Synthesis and optical property of one-dimensional spinel ZnMn<Subscript>2</Subscript>O<Subscript>4</Subscript> nanorods

Spinel zinc manganese oxide (ZnMn₂O₄) nanorods were successfully prepared using the previously synthesized α-MnO₂ nanorods by a hydrothermal method as template. The nanorods were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-Vis absorption, X-ray photoelectron spectroscopy, surface photovoltage spectroscopy, and Fourier transform infrared spectroscopy. The ZnMn₂O₄ nanorods in well-formed crystallinity and phase purity appeared with the width in 50-100 nm and the length in 1.5-2 μm. They exhibited strong absorption below 500 nm with the threshold edges around 700 nm. A significant photovoltage response in the region below 400 nm could be observed for the nanorods calcined at 650 and 800°C.     

Fabrication of core/shell ZnWO<Subscript>4</Subscript>/carbon nanorods and their Li electroactivity

Carbon-coated ZnWO₄ [C-ZW] nanorods with a one-dimensional core/shell structure were synthesised using hydrothermally prepared ZnWO₄ and malic acid as precursors. The effects of the carbon coating on the ZnWO₄ nanorods are investigated by thermogravimetry, high-resolution transmission electron microscopy, and Raman spectroscopy. The coating layer was found to be in uniform thickness of approximately 3 nm. Moreover, the D and G bands of carbon were clearly observed at around 1,350 and 1,600 cm^-1, respectively, in the Raman spectra of the C-ZW nanorods. Furthermore, lithium electroactivities of the C-ZW nanorods were evaluated using cyclic voltammetry and galvanostatic cycling. In particular, the formed C-ZW nanorods exhibited excellent electrochemical performances, with rate capabilities better than those of bare ZnWO₄ nanorods at different current rates, as well as a coulombic efficiency exceeding 98%. The specific capacity of the C-ZW nanorods maintained itself at approximately 170 mAh g^-1, even at a high current rate of 3 C, which is much higher than pure ZnWO₄ nanorods.     

Preparation and properties of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods as supercapacitor material

Co₃O₄ nanorods have been successfully synthesized by thermal decomposition of the precursor prepared via a facile and efficient microwave-assisted hydrothermal method, using cetyltrimethylammonium bromide (CTAB) with ordered chain structures as soft template for the first time. The obtained Co₃O₄ was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical measurements. The results demonstrate that the as-synthesized nanorods are single crystalline with an average diameter of about 20 to 50 nm and length up to several micrometers. Preliminary electrochemical studies, including cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS) measurements, are carried out in 6 M KOH electrolyte. Specific capacitance of 456 F g⁻¹ for a single electrode could be achieved even after 500 cycles, suggesting its potential application in electrochemical capacitors. This promising method could provide a universal green chemistry approach to synthesize other low-cost and environmentally friendly transition metal hydroxide or oxide.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript>@TiO<Subscript>2</Subscript>-OSO<Subscript>3</Subscript>H: an efficient hierarchical nanocatalyst for the organic quinazolines syntheses

A sulfonic acid functionalized titanium dioxide quasi-superparamagnetic nanocatalyst Fe₃O₄@SiO₂@TiO₂-OSO₃H with average size of 61 nm and semispherical shape with surface area about 97 m² g^?1 with saturation magnetization 17.7 emu g^?1 and the coercivity 9.84 Oe was successfully synthesized. The structure and morphology of the nanocatalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy, X-ray diffraction pattern, transmission electron microscopy, field-emission scanning electron microscopy, vibrating sample magnetometer and Brunauer–Emmett–Teller surface area analysis. The catalytic usage of the nanocatalyst was exemplified in synthesis of 2,3-dihydroquinazolin-4(1H)-one and spiroquinazolin-4(3H)-one derivatives in deep eutectic solvents (DESs) based on choline chloride and urea. We suggest that the synergistic effects in catalytic activities of titanium dioxide, organic acid and the CO₂ capture property of DES are the main reasons for the improvement of catalytic activity. The synthesized spiroquinazolinones and dihydroquinazolinones derivatives were characterized by FT-IR, ¹H and ¹³C nuclear magnetic resonance spectroscopy. The magnetic nanocatalyst exhibit high catalytic activity and can be simply separated from reaction media by an external magnet in a few seconds and could be reused for six cycles without significant loos in activity, which indicates the good immobilization of sulfonic acid on the magnetic titanium dioxide support. Furthermore, the solvent which has been used in this work can be readily isolated and reused for several times.     

Preparation and characterization of spindle-like Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> mesoporous nanoparticles

Magnetic spindle-like Fe₃O₄ mesoporous nanoparticles with a length of 200 nm and diameter of 60 nm were successfully synthesized by reducing the spindle-like α-Fe₂O₃ NPs which were prepared by forced hydrolysis method. The obtained samples were characterized by transmission electron microscopy, powder X-ray diffraction, attenuated total reflection fourier transform infrared spectroscopy, field emission scanning electron microscopy, vibrating sample magnetometer, and nitrogen adsorption-desorption analysis techniques. The results show that α-Fe₂O₃ phase transformed into Fe₃O₄ phase after annealing in hydrogen atmosphere at 350°C. The as-prepared spindle-like Fe₃O₄ mesoporous NPs possess high Brunauer-Emmett-Teller (BET) surface area up to ca. 7.9 m² g^-1. In addition, the Fe₃O₄ NPs present higher saturation magnetization (85.2 emu g^-1) and excellent magnetic response behaviors, which have great potential applications in magnetic separation technology.     

Crystallization Behavior of Amorphous Zr<Subscript>55</Subscript>Cu<Subscript>20</Subscript>Ni<Subscript>10</Subscript>Al<Subscript>10</Subscript>Ti<Subscript>5</Subscript> Alloy

In the present study, the crystallization behavior and thermal stability of amorphous Zr₅₅Cu₂₀Ni₁₀Al₁₀Ti₅ alloy, obtained by melt-spinning, have been investigated using X-ray diffraction (XRD), differential thermal analysis (DTA) and transmission electron microscopy (TEM). The activation energy for crystallization has been evaluated by the Kissinger method, and it has been found that E _x obtained from the crystallization onset temperature (T _x) is lower than E _p determined by the crystallization peak temperature (T _P). During the continuous annealing process, ZrO and h-Al₃Zr₅ phases firstly precipitate from the amorphous matrix, then Zr₂Ni_0.66O_0.33 phase forms continuously and its relative content increases with increasing annealing temperature. However, no crystalline phases have been observed during the isothermal annealing process at 733 K (below T _x) for 90 min. The atomic clusters can keep the stability state through adjusting the short-range ordering.     

Formation of CuCr<Subscript>2</Subscript>Se<Subscript>4</Subscript> ferromagnetic spinel microcrystals in a chalcogenide glass matrix

Crystals of the CuCr₂Se₄ ferromagnetic spinel and spinel-based solid solutions are shown to form in glass-forming alloys of the Cu₂Se-As₂Se₃-Cr₂Se₃-Se system containing Cr₂Se₃ at a content greater than 0.005 mole fractions. The crystalline phases are identified by the magnetochemical method (from the Curie temperatures) and X-ray diffraction analysis. According to electron microscopy, the crystal sizes are equal to several micrometers. IR irradiation of the samples in a magnetic field leads to an increase in the magnetization. The excess magnetization disappears after the external magnetic field is removed.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Tveryanovich, Kim, Rusnak, Turkina, Korzinin.     

Synthesis and gas sensing properties of SnO<Subscript>2</Subscript> nanoparticles with different morphologies

The SnO₂ particles with different morphologies of nanorod, nanosheet, nanoparticle and nanodot were synthesized by liquid-phase methods. In addition, Pt was loaded on each prepared SnO₂ by dispersing SnO₂ particles into PtCl₄ ^2? aqueous solutions containing 0.67 vol% methanol, followed by UV light irradiation for 6 h. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller measurement. The gas sensing properties of the synthesized SnO₂ were tested by detecting the change in electric resistivity in flowing aceton and methanol gases with nitrogen base. The gas sensing properties greatly changed depending on not only the specific surface area, but also the exposed crystal plane, i.e., the SnO₂ nanorods exposing (111) planes showed the excellent sensitivity and quick response ability, indicating the excellent gas sensing ability of the (111) plane. Furthermore, the Pt loading exceedingly enhanced the gas sensing properties.     

Low-Temperature Preparation of Superparamagnetic CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Microspheres with High Saturation Magnetization

Based on a low-temperature route, monodispersed CoFe₂O₄ microspheres (MSs) were fabricated through aggregation of primary nanoparticles. The microstructural and magnetic characteristics of the as-prepared MSs were characterized by X-ray diffraction/photoelectron spectroscopy, scanning/transmitting electron microscopy, and vibrating sample magnetometer. The results indicate that the diameters of CoFe₂O₄ MSs with narrow size distribution can be tuned from over 200 to ~330 nm. Magnetic measurements reveal these MSs exhibit superparamagnetic behavior at room temperature with high saturation magnetization. Furthermore, the mechanism of formation of the monodispersed CoFe₂O₄ MSs was discussed on the basis of time-dependent experiments, in which hydrophilic PVP plays a crucial role.     

Single-crystalline nanoporous Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> nanotubes

Single-crystalline nanoporous Nb₂O₅ nanotubes were fabricated by a two-step solution route, the growth of uniform single-crystalline Nb₂O₅ nanorods and the following ion-assisted selective dissolution along the [001] direction. Nb₂O₅ tubular structure was created by preferentially etching (001) crystallographic planes, which has a nearly homogeneous diameter and length. Dense nanopores with the diameters of several nanometers were created on the shell of Nb₂O₅ tubular structures, which can also retain the crystallographic orientation of Nb₂O₅ precursor nanorods. The present chemical etching strategy is versatile and can be extended to different-sized nanorod precursors. Furthermore, these as-obtained nanorod precursors and nanotube products can also be used as template for the fabrication of 1 D nanostructured niobates, such as LiNbO₃, NaNbO₃, and KNbO₃.     

Synthesis and properties of the composite ceramics from nanocrystalline Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-30% Y<Subscript>0.1</Subscript>Zr<Subscript>0.9</Subscript>O<Subscript>2</Subscript> prepared from a water-alcohol solution

The hydrogel of the mixed oxide Al₂O₃-30% Y_0.1Zr_0.9O₂ was prepared by precipitation of ammonia from a water-alcohol mixture (1 : 5). The Al₂O₃-30% Y_0.1Zr_0.9O₂ compound thus synthesized was characterized using differential scanning calorimetry, transmission electron microscopy, and the BET adsorption method. The obtained sample consisted of spherical particles with an average size of 16–20 nm and a specific surface area of 167 m²/g. The Al₂O₃-30% Y_0.1Zr_0.9O₂ powder was pressed at 300 MPa and then calcinated at 1600°C for 2 h in air. The topographic and structural features of the prepared ceramics were determined using atomic force microscopy and X-ray electron probe microanalysis. The porosity, the Vickers microhardness, and the tensile strength were determined by mercury porometry.     

Recyclable Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@Tween20@Ag Nanocatalyst for Catalytic Degradation of Azo Dyes

Silver nanoparticles supported on superparamagnetic iron oxide (SPION)-Tween20 nanocomposite were prepared by a combined polyol and chemical reduction routes. The morphology, composition and structure of Fe₃O₄@Tween20@Ag nanocatalyst were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy, energy dispersive X-ray spectroscopy, thermal gravimetric analyzer, and X-ray powder diffraction. In addition the magnetic properties were evaluated with vibrating sample magnetometry. It was found that Fe₃O₄@Tween20@Ag nanocatalyst could catalyze the degradation of various organic azo dyes and could easily be recovered from the reaction medium with external magnet. Also, the magnetic catalyst can be succesfully recycled and reused for at least five successive degradation cycles of methyl orange, methylene blue and Rhodamine B, confirming a high recycling efficiency. The cost effective and recyclable Fe₃O₄@Tween20@Ag nanocatalyst provide an novel nanomaterials architecture for environmental remediation applications.     

Heat treatment of silica-fiber-reinforced BN-Si<Subscript>3</Subscript>N<Subscript>4</Subscript> matrix composite

A new wave-transparent composite reinforced by silica fibers with a hybrid matrix comprising BN and Si₃N₄ was prepared by precursor infiltration and pyrolysis, and it was heat-treated at elevated temperatures. The variations of the composite during heat treatments were characterized and investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The as-received composite exhibits good mechanical properties, and it is almost amorphous. When treated at 1600°C, it turned brittle, and silica fibers in it were fused; the composite showed a good crystalline form. When treated at 2100°C, the composite broke into pieces, and the composition showed only BN. Si₃N₄ was decomposed, and silica fibers were volatilized. The presence of BN probably affected the phase transitions of silica fibers. __________ Translated from Novye Ogneupory, No. 8, pp. 49–52, August 2007.     

Synthesis and Characterization of Cobalt-Doped WS<Subscript>2</Subscript> Nanorods for Lithium Battery Applications

Cobalt-doped tungsten disulfide nanorods were synthesized by an approach involving exfoliation, intercalation, and the hydrothermal process, using commercial WS₂ powder as the precursor and n-butyllithium as the exfoliating reagent. XRD results indicate that the crystal phase of the sample is 2H-WS₂. TEM images show that the sample consists of bamboo-like nanorods with a diameter of around 20 nm and a length of about 200 nm. The Co-doped WS₂ nanorods exhibit the reversible capacity of 568 mAh g⁻¹ in a voltage range of 0.01–3.0 V versus Li/Li⁺. As an electrode material for the lithium battery, the Co-doped WS₂ nanorods show enhanced charge capacity and cycling stability compared with the raw WS₂ powder.     

Mercury ion adsorption on AC@Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-NH<Subscript>2</Subscript>-COOH from saline solutions: Experimental studies and artificial neural network modeling

An efficient, novel functionalized supported magnetic nanoparticle (AC@Fe₃O₄-NH₂-COOH) has been synthesized by co-precipitation method for removal of mercury ions from saline solutions. High dispersed supported magnetic nanoparticles with particle sizes less than 30 nm were formed over activated carbon derived from local walnut shell. Surface characterizations of supported magnetic nanoparticles were evaluated by Boehm test, Brunauer- Emmett-Teller (BET) surface area, X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and X-ray fluorescence (XRF). A three-layer artificial neural network (ANN) code was developed to predict the Hg (II) ions removal from aqueous solution by AC@Fe₃O₄-NH₂-COOH. The three-layer back-propagation (BP) is configured of tangent sigmoid transfer function (tansig) at hidden layer with eight neurons for AC@Fe₃O₄-NH₂-COOH, and linear transfer function (purelin) at output layer. According to the calculated MSEs, Levenberg-Marquardt algorithm (LMA) was the best training algorithm among others. The linear regressions between the predicted and experimental outputs were proven to be a good agreement with a correlation coefficient of about 0.9984 for five model variables. Maximum adsorption capacity was achieved 80mg/g by Langmuir isotherm at pH of 7 and salinity of 25,000 ppm. Kinetic studies illustrated that mercury adsorption follows pseudo-second-order.     

Modification of Mg<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> nanotubes by magnetite nanoparticles

The magnetite nanoparticles and nanocomposite “Nanotube of hydrosilicate Mg—magnetite nanoparticles—Mg-ChR-NT/Fe₃O₄-NP” were obtained by coprecipitation. The composition of the synthesized samples has been established by X-ray diffraction. Using transmission electron microscopy, the presence of magnetite nanoparticles has been detected both inside the NTs and at the external surface of the NT walls. The specific surface of the NTs, nanoparticles, and composite is determined.     

Structure and electrical properties of sputtered TiO<Subscript>2</Subscript>/ZrO<Subscript>2</Subscript> bilayer composite dielectrics upon annealing in nitrogen

The high-k dielectric TiO₂/ZrO₂ bilayer composite film was prepared on a Si substrate by radio frequency magnetron sputtering and post annealing in N₂ at various temperatures in the range of 573 K to 973 K. Transmission electron microscopy observation revealed that the bilayer film fully mixed together and had good interfacial property at 773 K. Metal-oxide-semiconductor capacitors with high-k gate dielectric TiO₂/ZrO₂/p-Si were fabricated using Pt as the top gate electrode and as the bottom side electrode. The largest property permittivity of 46.1 and a very low leakage current density of 3.35 × 10^-5 A/cm² were achieved for the sample of TiO₂/ZrO₂/Si after annealing at 773 K.     

EPR study of compounds in the LaAlO<Subscript>3</Subscript>-La<Subscript>0.67</Subscript>Sr<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> system

The EPR spectra of compounds in the LaAlO₃-La_0.67Sr_0.33Mn _y O₃ system at a frequency of 9.4 GHz have been investigated at the temperatures T = 77 and 300 K as a function of the manganese concentration y (y = 0.015, 0.030, 0.080). It has been revealed that, in the paramagnetic state at y = 0.015, there exist isolated Mn²⁺ and Mn⁴⁺ ions, which has been confirmed by simulating the EPR spectra. The parameters of the EPR spectra have been determined. The effective magnetic moments μ_eff of the Mn²⁺ and Mn⁴⁺ ions have been calculated from the EPR spectra. It has been demonstrated that an increase in the Mn concentration leads to a decrease in the number of isolated ions and to the formation of new spin clusters. This manifests itself in the predominance of a broad line with weak traces of the hyperfine structure due to the isolated manganese ions.     

Investigation of a new lead-free Bi<Subscript>0.5</Subscript>(Na<Subscript>0.40</Subscript>K<Subscript>0.10</Subscript>)TiO<Subscript>3</Subscript>-(Ba<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>)TiO<Subscript>3</Subscript> piezoelectric ceramic

Lead-free piezoelectric compositions of the (1-x)Bi_0.5(Na_0.40K_0.10)TiO₃-x(Ba_0.7Sr_0.3)TiO₃ system (when x = 0, 0.05, 0.10, 0.15, and 0.20) were fabricated using a solid-state mixed oxide method and sintered between 1,050°C and 1,175°C for 2 h. The effect of (Ba_0.7Sr_0.3)TiO₃ [BST] content on phase, microstructure, and electrical properties was investigated. The optimum sintering temperature was 1,125°C at which all compositions had densities of at least 98% of their theoretical values. X-ray diffraction patterns that showed tetragonality were increased with the increasing BST. Scanning electron micrographs showed a slight reduction of grain size when BST was added. The addition of BST was also found to improve the dielectric and piezoelectric properties of the BNKT ceramic. A large room-temperature dielectric constant, ε _r (1,609), and piezoelectric coefficient, d ₃₃ (214 pC/N), were obtained at an optimal composition of x = 0.10.     

A general method for preparing tellurides: Synthesis of PbTe,Ni<Subscript>2</Subscript>Te<Subscript>3</Subscript>, and Cu<Subscript>7</Subscript>Te<Subscript>5</Subscript> from solutions under microwave radiation

Nanocrystals of binary metal tellurides, such as PbTe, Ni₂Te₃, and Cu₇Te₅, are synthesized by the polyol method under microwave radiation and studied using X-ray powder diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and photoacoustic spectroscopy. Binary tellurides are formed only in the case when ethylene glycol is used as a reducing agent and only when the reaction is carried out under microwave radiation. No product is formed when the reactions are performed using a conventional technique of heating. The synthesis of the aforementioned metal tellurides is described, and the proposed mechanism of the reaction is discussed.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, O. Palchik, Kerner, Gedanken, V. Palchik, Slifkin, Weiss.