Amorphous Carbon Shell Research Articles

Facile fabrication of ultrathin carbon layer encapsulated air-stable Mg nanoparticles with enhanced hydrogen storage properties

In this work, we present a facile way to fabricate ultrathin carbon layer encapsulated air-stable Mg nanoparticles (Mg@C NPs) by methane plasma metal reaction method. Compared with pure Mg NPs, the carbon layer can not only reduce particle size but also prevent Mg from oxidation. By adjust methane from 10 to 300 ml, average size of Mg@C NPs reduces from 140 to 60 nm and thickness of carbon layer increases from 1 to 4 nm. After exposure in air for 3 months, little MgO can be detected in Mg@C NPs. In these Mg@C samples, Mg@C (CH4:50 ml) with size of 80 nm and ultrathin amorphous carbon shell of 3 nm shows the highest hydrogen capacity of 6.3 wt% H2. In comparison, the hydrogen capacities of Mg@C (CH4:10 ml) and Mg@C (CH4:300 ml) are only 5.4 wt% H2 and 4.3 wt% H2, respectively. Mg@C (CH4:50 ml) also displays the highest hydrogenation and dehydrogenation rates which can absorb 4.8 wt% H2 within 10 min at 573 K and desorb 5.0 wt% H2 within 20 min at 623 K. The apparent energies for hydrogenation and dehydrogenation of Mg@C (CH4:50 ml) are 64.1 and 107.2 kJ mol−1, both smaller than Mg@C (CH4:10 ml) of 66.7 and 118.9 kJ mol−1 and Mg@C (CH4:300 ml) of 67.7 and 137.8 kJ mol−1. The enhanced hydrogen storage properties of Mg@C (CH4:50 ml) are attributed to smaller particles size and excellent antioxidant properties provided by the ultrathin carbon layer.

Facile synthesis of carbon-coated SiO/Cu composite as superior anode for lithium-ion batteries

Carbon-coated SiO/Cu composites are facilely prepared via Cu deposition combined with carbon coating on SiO nanoparticles. Transmission and scanning electron microscopic images reveal that the composites exhibit microstructures comprising amorphous carbon shell and Cu-deposited SiO core with sizes ranging from 100 to 200 nm. The electrochemical test results indicate that the initial reversible specific capacity of the as-prepared anodes reach up 1140 mAh g−1 at a current density of 100 mA g−1, combined with an excellent cycling performance with capacity retention of 88.3% over 150 cycles and a good rate-capability. The deposited Cu particles disperse along the surfaces of SiO nanoparticles, providing an efficient electron pathway from the current collector to most of the surface area of the active material. Meanwhile, the carbon layer plays a role in keeping the holistic electric conductivity and acts as soft media to accommodate part of the significant volume change of the active materials. The synergistic effect of deposited Cu and amorphous carbon layer encourage the composites to maintain good conductive network and structural integrity during cycling. This, in turn, results in excellent electrochemical performances.

Encapsulating V2O3 nanorods into carbon core-shell composites with porous structures and large specific surface area for high performance solid-state supercapacitors

V2O3@C core-shell nanorods with porous structures and large specific surface area were synthesized using V2O5 nanowires as the source of core and glucose as the source of shell by a facile hydrothermal route combination of heat treatment. As-prepared V2O3@C nanorods comprised of core-shell structures with crystalline V2O3 cores and amorphous carbon shells. Nitrogen adsorption-desorption isotherms revealed that V2O3@C core-shell nanorods displayed BET specific surface area as high as 219 m2·g−1 and had hierarchical porous structures. Electrochemical properties of V2O3@C core-shell nanorods as supercapacitor electrode were studied and showed their measured capacitance was based on the pseudocapacitance. Specific capacitances of V2O3@C core-shell nanorods measured 228, 221, 207, 158 and 127 F·g−1 at current densities of 0.5, 1, 2, 5 and 10 A·g−1, respectively. Results showed V2O3@C core-shell nanorods displayed higher specific capacitance than values of carbon spheres (4 F·g−1 at 1 A·g−1) and V2O3 nanomaterials (49 F·g−1 at 1 A·g−1). Asymmetric supercapacitor device assembled from V2O3@C core-shell nanorods and activated carbon (V2O3@C//C) showed specific capacitances of 0.297, 0.274, 0.230, 0.194 and 0.169 F·cm−2 at current densities of 0.5, 1, 2, 5 and 10 mA·cm−2, respectively. It showed higher specific capacitance than that of V2O3//C device (0.219 F·cm−2 at 1 mA·cm−2). A capacitance retention of 86% for V2O3@C//C device after 1000 cycles indicated that V2O3@C had good cycling performance for supercapacitor application. Present findings suggested that V2O3@C core-shell nanorods could be considered as potential materials for high-performance energy storage materials.

Vertical-Aligned Li2 S-Graphene Encapsulated within a Carbon Shell as a Free-Standing Cathode for Lithium-Sulfur Batteries.

Construction of a novel matrix with both high conductivity and an excellent confinement effect for polysulfides is of great importance for developing high-performance lithium-sulfur (Li-S) batteries. In this work, we have developed a double-modification strategy to integrate lithium sulfide (Li2 S) into a conductive composite network consisting of vertical graphene (VG) arrays and an amorphous carbon shell, forming an integrated cathode (VG/Li2 S-C). Facile liquid-solution/evaporation methods in combination with chemical vapor deposition were successfully adopted for preparation of the above cathode. Due to the enhanced electrical conductivity and noticeable blocking effect for the shuttle of polysulfides, the binder-free flexible VG/Li2 S-C cathode exhibits high rate performance and reinforced cycles (656.2 mAh g-1 after 100 cycles). The pronounced electrochemical performance is ascribed to the unique architecture with a coherent conductive network of VG and the carbon shell, which not only provides a conductive network for fast reaction kinetics, but also forms a durable protective shield to suppress the shuttle of polysulfides. Our research further demonstrates the synergistic effectiveness by means of inner and outer carbon matrixes for electrochemical enhancement of Li-S batteries.

Highly efficient one-step synthesis of carbon encapsulated nanocrystals by the oxidation of metal π-complexes

Various carbon encapsulated nanocrystals, including MnS and MnO, Cr2O3, MoO2, Fe7S8 and Fe3O4, and ZrO2, are prepared in one step and in situ by a simple and highly efficient synthesis approach. The nanocrystals have an equiaxed morphology and a median size smaller than 30 nm. Tens and hundreds of these nanocrystals are entirely encapsulated by a wormlike amorphous carbon shell. The formation of a core–shell structure depends on the strongly exothermic reaction of metal π-complexes with ammonium persulfate in an autoclave at below 200 °C. During the oxidation process, the generated significant amounts of heat will destroy the molecular structure of the metal π-complex and cleave the ligands into small carbon fragments, which further transform into an amorphous carbon shell. The central metal atoms are oxidized to metal oxide/sulfide nanocrystals. The formation of a core–shell structure is independent of the numbers of ligands and carbon atoms as well as the metal types, implying that any metal π-complex can serve as a precursor and that various carbon encapsulated nanocrystals can be synthesized by this method.

Bottom-up diamond nanorod growth in HFCVD from nanocrystalline diamond film as a template-free method

Nanocrystalline diamond (NCD) films are being used in a large number of applications. Also, diamond nanorods (DNRs) exhibit distinctive features that are not present in diamond films, because of the tunable large surface-to-volume ratio and tubular configuration. In this work, we report on the synthesis of DNRs by means of the bottom-up and template-free method from NCD films by the hot filament chemical vapor deposition system. The substrate materials used for diamond deposition were stainless steel (AISI 316) and chromium nitride-coated stainless steel. On both substrates, NCD films and then DNRs have been synthesized. The micro-Raman confirms that the synthesized structure is NCD. In addition, the grazing incident x-ray diffraction pattern confirms the presence of cubic diamond and rhombohedral diamond as a film on the CrN and Cr2N interlayer. Also, the DNRs are encased in an amorphous carbon (a-C) shell. The DNRs are grown on the NCD grains by a bottom-up technology and template-free method. Their orientations are almost random in the diamond thin-film surface. In addition, the density of DNRs on the NCD film for the CrN interlayer is more than for the stainless-steel substrate. The NCD/DNR films are dense, adhesive, continuous, and almost uniform on the CrN-coated stainless-steel substrate.

Ultrahigh permittivity of polymer nanocomposites based on surface-modified amorphous carbon/MWCNTs shell/core structured nanohybrids

The key matter to achieve excellent dielectric properties is not only improving the interfacial bonding between nanocarbon materials and polymer matrix but also preventing the direct contact of adjacent nanocarbon materials. Unfortunately, few works have provided a feasible route to address these problems simultaneously. In this work, surface-modified amorphous carbon/MWCNTs shell/core structured nanohybrids (s-AC@MWCNTs) are prepared using a facile and environmentally friendly approach. On one hand, the amorphous carbon shell can isolate MWCNTs from direct contact. On the other hand, the surface modification of amorphous carbon shell obviously improves the interfacial bonding between s-AC@MWCNTs and poly (vinylidene fluride) (PVDF) matrix. As a result, the s-AC@MWCNTs can be monodispersed into the PVDF matrix to form numerous microcapacitors and thus enhance the dielectric performance of PVDF by ∼4 orders of magnitude. The largest dielectric constant of s-AC@MWCNTs/PVDF composites can reach 43800 while maintaining a suppressed dielectric loss below1.8.

Electrochemical behavior of carbonic precursor with Na3V2(PO4)3nanostructured material in hybrid battery system

The nanostructured Na3V2(PO4)3 (NVP) cathode material has been synthesized using the sol-gel route for different molar fractions of citric acid as a carbon source during the synthesis. The nanostructured NVP as cores with carbonic shell structures are fabricated with two different citric acid molar ratios. The thermal treatment has been optimized to convert the amorphous carbon shell into graphitic carbon to realize the better electrical conductivity and thus effective electron transfer during the electrochemical charge transfer process. The X-ray diffraction measurements confirmed the rhombohedral crystallographic phase (space group R-3c) with average crystallite size ~28 ± 5 nm. The coin cells are assembled in a hybrid rechargeable electrochemical cell configuration with lithium as a counter electrode and LiPF6-EC:DEC:DMC (1:1:1 ratio) as the electrolyte. The electrochemical charge/discharge measurements are carried out at C/10 and C/20 rates and the measured specific capacities are 80 and 120 mAhg−1 for samples with lower and higher citric acid molar ratios, respectively. The studies suggest that NVP can be used as an effective cathode material in hybrid electrochemical cells, and a higher concentration of citric acid may result in the effective carbonic shell for optimal electron transfer and thus enhanced electrochemical performance.

Amorphous FeCrNi/a-C:H coatings with self-organizednanotubular structure

Amorphous FeCrNi/a-C:H coatings are deposited by pulsed magnetron sputtering of austenitic stainless steel in argon/acetylene atmosphere. High-resolution transmission electron microscopy, electron energy loss spectroscopy and energy dispersive X-ray mapping reveal a pronounced nanotubular structure consisting of metallic cores that thread along the film growth direction and are encapsulated by amorphous carbon shells in a cream-roll fashion. The coatings exhibit excellent mechanical, tribological, and anti-corrosion properties.

Facile synthesis of a Sn/SnO 2 @C ternary composite with superior broader frequency performance

Abstract Core-shell ternary composite composed of a Sn/SnO 2 nanoparticle core and amorphous carbon shell were successfully prepared by a simple hydrothermal route. Crystal phase structure, composition, morphology of the final product were characterized by the transmission electron microcopy, X-ray photoelectron (XPS) and Raman technique. This ternary composite presented excellent electromagnetic absorption properties if applied to treat the electromagnetic interference issue (EMI). The optimal effective absorption frequency covered 6.8 GHz with a thin coating thickness, which was quite better than Sn@C and SnO 2 @C binary composite. The improvement electromagnetic absorption mechanism was attributed to the moderate permittivity value which ensure the balanced impedance matching and dielectric loss ability. Besides, the probably interface polarization effect was proposed in this research which benefited to the attenuate electromagnetic wave.

Influence of a magnetic field on the formation of carbon dust particles in very low-pressure high-density plasmas

Carbon dust particles with radius of a few hundreds of nanometers are formed in a steady-state plasma produced by an electromagnetic surface wave at 200 MHz in very low-pressure conditions. The influence of an applied magnetic field is evidenced by ex situ methods (scanning and transmission electron microscopy, Raman spectroscopy). The observed spherical dust particles are formed of aggregates of graphite nanocrystals embedded in amorphous carbon shells. In addition, the size of the dust particles increases with the magnetic field intensity. Growth occurs as the particles are confined near the sheath edge and their confinement is improved by applying a magnetic field as the corresponding electric field increases in this region. As a consequence, the average dust particle radius is directly related to the magnetic field intensity.

Visible-light-driven photocatalysis with dopamine-derivatized titanium dioxide/N-doped carbon core/shell nanoparticles

Titanium dioxide/N-doped carbon core/shell nanoparticles enabling efficient visible-light-driven photocatalytic degradation of rhodamine B, considered a model compound for water-soluble environmental pollutants, were successfully prepared by the carbonization of dopamine-grafted TiO2 nanoparticles. These precursor nanoparticles were prepared via simple ligand-to-metal charge transfer (LMCT) between TiO2 nanoparticles and dopamine. Owing to the incorporation of Ti–O–C chelating bonds and the subsequent narrowing of the optical band gap, the dopamine-derivatized photocatalyst demonstrated enhanced activity compared with that of commercial photocatalysts and promoted the photocatalytic degradation of rhodamine B under both UV light and visible light. This LMCT-mediated incorporation of thin amorphous N-doped carbon shells onto the surface of semiconducting photocatalysts may be widely applicable for the generation of novel and robust hybrid materials with enhanced photocatalytic activities for many applications.

Fabrication and nanostructure control of super-hierarchical carbon materials from heterogeneous bottlebrushes.

Advances in the performances of many modern materials fundamentally depend upon the exploitation of new micro/nanostructures. Therefore, ingenious design of hierarchical structures through the mimicking of natural systems is of increasing importance. Currently, there is an urgent need for creation of multidimensional carbonaceous structures by integrating a customized hierarchical pore architecture and hybrid carbon framework. Here we report the pioneering fabrication of novel super-hierarchical carbons with a unique carbonaceous hybrid nanotube-interconnected porous network structure by utilizing well-defined carbon nanotube@polystyrene bottlebrushes as building blocks. Hypercrosslinking of such heterogeneous core-shell structured building blocks not only allows for constructing amorphous microporous carbon shells on the surface of graphitic carbon nanotube cores, but also leads to formation of covalently interconnected nanoscale networks. Benefiting from such a well-orchestrated structure, these super-hierarchical carbons exhibit good electrochemical performances. Our findings may open up a new avenue for fabrication of unique and unusual functional carbon materials which possess well-orchestrated structural hierarchy and thus generate valuable breakthroughs in many applications including energy, adsorption, separation, catalysis and medicine.

Formation of Titanium Carbide (TiC) and TiC@C core-shell nanostructures by ultra-short laser ablation of titanium carbide and metallic titanium in liquid

Laser ablation of bulk target in liquid allows to obtain stable nanoparticles and nanostructures, also in metastable phases, limiting the use of hazardous reagents and extreme reaction conditions. Titanium carbide (TiC) is a ceramic compound with several technological applications ranging from biocompatible materials to wear resistant coatings. The possibility to obtain core/shell structures expands its range of application due to the ability of modify the surface properties of the core ceramic material. TiC and metallic titanium targets have been ablated by means of an ultra-short laser source in different liquid media (water, acetone, n-hexane and toluene). The obtained colloidal solutions have been characterized by TEM, XRD and micro-Raman analysis. In all the used experimental conditions TiC nanoparticles have been produced. During water and acetone mediated ablations, the oxidation of titanium has been observed, whereas by using oxygen free solvents, such as n-hexane and toluene, core/shell TiC nanoparticles embedded in amorphous and graphitic carbon shell, respectively, have been obtained.

Graphitic cage transformation by electron-beam-induced catalysis with alkali-halide nanocrystals

We found that alkali-halide nanocrystals, such as KCl and NaCl, have strong catalytic capability to form graphitic carbon cages from amorphous carbon shells under electron beam irradiation. In addition to the electron beam irradiation strongly inducing the decomposition of alkali-halide nanocrystals, graphene fragments were formed and linked together to form the final product of thin graphitic carbon cages after the evaporation of alkali-halide nanocrystals. The required electron dose was approximately 1 to 20 C/cm2 at 120 keV at room temperature, which was about two orders of magnitude smaller than that required for conventional beam-induced graphitization. The “knock-on” effect of primary electrons strongly induced the decomposition of the alkali-halide crystal inside the amorphous carbon shell. However, the strong ionic cohesion quickly reformed the crystal into thin layers inside the amorphous shell. The bond excitation induced by the electron beam irradiation seemed to enhance strongly the graphitization at the interface between the outer amorphous carbon shell and the inner alkali-halide crystal.

Amorphous carbon shell on Si particles fabricated by carbonizing of polyphosphazene and enhanced performance as lithium ion battery anode

A novel strategy was employed to introduce a carbon layer on Si particle to overcome the intrinsic poor electrical conductivity and significant volume change. The carbon layer was fabricated by forming polyphosphazene coating through a facile precipitation polymerization method, followed by carbonization. As a result of formation of core-shell structure, the Si anode exhibited improved cycling stability (740mAh/g remained after 100 cycles) and rate capability (300mAh/g at a rate 2C). In addition, 99% coulombic efficiency was remained after 100 cycles.

Microscopic Electrical Conductivity of Nanodiamonds after Thermal and Plasma Treatments

ABSTRACTAtomic force microscopy (AFM) is used to measure local electrical conductivity of HPHT nanodiamonds (NDs) dispersed on Au substrate in the as-received state and after thermal or plasma treatments. Oxygen-treated NDs are highly electrically resistive, whereas on hydrogen-treated NDs electric current around -200 pA at -2 V is detected. The as-received NDs as well as NDs after an underwater radio-frequency (RF) plasma or laser irradiation (LI) treatments contain both electrically conductive (two types: highly and weakly conductive) and highly resistive particles. The higher conductivity is attributed to H-terminated (RF) or graphitized (LI) NDs. The lower conductivity is attributed to NDs with hydrogenated amorphous carbon shell.

A general strategy toward transition metal carbide/carbon core/shell nanospheres and their application for supercapacitor electrode

A general and straightforward strategy was developed for fabricating transition metal carbide (TMC)/carbon (C) core/shell nanospheres (NSs) by laser ablation of transition metals in acetone/ethanol liquid. Various TMC/C core/shell NSs such as TaC/C, NbC/C, HfC/C, and MoC/C core/shell NSs were successfully fabricated, highlighting the generality of this method. Crucially, this approach is green, facile, catalyst-free, and especially can be operated under ambient environments. Interestingly, all of the as-synthesized TMCs in the NS cores showed a cubic phase and structures similar to that of NaCl-type. The cores were further encapsulated by amorphous carbon shell with different thickness. As an example of the functional properties of these compound materials, the TaC/C core/shell NSs obtained were investigated as a supercapacitor electrode, which showed a large specific capacitance, excellent rate capability and remarkable cycling ability, revealing that the NSs could be used as new electrode materials for electrochemical energy storage. The photoluminescence of TaC/C core/shell NSs exhibited strong emission under the specific excitation wavelength at room temperature, showing potential biomedical applications due to the good biocompatibility of carbon shell. Besides, the basic physical and chemical reactions involved in the unique formation mechanism under highly nonequilibrium states induced by ultrafast laser ablation were discussed.

Facile synthesis of CdS/C core–shell nanospheres with ultrathin carbon layer for enhanced photocatalytic properties and stability

In this work, we described a facile one-pot hydrothermal process developed to synthesize CdS/C core–shell nanospheres successfully. The as-prepared CdS/C core–shell nanospheres are with 100nm in diameter and the amorphous carbon shell is with several nanometers in thickness. The phase, morphology and structures of the samples were investigated by X-ray power diffraction (XRD) analyses, field-emission scanning electron microscopy (FESEM, JEOL-6700F) and transmission electron microscopy (TEM, JEOL 3010); respectively. The as-prepared CdS/C core–shell nanospheres showed enhanced photocatalytic properties and photostability compared to the single counterpart of CdS nanospheres owing to the efficiently separation of photogenerated electrons (e−) and holes (h+) derived from the photocatalyst. In addition, the as-prepared CdS/C core–shell nanospheres might find wide application in wastewater treatment, solar cells, lithium ion batteries, etc.

Synthesis of BiVO4@C Core-Shell Structure on Reduced Graphene Oxide with Enhanced Visible-Light Photocatalytic Activity.

Herein, a facile strategy for the controllable synthesis of BiVO4@C core-shell nanoparticles on reduced graphene oxide (RGO) is reported. The BiVO4 particle size can be controlled in the process by adjusting the volume ratio of glycerol in the sol-gel solution. The glycerol layers adsorbed on BiVO4 (BiVO4@glycerol) made it possible to form hydrogen bonds between BiVO4@glycerol and graphene oxide with the assistance of ultrasound. After thermal treatment, glycerol adsorbed on the BiVO4 particles formed amorphous carbon shells to link the particles and RGO. As a result, the obtained RGO-BiVO4@C nanocomposite showed a five times higher rate in O2 evolution from water under visible-light irradiation. Also, it demonstrated a six times higher photocatalytic performance enhancement than that of pure BiVO4 in the degradation of Rhodamine B. The enhanced performance is attributed to the carbon shells that restrict the growth of BiVO4 , the reduced graphene oxide that improves the electronic conductivity of the composite, and importantly, the bonds formed between the carbon shells and RGO that reduce the recombination loss of photogenerated charges effectively. The strategy is simple, effective, and can be extended to other ternary oxides with controlled size and high performance.