Hexagonal Nanoarchitecture of Composite Monolayer of Magnetite Nanoparticles and Geminus Surfactant 1,3‐Propylenebis(dodecyldimethylammonium) Dibromide

Negatively charged magnetite nanoparticles with an average size of about 10 nm have been synthesized by a chemical coprecipitation method using sodium dodecyl benzene sulphonate as a surface modifying reagent. Composite Langmuir monolayer of Fe₃O₄ nanoparticles and geminus surfactant 1,3‐propylenebis(dodecyldimethylammonium) dibromide (C₁₂‐C₃‐C₁₂) was prepared on the subphase of Fe₃O₄ nanoparticle hydrosols. In the presence of the magnetite nanoparticles, the collapse pressure of the composite monolayer and the limited mean molecular area of C₁₂‐C₃‐C₁₂ are higher than those on pure water subphase. Transmission electron microscopy observation of a C₁₂‐C₃‐C₁₂/Fe₃O₄ nanoparticle complex shows that Fe₃O₄ nanoparticles and geminus surfactant had an unexpected hexagonal nanoarchitecture at the air‐liquid interface when the surface pressure of the composite monolayer increased to about 12 mN·m^?1. A mechanism for constructing the particular nanopatterned configuration of the C₁₂‐C₃‐C₁₂/Fe₃O₄ nanoparticle complex in the Langmuir layer directly from the unique molecular structure of the geminus surfactant and the interfacial interactions between C₁₂‐C₃‐C₁₂ and the components in the subphase was proposed.     

Preparation and Properties of Iron and Iron Oxide Nanocrystals in MgO Matrix

We have prepared α-iron and magnetite (Fe₃O₄) nanoparticles in MgO matrix from a mixture of nanocrystalline Fe₂O₃ with Mg(H,O) powders calcinated in hydrogen. This procedure yielded spherical magnetic nanoparticles embedded in MgO. Transmission electron microscopy and Mössbauer spectroscopy were used for structure and phase analysis. The measurements of magnetic properties showed increased coercivity of the nanocomposite samples.     

Mechanochemical Activation of Magnetite Nanoparticles

Using Mössbauer spectroscopy as a function of ball milling time, it was found that nanomagnetite behaves differently than magnetite during mechanochemical activation. The phase sequence is determined by the original particle size of the powder. Magnetite suffers a phase transformation to hematite, while nanomagnetite (d = 19nm) gives rise to superparamagnetism as effect of prolonged milling.     

生物磁铁矿的磁各向异性与磁接收器

磁铁矿是分布广泛且非常重要的亚铁磁材料,也广泛分布在生物体中。生物体中的磁铁矿具有完美的晶体结构,大多为超顺磁颗粒或单畴颗粒,且大多呈链状分布,具有明显的磁各向异性。生物体中存在“磁接收器”,生物磁铁矿是“磁接收器”的生物物理基础。本文中,从超顺磁磁铁矿颗粒和单畴磁铁矿颗粒的物理特性出发,主要是从它们的磁各向异性特性的基础上描述了生物磁铁矿和“磁接收器”的工作机制,即在某些条件下,在外界地磁场强度量级的磁场作用下,超顺磁颗粒或单畴颗粒可以诱导产生足够强的磁场,使邻近的晶体可以相互吸引或排斥,这些粒子间的相互作用可以改变晶体颗粒束所在的外围机体形状,而神经系统可以探测到单独的粒子束或一列粒子束的扩张或收缩,因此生物体就可以探测到磁场的方向以及强度等磁场参量。     

Facile Green Synthesis of Magnetic Fe3C@C Nanocomposite using Natural Magnetite

One simple and environmental friendly synthesis strategy for preparing low-cost magnetic Fe\begin{document}$ _3 $\end{document}C@C materials has been facilely developed using a modified sol-gel approach, wherein natural magnetite acted as the iron source. A chelating polycarboxylic acid such as citric acid (CA) was employed as the carbon source, and it dissolved Fe very effectively, Fe\begin{document}$ _3 $\end{document}O\begin{document}$ _4 $\end{document} and natural magnetite to composite an iron-citrate complex with the assistance of ammonium hydroxide. The core-shell structure of the as-prepared nanocomposites was formed directly by high-temperature pyrolysis. The Fe\begin{document}$ _3 $\end{document}C@C materials exhibited superparamagnetic properties (38.09 emu/mg), suggesting potential applications in biomedicine, environment, absorption, catalysis, etc.     

The fabrication of hollow magnetite microspheres with a nearly 100% morphological yield and their applications in lithium ion batteries

Hollow Fe_3O_4(H-Fe_3O_4) microspheres were fabricated through a facile one-step solvothermal synthesis,which was performed in an ethylene glycol(EG)–diethylene glycol(DEG) mixed solvent using polyethylene glycol(PEG) as the stabilizer. The addition of DEG increased the viscosity of the system,which caused the Fe_3O_4 primary crystal to aggregate slower and the morphological yield to approach nearly 100%. The as-prepared hollow Fe_3O_4 microspheres show promise for application in lithium ion battery anodes and showed a reversible specific capacity of 453.3 mAh g~(-1) after 50 cycles at 100 mA g~(-1).     

Electrochemical Stability of the Reconstructed Fe3O4(001) Surface

Establishing the atomic-scale structure of metal-oxide surfaces during electrochemical reactions is a key step to modeling this important class of electrocatalysts. Here, we demonstrate that the characteristic (√2×√2)R45° surface reconstruction formed on (001)-oriented magnetite single crystals is maintained after immersion in 0.1 M NaOH at 0.20 V vs. Ag/AgCl and we investigate its dependence on the electrode potential. We follow the evolution of the surface using in situ and operando surface X-ray diffraction from the onset of hydrogen evolution, to potentials deep in the oxygen evolution reaction (OER) regime. The reconstruction remains stable for hours between −0.20 and 0.60 V and, surprisingly, is still present at anodic current densities of up to 10 mA cm⁻² and strongly affects the OER kinetics. We attribute this to a stabilization of the Fe₃O₄ bulk by the reconstructed surface. At more negative potentials, a gradual and largely irreversible lifting of the reconstruction is observed due to the onset of oxide reduction.     

Shape diversity in particles obtained by low temperature pyrolysis of ferrocene

Synthesis experiments, made in a hermetically closed steel container through pyrolytical decomposition of various mixtures like ferrocene and xylene; ferrocene and water; ferrocene, xylene and water in different ratios have resulted in emergence of different in shape particles. The necessary for the realization of each experiment temperature increases linearly with 20 K/min up to the needed temperature and decreases mostly with no delay with a cooling rate of 30 K/min down to room temperature. The obtained particles are shaped as spheres, entirely or partially finished octahedrons or resemble stars. The spheres are perfect in shape and consist of pure incompletely graphitisized carbon. The octahedron and star‐like shaped particles, synthesized in the presence of ferrocene as precursor, have magnetite nuclei and carbon coating. Particle morphology has been examined by Scanning (SEM) and Transmission Electron Microscopy (TEM) and their chemical composition and crystal structure by the means of X‐ray diffraction (XRD), Mössbauer spectroscopy and Electron Probe X‐ray Micro Analysis and Energy Dispersive X‐ray Spectrometry (EDS). Based on the results obtained it has been concluded that the synthesized particle morphology depends on the simultaneous proceeding magnetite crystal growing and crystal coating with partially graphitisized carbon deposit. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of ferric ions on the morphology and size of magnetite nanocrystals synthesized by ultrasonic irradiation

Two‐dimensional plate‐like Fe₃O₄ nanocrystals and nanoparticles could be synthesized by a simple one‐step sonochemical method through ultrasonic irradiation in reverse co‐precipitation solution at low temperature. This technique provided a facile and rapid way to prepare Fe₃O₄nanocrystals with different morphology and size. Magnetite nanoplates were synthesized with only ferrous salt adding into alkali solution, and adding ferric ions with low molar ratio in the metal salts solution would lead to the formation of very small magnetite nanoparticles (∼10 nm). The size of as‐prepared magnetite nanoparticles increased with increasing reaction temperature and showed narrow size distribution, the standard deviation less than 2 nm. This investigation indicated that ferric ions had significant influence on the morphology of Fe₃O₄ nanocrystals. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Factors affecting the 13.56-MHz radio-frequency-mediated heating of gold nanoparticles

The use of radio-frequency (RF) energy for the thermal activation of tumor-targeted nanoparticles (NPs) is a promising non-invasive hyperthermic treatment because RF waves penetrate deep through tissue. Nonetheless, while the approach has been demonstrated using gold (Au) and iron oxide NPs, the RF-mediated heating mechanism of AuNPs has been controversial. A part of the reason is that measuring and modeling the heating of AuNPs in an RF field is a complex endeavor that depends on the chemical and physical properties of the AuNPs, interfacial phenomena involving AuNP coatings and the sample medium, and the antenna design and characteristics of the RF field. Herein, the mechanisms and factors affecting the 13.56-MHz RF-mediated heating of AuNPs are reviewed, a new factor concerning the thermal isolation of RF antennae is presented, and the ability of a new water-free cooling system to thermally isolate samples from the heat generated by metal RF-induction coils is demonstrated.