Controlled Growth of SrxBa1−xNb2O6 Hopper- and Cube-Shaped Nanostructures by Hydrothermal Synthesis

Controlling the shape and size of nanostructured materials has been a topic of interest in the field of material science for decades. In this work, the ferroelectric material Sr_xBa_1−xNb₂O₆ (x=0.32–0.82, SBN) was prepared by hydrothermal synthesis, and the morphology is controllably changed from cube-shaped to hollow-ended structures based on a fundamental understanding of the precursor chemistry. Synchrotron X-ray total scattering and PDF analysis was used to reveal the structure of the Nb-acid precursor, showing Lindqvist-like motifs. The changing growth mechanism, from layer-by-layer growth forming cubes to hopper-growth giving hollow-ended structures, is attributed to differences in supersaturation. Transmission electron microscopy revealed an inhomogeneous composition along the length of the hollow-ended particles, which is explained by preferential formation of the high entropy composition, SBN33, at the initial stages of particle nucleation and growth.     

Untersuchungen zur Struktur des Triglycinsulfats mit Hilfe der hochauflösenden magnetischen Kernresonanzspektroskopie im Festkörper

Investigations of the Structure of Triglycinsulfate by High Resolution Magnetic Resonance in Solids Measurements were performed in the ferroelectric and paraelectric phase of TGS monocrystals with the aid of multiple pulse experiments for high resolution magnetic proton resonance in solids. The contributions to the spectra, which are to be expected theoretically from the different proton groups (NH₃, CH₂, OH), were calculated and compared with the corresponding experimental results. Splittings are discussed, which occur as a consequence of the ¹⁴N? ¹H-interaction and indicate changes at the phase transition point. The anisotropy of the effective chemical shift tensor caused by the rotation of NH₃-groups and the anisotropy of the chemical shift tensor of OH-groups were determined.     

The use of hydrothermal methods in the synthesis of novel open-framework materials

The preparation of inorganic compounds, exhibiting open-framework structures, by hydrothermal methods has been presented. To illustrate the efficacy of this approach, few select examples encompassing a wide variety and diversity in the structures have been provided. In all the cases, good quality single crystals were obtained, which were used for the elucidation of the structure. In the first example, simple inorganic network compounds based on phosphite and arsenate are described. In the second example, inorganic-organic hybrid compounds involving phosphite/arsenate along with oxalate units are presented. In the third example, new coordination polymers with interesting structures are given. The examples presented are representative of the type and variety of compounds one can prepare by careful choice of the reaction conditions.     

Capture of CO<Subscript>2</Subscript> from flue gas by vacuum pressure swing adsorption using activated carbon beads

Vacuum pressure swing adsorption (VPSA) for CO₂ capture has attracted much research effort with the development of the novel CO₂ adsorbent materials. In this work, a new adsorbent, that is, pitch-based activated carbon bead (AC bead), was used to capture CO₂ by VPSA process from flue gas. Adsorption equilibrium and kinetics data had been reported in a previous work. Fixed-bed breakthrough experiments were carried out in order to evaluate the effect of feed flowrate, composition as well as the operating pressure and temperature in the adsorption process. A four-step Skarstrom-type cycle, including co-current pressurization with feed stream, feed, counter-current blowdown, and counter-current purge with N₂ was employed for CO₂ capture to evaluate the performance of AC beads for CO₂ capture with the feed compositions from 15–50% CO₂ balanced with N₂. Various operating conditions such as total feed flowrate, feed composition, feed pressure, temperature and vacuum pressure were studied experimentally. The simulation of the VPSA unit taking into account mass balance, Ergun relation for pressure drop and energy balance was performed in the gPROMS using a bi-LDF approximation for mass transfer and Virial equation for equilibrium. The simulation and experimental results were in good agreement. Furthermore, two-stage VPSA process was adopted and high CO₂ purity and recovery were obtained for post-combustion CO₂ capture using AC beads.     

Converting drugs into gelators: supramolecular hydrogels from N-acetyl-L-cysteine and coinage-metal salts

Here we present the concept of metallophilic hydrogels, supramolecular systems in which the gelator species are metal-thiolates that self-assemble through metallophilic attractions. The principle is applied for a small drug, the mucolytic agent N-acetyl-l-cysteine (NAC), which readily forms hydrogels in the presence of Au(iii), Ag(i) and Cu(ii) salts. The resulting transparent hydrogels present pH induced sol/gel transition. Scanning electron microscopy (SEM) measurements reveal a microporous structure in form of flakes for the three of them. The low pH at which these hydrogels are formed (pH < 4) limits their direct use as drug-delivery systems, but still this system constitutes a novel method for easy and fast conversion of small drugs into potent hydrogelators. Future developments will help to fully develop the idea in order to create a new class of supramolecular drug-delivery systems.     

Convenient synthesis of fluorazone derivatives by one-pot pyrrolation/cyclization of anthranilic acids

A series of fused heterocyclic compounds based on a fluorazone structure has been prepared from anthranilic or ortho-aminoheteroaryl carboxylic acids by one-pot sequential pyrrolation/cyclization catalyzed by 4-chloropyridine hydrochloride, in generally good yield.     

1,4‐Phenylenebis(methylene) bis(9H‐carbazole‐9‐carbodithioate)

The molecules of the title compound, C₃₄H₂₄N₂S₄, lie across centres of inversion in the space group P2₁/n. The spacer unit linking the benzene rings and carbazole units is effectively planar, while the carbazole unit itself is slightly folded. Molecules are linked into sheets by a single C—H...π(arene) hydrogen bond and the hydrogen‐bonded sheets are themselves linked into a three‐dimensional framework structure by a single π–π stacking interaction.