Direct ultrasonic-assisted synthesis of sphere-like nanocrystals of spinel Co3O4 and Mn3O4

A simple sonochemical method was developed to synthesize uniform sphere-like or cubic Co(3)O(4) and Mn(3)O(4) nanocrystals by using acetate salts and sodium hydroxide or tetramethylammonium hydroxide (TMAH) as precursors. Influence of some parameters such as time of reaction, alkali salts, and power of the ultrasound and the molar ratio of the starting materials on the size, morphology and degree of crystallinity of the products was studied. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), FTIR spectroscopy, Thermal gravimetry analysis and differential thermal analysis (TGA/DTA) were used to characterize the nanocrystals.     

Ultrasound-assisted coating of polyester fiber with silver bromide nanoparticles

The growth of silver bromide nanoparticles on polyester fiber was achieved by sequential dipping steps in alternating bath of potassium bromide and silver nitrate under ultrasound irradiation. The effects of ultrasound irradiation, concentration and sequential dipping steps in growth of the AgBr nanoparticles have been studied. Particle sizes and morphology of nanoparticle are depending on power of ultrasound irradiation, sequential dipping steps and concentration. These systems depicted a decrease in the particles size accompanying an increase in the sonication power. Results suggest that an increasing of sequential dipping steps and concentration led to an increasing of particle size. The physicochemical properties of the nanoparticles were determined by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM).     

Ultrasound-promoted coating of silk yarn with different morphology of magnesium hydroxide nanostructures

The growth of magnesium hydroxide nanostructures on silk yarn was achieved by sequential dipping steps in alternating bath of magnesium nitrate and potassium hydroxide under ultrasound irradiation. The effects of ultrasound irradiation, concentration, pH and sequential dipping steps on growth of the Mg(OH)₂ nanostructures have been studied. Morphology of the nanostructures, depending on pH and with decreasing pH from 13 to 8, changed from nanoparticle to nanoneedle. Results show a decrease in the particles size as the concentration and sequential dipping steps increased. The physicochemical properties of the nanostructures were determined by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and wavelength dispersive X-ray (WDX).     

Effect of a SiO2 coating on the magnetic properties of Fe3O4 nanoparticles

In this work the effect of a SiO2 coating on the magnetic properties of Fe3O4 nanoparticles obtained by the sol-gel method is analyzed. Two sets of samples were prepared: Fe3O4 nanoparticles and Fe3O4@SiO2 core-shell composites. The samples display the characteristic spinel structure associated with the magnetite Fe3O4 phase, with the majority of grain sizes around 5-10 nm. At room temperature the nanoparticles show the characteristic superparamagnetic behavior with mean blocking temperatures around 160 and 120 K for Fe3O4 and Fe3O4@SiO2, respectively. The main effect of the SiO2 coating is reflected in the temperature dependence of the high field magnetization (μ(0)H = 6 T), i.e. deviations from the Bloch law at low temperatures (T < 20 K). Such deviations, enhanced by the introduction of the SiO2 coating, are associated with the occurrence of surface spin disordered effects. The induction heating effects (magnetic hyperthermia) are analyzed under the application of an AC magnetic field. Maximum specific absorption rate (SAR) values around 1.5 W g(-1) were achieved for the Fe3O4 nanoparticles. A significant decrease (around 26%) is found in the SAR values of the SiO2 coated nanocomposite. The different heating response is analyzed in terms of the decrease of the effective nanoparticle magnetization in the Fe3O4@SiO2 core-shell composites at room temperature.     

Room-temperature synthesis of Mn3O4 nanorods

Nanocrystalline Mn₃O₄ hausmannite has been easily prepared from manganese(II) acetate tetrahydrated, dissolved in a mixture of N,N’-dimethylformamide (DMF) and water (10%) at room temperature, without post-treatment of heating. Stability of the Mn₃O₄ colloidal dispersion was monitored by UV-visible electronic absorption spectroscopy. X-ray powder diffraction (XRD) pattern demonstrates its good phase purity. Analysis by transmission electron microscopy (TEM) image shows homogeneous nanorods with a narrow size distribution, being the average diameter and length of 6.58 nm and 17.44 nm, respectively. Moreover, the facility of the hausmannite nanorods to adhere to glass wall in this solvent mixture has allowed the formation of thin films which were analyzed by atomic force microscopy (AFM). PACS 81.07.Bc; 81.16.Be; 61.46.+w     

A novel non-thermal process of TiO2-shell coating on Fe3O4-core nanoparticles

In this work magnetite (Fe₃O₄) nanoparticles coated with titanium dioxide (TiO₂) were prepared by a novel non-thermal method. In this method, magnetite and pure TiO₂ (anatase) nanoparticles were individually prepared by the sol–gel method. After modifying the surface of magnetite nanoparticles by sodium citrate, titanium dioxide was coated on them without using conjunction or heat treatment to obtain Fe₃O₄:TiO₂ core–shell nanoparticles. XRD, EDX, SEM, TEM and VSM were used to investigate the structure, morphology and magnetic properties of the samples. The average crystallite size of the powders was measured by Scherrer's formula. The results obtained from different measurements confirm the formation of Fe₃O₄:TiO₂ core–shell nanoparticles with a decrease in saturation magnetization. Hysteresis loops of the core–shell nanoparticles show no exchange bias effects, which confirms that there is no interaction or interdiffusion at the interface.     

Improvement electrochemical performance of Li1.5Ni0.25Mn0.75O2.5 with Li4Ti5O12 coating

Layered cathode Li_1.5Ni_0.25Mn_0.75O_2.5 has been synthesized and coated by Li₄Ti₅O₁₂. The pristine and coated Li_1.5Ni_0.25Mn_0.75O_2.5 powders are characterized by X-ray diffraction (XRD), indicating the materials remained the layered structure before and after coating. The coated Li₄Ti₅O₁₂ has been detected by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (DEX). The electrochemical performance, especially rate performance of Li_1.5Ni_0.25Mn_0.75O_2.5 electrode, is improved effectively after Li₄Ti₅O₁₂ coating. The first discharge capacity, coulombic efficiency, and capacity retention of Li₄Ti₅O₁₂-coated Li_1.5Ni_0.25Mn_0.75O_2.5 electrode are 244 mA h g^?1, 81.5 %, and 98.3 % after 50 cycles, respectively. The Li₄Ti₅O₁₂-coated Li_1.5Ni_0.25Mn_0.75O_2.5 electrode exhibits 108 mA h g^?1 at 10 °C rate. Electrochemical impedance spectroscopy (EIS) results show that the charge transfer resistance (R _ct) of Li_1.5Ni_0.25Mn_0.75O_2.5 electrode decreases after coating, which is due to the existence of Li₄Ti₅O₁₂ with high lithium ion diffusion coefficient and suppression of the solid electrolyte interfacial (SEI) layer development and is responsible for the excellent rate capability and cyclic performance.     

Catalytic precursors: (Fe,Mn)3O4 and γ-(Fe,Mn)2O3

Iron-manganese oxide catalysts are known to influence the production of short chain hydrocarbons in the Fischer-Tropsch-synthesis process. XRD, XRF, gravity measurements and Mössbauer-effect spectroscopy has been used to study a catalytic precursor made by coprecipitation of iron and manganese oxides. The sample is characterized as a mixture of two compounds with the same iron to manganese ratio. The two compounds are cubic spinels with the same crystallographic parameters, however, one compound is a defect spinel while the other is not. In the Mössbauer studies the defect spinel shows superparamagnetic relaxation behavior—fluctuations of the magnetization vector along two opposite easy directions, while the non-defect spinel shows evidence of collective excitations—fluctuations of the magnetization vector in directions close to the easy direction. These properties are related to the particle sizes.     

Synthesis and properties of Au-Fe3O4 and Ag-FeaO4 heterodimeric nanoparticles

Monodisperse Au-Fe3O4 heterodimeric nanoparticles （NPs） were prepared by injecting precursors into a hot reaction solution. The size of Au and Fe3O4 particles can be controlled by changing the injection temperature. UVis spectra show that the surface plasma resonance band of Au-Fe3O4 heterodimeric NPs was evidently red-shifted compared with the resonance band of Au NPs of similar size. The as-prepared heterodimeric Au-Fe3O4 NPs exhibited superparamagnetic properties at room temperature. The Ag-Fe3O4 heterodimeric NPs were also prepared by this synthetic method simply using AgNO3 as precursor instead of HAuCl4. It is indicated that the reported method can be readily extended to the synthesis of other noble metal conjugated heterodimeric NPs.     

Electrostatic self-assembly of Fe3O4 nanoparticles on carbon nanotubes

Carbon nanotubes (CNTs)-based magnetic nanocomposites can find numerous applications in nanotechnology, integrated functional system, and in medicine owing to their great potentialities. Herein, densely distributed magnetic Fe₃O₄ nanoparticles were successfully attached onto the convex surfaces of carbon nanotubes (CNTs) by an in situ polyol-medium solvothermal method via non-covalent functionalization of CNTs with cationic surfactant, cetyltrimethylammonium bromide (CTAB), and anionic polyelectrolyte, poly(sodium 4-styrenesulfonate) (PSS), through the polymer-wrapping technique, in which the negatively charged PSS-grafted CNTs can be used as primer for efficiently adsorption of positively metal ions on the basis of electrostatic attraction. X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analysis have been used to study the formation of Fe₃O₄/CNTs. The Fe₃O₄/CNTs nanocomposites were proved to be superparamagnetic with saturation magnetization of 43.5 emu g^?1. A mechanism scheme was proposed to illustrate the formation process of the magnetic nanocomposites.     

Ultrasound-assisted microwave preparation of Ag-doped CdS nanoparticles

Ag-doped CdS nanoparticles were synthesized by an ultrasound-assisted microwave synthesis method. The X-ray diffraction patterns reveal a structural evolution from cubic to hexagonal with increasing molar ratios of Ag⁺/Cd²⁺ from 0% to 5%. It shows that the Ag-doped hexagonal CdS nanoparticles are polycrystal. The X-ray photoelectron spectroscopy of the CdS nanoparticles doping with 5% Ag⁺ shows that the doped Ag in CdS is metallic. Simultaneously, the characteristic Raman peaks of the CdS nanoparticles enhance with increasing Ag⁺ concentrations. The photocatalytic activity of different Ag-doped samples show a reasonable change due to different ratios of Ag which doped into CdS.     

Magnetically induced controlled release from glucose-modified liposomes loaded with Fe3O4 nanoparticles

Journal of Nanoparticle Research - Nd–Fe–B magnetic materials were prepared using the binary alloy method with addition of Ho nanopowder to grain boundaries to improve the magnetic,...     

Synthesis of GaP nanowires with Ga2O3 coating

Zinc-blende-type face centred cubic structure GaP nanowires with Ga₂O₃ coating were synthesized by heating Ga₂O₃ and red phosphorus powder with the assistance of NH₃ and Ar at 1323 K. The GaP/Ga₂O₃ nanowires have a uniform size distribution with diameters ranging from tens of nm to hundreds of nm and lengths up to several micrometres. The inner GaP nanowires have almost a single-crystal structure with twin defects and have the 111 direction as preferential growth direction. Outer Ga₂O₃ layers were polycrystalline and acted as a protection layer for the inner GaP nanowires to permit their use at high temperature. The GaP/Ga₂O₃ structure may have potential applications in future nanodevice design. PACS 81.07.Bc; 81.16.Pr     

Silicon solar cells with Al2O3 antireflection coating

The paper presents the possibility of using Al₂O₃ antireflection coatings deposited by atomic layer deposition ALD. The ALD method is based on alternate pulsing of the precursor gases and vapors onto the substrate surface and then chemisorption or surface reaction of the precursors. The reactor is purged with an inert gas between the precursor pulses. The Al₂O₃ thin film in structure of the finished solar cells can play the role of both antireflection and passivation layer which will simplify the process. For this research 50×50 mm monocrystalline silicon solar cells with one bus bar have been used. The metallic contacts were prepared by screen printing method and Al₂O₃ antireflection coating by ALD method. Results and their analysis allow to conclude that the Al₂O₃ antireflection coating deposited by ALD has a significant impact on the optoelectronic properties of the silicon solar cell. For about 80 nm of Al₂O₃ the best results were obtained in the wavelength range of 400 to 800 nm reducing the reflection to less than 1%. The difference in the solar cells efficiency between with and without antireflection coating was 5.28%. The LBIC scan measurements may indicate a positive influence of the thin film Al₂O₃ on the bulk passivation of the silicon.     

H2O2氧化法制备Fe3O4纳米颗粒及与共沉淀法制备该样品的比较

在近中性条件下,利用H2O2氧化Fe(OH)2胶体成功制备了Fe3O4纳米颗粒.分别利用透射电镜(TEM),x射线衍射仪(XRD),振动样品磁强计(VSM)和超导量子干涉仪(SQUID)对样品的形貌,结构,宏观磁性进行了表征和测量.TEM图像表明样品为球形颗粒,直径大小约18nm,且分布较均匀.XRD结果表明样品为立方尖晶石结构.穆斯堡尔谱测量表明样品室温下对应两套六线谱,样品的晶体结构存在缺陷,内磁场略小于块体Fe3O4的值.宏观磁测量表明样品的饱和磁化强度可达67×10-3A·m2/g,在20 K出现了Verwey转变.选择该法制备的Fe3O4纳米颗粒与共沉淀法得到的样品作了磁性比较.宏观磁测量表明共沉淀法制备的样品在外磁场为1T时仍未饱和,磁化强度仅为46×10-3A·m2/g,在178K出现了超顺磁转变温度,且在测量温度范围内没有发现Verwey转变.     

The effect of colossal magnetoresistance in SmCu3Mn4O12 perovskite-like oxide

Journal of Experimental and Theoretical Physics - The magnetoresistance effect in the SmCu3Mn4O12 compound with a perovskite-like structure is investigated for the first time. It is found that an...