Plasma-assisted synthesis of carbon encapsulated magnetic nanoparticles with controlled sizes correlated to smooth variation of magnetic properties

This paper reports rapid, continuous and carbon-nanotube free synthesis of carbon encapsulated magnetic nanoparticles by thermal-plasma expansion technique, which combines the typical advantages of high-temperature plasma assisted synthesis method with efficient particle-size control. Core nanocrystals were encapsulated with few layers of graphitized carbon, which could provide protection against both oxidation and intense chemical treatment. The average iron/iron-carbide nanoparticle diameter (7.7, 9 and 10 nm) and the width of the size distribution increased with pressure in the sample collection chamber, as a result of the decreasing quenching rate of the plasma jet. This also resulted in the smaller particles remaining frozen predominantly in the high-temperature γ-Fe phases, part of which was oxidized subsequently and eliminated preferentially during the purification process. All samples could be correlated with smooth variation of magnetic properties; saturation magnetization, remnant magnetization and coercive-field enhancing with increasing chamber pressure or average particle size. The low pressure synthesized sample with smallest average particle size approached super-paramagnetic behavior (saturation magnetization = 51.8 emu/g, ratio of remnant to saturation magnetization = 4.9 and coercive field = 52 Oe), which may be ideal for biomedical applications. High-pressure samples on the other hand have a higher saturation magnetization (76.3 emu/g) and coercive fields (123 Oe).     

Direct synthesis of carbon nanotubes decorated with size-controllable Fe nanoparticles encapsulated by graphitic layers

A simple method has been developed for direct synthesis of magnetic multi-walled carbon nanotubes (MWCNTs) homogeneously decorated with size-controllable Fe nanoparticles (Fe-NPs) encapsulated by graphitic layers on the MWCNT surface by pyrolysis of ferrocene. These composites have similar C/Fe atomic ratio of ∼10 and exhibit sufficiently high saturation magnetization for magnetic separation in a liquid phase. Moreover, with 0, ∼1, ∼2 wt% sulfur as growth promoter, the size of Fe-NPs can be controlled with an average diameter of ∼5, ∼22 and ∼42 nm, respectively. When compared to time-consuming wet-chemical methods, the simplicity of this method should allow easy large-scale production of these magnetically functionalized MWCNTs, which can be used as catalyst supports with high stability for effective magnetic separation in liquid-phase reactions, especially under acid/basic conditions.     

Preparation and characterization of carbon nanofluid by a plasma arc nanoparticles synthesis system

Heat dissipation from electrical appliances is a significant issue with contemporary electrical devices. One factor in the improvement of heat dissipation is the heat transfer performance of the working fluid. In this study, we used plasma arc technology to produce a nanofluid of carbon nanoparticles dispersed in distilled water. In a one-step synthesis, carbon was simultaneously heated and vaporized in the chamber, the carbon vapor and particles were then carried to a collector, where cooling furnished the desired carbon/water nanofluid. The particle size and shape were determined using the light-scattering size analyzer, SEM, and TEM. Crystal morphology was examined by XRD. Finally, the characterization include thermal conductivity, viscosity, density and electric conductivity were evaluated by suitable instruments under different temperatures. The thermal conductivity of carbon/water nanofluid increased by about 25% at 50°C compared to distilled water. The experimental results demonstrated excellent thermal conductivity and feasibility for manufacturing of carbon/water nanofluids.     

The synthesis of carbon coated Fe, Co and Ni nanoparticles and an examination of their magnetic properties

Carbon coated Fe, Co and Ni nanoparticles (Fe@C, Co@C, and Ni@C, respectively) have been produced by high pressure chemical vapour deposition. Scanning electron microscopy images prove that carbon coated particles with a Fe, Co, and Ni core are formed. High-resolution transmission electron microscopy images show that the nanoparticles have a size distribution from 2 to 100 nanometers and display the core/shell structure with one or more particles forming the core in a particular shell. From X-ray diffraction peaks the phase of the core material is confirmed and the average particle size is determined from the width of the peaks to be 16, 21, and 19 nm for Fe@C, Co@C, and Ni@C, respectively. The coated nanoparticles are ferromagnetic at least up to 400 K. AC magnetic heating studies have been performed which imply their potential for applications in hyperthermia therapy.     

Synthesis and characteristics of carbon encapsulated magnetic nanoparticles produced by a hydrothermal reaction

A novel process to synthesize carbon encapsulated magnetic nanoparticles was developed by heating an aqueous glucose solution containing Fe@Au (Au coated Fe nanoparticles) or Ni nanoparticles at 160–180 °C for 2 h. In comparison with traditional methods, such a hydrothermal approach is not only simple but also able to provide functional groups such as –OH on the surface of carbon sphere. Only pure Fe nanoparticles did not favor the formation of carbon encapsulated magnetic nanoparticles due to the oxidation of Fe nanoparticles by H₂O during the reaction and their surfaces had to be coated by an Au shell in advance. The results of TEM, HRTEM, XRD, XPS and vibration sample magnetometer characterization show that uniform carbon spheres containing some embedded Fe@Au nanoparticles with a saturation of 14.6 emu/g are obtained and the size of a typical product is 200 nm. Carbon encapsulated Ni nanoparticles have been successfully prepared in the same way.     

Surface properties of carbons obtained from hexachlorobenzene and hexachloroethane by combustion synthesis

The paper describes the combustion synthesis of carbon materials from hexachloroethane (C₂Cl₆), hexachlorobenzene (C₆Cl₆), and a mixture of these compounds. The chemical composition (elemental analysis), structural composition (XRD, Raman spectroscopy), microstructure (SEM), surface physicochemical properties (low-temperature nitrogen adsorption, XPS, FTIR) and electrochemical behavior (cyclic voltammetry) of the solid reaction products were investigated. Their unique structural and surface properties depend on the chemical composition of the starting compounds. The properties of the carbon samples tested are much like those of carbon black, but the material from hexachloroethane exhibits the most distinctly amorphous features. In contrast, the adsorptive properties (porous structure) of the sample obtained from hexachlorobenzene tend to resemble those of activated carbon.     

Preparation and microwave absorption properties of Fe-doped SiC powder obtained by combustion synthesis

Fe-doped SiC powders were synthesized via combustion reaction of the Si and C system in a 0.1 MPa nitrogen atmosphere using iron as the dopant. The prepared powders have fine spherical particles and narrow particle size distribution. The electric permittivities of SiC samples were determined in the frequency range of 8.2–12.4 GHz. Results show that the permittivity of SiC increases with the increasing iron contents. The 5% Fe-doped SiC powder with 2 mm or 2.5 mm thickness exhibits the best microwave absorption over the frequencies ranging from 8.2 to 12.4 GHz.     

低温自蔓延燃烧合成Li1.2Fe0.2Mn0.6O2纳米颗粒及电化学性能

利用自蔓延燃烧在450℃低温下合成了Li1.2Fe0.2Mn0.6O2纳米颗粒(LFMO-450),借助XRD、SEM和TEM及恒流充放电测试研究了其晶体结构、微观形貌、超微结构和电化学性能.结果表明,样品LFMO-450具有良好的α-NaFeO2层状结构,为粒径分布于45～88 nm的纳米颗粒.恒流充放电测试结果表明...     

Mesoporous alumina obtained by combustion synthesis without template

Mesoporous alumina has been synthesised by the solution combustion synthesis method. While often the synthesis of mesoporous materials with a relatively narrow pore distribution requires the use of a template, this technique allows a simple and rapid synthesis of pure alumina without the use of any templating agent: by regulating the synthesis conditions is possible to obtain from relatively low surface area α-alumina to high surface mesoporous γ-alumina. The porosity of the latter was assessed chiefly by density functional method and was found to be in the range 2.8–3.5 nm. Low angle X-ray diffraction experiments demonstrated a partial ordering of the structure, with a periodicity in the range 5.5–6.9 nm. The addition of lanthanum to the alumina was tested and found to confer a good temperature resistance to the alumina, without modifying the mesoporous structure. After a prolonged heat treatment at 900 °C the mesoporosity of lanthanum-modified samples was retained, even if the pores size increased and the specific surface area decreased.     

Permalloy/alumina soft magnetic composite compacts obtained by reaction of Al-permalloy with Fe2O3 nanoparticles upon spark plasma sintering

Composite sintered soft magnetic materials of permalloy/alumina type have been obtained by reactive spark plasma sintering. The composite compacts have been obtained by sintering of Ni71.25Fe23.75Al5 alloy with 3 and 5% (wt.) Fe₂O₃ nanoparticles. The Ni based alloy with large particles (up to hundreds of μm) have been covered by a thin layer of iron ferric oxide nanoparticles (20–40 nm). The as obtained composite particles have been subjected to sintering process using a homemade installation at 900 °C for 10 min. Upon sintering process several reactions between Ni-based alloy and iron oxide are induced, the main phase resulting from reaction is alumina-Al₂O₃ as it results by X-ray diffraction investigations. According to the scanning electron microscopy and energy dispersive X-ray spectroscopy investigations, alumina forms a matrix embedding the Ni-based particles. The alumina matrix is continuous, but the layer has large variation in width, and offers a high electrical resistivity. A mechanism of formation is proposed for the alumina matrix composite compacts when using Al-permalloy powder and iron oxide. The compacts have been tested in DC and AC for magnetic characteristics.     

Cathodoluminescence of fluorine doped amorphous carbon nanoparticles deposited by a filtered cathodic arc plasma system

The fluorine doped amorphous carbon nanoparticles (a-C:F NPs) films with sizes 50-100 nm were deposited on polyethylene terephthalate in an atmosphere of CF₄ by a 90°-bend magnetic filtered cathodic arc plasma system. The surface morphology of a-C:F NPs films was observed by field emission scanning electron microscope and atomic force microscope. The microstructure and chemical bonding nature of the a-C:F NPs films were investigated by Raman, X-ray diffraction and X-ray photoelectron spectroscopy. This work presents cathodoluminescence (CL) spectra of a-C:F NPs films obtained at 1.9-2.4 eV and verifies luminescence from a-C:F NPs films in the visible region. The incorporation of fluorine into the carbon network results in orange emission (∼2.03 eV) due to the transitions between fluorine-related electron levels and σ* states, and the red emission (∼1.97 eV) results from the recombination of carriers in the valence π and conduction π* states. The peak at ∼2.10 eV may result from the defects of the structures in a-C:F NPs films.     

Surface modification of graphite encapsulated iron nanoparticles by plasma processing

The graphite encapsulated iron nanoparticles were fabricated by using arc discharge method. The synthesized nanoparticles were pre-treated by an inductively-coupled RF Ar plasma and then post-treated by NH₃ plasma under various gas pressures and treatment times. Analyses of XPS spectra have been carried out to study the effect of the plasma treatment on the surface modification of nitrogen-containing groups. The morphological changes of the particles surface by plasma treatment have also been analyzed by using HR-TEM. Present results show that the highest values of N/C atomic ratio of 5.4 % is obtained by applying 10 min of Ar plasma pre-treatment and 2 min of NH₃ plasma post-treatment conducted in RF power of 80 W and gas pressure of 50 Pa.     

Novel method for synthesis of Fe core and C shell magnetic nanoparticles

Using a newly developed method, carbon-encapsulated iron (Fe) nanoparticles were synthesized by plasma due to ultrasonication in toluene. Fe core with carbon shell nanoparticles were characterized using Transmission Electron Microscopy (TEM) and High Resolution Transmission Electron Microscopy (HRTEM). Fe nanoparticles of diameter 7–115 nm are encapsulated by 7–8 nm thick carbon layers. There was no iron carbide formation observed between the Fe core and the carbon shell. The Fe nanoparticles have body centered cubic (bcc) crystal structure. Synthesized nanoparticles showed a saturation magnetization of 9 A m²/kg at room temperature. After thermal treatment crystalline order of the nanoparticles improved and saturation magnetization increased to 24 A m²/kg. We foresee that the carbon-encapsulated Fe nanoparticles are biologically friendly and could have potential applications in Magnetic Resonance Imaging (MRI) and photothermal cancer therapy.     

Simple synthesis of mesoporous carbon with magnetic nanoparticles embedded in carbon rods

Magnetically separable ordered mesoporous carbon containing magnetic nanoparticles embedded in the carbon walls was synthesized using a simple synthetic procedure. The resulting magnetically separable mesoporous carbon was denoted as M-OMC (magnetically separable ordered mesoporous carbon) poly(pyrrole) with residual Fe²⁺ ions in the mesoporous channel was converted to carbon material containing superparamagnetic nanoparticles. The size of the magnetic nanoparticles obtained was restricted by the channel size of the SBA-15 silica template, which resulted in the generation of superparamagnetic nanoparticles embedded in the carbon rods. The blocking temperature of M-OMC is 110 K. Pore size and textural property of M-OMC is similar to that of hexagonally ordered mesoporous carbon fabricated using SBA-15 silica as a template. The saturation magnetization of M-OMC is ca. 30.0 emu/g at 300 K, high enough for magnetic separation.     

Effect of ZnO nanoparticles obtained by arc discharge on thermo‐mechanical properties of matrix thermoset nanocomposites

Through the development of nanotechnology it has been widely studied the morphology and size control in nanopowders synthesis. However, most of these techniques are successful to synthesize nanopowders in a small scale. In this research, a large semi‐industrial scale synthesis method is proposed, named continuous arc discharge in controlled atmosphere (DARC‐AC). Using this technique, it is possible to directly obtain clean nanostructures (low amount of impurities) with more than 90% of particles below 100 nm. In this study, the method utilizes metallic zinc and oxygen as precursors in order to produce ZnO. The ZnO nanopowders were incorporated in a thermoset polymer (epoxy resin) to study their influence on the thermo‐mechanical properties of the matrix. As main results, the mechanical properties of the nanocomposite epoxy/ZnO nanoparticles (ZnO‐NPs) do not differ from the original properties of the epoxy resin. Nevertheless, thermal behavior, conductivity, and diffusivity properties of the nanocomposite are improved. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43631.     

Size dependence of optical and magnetic properties of nickel oxide nanoparticles fabricated by electric arc discharge method

Nickel oxide nanoparticles with an average size of between 28 and 62 nm were fabricated by electric arc discharge method. The electric currents of 10, 100, 200, 300 and 400 A and oxygen pressures of 1, 2 and 3 atm. were tested. High yield production was observed for the samples prepared at low arc current. The samples were characterized using XRD and FESEM measurements. XRD results showed that the samples were pure and single phase of nickel oxide with cubic structure. The produced nanoparticles were cubic shaped and the average particle sizes increased by increasing the arc pressure, but decreased by increasing the arc current and their size distributions were uniform. The magnetic measurements confirmed a soft ferromagnetic behavior for the nickel oxide nanoparticles at low field region but the hysteresis loop tended to be antiferromagnetic like for the higher fields. By decreasing the particle size from 62 nm, the coercivity (H_c) increased but decreased when the particle size was less than about 57 nm. Such magnetic behavior which can be common for antiferromagnetic nanoparticles was interpreted based on a core-shell model.     

Photoluminescent carbon nanoparticles produced by confined combustion of aromatic compounds

We report new photoluminescent carbon nanoparticles having an average particle size of 50 nm. When dispersed in chloroform and excited with 325 nm wavelength, the solution showed strong photoluminescence at 475 nm with 12–13% quantum yield. A well dispersed photoluminescent solution can also be prepared with ethanol, xylene or hexane using the nanoparticles. The nanoparticles were prepared by a simple confined combustion of an aromatic compound such as benzene, toluene, xylene or a mixture thereof in air.     

Synthesis of Fe/Fe3C nanoparticles encapsulated in nitrogen-doped carbon with single-source molecular precursor for the oxygen reduction reaction

Ammonium ferric citrate (AFC) was used as a single-source molecular precursor to prepare Fe/Fe₃C nanoparticles encapsulated in nitrogen-doped carbon by pyrolysis in Ar atmosphere followed by acid-leaching. Comparative studies, using citric acid and ferric citrate as the precursors, indicated that the ammonia and ferric ion in AFC and the pyrolysis temperature affected the composition of iron species and the properties of carbon in AFC-derived materials. Above the pyrolysis temperature of 600 °C, the iron species were Fe/Fe₃C, and the carbon had a hollow graphitic nanoshell structure in AFC-derived materials. The specific surface area and content of nitrogen element decreased with increasing pyrolysis temperature. The AFC-derived material pyrolyzed at 600 °C had the optimal graphitization degree, specific surface area (489 m² g⁻¹) and content of nitrogen (1.8 wt.%), thus resulted in the greatest activity for oxygen reduction reaction among the AFC-derived materials pyrolyzed at different temperatures. The AFC-derived material pyrolyzed at 600 °C exhibited improved methanol-resistance ability compared with Pt/C catalyst.