90 research outputs found
Metal organic framework nanosheets in polymer composite materials for gas separation
[EN] Composites incorporating two-dimensional nanostructures within polymeric matrices have 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 freestanding nanosheets has proved challenging. We present a bottom-up synthesis strategy for dispersible copper 1,4-benzenedicarboxylate MOF lamellae of micrometre lateral dimensions and nanometre 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 increase 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 with 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.The research leading to these results has received funding (J.G., B.S.) from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement no. 335746, CrystEng-MOF-MMM. T.R. is grateful to TUDelft for funding. G.P. acknowledges the A. von Humboldt Foundation for a research grant. A.C., I.L. and F.X.L.i.X. thank Consolider-Ingenio 2010 (project MULTICAT) and the ‘Severo Ochoa’ programme for support. 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Unravelling surface and interfacial structures of a metal–organic framework by transmission electron microscopy
Metal-organic frameworks (MOFs) are crystalline porous materials with designable topology, porosity and functionality, having promising applications in gas storage and separation, ion conduction and catalysis. It is challenging to observe MOFs with transmission electron microscopy (TEM) due to the extreme instability of MOFs upon electron beam irradiation. Here, we use a direct-detection electron-counting camera to acquire TEM images of the MOF ZIF-8 with an ultralow dose of 4.1 electrons per square ångström to retain the structural integrity. The obtained image involves structural information transferred up to 2.1 Å, allowing the resolution of individual atomic columns of Zn and organic linkers in the framework. Furthermore, TEM reveals important local structural features of ZIF-8 crystals that cannot be identified by diffraction techniques, including armchair-type surface terminations and coherent interfaces between assembled crystals. These observations allow us to understand how ZIF-8 crystals self-assemble and the subsequent influence of interfacial cavities on mass transport of guest molecules
Influence of glycemic control on the levels of subgingival periodontal pathogens in patients with generalized chronic periodontitis and type 2 diabetes
SUPERCONDUCTING POLOIDAL COILS FOR THE REACTING PLASMA PROJECT PERFORMANCE TEST OF A MODEL COIL AT A PULSING RATE OF ABOUT 200 T/s
On décrit l'étude, la construction et les essais d'une bobine supraconductrice puisée avec des variations de champs très rapides. Le fonctionnement en mode pulsé a été obtenu par la décharge d'une capacité dans un circuit de blocage. En utilisant une tension aux bornes maximale de 8 kV, on a chargé la bobine jusqu'à 4 T avec un taux de variation de 200 T/s. Les pertes étaient de 0,2 % de l'énergie stockée par cycle. Ces résultats apportent la démonstration de la faisabilité de bobines poloïdales supraconductrices pour des tokamaks de taille moyenne.The design, construction and testing of a superconducting pulse coil with high field ramp rates are described. The pulse operation has been done by a condenser discharge with a clamp circuit. The coil was charged up to 4 T at a pulsing rate of 200 T/s by applying the maximum terminal voltage of 8 kV. The a.c. loss per pulse was 0.2 % of the stored energy. These results demonstrate the feasibility of superconducting poloidal coils for medium size tokamaks
Hepatocellular Carcinoma in a Case of Wilson's Disease Treated with Radiofrequency Ablation Therapy
Dilithium cyclohexanediacetate: A layered coordination polymer with non-valent hydrophobic contacts
Influence of solution pH and reaction atmosphere on the morphology of SrTiO3 nanocubes synthesized by thermohydrolysis
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