Carbon-encapsulated Nanoparticles Research Articles

Synergizing Single-Atom and Carbon-Encapsulated Nanoparticles of Fe for Efficient Oxygen Reduction and Durable Zn–Air Batteries

Synergizing Single-Atom and Carbon-Encapsulated Nanoparticles of Fe for Efficient Oxygen Reduction and Durable Zn–Air Batteries

Highly dispersed carbon-encapsulated FeS/Fe3C nanoparticles distributed in Fe-N-C for enhanced oxygen electrocatalysis and Zn-air batteries

Transition metal single-atom catalysts (SACs) have been widely used in oxygen reduction reactions (ORR) and oxygen evolution reaction (OER) due to its greatest atomic utilization and low costs, which catalytic performance can be further enhanced by electron distribution adjustment. Herein, we synthesized a carbon-encapsulated FeS/Fe3C nanoparticles doped carbon-based Fe single atom catalyst from fluid catalytic cracking (FCC) slurry though a one-pot pyrolysis. The synergistic effect between FeS/Fe3C nanoparticles and Fe single atom structure (FeNx) promotes the ORR/OER processes, which may due to the reduction of the adsorption free energy of intermediates. Meanwhile, the polyaromatic hydrocarbon in FCC slurry enhances the graphitization of catalyst to facilitate charge transfer in electrocatalysis process, and the carbon-encapsulated nanoparticles sites possess higher stability and dispersion. As a result, the optimized catalyst (FeS/Fe3C@Fe-N-C) presents a high nanoparticles dispersion and graphitization level, which has a higher ORR catalytic ability (E1/2 = 0.91 V vs RHE) compared with commercial Pt/C (20 wt%, E1/2 = 0.879 V vs RHE) and a similar OER catalytic ability (E10 = 0.1.506 V vs RHE) compared with RuO2 (E10 = 1.518 V vs RHE). A liquid Zn-air battery assembled with FeS/Fe3C@Fe-N-C show a peak power density of 113 mW cm−2 and an open potential of 1.432 V. This work sheds light on a new method to design transition metal active sites carbon based single-atom catalyst for enhanced ORR and OER processes.

Preparation of Carbon Encapsulated Magnetic FeCo Alloy Nanoparticles Supported on Carbon Nanotubes for Enhanced Microwave Absorption

A mixture of multi-walled carbon nanotubes in an ethanol solution of Fe(NO3)3.9H2O and Co(NO3)2.6H2O, were used to prepare an Fe2O3-CoO catalyst supported on carbon nanotubes by a supercritical fluid drying method. The carbon encapsulated FeCo nanoparticles were prepared by the catalytic decomposition of methane over the catalyst at 850°C for 30 mins. The morphology and microstructure of the catalyst and carbon encapsulated nanoparticles (CEP) were characterized by XRD, FESEM, EDS and TEM analyses. The electromagnetic characteristics and microwave absorption properties of the CEP product were also studied. Results show that the CEP product possesses high complex permittivity and good permeability in the microwave frequency range from 2 to 18 GHz. The maximum absorption peak was observed at 9.44 GHz for a large reflection loss (R) of 13.3 dB, with a band width of 7.4 GHz and 2.56 GHz, at R <- 5 dB and R <- 10 dB, respectively.

Synthesis of Carbon-Encapsulated Iron and Iron Nitride Nanoparticles from Ferrocene Through Reactive Radio-Frequency Thermal Plasma.

In this paper, carbon-encapsulated nanoparticles of iron and iron nitride were synthesized using ferrocene by reactive radio-frequency thermal plasma. The properties of the prepared nano-powders were investigated by TEM, XRD, Raman spectroscopy and VSM. The samples obtained with zero-nitrogen plasma, contains the carbon-encapsulated iron nanoparticles. There cores mainly composed of ferromagnetic α-Fe and paramagnetic γ-Fe, with carbon shell thicknesses of about 5 nm. The samples synthesized by the plasma with varying nitrogen flow rates, mainly consists of iron nitride and oxide having spherical and irregular shape with deteriorated and disappearing carbon shell. Particle size in all samples were 20-90 nm. Synthesized sample at zero-nitrogen condition showed a room-temperature saturation magnetization of 19.65 emu/g, with a coercivity of 375.1 Oe. The sample prepared with optimal nitrogen flow rate had a saturation magnetization of 35.25 emu/g at room temperature, with a coercivity and remanence of 49.1 Oe and 0.56 emu/g, respectively.

Fabrication of Carbon Encapsulated ZrC Nanoparticles by Electrical Explosion of Zr Wire in Ethanol

The method of electrical explosion of metal wire in organic liquid was adopted to prepare carbon encapsulated nanoparticles. In the medium of absolute ethyl alcohol, under the high-voltage pulse current (HVPC), the high purity zirconium wire became fusion, gasification, expansion and explosion, accompanied with separating of carbon out of ethanol and reaction of carbon and zirconium, and carbon encapsulated ZrC nanoparticles formed. The energy, voltage and current in the experiments were measured to analyze the influence of them on the products. The products were analyzed by X-ray diffraction technique (XRD), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The results show that the carbon encapsulated ZrC nanoparticles are fabricated successfully. The diameter range is between 10~150 nm. For the voltage of 4, 8 and 12 kV, the average size of the products is 24.9, 41.4 and 43.9 nm, respectively. Finally, the procedure and mechanism of fabrication of the carbon encapsulated ZrC nanoparticles were discussed preliminarily.

Synthesis of ZrC and HfC nanoparticles encapsulated in graphitic shells from mechanically milled Zr-C and Hf-C powder mixtures

Abstract This work was aimed at evaluating a synthesis route based on the combination of mechanical milling and annealing of metal-carbon powder mixtures for the production of carbon-encapsulated nanoparticles of zirconium and hafnium carbides ZrC and HfC. These structures differ from those previously synthesized via this route by the high melting point and the high enthalpy of formation of the material of the particle core. During high-energy mechanical milling of the metal-amorphous carbon powder mixtures of the Zr-1.2C am and Hf-1.2C am compositions, nano-sized particles of carbides were synthesized, and during subsequent annealing of the products of milling at 750 °C in argon, these particles became encapsulated in graphitic shells. The graphitic shells covering the surface of the carbide particles are believed to form through decomposition of supersaturated solid solutions of carbon in the carbides forming during milling as a result of local melting/rapid solidification and generation of defects in the crystalline lattices of the carbides in the solid state under the impacts of the milling balls. This study has shown that nanoparticles of ZrC and HfC encapsulated in graphitic shells can be obtained by a simple and technologically attractive method based on high-energy mechanical milling of carbon-rich Zr-C and Hf-C mixtures.

Synthesis of Carbon-Encapsulated Iron Nanoparticles by Gaseous Detonation of Hydrogen and Oxygen at Different Temperatures within Detonation Tube

Abstract Using ferrocene as precursor, the mixed gas of hydrogen and oxygen as the source of explosion, the carbon encapsulated iron nanoparticles were prepared in a detonation tube. The influences of initial reactive temperature and heat treatment on the products of particles were studied. The characteristics of detonation products were tested by X-ray diffraction (XRD), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). Results show that the carbon encapsulated nanoparticles exhibit the shapes of sphere or spheroid. With reaction temperature increasing, the grain sizes of carbon encapsulated iron nanoparticles are 30∼50 nm and tend to be uniform, which indicates that the initial reaction temperature directly affects the grain sizes of the generated particles. Through the analysis of magnetic hysteresis loops of detonation products, the saturated magnetization (Ms) decreases as the temperature of heat treatment increases, and the hysteresis loops are in a relatively “thin” shape, but still have higher coercivity, indicating that the synthesized carbon-encapsulated iron nanomaterials present the dual natures of the hard magnetic and the paramagnetic.

Chemical Functionalization of Magnetic Carbon-Encapsulated Nanoparticles Based on Acid Oxidation

Carbon-encapsulated nickel nanoparticles were used as the representative magnetic carbon-encapsulated nanoparticles for chemical functionalization. After oxidation with the mixed acid of H2SO4/HNO3 under a moderate ultrasonic bath, carboxylic acid groups (-COOH) were effectively generated on the fullerene-like carbon shells, which in turn were utilized to covalently link octadecylamine through an amide reaction. The whole chemical process is well characterized by many methods such as Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetry-differential scanning calorimetry, transmission electron microscopy, and so on, and the self-consistent experimental results were obtained. The results suggested that the magnetic nanoparticles could be well protected, while their magnetic properties could be utilized to guide the transfer of the grafted functional species on the particle surface. This provides many possibilities for potential applications in chemical and biochemical fields.

One-step synthesis and enhanced blue emission of carbon-encapsulated single-crystalline ZnSe nanoparticles

Carbon-encapsulated ZnSe nanoparticles with diameters about 50nm were synthesized by noncatalytic one-step thermal evaporation method. The ZnSe cores have a wurtzite crystal structure. The as-synthesized products are uniform and composed of single-crystalline ZnSe nanoparticles enwrapped with polycrystalline graphite layers. The photoluminescence measurement of the carbon-encapsulated nanoparticles shows that the blue emission enhances dramatically compared with the naked ZnSe nanoparticles. This synthetic strategy might exploit a favorable route to synthesize carbon-encapsulated semiconductor nanostructures, which are potentially important for optoelectronic nanodevices.

Synthesis, structures and magnetic properties of carbon-encapsulated nanoparticles via thermal decomposition of metal acetylide

A new low-temperature synthetic method for carbon-encapsulated metal and metal carbide nanoparticles was developed, where the metal cation M 2+ is reduced by C 2 2 - . In this method, metal cations form ( M 2 + C 2 2 - ) n clusters at the beginning, followed by neutralization and segregation. Formations of metallic tin and cobalt, and metastable carbides of cobalt, palladium and nickel are evidenced by powder X-ray diffractions. TEM observation reveals that the nanoparticles are encapsulated in carbon shells despite the low temperature treatment. The formation of the metastable carbides and carbon shells can be explained by the carbon-rich precursor, acetylide clusters. Surplus carbon atoms tend to be excluded from the metal–carbon cores even at low temperature, automatically forming carbon shells.

Morphology, structure, and growth of nanoparticles produced in a carbon arc.

The morphology and crystalline microstructure of carbon-encapsulated nanoparticles produced in a Huffman-Kr\atschmer fullerene reactor are studied systematically as a function of location within the reactor. X-ray powder diffraction and high-resolution transmission electron microscopy are used to characterize powder harvested from the reactor walls and the inner and outer cores of the cathode deposit. We observe increased graphitization and crystallinity, more faceting, and more gaps between the nanoparticle and the encapsulating carbon cages in the cathode deposit when compared to the wall powder. We propose a growth model based on gas-phase nucleation to explain these observations, linking carbon arc nanoparticle synthesis to existing work on gas aggregation cluster sources.