1,720,985 research outputs found
Synthesis, characterization and crystal structure of 6-Chloro-4,4′-dimethyl-2,2′-bipyridine and 4,4′-Dimethyl 2,2′-bipyridine N-Oxide
No full textRationalization of liquid assisted grinding intercalation yields of organic molecules into layered double hydroxides by multivariate analysis
No full textThe Liquid Assisted Grinding (LAG) method for the fast and facile preparation of organic-intercalated Layered Double Hydroxide (LDH) nanocomposites allowing the production of low cost, stable and efficient functional materials, is here employed to rationalize the features of the organic compounds that most likely undergo easy intercalation. LAG method was exploited to determine in a short time which molecules can be successfully intercalated into LDH. A straightforward rationalization of the intercalation yield results was not possible since no individual feature (such as bulkiness or pK(a)) could alone describe the intercalation behaviour of the whole set of molecules. Therefore, Principal Component Analysis (PCA) together with the use of molecular descriptors to classify molecules, were mutuated from the chemometric approach, widely used in analytical chemistry and applied successfully, for the first time, to a novel area of materials science. A set of molecular descriptors were chosen to cover different features of the molecule (physicochemical, topological, geometrical etc.) and then screened by statistical methods to understand which descriptors affected the intercalation yield. Then PCA allowed us to highlight the presence of various mechanisms, involved in the LAG intercalation and to separate the samples along PC3 as a function of yield. Finally, the classification tree method allowed us to understand the various mechanisms of intercalation and to classify molecules in groups, related to their yield. These groups can be used to estimate the expected yield as a function of the molecular descriptors. The molecules more apt to LAG have medium-low molecular weight, high flexibility and low refractivity. Conversely large and hydrophobic molecules and, surprisingly, small but rigid molecules have a small success rate concerning LAG intercalation. The behaviour of this last class of molecules, that should be in principle easily intercalated by LAG but which was identified by the present study as a difficult case, was thus tested using two molecules and the prediction of the chemometric study was confirmed
PCA Analysis of In Situ X-ray Powder Diffraction and Imaging Data Shedding New Light on Solid-State Transformations: The Crystallization of Low Temperature Eutectic Mixtures
No full textEutectic mixtures are usually studied by differential scanning calorimetry (DSC), able to identify the transition temperatures, possible hysteresis, and investigate the energetic features of transformations. However, DSC is not able to give compositional, structural, or morphological information. A new approach is proposed exploiting powder X-ray diffraction (XRPD) and imaging to overcome the issues posed to diffraction by the presence of an amorphous liquid phase. Principal component analysis (PCA) is applied blindly to in situ XRPD data from both solid and liquid phases in an approach called differential scanning diffraction (DSD), with PCA scores being the reaction coordinate of melting or crystallization steps. PCA was used in a similar way to analyze the imaging data in what was named differential scanning imaging (DSI). Exploiting this approach, the structural and morphological changes during phase transitions can be characterized by XRPD and imaging respectively, complementarily to the energetic effects probed by DSC. Melting and crystallization points can be identified together with the hysteresis between downward and upward temperature ramps, by the structural and morphological viewpoints. A three-component mixture (NaBr, KCl, and water), with wide industrial applications, was studied to describe the behavior around the eutectic composition and examine how small mixture changes can affect the transition temperature and the freezing/melting behaviors. The phase composition at the solid state was elucidated and a new phase of NaBr was identified and its lattice parameters were obtained by XRPD. DSD and DSI resulted complementary to traditional DSC data with many potential applications in solid state chemistry and materials science
Crystal packing and layered morphology relationships in naphthalene sulfonate compounds
No full textThe crystal structure of sodium naphthalene 2-sulfonate (Na2-NS) is reported. This compound raised the attention as a pollutant, being widely used in industry, and its intercalation in inorganic matrices, such as layered double hydroxides (LDH), could be a suitable removal strategy. The crystal structure of the title compound, despite its simplicity, is not known in the literature, so we looked for a strategy to grow crystals suitable for a single crystal study. Although many attempts were made to recrystallize it, Na2-NS grows in bunches of very thin laminae, with a high degree of mosaicity and intergrowth, explaining the absence of a reported crystal structure. The crystal structure shows layers of Na+ cations with the organic part arranged in between. The crystals grow easily in the layer plane, whilst the growth perpendicular to the layers is driven by weak non-bonding interaction and thus unfavored. The crystal packing features were related to the density of charges in the cationic layer with respect to the size of the anion. By comparing the crystal structures of 2-NS salts with different cations, and with or without an amino substituent in different positions, it was possible to find the relationship between the density of the positive charges and the deepness of interdigitation of the 2-NS moieties. We exploited this information to shed light on the structural features of 2-NS and related compounds intercalated into LDH. The X-ray powder diffraction pattern of 2-NS intercalated LDH (V. Toson, E. Conterosito, L. Palin, et al. Facile intercalation of organic molecules into hydrotalcites by liquid-assisted grinding: yield optimization by a chemometric approach. Cryst. Growth Des. 2015, 15, 5368) resulted consistent with a crystal packing characterized by the partial interdigitation of the 2-NS anions
Crystal structure and solid-state transformations of Zn-triethanolamine-acetate complexes to ZnO
No full textThe rapid and massive formation of a foamy precipitate while reacting zinc acetate (Zn(Ac)2) and triethanolamine (TEA) in proper conditions led to an unravelled complex and a molecular tetra- metallic zinc cluster: their synthesis was optimised and they were characterised by single crystal X-ray diffraction. The structure shows the direct link of the acetate anion to the Zn cation, a feature not observed in parent compounds. The structural and chemical evolution of these materials upon heating have been studied, targeting the production of zinc oxide thin films or particles with particular properties. The phase transitions occurring during thermal treatments and the conversion to ZnO were studied by in situ X-ray powder diffraction, thermo-gravimetry and Raman spectroscopy. The cluster structure can be considered an even more interesting precursor for zinc oxide as nano-aggregates of four ZnO moieties are already present and the formation of ZnO particles requires a smaller number of broken and newly formed bonds. A third metastable hydrated phase was identified, but not structurally characterised because of its instability, thus completing the exploration of the polymorph landscape of the title compound
Single step eco-efficient mild chemical process for the total valorisation of rice husk: a focus on the inorganics as a cement additive
No full textThe rice husk biomass remaining from the industrial processing of rice constitutes approximately 25 wt% of the edible rice produced, and its disposal is challenging due to its high silica content. Here, we describe the optimization of a single step innovative chemical process for the conversion of rice husk-based biomass into useable products which tackles all fractions of the input biomass. The chemical process consists of a single step hydrothermal low temperature treatment of rice husk biomass leading to three easy-to-recover fractions. With appropriate chemical treatments, each of these fractions can serve specific applications effectively, overcoming the issues present in the original biomass. This paper will present the treatment method and the optimization of chemical conditions for ideal fractionation as well as include the characterization of the recovered materials. Additionally, the paper will explore the use of one of these materials—the inorganic precipitate fraction (P), which is rich in calcium silicate hydrate (C-S-H) phase—as an additive to promote C-S-H nucleation in cementitious materials. The process also yields a liquid fraction (S) rich in sugars and soluble inorganic species, and a fibrous fraction (HR) containing lignin and cellulose residues. All these components were characterized to assess their suitability for potential applications. A detailed study on the application of these materials in the fields of plant biology and polymer science will be presented in (a) subsequent publication(s). The three fractions were characterized by a multi-technique approach involving PXRD, XRF, TGA/DSC, Electron microscopy and NMR. The above chemical process can be extended to any straw and husk-based cereal crops (wheat or barley), broadening and strengthening the bio-based industries and improving the circularity of food-related byproducts
The Syntheses and Crystal Structures of the First Disiloxane-1,3-Dithiol and Its Cadmium Complex
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