Influence of thickness on the properties of solution-derived LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> thin films

LiMn₂O₄ thin films of different thickness were derived from solution deposition and heat treated by rapid thermal annealing. The phase identification and surface morphology were studied by X-ray diffraction and scanning electron microscopy. The electrochemical properties of the films were examined by galvanostatic charge-discharge experiments and electrochemical impedance spectroscopy. LiMn₂O₄ thin films of different thickness derived from solution deposition and rapid thermal annealing are homogeneous and crack free with the grain size between 20 nm and 50 nm. The specific capacity of these films is between 42 and 47 μAh·cm²·μm⁻¹. The capacity decreases with the increase of discharge current density. The capacity loss per cycle increases from 0.012% to 0.16% after being cycled 50 times as the film thickness increases from 0.18 μm to 1.04 μm. The lithium diffusion coefficients of these films are in the same order of 10⁻¹¹ cm²·s⁻¹.     

3D Interconnected MoO<Subscript>2</Subscript> Nanocrystals on Nickel Foam as Binder-free Anode for Li-ion Batteries

MoO₂ nanocrystals (NCs) on Ni foam were simply synthesized via a facile hydrothermal method and a dip-coating method. It was worth noting that ultrafine interconnected MoO₂ nanocrystals (about 10 nm) were uniformly anchored on Ni foam to fabricate a particular three-dimensional architecture, which may provide more active sites and shorter transmission pathways for lithium ions. As binder-free anode, MoO₂ NCs on Ni foam deliver a high initial discharge capacity of 990 mAh·g^-1 and retain a reversible capacity of 924 mAh· g^-1 after 100 cycles at a current density of 0.1 C. More importantly, when the current density returns from 2 C to 0.1 C, the capacity recovers to 910 mAh·g^-1 (about 92% of the original high capacity), suggesting excellent cycling stability and rate capability. The particular 3D electrode as binder-free anode makes it a promising anode candidate for high-performance lithium-ion batteries.     

Solvothermal synthesis and electrochemical properties of octahedral cobalt oxide decorated with Ag<Subscript>2</Subscript>O

Octahedral CoO with nanostructures decorated with Ag nanoparticles was prepared via a facile solvothermal approach. After being annealed at 500 °C for 1 h, an electrochemical capacitor material of Co₃O₄ decorated with Ag₂O was obtained. The cyclic voltammetry and galvanostatic charge-discharge were used to evaluate the electrochemical properties of the as-prepared products. The results indicated that the as-prepared samples exhibited fine pseudo-capacitive performance, and the surface modifications of Ag₂O can significantly increase the capacitance of the Co₃O₄ material. The specific capacitance of Ag₂O/Co₃O₄ composite electrode was up to 217.6 F·g^?1, which was 3.35 times as high as that of pure Co₃O₄. Moreover, Ag₂O/Co₃O₄ composite showed an excellent cycle performance, and 65.3% of specific capacitance was maintained after 200 cycles.     

Electrochemical Sensing of Heavy Metal Ions based on Monodisperse Single-crystal Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Microspheres

Single-crystal Fe₃O₄ with monodisperse microspheres structure has been used for individual electrochemical detection of heavy metal ions. Morphology and structure of the as-prepared Fe₃O₄ microspheres were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Meanwhile the electrochemical properties of the Fe₃O₄ microspheres modified glass carbon electrodes (GCE) were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and the enhanced electrochemical response in stripping voltammetry for individual detection of Pb(II), Hg(II), Cu(II), and Cd(II) was evaluated using square wave anodic stripping voltammetry (SWASV). With high specific surface area and excellent catalytic activity toward heavy metal ions, the as-prepared monodisperse and single-crystal Fe₃O₄ microspheres show a preferable sensing sensitivity (22.2 μA/μM) and limit of detection (0.0699 μM) toward Pb(II). Furthermore, the electrochemical sensor of Fe₃O₄ microspheres exhibits excellent stability and it also offers potential practical applicability for the determination of heavy metal ions in real water samples. This study provides a potential simple and low cost iron oxide for the construction of sensitive electrochemical sensors applied to monitor and control the pollution of toxic metal ions.     

Two-step synthesis of TiC<Subscript>0.7</Subscript>N<Subscript>0.3</Subscript>@WC-MoC<Subscript>2</Subscript> core-shell microspheres and fabrication of TiC<Subscript>0.7</Subscript>N<Subscript>0.3</Subscript>@WC-MoC<Subscript>2</Subscript>-based cermets by SPS

The precursor with TiC0.7N0.3@WO3-MO3 microspheres were prepared by a novel method from the WO3-MoO3 sol dipping. Subsequently, TiC0.7N0.3@WC-MoC2 core-shell structural microspheres were successfully obtained by carburizing the precursor at 900 °C in a flowing mixture of CH4 (20 ml·min-1) and H2 (200 ml·min-1) for 2 h. Then TiC0.7N0.3@WC-MoC2-15Co cermets were prepared utilizing the core-shell powders by spark plasma sintering (SPS). Powders of the precursors with TiC0.7N0.3@WO3-MO3 microspheres, TiC0.7N0.3@WC-MoC2 microspheres and TiC0.7N0.3@WC-MoC2-15Co cermets were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The obtained TiC0.7N0.3@WC-MoC2 microspheres have a dense WC-MoC2 coatings shell. The thickness of the shell could be easily controlled by adjusting the number of sol dipping cycles. It was found that the TiC0.7N0.3@WC-MoC2 microspheres were more beneficial to fabricate the "core-rim" structures by SPS.     

Magnetically Recoverable PEI/Titanate@Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Photocatalysts: Fabrication and Photocatalytic Properties

The magnetically separable ternary polyetherimide/titanate@Fe₃O₄ (PTF) photocatalysts of special heterostructure between magnetite (Fe₃O₄) microspheres and titanates nanosheets modified by polyetherimide (PEI) were successfully fabricated via a simple facile hydrothermal deposition method. The as-prepared photocatalysts were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, Transmission electron microscopy and UV-vis diffuse reflectance spectroscopy etc. The results showed that the as-fabricated material had a structure of Fe₃O₄ microspheres coated with titanates nanosheets modified by PEI. The special interfacial contact between 3D microsphere and 2D nanosheets in the nanoarchitectures was formed via electrostatic attraction. Furthermore, the resulted photocatalysts were tested by degradation reaction of methylene blue under visible light irradiation and demonstrated an enhanced performance than the pure Fe₃O₄ microspheres, and the photocatalytic activity enhanced with the molar ratio of Fe₃O₄ microspheres and modified titanate gradually, which was attributed to the expansion of the surface area and the different electrostatic contact between the Fe₃O₄ microspheres and titanate nanosheets. Moreover, the obtained results revealed the high yield magnetic separation and efficient reusability of PTF-5 (96.7%) over 3 times reuse.     

Thermal stability of LiFePO<Subscript>4</Subscript>/C-LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> blended cathode materials

Safety is important to lithium ion battery materials. The thermal stability of LiFePO₄/C-LiMn₂O₄ blended cathode materials is characterized by using TG, XRD, and SEM etc. The results show that LiFePO₄/C-LiMn₂O₄ possesses a worse thermal stability than pure spinel LiMn₂O₄ and pure olivine LiFePO₄/C. When LiFePO₄/C-LiMn₂O₄ blended cathode materials are sintered at 500°C under Ar atmosphere, the sintered cathode materials emit O₂, and appear impurity phases (Li₃PO₄, Fe₂O₃, Mn₃O₄). It is deduced that some chemical reactions take place between different materials, which leads to a worse discharge specific capacity. LiFePO₄/C-LiMn₂O₄ blended cathode materials, therefore, need to be managed and controlled strictly for the sake of thermal stability and safety.     

Synthesis and Characterization of LiCoxMn2-xO4 Cathode Materials

LiCoxMn2.04 cathode materials for lithium ion batteries were synthesized by mechanical activation-solid state reaction at 750 ℃ for 24 h in air atmosphere, and their crystal structure, morphology, element composition and electrochemical performance were characterized with XRD, SEM, ICP-AES and charge-discharge test. The experimental results show that all samples have a single spinel structure, well formed crystal shape and uniformly particle size distribution. The lattice parameters of LiCo Mn2-xO4 decrease and the average oxidation states of manganese ions increase with an increase in Co content. Compared with pure LiMn2O4, the LiCo Mn2xO4 （x=0.03-0.12） samples show a lower special capacity, but their cycling life are improved. The capacity loss of LiCo009Mn191O4 and LiCo0.1Mn1.88O4 is only 1.85% and 0.95%, respectively, after the 20th cycle. The improvement of the cycle performance is attributed to the substitution of Co at the Mn sites in the spinel structure, which suppresses the Jahn-Teller distortion and improves the structural stability.     

Effect of Fe(III) impurity on the electrochemical performance of LiFePO<Subscript>4</Subscript> prepared by hydrothermal process

Lithium iron phosphate (LiFePO₄) was synthesized from LiOH, FeSO₄ and H₃PO₄ by a hydrothermal process at 180°C. The samples were characterized by X-ray diffraction, scanning electron microscopy and chemical analysis. Electrochemical performance of the samples was tested in terms of charge-discharge capacity and cycling behavior. The results indicated that Fe(III) impurity had obviously effect on the electrochemical properties of LiFePO₄, and the formation of Fe³⁺ was caused by the oxidation of Fe²⁺ in the dissolving and feeding processes accompanying the increase of pH value. It was found that the precipitation separation was effective in decreasing the content of Fe³⁺ in the solution of FeSO₄ and the sealed feeding was useful in preventing the conversion of Fe²⁺ to Fe³⁺. When the content of Fe³⁺ < 0.5 wt%, the hydrothermally synthesized LiFePO₄ calcined at 750°C with sucrose as carbon source exhibited an initial discharge capacity of 154.9 mAh·g⁻¹ at the rate of 0.1 C (1 C = 150 mA·g⁻¹) and the cycling retention rate could reach 98% after 50 cycles at room temperature.     

Facile synthesis of nanocrystalline Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> thin film

A novel and facile synthesis route for the manufacture of transparent and uniform self-assembled nanocrystalline Cr2O3 (nc-Cr2O3) thin films with different morphology was reported, utilizing chromium nitrate as the inorganic source and triblock copolymer F127 as the morphology-directing agent by the evaporation-induced assembly (EIA) method. X-ray powder diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), N2-sorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the as-prepared nc-Cr2O3 thin films. The Cr2O3 thin film with different morphology was obtained by changing the relative humidity. The possible formation mechanism of the nc-Cr2O3 thin films with different morphologies was discussed.     

Preparation and electrochemical performance of spherical Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> as anode materials for Li-ion batteries

Fe₃O₄ nano-powder was prepared by the hydrothermal method. The structure and morphology of the product were characterized by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The as-prepared powder has regularly spherical morphology, and the average size of product is about 25 nm. The possible application use of this material as the active mass of anode for rechargeable Li batteries was examined by cyclic voltammeter (CV), galvanostatic charge/discharge. The experimental results showed that this material exhibited large specific capacity at the first cycle, and the discharge and charge capacity retention of this electrode are 37.04% and 48.76%, respectively. Furthermore, the impedance change of Fe₃O₄ electrode under different cycle number and potential was examined.     

Structure and electrochemical properties of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>−<Emphasis Type="Italic">x</Emphasis>F<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

LiMn₂O₄−_xF_x prepared by the sol-gel method has a perfect crystal formation. The crystal particle size of the material was medium and distributed uniformly. The substitution of F for O increased the specific capacity of the material at the cost of the cycleability. The explanation of this results is that the F decreases the valence of Mn, that is, more Mn³⁺ and less Mn⁴⁺ exist in the material. The increase of Mn³⁺ will improve the initial specific capacity and Mn³⁺ is the original reason for Jahn-Teller effect that caused the poor cycleability of the cathode material by the micro-distortion of the crystal structure. In addition, the expanded measurement of the crystal lattice is also the reason for the poor cycleability. Therefore, the results of F-substitution and cation-substitution are opposite. If the two methods are combined, they can compensate the inability each other and the satisfactory results may be obtained. XIA Jun-lei: Born in 1977 Funded by the National Natural Science Foundation of China (No. 59972026)     

The Mechanism of Sol-Gel Synthesis of Normal Spinel LiMn2O4 with Chelation of Citric Acid

The sol-gel process of citric acid chelating with metal cations for the synthesis of normol spinel LiMn2O4 and the reaction mechanion mechavism were investigated by means of XRD,TG-DTA,and SEM ,the results show that at the beginning lithium citrate and chelate compound of citic acid with manganese ions formed ,and then with heating the esterification and condensation reacions occured between them and glyol ,The products obtained are polymers in which metal cations are distibuted homogeneously on atomic scale that ensur hight reacivity to cations of Li^ and Mn^2 ,Firing the gel grepared by this process ,the lattice diffusions of solid reactant ions caused by non-homogeneity of reactants are elinimated and avoided .At 400℃ phase-pure LiMn2O4 with nanometer scale crystallization having precise stoichiometry and perfect crystallization can be obtained ,The model of chelate coordinated of double -molecule between citric acid and Mn^2 in the gel network is proosed ,It is important for explaining the dispersion state of Mn^2 and the formaiton process of gel by this model.     

Synthesis and characterization of biomimetic Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/coke magnetic nanoparticles composite material

A composite material (Fe₃O₄/Coke) using coke supported Fe₃O₄ magnetic nanoparticles was successfully prepared via an in-situ chemical oxidation precipitation method and characterized by SEM, XRD, Raman, and FTIR. The results showed that the Fe₃O₄ nanoparticles existed steadily on the surface of coke, with better dispersing and smaller particle size. The catalytic ability of Fe₃O₄/Coke were investigatied by degrading p-nitrophenol (P-NP). The results showed that the apparent rate constant for the P-NP at 1.0 g·L^?1 catalyst, 30 mmol·L^?1 H₂O₂, pH=3.0, 30 °C and the best ratio of Coke/Fe₃O₄ 0.6, was evaluated to be 0.027 min^–1, the removal rate of COD_Cr was 75.47%, and the dissolubility of Fe was 2.42 mg·L^–1. Compared with pure Fe₃O₄, the catalytic ability of Fe₃O₄/Coke in the presence of H₂O₂ was greatly enhanced. And Fe₃O₄/Coke was a green and environmental catalyst with high catalytic activity, showing a good chemical stability and reusability.     

Preparation and ferroelectric properties of Bi<Subscript>3.4</Subscript>Ce<Subscript>0.6</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films grown by sol-gel method

We have investigated the preparation and properties of Bi_3.4Ce_0.6Ti₃O₁₂ thin films. The Bi_3.4Ce_0.6Ti₃O₁₂ thin films were fabricated on the Pt/Ti/SiO₂/Si substrates using sol-gel method. The structure and morphology of the films were characterized using X-ray diffraction and atomic force microscopy. The thin films showed a perovskite phase and dense microstructure. The dielectric constant and the dissipation factor of the Bi_3.4Ce_0.6Ti₃O₁₂ thin films were about 172 and 0.031 at 1 kHz, respectively. The 2P _r and 2E _c of the Bi_3.4Ce_0.6Ti₃O₁₂ thin films were 67.1 μC/cm² and 299.7 kV/cm, respectively, under an applied field of 600 kV/cm. The Bi_3.4Ce_0.6Ti₃O₁₂ film did not show fatigue up to 4.46×10⁹ switching cycles at a frequency of 1 MHz, and showed good insulating behavior according to the test of leakage current. Supported by the Natural Science Foundation of Hubei Province (Grants No. 2004ABA082)     

Adsorption of BSA on carbon-coated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> microspheres activated with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride

Carbon-coated Fe₃O₄ (Fe₃O₄/C) microspheres activated with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) were prepared, characterized and applied to adsorb bovine serum albumin (BSA). The prepared magnetic microspheres had spherical core-shell structure with a uniform and continuous carbon coating coupled with activation by EDC, and possessed superparamagnetic characteristics. The experimental results showed that the adsorption amount of BSA on the EDC-activated Fe₃O₄/C (Fe₃O₄/C-EDC) microspheres was higher than that on the Fe₃O₄/C microspheres. The maximum adsorption of BSA on Fe₃O₄/C-EDC microspheres occurred at pH 4.7, which was the isoelectric point of BSA. At low concentrations (below 1.0 M), salt had no noticeable effect on BSA adsorption. The BSA adsorption of Fe₃O₄/C-EDC microspheres had a better fit to the Langmuir model than the Freundlich isotherm and Temkin isotherm model, and the kinetic data were well described by the pseudo-second-order model. The adsorption equilibrium could be reached within 20 min. High desorption efficiency (97.6%) of BSA from Fe₃O₄/C-EDC microspheres was obtained with 0.5 M Na₂HPO₄ (pH 9.4) as the desorbent.     

Controlled preparation of monodisperse CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles by a facile method

CoFe2O4 nanoparticles (NPs) were synthesized by coprecipitation method using FeCl3·6H2O and CoCl2·6H2O as precursors.The synthesized conditions were optimized,such as added means of precipitator,quantity of precipitator,the mol ratio of Fe 3+ to Co2+,reaction temperature and pH value.The synthesized material was characterized by XRD,TEM,FTIR,EDS,Raman and its magnetic properties were studied by VSM.The experimental results confirm that the sample is cubic spinel structure CoFe2O4 with a narrow size distribution and a good dispersion feature.CoFe2O4 NPs with well-controlled shape and size was obtained at 70℃.The magnetic properties indicate superparamagnetic behavior and good saturated magnetization.     

Preparation of MWNTs/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites and their mechanical and electrical properties

Since their discovery by Iijima[1], carbon nanotubes (CNTs) have been the focus in novel materials research. Theoretical and experimental studies show[2-9] that CNTs have extraordinary mechanical and electrical properties. Krishnan et al.[2] have reported that the mean value of Young’s modulus of single-wall nanotubes (SWNTs) is 1.25 TPa. Yu et al.[3] measured Yang’s modulus of multi-wall nanotubes (MWNTs) between 270 and 950 GPa and breaking strength between 11 and 63 GPa. The ele…     

Optical waveguide and nonlinear properties of Bi<Subscript>3</Subscript>NdTi<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films

Neodymium-substituted bismuth titanate (Bi₃NdTi₃O₁₂, BNT) thin films were prepared on quartz substrates by a metal-organic solution deposition process. The crystalline structure was evaluated by X-ray diffraction. Waveguide property was investigated by using prism coupling technique and optical transmittance measurement. The optical nonlinearities of the film were measured by the top-hat Z-scan techniques and a large positive nonlinear refractive index, nonlinear refractive coefficient and two-photon absorption coefficient were determined to be 3.84 × 10⁻⁷ esu, 0.7523 cm²/GW and 4.81 × 10⁴ cm/GW, respectively. These results reveal that the BNT film may be a kind of new multifunctional materials.     

Effect of La doping on microstructure and ferroelectric properties of Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films prepared by sol-gel method

The Bi4Ti3Oi2 and Bi3.25La0.75Ti3O12 thin films were prepared on the Pt/Ti/SiO2/Si substrate using the sol-gel method. The effect of La doping on the microstructure and ferroelectric properties of Bi4Ti3O12 films were investigated. Both the Bi4Ti3O12 and Bi3.25La0.75Ti3O12 thin films exhibited typical bismuth layered perovskite structure. The 2Pr （remanent polarization） value of Bi3.25La0.75Ti3O12 thin films is 18.6 μC/cm^2, which is much larger than that of Bi4Ti3O12 thin films. And the Bi3.2eLa0.75Ti3O12 films show fatigue-free behavior, while the Bi4Ti3O12 thin films exhibit the fatigue problem. The mechanism of improvement of La doping was discussed.