or cis-stilbene) and were characterized by elemental analysis, thermogravimetry and powder X-ray diffraction. The insertion of guest molecules and their conformation were inferred from Raman and FTIR spectra and from single-crystal X-ray diffraction and confronted with computational simulation. The magnetic and photomagnetic behaviors of the framework are significantly altered by the different guest molecules and different conformations. On the other hand, photoisomerization …
Surface functionalization of metal-organic frameworks for improved moisture resistance
2018
Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. However, the main issue limiting their applicability is their poor stability in humid conditions. The common methods to overcome this problem involve the formation of strong metal-linker bonds by using highly charged metals, which is limited to a number of structures, the introduction of alkylic groups to the framework by post-synthetic modification (PSM) or chemical vapour deposition (CVD) to enhance overall hydrophobicity of the framework. These last two usually provoke a drastic reduction of the porosity of the material. These strategie…
Nanosheets of Two-Dimensional Magnetic and Conducting Fe(II)/Fe(III) Mixed-Valence Metal-Organic Frameworks.
2017
We report the synthesis, magnetic properties, electrical conductivity, and delamination into thin nanosheets of two anilato-based Fe(II)/Fe(III) mixed-valence two-dimensional metal–organic frameworks (MOFs). Compounds [(H3O)(H2O)(phenazine)3][FeIIFeIII(C6O4X2)3]·12H2O [X = Cl (1) and Br (2)] present a honeycomb layered structure with an eclipsed packing that generates hexagonal channels containing the water molecules. Both compounds show ferrimagnetic ordering at ca. 2 K coexisting with electrical conductivity (with room temperature conductivities of 0.03 and 0.003 S/cm). Changing the X group from Cl to Br leads to a decrease in the ordering temperature and room temperature conductivity tha…
RGB imaging system for mapping and monitoring of hemoglobin distribution in skin
2011
A prototype R-G-B imaging system for mapping of skin hemoglobin distribution has been designed and tested. Device basically consists of a commercial RGB sensor (CMOS, max. frame rate 87 fps for VGA resolution), RGB LED ringlight illuminator and orthogonally orientated polarizers for reducing specular reflectance. The system was examined for monitoring of hemoglobin concentration changes during specific provocations - arterial/venous occlusions and heat test. Hemoglobin distribution maps of several skin malformations were obtained, as well.