High-capacity LiV3O8 thin-film cathode with a mixed amorphous–nanocrystalline microstructure prepared by RF magnetron sputtering

LiV₃O₈ thin films with a mixed amorphous–nanocrystalline microstructure were deposited on stainless steel substrates using radio-frequency (RF) magnetron sputtering for the first time. The films exhibited good performance as a cathode material for lithium ion batteries. Results indicate that the film electrodes had a smooth surface and consisted mainly of an amorphous structure containing nanocrystalline zones dispersed within it. Depending on its microstructure, the films delivered an initial discharge capacity as high as 382 mAh/g and exhibited good capacity retention, with discharge capacity of 301 mAh/g after 100 cycles representing a loss rate of 0.21% per cycle.     

Surface-enhanced Raman scattering and catalytic activity studies over nanostructured Au–Pd alloy films prepared by DC magnetron sputtering

Research on Chemical Intermediates - Nanostructured Au33Pd67 alloy films were fabricated on glass using one-step air plasma DC magnetron sputtering. The films exhibited highly sensitive detection...     

Anticorrosive cerium-based coatings prepared by the sol–gel method

The development of efficient anti-corrosion and environmentally friendly coating systems are needed for the replacement of the highly toxic Cr-based conversion coatings for corrosion protection of aluminum alloys. In this study, we demonstrate that the direct application of ceramic cerium-based sol–gel coatings to AA7075-T6 substrates produces high-performance anti-corrosion layers. Electrochemical experiments and analyses of the microstructure demonstrate that the protective layers are very efficient for the passivation of the alloy surfaces operating as both passive and active barrier for corrosion protection.     

Study of tri-layer antireflection coatings prepared by sol–gel method

Antireflective coatings (ARCs) on tri-layer thin film stacks were studied in this paper. Silica sols have been prepared by acid-catalyzed or base-catalyzed hydrolysis and condensation reactions of tetraethyl orthosilicate. Antireflective nanometric SiO₂/TiO₂ films are formed on both sides of the glass substrates by combining the sol–gel method and the dip-coating technique. Seen from the transmittance spectra of different films, a maximum light transmittance of 99.9% was obtained at the band of 300–800 nm. Scanning electron microscope (SEM) and atomic force microscopy (AFM) confirm the well-covered surface morphology. By the SEM observations we can see that the films are full of coverage on glass surface and containing no voids or cracks. The image root mean square roughness of the two types of ARCs provided by the AFM is 1.21 and 3.04 nm, respectively. Furthermore, a surface profiler was used to determine the thickness of each layer in the obtained multi-layer coating system.     

Manufacturing of ceramic nanomaterials in Ti–Si–C–N system by sol–gel method

Problems concerning sol–gel synthesis of ceramic nanomaterials, methods of investigation of these materials and of processes proceeding with their participation have been presented. One-component nc-TiC, nc-TiN and multi-component TiC + SiC + C and Ti(C,N) + Si(C,N) + Si₃N₄, powders have been investigated. The sol–gel synthesis is carried out in two stages: low-temperature, in which the raw nc-TiC_x product is obtained, and high-temperature one. In the high-temperature stage carbonization of carbides and elimination of excessive organic compounds, being the source of carbon in carbonization process, take place. It has been demonstrated that the oxygen, present at trace level in argon, can react with components of the system in certain range of temperature, influencing the quality of obtained product. High-temperature oxidation resistance of investigated materials in dry air was also determined, applying kinetic methods. TG-DSC measurement data were used as the basis of kinetic analysis. The method of investigation has been presented at the example of TiC + SiC + C powder oxidation. Is has been demonstrated, that in case of multi-component materials, components were oxidized in temperature ranges characteristic for pure phases.     

On the structural composition and stability of Fe–N–C catalysts prepared by an intermediate acid leaching

The development of highly active and stable non-noble metal catalysts (NNMC) for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEM-FC) becomes of importance in order to enable cost reduction. In this work, we discuss the structural composition as derived from Fe-57 Mößbauer spectroscopy and X-ray diffraction, catalytic performance determined by a rotating (ring) disk electrode (RRDE) technique and stability evaluation of our Fe–N–C catalysts prepared by an intermediate acid leaching (IAL). The advantage of this IAL is given by a high density of active sites within the catalyst, as even without sulphur addition, an iron carbide formation and related disintegration of active sites are inhibited. In addition, our accelerated stress tests illustrate better stability of the sulphur-free IAL catalyst in comparison to the sulphur-added one.     

The photocatalytic properties of Ti–Mo oxides prepared by a simple sol–gel route

Powders containing mixtures of titania and molybdite in different ratios were prepared by sol–gel processing. The sols were dried and subsequently calcined at 300, 500 and 700 °C. Depending on the ratio of Ti and Mo in the initial sol and the calcination temperature, Ti-doped MoO₃, TiO₂/MoO₃ or Mo-doped TiO₂ have been formed. The as prepared samples were characterised by scanning electron microscopy with attached X-ray dispersive energy analysis, X-ray diffractometry, Raman spectroscopy, gas adsorption and optical characterisation by ultraviolet/visible spectroscopy. The latter was used for the analysis of the photocatalytic properties on the decolourisation of methylene blue solutions under visible light irradiation. The phase composition, the specific surface and the photocatalytic activity were influenced by the molybdenum content and the calcination temperature. The final molybdenum content in the samples additionally depends on the calcination temperature. The optimum photocatalytic properties were observed or Ti-doped MoO₃.     

Sequential double α-arylation of N-allylureas by asymmetric deprotonation and N→C aryl migration

On lithiation with lithium amides, N-allyl-N'-aryl ureas undergo rearrangement with transfer of the aryl ring from N to the allylic α carbon. From the α-arylated products, a further aryl transfer under the influence of a chiral lithium amide allows the enantioselective construction of 1,1-diarylallylamine derivatives. Stereoselectivity in these reactions results from the enantioselective formation of a planar chiral allyllithium under kinetic control.     

Ullmann-type C–N coupling reaction catalyzed by CuI/metformin

A facile and efficient method for Ullmann-type C–N coupling reaction of amine and aryl halide catalyzed by CuI/metformin in EtOH is described. The advantages of this method are the use of an inexpensive and readily available catalyst and ligand, easy workup, shorter reaction time, improved yields, and the use of green solvent. Furthermore, this procedure is applied successfully for the modification of natural products, such as Vindoline and Tabersonin.     

Propane oxidative dehydrogenation over V-containing mixed oxides derived from decavanadate-exchanged ZnAl–layered double hydroxides prepared by a sol–gel method

The catalytic properties of ZnAlVO mixed oxides derived from decavanadate-exchanged ZnAl–layered double hydroxide (LDH) precursors prepared by a sol–gel method (ZnAlVO–LDHx,y) were investigated in the oxidative dehydrogenation of propane and compared with those of supported catalysts obtained by conventional impregnation of NH₄VO₃ on ZnO (ZnVO-I,y) and ZnAlO mixed oxide (ZnAlVO-I,y) supports. The effects of composition and calcination time on the catalytic behavior were particularly examined. Higher propane conversions were achieved at higher vanadium content and calcination time of the precursors. The LDH-derived catalysts were the most active ones in all the temperature range studied (300–425 °C). The order of activity for propane conversion for the different catalyst families varies as ZnAlVO–LDHx,y > ZnAlVO-I > ZnVO-I and follows the strength of the Lewis and Brønsted acid sites determined by monitoring of pyridine adsorption by Fourier transform infrared spectroscopy, whereas the propene selectivities are close together in agreement with the similar densities of basic sites determined by CO₂–temperature-programmed desorption measurements. It was indeed established that the acidity, rather than the nature of the crystalline phases, the reducibility, or the specific surface area of the samples, governs the catalytic activity.     

Electrosynthesis of nanocomposite polymer coatings based on 1-vinyl-1,2,4-triazole–crotonaldehyde copolymers

Russian Journal of Applied Chemistry - The possibility of electrochemical preparation of metal–polymer nanocomposites and coatings on pure iron and steel electrode by combining the...     

Nanoreinforced hemicellulose-based hydrogels prepared by freeze–thaw treatment

A novel hybrid hydrogel was prepared from hemicelluloses, polyvinyl alcohol, and chitin nanowhiskers by the freeze–thaw technique. The hydrogel was characterized by Fourier-transform infrared (FT-IR) spectrometry, scanning electron microscopy, X-ray diffraction analysis, cross-polarization (CP)/magic-angle spinning (MAS) ¹³C nuclear magnetic resonance (NMR), and swelling property and compressive strength measurements. Atomic force microscopy images of chitin implied that the size of whiskers reached nanometer level with average length of about 200 nm and width of 40 nm. The FT-IR and NMR results indicated that physical cross-linking rather than chemical reaction occurred during the gelation process. The mechanical properties of the hydrogels were significantly improved with increasing proportion of chitin nanowhiskers, with the highest compressive stress of 9.6 MPa being found for Gel-0.5. The results showed that the repeated freeze–thaw cycles induced physical cross-linking of packed chains by hydrogen bonds among the polymers, and the concentration of chitin nanowhiskers affected the hydrogel morphology and properties. It is suggested that hydrogels with good mechanical properties can be successfully prepared by this physical method, offering promise for tissue engineering applications.     

Carbon nanofiber–copper composite powder prepared by electrodeposition

Carbon nanofiber–copper composite powder is prepared by an electrodeposition process using a copper plating bath containing homogeneously dispersed carbon nanofibers. Particles of the composite with a spiky ball structure are accumulated on the plating electrode during the initial stage of electroplating, and can be separated easily to give a powder carbon nanofiber–copper composite. The particle size can be controlled by selecting appropriate electroplating conditions.     

Ring opening of heterocycles containing a C–N double bond: a simple synthesis of imides promoted by acyl palladium species

A detailed study on the reactivity of various heterocycles, containing a C–N double bond, with acyl palladium species, generated in situ from allyl or benzyl halides and CO, has been performed. While the cyclic imine 2-methyl-1-pyrroline reacted with acyl-palladium intermediates to give a bicyclic β-lactam, other heterocycles containing a C–N double bond conjugated with a heteroatom (O or N), showed a ring-opening reaction leading to functionalized imides with high structural diversity. Such methodology represents a simple and direct way to prepare structurally complex imides. Moreover, a reaction mechanism, involving cationic intermediates, was also proposed.