Synthesis and electrochemical properties of layered Li[Ni0.333Co0.333Mn0.293Al0.04]O2−zFz cathode materials prepared by the sol–gel method

The cathode-active materials, layered Li[Ni_0.333Co_0.333Mn_0.293Al_0.04]O_2−zF_z (0 ≤ z ≤ 0.1), were synthesized from a sol–gel precursor at 900 °C in air. The influence of Al–F co-substitution on the structural and electrochemical properties of the as-prepared samples was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and electrochemical experiments. The results showed that Li[Ni_0.333Co_0.333Mn_0.293Al_0.04]O_2−zF_z has a typical hexagonal structure with a single phase, the particle sizes of the samples tended to increase with increasing fluorine content. It has been found that Li[Ni_0.333Co_0.333Mn_0.293Al_0.04]O_1.95F_0.05 showed an improved cathodic behavior and discharge capacity retention compared to the undoped samples in the voltage range of 3.0–4.3 V. The electrodes prepared from Li[Ni_0.333Co_0.333Mn_0.293Al_0.04]O_1.95F_0.05 delivered an initial discharge capacity of 158 mAh⁻¹ g and an initial coulombic efficiency is 91.3%, and the capacity retention at the 20th cycle was 94.9%. Though the F-doped samples had lower initial capacities, they showed better cycle performances compared with F-free samples. Therefore, this is a promising material for a lithium-ion battery.     

Corrosion kinetics and patina evolution of galvanized steel in a simulated coastal-industrial atmosphere

The corrosion kinetics and patina (corrosion products) layer evolution of galvanized steel submitted to wet/dry cyclic corrosion test in a simulated coastal-industrial atmosphere was investigated. The results show that zinc coating has a greater corrosion rate during the initial period and a lower corrosion rate during the subsequent period, and the patina composition and structure can greatly affect the corrosion kinetics evolution of zinc coating. Moreover, Zn₅(OH)₆(CO₃)₂ and Zn₄(OH)₆SO₄ are identified as the main stable composition and exhibit an increasing relative amount; while Zn₁₂(OH)₁₅Cl₃(SO₄)₃ cannot stably exist and diminish in the patina layer as the corrosion develops.     

Low-valence ion addition induced more compact passive films on nickel-copper nano-coatings

Ni-Cu nano-coatings were prepared by pulsed electroplating technique in the baths containing various amount of boric acid. Their microstructure, morphologies and corrosion resistance were characterized in detail. The addition of boric acid strongly influences on the microstructure of the Ni-Cu coatings. The coating with a grain size of 130 nm, obtained from the bath containing 35 g L⁻¹ boric acid, shows the highest corrosion resistance. This is attributed to the low-valence Cu ion (Cu⁺) additions in nickel oxide, which could significantly decrease the oxygen ion vacancy density in the passive film to form a more compact passive film. The higher Cu⁺ additions and the lower diffusivity of point defects (D₀) are responsible for the formation of more compact passive film on the coating obtained from the bath with 35 g L⁻¹ boric acid.     

Nanocrystalline pirochromite spinel through solution combustion synthesis

The production of magnesium–chromium oxides by solution combustion synthesis was investigated using glycine and urea for the first time. Ammonium dichromate, urea/glycine and ammonium nitrate aqueous solutions were used as the precursors of the oxides. The effect of different reaction parameters, such as fuel richness, stoichiometry and fuel leanness was evaluated; such parameters were modified by changing the reagents and the fuel/oxidant ratio. The results suggest that glycine is an interesting complexing/combustible agent for ammonium dichromate to produce chromite spinel. Addition of extra ammonium nitrate to stoichiometric compositions improved the specific surface area and reduced the crystallite size. The highest specific surface area (153.40 m²/g) was obtained for the stoichiometric fuel/oxidant mixtures containing glycine as combustible in combination with ammonium nitrate; however, the smallest crystallite size (approximately 9 nm) of Pirochromite (MgCr₂O₄) was synthesized using urea as combustible.     

Magnetooptics of single and microresonator iron-garnet films at low temperatures

We have investigated the low-temperature behavior of the optical and magneto-optical properties of (Bi, Gd, Al)-substituted yttrium iron-garnet films that are either single or microresonator, i.e. sandwiched between two dielectric Bragg mirrors. It was shown that the magneto-optical properties of the microresonators with a magnetic film core are mainly determined by the properties of the constituent magnetic films. Special attention was paid to the compositions possessing magnetic compensation temperatures. The phenomenon of the temperature hysteresis was found and discussed for several samples. This testifies the fact that the magnetic moment reorientation in a magnetic field occurs by the full cycle of the first-order phase transitions “collinear phase – non-collinear phase – collinear phase”. The Faraday hysteresis curves at around magnetic compensation temperatures are demonstrated to be very informative concerning composition of a sample. In particular, the hysteresis curves measured for the magnetic films on the garnet substrates showed bursts that indicates formation of a transition layer.     

Two Keggin compounds constructed from tri −/tetra-nuclear Cu clusters linked mono copper(II)-substituted phosphomolybdates

Two new compounds based on mono copper(II)-substituted phosphomolybdate, [Cu₄(tea)₆(H₄PMo₁₁CuO₃₉)(PMo₁₂O₄₀)]₂·33H₂O (1) and [Cu₃(tea)₆(H₂O)₂(H₂PMo₁₁CuO₃₉)₂]₂·30H₂O (2) (tea = 2- [1,2,4]triazol-4-yl-ethylamine), have been synthesized under hydrothermal conditions. Compound 1 owns tetra-nuclear clusters [Cu₄(tea)₆], linking a pair mono copper(II)-substituted and saturated Keggin anions to form a 2D structure. Compound 2 contains tri-nuclear clusters [Cu₃(tea)₆], fusing four mono copper(II)-substituted anions to construct a discrete four-membered cycle structure.     

Correlation between the adsorption ability and reduction degree of graphene oxide and tuning of adsorption of phenolic compounds

Graphene oxide (GO) was prepared with a modified Hummers method and then reduced to different reduction degrees by using hydrazinehydrate. The obtained GO and reduced GO (RGO) were characterized. It was found that the reduction removed most of the oxygen-containing functional groups on the surface of GO. By using naphthalene as a probe, the interaction between RGO and organic molecules was evaluated with NMR. It was confirmed that the reduction of GO increased significantly the interaction between the π system of graphene and the π unit of organic molecules. The thermodynamic analysis indicated that the adsorption was a spontaneous, exothermic and entropy-decreasing process. It was observed that the adsorption capacities were generally increased with increasing the reduction degree of GO. The chemical structures of phenolics also affected their adsorption on RGO. The adsorption of the phenolics on RGO was enhanced by introducing electron-donating and withdrawing functional groups on the benzene ring. Depending on the chemical structures of phenolics, the surface reduction of GO to RGO-1 significantly increased the adsorption capacity for phenolics by a factor as large as 235%. A possible adsorption mechanism and correlation between the adsorption ability, reduction degree of GO and chemical structures of phenolics was discussed.     

Effects of aluminium nitride silane-treatment on the mechanical and thermal properties of polybenzoxazine matrix

A new kind of polymer composite, produced from the typical polybenzoxazine and 0–30 wt-% native and silane-treated aluminium nitride (T-AlN), was investigated. The mechanical tests revealed a significant increase in the microhardness and flexural properties upon adding the T-AlN particles compared to that obtained from the untreated ones. By adding 0–30 wt-% T-AlN, the tensile moduli were accurately reproduced by the Halpin-Tsai and Nielsen models. At 30 wt-% T-AlN, dynamic mechanical analysis showed a significant increase in the storage moduli and the glass transition temperature (T_g), reaching 3.2?GPa and 217°C, respectively. The thermal stability of these materials was significantly improved upon the addition of the T-AlN fillers. These improvements are attributed to the high thermal and mechanical properties of the fillers and their good dispersion and adhesion in and to the matrix as revealed by a morphological analysis.     

Inorganic-organic hybrid supramolecular material based on the highest connection of a Keggin arsenotungstate with electro-/photo-catalytic properties

An extraordinary supramolecular hybrid material based on the Keggin arsenotungstate, (Hbimb)₃[AsW₁₂O₄₀]·H₂O (1) (bimb = 1,4-bis(imidazol-l-yl)butane) has been synthesized under hydrothermal condition and characterized by elemental analysis, infrared (IR), thermogravimetry (TG), X-Ray Diffractomer (XRD), and single-crystal XRD. In compound 1 the {AsW₁₂O₄₀} cluster is linked to 14 organic ligands through their surface oxygen atoms, which are further embraced by 20 polyanions analogs to form a tightly packed 3D supramolecular network with a (4⁵·6)(4⁵²·6³⁸·8)(4⁹·6)₂ topology via strong hydrogen bonds and supramolecular interactions. Compound 1 represents the highest connectivity of Keggin supramolecular arsenotungstate, which exhibits electrocatalytic behaviors for reduction of H₂O₂ and high efficiency degradation capability for two typical dyes methylene blue (MB) and rhodamine B (RhB) under UV light.