This work presents an experimental investigation of water adsorption in metal–organic frameworks (MOFs) at room temperature and up to 90% relative humidity. Structural degradation of the materials ...after regeneration is analyzed via powder X-ray diffraction (PXRD) and nitrogen adsorption measurements. MOFs with open metal sites are quite hydrophilic but appear to maintain their structure according to PXRD. However, significant surface area loss indicates that decomposition is occurring and is likely an attribute of oxygen presence during the regeneration procedure. Materials with copper paddle-wheel (HKUST-1), 5-coordinated magnesium (Mg MOF-74), and 7-coordinated zirconium (UiO-66(-NH2)) maintain good structural stability, while Zn-COOH containing MOFs (DMOF-1; DMOF-1-NH2; UMCM-1) undergo complete loss of crystallinity.
In the synthesis of the microporous metal–organic framework copper 1,4‐benzenedicarboxylate Cu(BDC), solvent exchange with methanol prior to recrystallization lowers the desolvation temperature to ...160 °C and produces more crystalline Cu(BDC). The solution to the crystal structure of Cu(BDC) has been determined by using ab initio quantum molecular calculations and refinement with synchrotron X‐ray powder diffraction data. This solution is in the P$\bar {1}$ space group with a = 5.25 Å, b = 9.67 Å, c = 10.77 Å, α = 90.29°, β = 91.06°, γ = 92.413°, and V = 546.04 Å3. The Brunauer–Emmett–Teller (BET) surface area was 903 m2 g–1 with 777 m2 g–1 of micropore surface area. The uptake of CO2 and CH4 up to 20 bar were 5.2 and 2.7 mmol g–1, respectively. These values are compared to those of 1,3,5‐benzenetricarboxylate Cu3(BTC)2, HKUST‐1 and used to show that the elevated metal‐site density per unit volume is responsible for a proportionally higher uptake on the basis of relative surface areas. The platelike particles with perpendicular pores are promising candidates for mixed‐matrix membranes.
The structure of copper 1,4‐benzenedicarboxylate Cu(BDC) has been determined by X‐ray powder diffraction and ab initio quantum mechanics (QM) calculations (P$\bar {1}$, 546.04 Å3). Extraction with methanol improves the Cu(BDC) crystallite quality. The Brunauer–Emmett–Teller (BET) surface area is 903 cm2 g–1, the CO2 uptake is 5.2 mmol g–1 at 20 bar, and the selectivity for CO2 over CH4 is 2–3.
Highly crystalline nonagglomerated ITO colloidal nanoparticles form an optically clear solution in nonpolar solvents. Their ∼5 nm diameter and narrow size distribution is achieved through a fatty ...acid mediated reaction, that lacks the need for high‐temperature annealing.
The metal–organic framework (MOF) Cu(4,4′-hexafluoroisopropylidene-bis-benzoate)1.5 (Cu–hfipbb) has been projected as an important new nanoporous material for fabricating membranes with applications ...in gas separation and CO2 capture, among others. Synthesis of submicrometer crystals of Cu–hfipbb, however, is impeded by several factors, including the extreme hydrophobicity of the hfipbb ligand. We report a fast synthesis of submicrometer particles of Cu–hfipbb via a sonochemical technique, at temperatures as low as 0 °C, and with the addition of 2-propanol to control the particle morphology. The particles were characterized by powder X-ray diffraction, thermogravimetry, light scattering, and electron microscopy to ascertain the effects of synthesis parameters on the size distribution, structure, and morphology. The presence of a small amount of 2-propanol substantially alters the particle morphology from needles to a more isotropic shape. The Cu–hfipbb particles produced by this approach are suitable for use in applications involving fabrication of membranes and thin films.
Chiral nanotube: A flexible porous homochiral SrSi2 framework of two types of single‐stranded helical nanotubes is presented (see structure). The CuI ions in the framework can be oxidized to CuII ...through single‐crystal‐to‐single‐crystal transformation forming a new, topologically equivalent phase, accompanied by an expansion in the unit cell volume of 12.51 %.
Summary
The concept of a finite body Dirichlet tessellation has been extended to that of a finite body Delaunay ‘triangulation’ to provide a more meaningful description of the spatial distribution of ...nonspherical secondary phase bodies in 2‐ and 3‐dimensional images. A finite body triangulation (FBT) consists of a network of minimum edge‐to‐edge distances between adjacent objects in a microstructure. From this is also obtained the characteristic object chords formed by the intersection of the object boundary with the finite body tessellation. These two sets of distances form the basis of a parsimonious homogeneity estimation. The characteristics of the spatial distribution are then evaluated with respect to the distances between objects and the distances within them. Quantitative analysis shows that more physically representative distributions can be obtained by selecting subgraphs, such as the relative neighbourhood graph and the minimum spanning tree, from the finite body tessellation. To demonstrate their potential, we apply these methods to 3‐dimensional X‐ray computed tomographic images of foamed cement and their 2‐dimensional cross sections. The Python computer code used to estimate the FBT is made available. Other applications for the algorithm – such as porous media transport and crack‐tip propagation – are also discussed.
Lay description
Many problems involve a group of things and the way they are arranged. For example, imagine that you were a salesperson selling door‐to‐door in a rainy city without an umbrella, you would choose paths that kept yourself dry by walking under awnings of different shapes and sizes, avoiding gaps in cover where possible. If you had a map illustrating where all the awnings were, how could you find the path where you would stay driest?
We present solutions to this problem and explore different ways to apply them. For example, you could use the map to find the locations of the shortest distances from the edge of one awning to the edge of another. Once you have these locations, you would also know the distance between the entrance points underneath each individual awning (as opposed to between two awnings). If you know both of these distances – between awnings and underneath them – you can find the path that keeps you driest between two different buildings.
Another application might be to evaluate two different cities for how dry you would stay on average, not knowing beforehand where you would have to go if you lived there. As before, you would compare the distances between and underneath all neighbouring awnings, however you might recognize that, although two awnings might technically be neighbours, as at an intersection, you would probably use a third one between the two to get from one to the other. So ignoring distances between awnings that aren't ‘relative’ neighbours would help you stay dry. You could also make a map of what a perfectly even awning arrangement might look like. You could then compare this ‘ideal awning arrangement’ to that of a real city as a way to determine how evenly real city's awnings are arranged.
Materials made from the mixture of two components can be like the awning and the street for the example above. Often we are interested in how something moves through these two‐component materials, therefore knowing how one component is arranged in another helps predict the path that a fluid or process will take as it moves through the material. It can tell us if the arrangement is uneven and allows for short cuts in one component or the other. The solutions we present to these problems can change the way that we measure and evaluate these two‐component materials.
A series of Zn–Cu 1,4-benzenedicarboxylate(bdc) metal organic frameworks(MOF) have been synthesized by introducing N,N -dimethylformamide(DMF) solutions of 1,4-benzenedicarboxylic acid to metal salt ...solutions with a range of concentrations of Cu(NO3)2 and Zn(NO3)2 across the entire composition range. At the Zn-rich side of the range, the presence of Cu(II) had the effect of changing the polymorph of the solid from the predominantly P21/n structure, associated with MOF-2, to the C2/m structure, shared with Cu(bdc). There was an associated change in crystal morphology that accompanied the addition of a Cu salt impurity. BET surface area measurements of the thermally desolvated product showed that the surface area of the Zn(bdc) increased with the addition of Cu. At the Cu-rich side, magnetic susceptibility measurements indicated that the presence of the Zn impurity increased the fraction of paramagnetic Cu centers, suggesting the formation of a large fraction of heterometallic secondary building units(hSBU) in the framework.
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