Preparation of carbon-encapsulated iron carbide nanoparticles by an explosion method

Fe₇C₃ nanocrystals encapsulated in carbon nanoparticles, with sizes ranging from 10 to 40 nm, were synthesized via the explosion of a hybrid xerogel containing oxidized pitch and iron nitrate. Explosion of the hybrid xerogel was induced by heat treatment. Transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) were employed to determine the structure of the nanoparticles in the explosion product. The results show that the Fe₇C₃ nanocrystals are nested inside amorphous carbon shells that protect them from oxidation by air.     

Synthesis of hermetically-sealed graphite-encapsulated metallic cobalt (alloy) core/shell nanostructures

Hermetically-sealed graphite encapsulated cobalt core/shell nanostructures have been prepared by the CO Boudouard reaction using in situ generated cobalt as the catalyst. Only core/shell nanostructures were obtained, rather than a mixture of cobalt nanoparticles with carbon nanotubes or nanofibers. The magnetic cobalt nanoparticles are highly crystallized with a hexagonal-close packed crystal phase (average diameter of ca. 25 nm) and coated with an 8–9 nm thick graphitic shell. The nanostructures have a high saturation magnetization of 85 emu/g and can be easily separated by an external magnet. The creation of the hermetically-sealed graphitic shell not only keeps the magnetic cobalt nanoparticles from reacting with strong mineral acids, but also has biocompatibility and makes further functionalization easy. A pseudo-planar aromatic molecule, xylenol orange, was used as the model molecule because it can be absorbed on the graphitic shell mainly by π–π stacking interaction. This was confirmed by Raman and ultraviolet–visible spectroscopy. Graphite encapsulated Fe₂Co and Fe_0.64Ni_0.36 alloy core/shell nanostructures were also fabricated by this method.     

Synthesis and characterization of carbon-encapsulated iron/iron carbide nanoparticles by a detonation method

Carbon-encapsulated iron-based nanoparticles with a core-shell structure were produced by detonation decomposition of explosive mixture precursors containing iron ion components. The size and magnetic properties of the as-prepared composite particles were revealed by X-ray powder diffraction, transmission electron microscopy and magnetic measurements. Results showed that the different sizes of the iron-based nanocrystal core and the thickness of the carbon shell could be yielded by adjusting the component materials of the explosive precursors during the course of these detonation chemical reactions. The composite particles had a body-centered cubic iron or iron carbide core with a coating of graphitic or amorphous carbon layers. Magnetic measurements indicated these composite nanoparticles were magnetic at the room temperature, with some variation in the values of saturation magnetization, remanences and coercive forces that depend on the size and grain composition.     

Synthesis of polypyrrole-coated core/shell nanoparticles

The synthesis, physical characterization and scale-up of conductive, re-dispersible core/shell nanoparticles containing polypyrrole (PPy) in the shell are described. The compressed powders/films show a DC conductivity which is considerably higher than that of commercial standard products based on PEDOT/PSS ('AL 4083' from H.C. Starck). The particles have excellent film-forming properties since thin films (50-100 nm) made by spin-coating from aqueous dispersions of the particles have an AFM film roughness of <15 nm even before annealing. The materials were tested as hole injection/smoothening layers in fluorescent OLED devices, and are in a comparable range to PEDOT/PSS-based materials in respect to performance (film forming, luminance, efficiency, and lifetime).     

Synthesis of carbon-encapsulated magnetic nanoparticles by pulsed laser irradiation of solution

A method for synthesizing carbon-encapsulated magnetic nanoparticles (CEMNPs) is reported. In the proposed method, a solution containing various metalocenes dissolved in xylene is irradiated with a nanosecond pulsed ultraviolet laser at room temperature and atmospheric pressure. Upon the completion of irradiation, CEMNPs (Fe-C, Ni-C, Co-C) with diameters ranging from a few nanometers to about 300 nm are produced in the solution. The material characteristics of these nanoparticles are then examined with electron microscopy, Raman spectroscopy, X-ray diffraction (XRD) and superconducting quantum interference device (SQUID) magnetometry. It was found that the magnetic nanoparticles coated with graphitic shells exhibit good stability in a high concentration HCl (10 mol) solution. The possible growth mechanisms of CEMNPs under the pulsed laser irradiation of the solution are then discussed.     

Synthesis of polystyrene/polythiophene core/shell nanoparticles by dual initiation

Polystyrene/polythiophene (PSt/PTh) core/shell nanoparticles were successfully synthesized via a one-pot Fe³⁺-catalyzed oxidative and soap-free emulsion polymerization process. A small amount of sodium styrene sulfonate (NaSS) was used to maintain the colloidal stability of the PSt/PTh nanoparticles. Hydrogen peroxide (H₂O₂) and a trace of iron chloride (FeCl₃) were used to carry out the free-radical polymerization of styrene and the oxidative polymerization of thiophene. The dual initiation characteristics of H₂O₂/FeCl₃ in the PSt/PTh core/shell nanoparticle formation were investigated by observing the time-evolution of the particle morphology. In addition, photoluminescent property, particle size distribution, core/shell morphology and the formation mechanism of the PSt/PTh nanoparticles were studied by spectrofluorophotometery, dynamic light scattering (DLS), in-situ IR, zeta-potential, and time-evolution field-emission scanning electron microscope (FE-SEM) analyses.     

Mechanism for the formation of PNIPAM/PS core/shell particles

A multi‐stage polymerization method was previously used to prepare PNIPAM/PS core/shell particles that exhibited uniform “raspberry‐like” structures. In this current study, this polymerization process was carefully investigated in order to elucidate the PS (polystyrene) shell formation mechanism. The results indicated that the “raspberry” structure is due to heterocoagulation of polystyrene domains onto PNIPAM (poly(N‐isopropylacrylamide)) particle surfaces. Different sizes and numbers of the PS domains can be obtained by varying the styrene feed rate. It was also found that linear PNIPAM may increase the compatibility between PNIPAM and PS polymers. In addition, this heterocoagulation mechanism for forming structured particles was successfully applied to a PNIPAM and Ludox^® colloidal silica nanoparticle system where a core/shell structure was also obtained. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40124.     

One-step preparation of amorphous iron nanoparticles by laser ablation

Amorphous Fe nanoparticles are always difficult to prepare by physical gas-phase methods though rapid cooling rates are applied. Here we report a physical preparation of pure amorphous Fe nanoparticles by laser ablation of a 0.5-mm-diameter Fe wire and the investigation of their formation mechanism. Amorphous Fe nanoparticles with a shell of γ-Fe₂O₃ and the sizes of 1–3 nm are obtained at the laser power densities above the ablation threshold. Finally, the as-prepared nanoparticles are characterized by XRD, TEM, XPS and VSM to discover the structure, morphology, surface composition, crystallization and magnetic property in detail. We find that the holistic explosive evaporation induced by the small-size target not by the processing parameters determines the nature of the amorphous Fe nanoparticles. The as-prepared amorphous Fe nanoparticles are crystallized at 400 °C with an increase of particle size to about 10 nm.     

Production of nanoparticles from natural hydroxylapatite by laser ablation

Laser ablation of solids in liquids technique has been used to obtain colloidal nanoparticles from biological hydroxylapatite using pulsed as well as a continuous wave (CW) laser. Transmission electron microscopy (TEM) measurements revealed the formation of spherical particles with size distribution ranging from few nanometers to hundred nanometers and irregular submicronic particles. High resolution TEM showed that particles obtained by the use of pulsed laser were crystalline, while those obtained by the use of CW laser were amorphous. The shape and size of particles are consistent with the explosive ejection as formation mechanism.     

Conjugated polymer mediated synthesis of nanoparticle clusters and core/shell nanoparticles

Two water soluble conjugated polymers, poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and ammonium ion stabilized poly(phenylene vinylene) (P2), are found to be able to reduce noble metal ions to zero-valent metals via a direct chemical deposition technique. Au nanoparticle clusters can be obtained through reduction of Au³⁺ ions by PEDOT:PSS and the electronic coupling between them can be controlled by HAuCl₄ concentration. Core/shell Ag/polymer nanostructures are prepared from reduction of Ag⁺ ions by P2, which have a ppb detection limit for 4-MBA using surface-enhanced Raman spectroscopy (SERS). This conjugated polymer mediated synthesis of metal nanoparticles may open a new avenue for fabricating nanomaterials and nanocomposites with tunable optical properties that are dominated by their structure and electronic coupling between nanoparticles.     

Multicolor core/shell silica nanoparticles for in vivo and ex vivo imaging

Biocompatible highly bright silica nanoparticles were designed, prepared and tested in small living organisms for both in vivo and ex vivo imaging. The results that we report here demonstrate that they are suitable for optical imaging applications as a possible alternative to commercially available fluorescent materials including quantum dots. Moreover, the tunability of their photophysical properties, which was enhanced by the use of different dyes as doping agents, constitutes a very important added value in the field of medical diagnostics.     

Precipitation of metallic nanoparticles inside silicate glasses by femtosecond laser pulses

Precipitation behaviors of metallic nanoparticles inside silicate glasses by femtosecond laser irradiation are studied in this work. Laser irradiation results easily in precipitation of metallic nanoparticles where colors depend in part on their sizes and quantities. Laser irradiation induced precipitation of metallic nanoparticles displays the different behaviors from that in the unirradiated area inside glasses and their mechanisms are investigated.     

One-step synthesis of γ-Fe2O3 nanoparticles by laser ablation

A Nd:YAG pulsed laser was used to ablate a 0.5-mm-diameter iron wire in a sealed chamber in a mixed gas flux of N₂ and O₂ to generate pure γ-Fe₂O₃ nanoparticles at atmospheric pressure. Structural characteristics and sizes of the prepared nanoparticles were determined by X-ray diffraction and TEM. The effects of laser power density, total mixed gas pressure and the oxygen ratio on the mean particle size were investigated, respectively. The results showed that the mean particle size decreased with the increase of the laser power density, total gas pressure and the oxygen ratio, respectively. Besides, the nanoparticle formation mechanism by laser ablation of iron wires was also discussed.     

Improving water desalination performance of electrospun carbon nanofibers by supporting with binary metallic carbide nanoparticles

Capacitive deionization (CDI) technology is proposed as an environmentally friendly way to desalinate brackish water samples with outstanding efficiency. Since the nanomaterial composition is the controlling factor in the measured activity of fabricated CDI cells, much efforts are directed to explore highly effective nanocomposites with increased electrosorptive capacity and enhanced regeneration behavior during operation for longer periods. Here, the electrospinning process was devoted to synthesize mixed cobalt and titanium carbides nanoparticles onto carbon nanofibers [Co–TiC@CNFs] using cobalt acetate tetrahydrate (CoAc) and titanium (IV) isopropoxide (TIP) as precursor salts and polyvinylpyrrolidone (PVP) as a carbon source. Electrospun mats were then calcined at 950 °C for 6 h using a tube furnace with passing argon gas. This formed nanoporous material could provide numerous pathways for increased ions adsorption with extraordinary electrical conductivity. This could explain its enhanced electrochemical properties as evidenced by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS) methods. A specific capacitance value of 979.40 F g^?1 was estimated for Co–TiC@CNFs as 7.42 times higher than that for bare CNFs. Furthermore, this nanohybrid material had a salt adsorption capacity of 33.10 mg g^?1 in 1.0 M NaCl solution at 1.2 V that highly exceeded the obtained ones for TiC [2.20 mg g^?1] and CNFs [8.20 mg g^?1]. Accordingly, modifying carbon nanofibers with metallic carbides can create suitable nano-constituents for promising CDI cell output.     

Polyyne formation by graphite laser ablation in argon and propane mixed gases

Laser ablation of graphite in argon/propane mixed gases was performed to elucidate the process of carbon cluster growth and hydrogen termination to form polyynes. The carbon-rich materials ejected by ablation were carried by the gas flow and captured by a cooled organic solvent, and then, the soluble products were analyzed by UV absorption. The yield of polyyne increased drastically with the increase of the propane ratios. The propane-ratio-dependent yields for polyynes of various lengths are consistent with a polyyne formation model based on H-abstraction reactions of carbon clusters.     

Factorial experimental design on synthesis of functional core/shell polymeric nanoparticles via differential microemulsion polymerization

Functionalized core/shell nanoparticles of the co‐polymer of methyl methacrylate (MMA) and glycidyl methacrylate (GMA) could be polymerized by differential microemulsion polymerization, using a small amount of surfactant (the weight ratio of sodium dodecyl sulfate (SDS)/monomer is 1 : 24). The core/shell nanoparticles have a high conversion, high molecular weight, and small particle size (25–30 nm). The statistical analysis indicated that SDS, water, and the interactionbetween SDS and water have a significant positive interaction between the MMA conversion to form the core nanoparticles. For the core‐shell polymer, [GMA], [GMA]*[SDS], and [GMA]* [water] have significant negative effects on conversion; whereas [SDS] and [water], [SDS]*[water] and [GMA]*[SDS]*[water] have positive effects on the conversion to form core/shell nanoparticles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fabrication of silver nanoparticles dispersed in palm oil using laser ablation

In this study we used a laser ablation technique for preparation of silver nanoparticles. The fabrication process was carried out by ablation of a silver plate immersed in palm oil. A pulsed Nd:YAG laser at a wavelength of 1064 nm was used for ablation of the plate at different times. The palm coconut oil allowed formation of nanoparticles with very small and uniform particle size, which are dispersed very homogeneously within the solution. The obtained particle sizes for 15 and 30 minute ablation times were 2.5 and 2 nm, respectively. Stability study shows that all of the samples remained stable for a reasonable period of time.     

Isotope scrambling in the formation of cyanopolyynes by laser ablation of carbon particles in liquid acetonitrile

Cyanopolyynes, H(CC)_nCN (n = 3–6), were formed by laser ablation of carbon particles in liquid acetonitrile. The molecules were separated according to the size n and characterized by UV absorption spectroscopy, mass spectroscopy in combination with gas-chromatographic separation, and nuclear magnetic resonance (NMR) spectroscopy. For the study of nascent carbon cluster distribution during the growth of the long carbon chain molecules, isotopomer distribution was analyzed by NMR spectroscopy for the product molecules. Two cyanopolyynes of HC₇N and HC₉N were isolated from solutions after laser ablation of isotope-enriched carbon powder (99% ¹³C) in liquid acetonitrile, CH₃CN, of natural isotopic abundance (1.1% ¹³C). With the observed chemical shift, δ, and spin–spin coupling constants, J_CH and J_CC, spectral simulation was made to determine relative abundance of possible isotopomeric forms for HC₉N. We found that the isotope of ¹²C, mostly from solvent molecules, contributes substantially for the part of carbon in the cyano group, –CN, in HC₉N. The isotopomer distribution observed for the sequence of H–CC–CC– was fairly explainable by a binomial, random distribution of the two carbon isotopes of ¹²C and ¹³C, reducing the concentration of ¹³C to 76–55%.     

Melt compounding of syndiotactic polypropylene nanocomposites containing organophilic layered silicates and in situ formed core/shell nanoparticles

Syndiotactic polypropylene (sPP) compounds containing organophilic layered silicates were prepared by means of melt extrusion at 220 °C using a corotating twin screw extruder in order to examine the influence of the silicate modification and the addition of maleic-anhydride-grafted isotactic polypropylene (iPP-g-MA) as compatibilizer on morphology development and mechanical properties. Synthetic sodium fluoromica was used as water-swellable layered silicate, which was rendered organophilic by means of cation exchange with protonated octadecylamine. Only compounding of the modified silicate in conjunction with iPP-g-MA afforded exfoliation and dispersion of individual silicate layers, encapsulated in an iPP-g-MA shell, within the polypropylene matrix. Interlayer distance increased with increasing content and increasing molecular weight of the compatibilizer. The Young's modulus of the nanocomposite increased fivefold from 490 to 2640 MPa. This was attributed to silicate nanoreinforcement and nucleation of sPP crystallization via the iPP-g-MA shell of the dispersed organophilic silicate nanoparticles. The yield stress was increased to 29 MPa with respect to 16 MPa for the bulk sPP. Morphology and mechanical properties were examined as a function of the silicate—and compatibilizer content.     

Preparation of core/shell PVP/PLA ultrafine fibers by coaxial electrospinning

This study investigated the process feasibility and stability of core/shell structured bicomponent ultrafine fibers of poly(vinyl pyrrolidone) (PVP) and poly(D ,L ‐lactide) (PLA) by coaxial electrospinning. The morphological structure of the core/shell ultrafine fibers was studied by means of scanning electron microscopy, transmission electron microscopy, and X‐ray photoelectron spectroscopy. Results suggested that PVP/PLA core/shell ultrafine fibers with drawbacks could be produced from 6 or 8% PVP solutions (inner) in the mixture of N,N‐dimethlformamide (DMF) and ethanol and a 22% PLA solution (outer) in DMF and acetone when the flow rates of inner and outer fluids were 0.05 and 0.1 mL/h, respectively. The tensile modulus and tensile strength of the core/shell PVP/PLA membrane were dramatically lower than those of the electrospun PLA membrane, and its water uptake was twice more than that of the PLA membrane. Membranes made from the biodegradable core/shell ultrafine fibers could be potentially used in loading bioactive molecules for tissue regeneration. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 39–45, 2006