Carbon-encapsulated Ni Nanoparticles Research Articles

Ni@CNT nanocomposites as novel highly effective carbocatalysts for Hydrogenation/Dehydrogenation reactions

A series of carbon-encapsulated Ni nanoparticles deposited on carbon nanotubes (Ni@CNT) with various Ni concentrations were prepared by a simple impregnation method. The structural and functional properties of Ni@CNT were determined by a typical set of physicochemical methods. The catalytic performance of Ni@CNT was evaluated in the model reactions of ethylene hydrogenation and dehydrogenation of ethane as a reverse reaction, as well as in liquid-phase hydrogenation of p-nitrotoluene and α-methylstyrene. The surface of the Ni@CNT samples does not contain Ni and corresponds to CNT. The content of Ni was found to strongly influence the catalytic properties of Ni@CNT. Samples containing 1% of Ni demonstrated the highest activity for both the hydrogenation of the C = C bond and the dehydrogenation of ethane. Our study has demonstrated that the facile fabrication of Ni@CNT can produce efficient catalysts for the hydrogenation of various organic compounds using molecular hydrogen. Our results suggest that the catalytic properties of these nanocomposites are primarily associated with the carbon surface and enhanced by the Schwab effect.

Three-dimensionally ordered macroporous carbon-encapsulated Ni nanoparticles for the preparation of magnetically recoverable catalyst

A colloidal templating method was applied to fabricate a composite of three-dimensionally ordered macroporous carbon-encapsulated Ni nanoparticles (3DOM Ni@C) by using citric acid and nickel nitrate as raw materials and polymethyl methacrylate (PMMA) microspheres as template. The products were characterized by XRD, TEM, ICP, TG-DTA, XPS, N2 adsorption-desorption and magnetic measurement. In 3DOM Ni@C, metallic Ni nanoparticles (4.0–7.0 nm) were tightly wrapped by multilayer graphitized carbon with a highly ordered three-dimensionally arrangement in a large scale. While sufficient citric acid was supplied, multilayer carbon nanotubes were formed with the Ni nanoparticles at one end of them. Cu-supported 3DOM Ni@C materials were found to be highly efficient for catalyzing the reduction of 4-nitrophenol (4-NP). The rate constant reached 0.0512 s−1 over 3.5%Cu/3DOM Ni@C-1. Importantly, the catalyst showed good recycling performance due to its magnetically recoverable property and the improved stability brought by the encapsulated structure.

Robust carbon-encapsulated Ni nanoparticles as high-performance electrocatalysts for the hydrogen evolution reaction in highly acidic media

The major challenges related to non-noble-metal electrocatalysts toward the hydrogen evolution reaction (HER) in an acidic environment are to overcome their low efficiency and poor stability. For this purpose, we propose a rational top-down method to construct a hybrid structure of nickel encased by a carbon shell (Ni@C) using CH4 as a carbon source and Ni wire as a sacrificing template during an electrical explosion of wire. The Ni@C nanoparticles are introduced as highly active and durable non-noble metal electrocatalysts for the HER. The optimized Ni@C (15%) core-shell catalyst (CH4/Ar = 15/85 pressure ratio) demonstrates the highest catalytic activity for the HER with an overpotential of 85 mV to drive a current density of -10 mA cm−2 and displays a low Tafel slope of 44 mV dec−1. Another virtue of Ni@C (15%) is its superior stability during an unattenuated HER chronoamperometry for over 24 h. Furthermore, it endures over 168 h submerging in 2 M H2SO4 solution without losing its catalytic activity for HER.

Onion-like Core-shell Ni@C supported on carbon nanotubes decorated with low Pt as a superior electrocatalyst for hydrogen evolution reaction

The development of cost-effective electrocatalysts for efficient hydrogen evolution reaction (HER) is of paramount significant for future renewable energy. Pt-based catalysts have been recognized as the most effective electrocatalysts for HER. Developing low-cost and excellent electrocatalysts is a crucial step to achieve its commercial application, because of its high cost and scarcity. In this study, we fabricate carbon encapsulated Ni nanoparticles (NPs) and low Pt NPs supported on carbon nanotubes (CNTs). These samples are synthesized through catalytic decomposition of methane on Ni/CNT catalyst, and Ni/CNT is prepared using the polyol reduction method. Ni@C and Pt are uniformly dispersed on the CNTs. Ni@C-10 with low Pt loading (0.49wt%) exhibits superior HER activity and excellent stability even higher than that of commercial 20wt% Pt/C. Ni@C-10 (Pt loading is 4.3 µg cm−2 on the working electrode) exhibits negligible onset potential, and only 40 mV vs RHE potential is required to support 10 mA cm−2 in 0.1 M H2SO4 aqueous solution, which is better than 19 mV of Pt/C (59 mV). It achieve a low Tafel slope of 31.7 mV dec−1 close to Pt/C (29.3 mV dec−1). After 2000 cycles, it exhibits negligible potential shift (1 mV). This study provides an avenue for developing the efficient catalysts for HER with low Pt loading.

Nanoribbon Superstructures of Graphene Nanocages for Efficient Electrocatalytic Hydrogen Evolution

Two-dimensional carbon architectures are attracting tremendous interests for various promising applications due to their outstanding electronic and mechanical properties, although it is a great challenge to rationally devise facile and operative methodologies to engineer their structural traits owing to complex synthetic processes. Herein, for the first time, we fabricate two-dimensional carbon nanoribbons via direct thermal exfoliation of one-dimensional Ni-based metal-organic framework (MOF) nanorods, in which interconnected graphitic carbon nanocages are self-assembled into a belt-like superstructure with carbon-encapsulated Ni nanoparticles immobilized on the surface. Due to the unparalleled structural superiority, the MOF-derived carbon nanobelts exhibit excellent catalytic performances in electrocatalytic hydrogen evolution. Importantly, the practical synthetic strategy may trigger the rapid development of carbon-based superstructures in many frontier fields.

Multiporous Carbon Encapsulated Ni Nanoparticles Promoting Glycerol Valorisation towards Hydrogenation against Rearrangement†

Summary of main observation and conclusionA dual‐templating method was used to synthesize a series of hierarchical carbon supports containing different proportions of spherical macropores (ca. 200 nm in diameter) and mesoporous channels (ca. 4 nm in diameter). These and some other conventional carbon materials were subsequently impregnated with Ni and tested for the conversion of glycerol. The hierarchical catalysts exhibited a significantly higher conversion (96%) and selectivity (77%) to 1,2‐propanediol, and the specificity selectivity coefficient (6.1) towards 1,2‐propanediol against lactic acid was three times higher than that observed over a conventional Ni/Cmicro catalyst (2.1). The enhanced performance of these materials, compared with the Ni nanoparticles supported on conventional carbon supports, was attributed to their high surface areas (> 1110 m2∙g−1) and large pore volumes (ca. 0.4 cm3∙g−1) permitting greater accessibility of substrate and/or intermediates to Ni active sites. Given that the concentration of accessible Ni sites in these materials is higher, a competitive benzilic‐acid‐rearrangement reaction to produce lactic acid was suppressed, leading to an enhanced hydrogenation selectivity to 1,2‐propanediol. This study evidences the potential benefits, which can be established from utilizing hierarchical support materials in the valorization of biomass.

A Freestanding Single-Wall Carbon Nanotube Film Decorated with N-Doped Carbon-Encapsulated Ni Nanoparticles as a Bifunctional Electrocatalyst for Overall Water Splitting.

Noble‐metal free, cost‐effective, and highly stable catalysts with efficient activity for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) have attracted tremendous research interest in recent years. Here, a flexible, self‐standing hybrid film comprising a N‐doped single‐wall carbon nanotube (SWCNT) network on which are anchored Ni nanoparticles encapsulated by a monolayer of N‐doped carbon (NCNi) is reported. The films are prepared by floating catalyst chemical vapor deposition followed by NH3 treatment. The material obtained at optimum conditions shows excellent bifunctional electrocatalytic activity in alkaline media with low overpotentials of 190 and 270 mV for HER and OER, respectively, to reach a current density of 10 mA cm−2. A current density of 10 mA cm−2 at 1.57 V is achieved when this freestanding and binder‐free rod‐shaped NCNi/SWCNT assembly is used as cathode and anode in 1 m KOH solution for overall water splitting, presenting one of the best values reported to date.

In-situ synthesis of carbon-encapsulated Ni nanoparticles decorated graphene nanosheets with high reactivity toward glucose oxidation and sensing

Using graphene oxides (GO) as carbon source and NaCl crystals as the solid dispersant, a three-dimensional carbon-based nanohybrid was prepared by anchoring carbon shells-encapsulated Ni nanoparticles onto the reduced graphene oxides nanosheets (Ni@C@rGO). The as-obtained Ni@C@rGO exhibits larger specific surface area and pore volume as well as higher reactivity toward glucose oxidation, compared with the prepared Ni@rGO by the same conditions without NaCl crystals. The higher electrochemical reactivity may be originated from the ultrathin carbon shells, high dispersion of active Ni nanoparticles, and high conductivity of the graphene substrates. To further explore its electrochemical applications, Ni@C@rGO was employed to construct a glucose sensing platform, offering a low detection limit (0.34 μM) and wide linear range (2–951 μM). It was successfully utilized to monitor the glucose level in human serums, and satisfactory results were obtained. This used preparation strategy is in favor of making more nanocomposites with superior electrochemical properties.

Fabrication of 3D Hierarchical Byttneria Aspera-Like Ni@Graphitic Carbon Yolk-Shell Microspheres as Bifunctional Catalysts for Ultraefficient Oxidation/Reduction of Organic Contaminants.

The search for earth-abundant, low-cost, recyclable, multifunctional as well as highly active catalysts remains the most pressing demand for heterogeneous catalytic elimination of pollutants in water environment remediation. Herein, a porous graphitic carbon-encapsulated Ni nanoparticles (NPs) hybrid (Ni@GC) is designed/constructed by direct pyrolysis of a Ni-based metal-organic framework (MOF) in N2 . The resulting Ni@GC exhibits a unique 3D hierarchical byttneria aspera-like yolk-shell structure with a high surface area, abundant active sites as well as good microwave (MW)-absorbing performance. The outstanding MW-driven oxidation of norfloxacin to inorganic molecules and direct catalytic reduction of 4-nitrophenol to less toxic and more useful chemical raw material (4-aminophenol) can originate from the synergistic effects, including the presence of both zero-valent Ni NPs as the active center and graphitic carbon as the protective layer/electron acceptor as well as unique porous yolk-void-shell structure, which facilitates the MW energy-harvesting and/or rapid mass transfer of the reactant/product in the channels and cavities. Accordingly, the localized surface plasmon resonance-excitation and electronic relay mechanism are proposed to account for the catalytic oxidation/reduction, respectively. This work provides a new strategy for the design/assembly of multifunctional metal@GC hybrids with a unique architecture and elucidates new opportunities for remediation of environmental water.

Facile Synthesis of Carbon-Encapsulated Ni Nanoparticles Embedded into Porous Graphite Sheets as High-Performance Microwave Absorber

The Ni@C nanohybrids were prepared by a unique and efficient method of annealing the organic carbon compound and metal nitrate. Morphology detection demonstrated the Ni nanoparticles were uniformly encapsulated into the carbon network. The microwave absorption of 10 wt % Ni@C nanohybrids with paraffin matrix was measured over the range of 1–18 GHz. The complex permittivity was adjusted by changing the carbon proportions because of the superior conductivity of graphite. The minimum reflection loss (RL) value of −56 dB was obtained at 15.8 GHz with a thickness of 1.8 mm and the effective absorption bandwidth (RL ≤ −10 dB) was 5.4 GHz. Therefore, the Ni@C nanohybrids have great potential to be utilized as a high-efficiency and lightweight microwave absorber.

In-situ synthesis of carbon capsulated Ni nanoparticles and their cooperative doping effects on superconducting properties of MgB2

Carbon-encapsulated Ni nanoparticles (the average diameter of the particles is 7–8 nm) in B matrix were successfully in situ synthesized by chemical vapor deposition (CVD) in order to solve the agglomeration of nanoparticles by traditional mixing method. The influences of CVD technique on the carbon yield, morphology and structure were well investigated based on model system, and the (MgB2)0.96Ni0.04 bulks containing 3.8, 8.2 and 8.5 wt% carbon were prepared at 750 °C. The X-ray diffraction patterns showed no substitution of Ni for Mg and less substitution of C for B during the synthesis process, whereas the TEM analysis suggested such decorated insertions with core-shell structure were stable within the MgB2 matrix and hopefully acted as pinning center due to the small size. In our experiment, although the advantage of nanoparticles was suppressed by the large amount of MgO impurities during the deposition process, a small enhancement of Jc was observed in the low field range, which indicated improved grain connectivity because of the refinement of MgB2 grains by inducing homogeneous nanoparticles. In view of this, a desirable Jc performance at high field could be further obtained under the control of MgO content.

Synthesis and Characterization of Carbon-Encapsulated Nickel Nanoparticles from De-Oiled Asphalt

Carbon-encapsulated Ni nanoparticles with the size of 5 to 30 nm were synthesized from de-oiled asphalt (DOA) by heat-treatment at 1800 °C with nickel powder. The nanoparticles exhibited well-constructed core-shell structures, with Ni cores and graphitic shells. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) examinations confirmed that the carbon-encapsulated Ni nanoparticles were uniformly dispersed in carbon matrix and the Ni nanoparticles were surrounded by several carbon layers with well ordered arrangement. The formation of the core-shell nanoparticles was selectively controlled by adjusting the ratio of de-oiled asphalt to nickel powders. The possible growth model for the carbon-encapsulated Ni nanoparticles was discussed briefly. This result presents a simple and controllable way to synthesize carbon-encapsulated nickel nanoparticles.

Surface characteristics of Ni catalystic films on growth behavior of multi-walled carbon nanotubes

The effect of the surface characteristics of Ni catalyst films on the growth behavior of multi-walled carbon nanotubes (MWCNTs) were investigated using Ni catalyst films prepared by different physical vapor deposition methods, electron-beam evaporation and sputtering. The growth behavior of MWCNTs was dependent upon the surface roughness of the Ni films. After a pretreatment process with NH 3, the root mean squares of surface roughness of e-beam evaporated and sputtered Ni catalyst films increased to 16.6 and 3.2 nm, respectively. Curled-MWCNTs and carbon-encapsulated Ni nanoparticles were formed on the Ni film deposited by e-beam evaporation while vertically aligned-MWCNTs were grown on the sputter-deposited film. In addition, the surface roughness of the Ni films affected the field emission properties of the MWCNTs. This was considered to originate from the specific growth behavior of the MWCNTs which was primarily caused by the initial surface roughness of the Ni films.

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 H 2O 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.

Scalable Production of Carbon Encapsulated Ni Nanoparticles by Water Arc Discharge: Structural and Magnetic Properties

An electric arc discharge in de-ionised water between a solid graphite cathode and an anode made by compressing Ni and C containing powders in a mass ratio of Ni:C = 7:3 was used here to prepare carbon encapsulated Ni nanoparticles in the form of powder suspended in water. The morphology of the produced material was analysed using high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The magnetic properties of the samples were determined using a Princeton vibrating sample magnetometer (VSM). Collection of the powder produced from different depths in the water container has proved to be an effective method for obtaining samples with narrow particle size distribution. Further material purification by dry NH4 plasma etching was used to remove the amorphous carbon content of the samples. XRD and HRTEM analysis showed that the material synthesized is fcc Ni particles with mean particle size ranging from 14 to 30 nm encapsulated in 2 to 5 graphitic cages. The data suggests that the process reported has the ability to mass-produce carbon encapsulated ferromagnetic nanoparticles with desired particle size distribution, and hence with controlled size-dependent magnetic properties.

Microstructure characterization and magnetic properties of nanomaterials

The microstructure and superparamagnetic properties of two systems of magnetic nano-particles are reviewed. A new type of magnetic core-shell Ni—Ce nanocomposite particle (15–50 nm) has been prepared. Typical HREM images and FFT patterns of HREM images showed that many planar defects (nanotwins and stacking faults) exist in the large Ni core zone (10–45 nm). The shell layers (3–5 nm) consist of an innermost Ni—Ce alloy and an outermost NiO oxide. FFT patterns from different regions of typical HREM images show well defined spots characteristic of core-shell nanocomposite materials. Magnetization measurements as a function of magnetic field and temperature showed that superparamagnetic behaviour is exhibited above the average block temperature (TB = 170 K). This superpara-magnetic relaxation was found to be modified by interparticle interactions that depend on the applied field and size distribution. In addition, antiferromagnetic order occurred with a Neél temperature TN of about 11 K. A spin-flip transition was observed below TN at a certain applied field. Novel carbon encapsulated Ni nanoparticles assemblies have been synthesized by modified arc-discharge under a methane atmosphere. The presence of carbon encapsulation is confirmed by HR-TEM lattice imaging, and nanodiffraction. The intimate and contiguous carbon fringe around these Ni nanoparticles is good evidence for complete encapsulation by carbon shell layers. Superparamagnetic property studies show that the blocking temperature TB is around 115K at 0.1 T applied field. Above TB, the magnetization M(H,T) can be described by the classical Langevin function L using the relation M/Ms(T = 0) = coth (μH/kT) — kT/μH. The particle size can be inferred from the Langevin fit (particle moment μ), which is a little larger than the HR-TEM observation. It is suggested that these assemblies of carbon encapsulated Ni nanoparticles have typical single-domain, field-dependent superparamagnetic relaxation properties, and this typical superparamagnetic behaviour is consistent with the Stoner—Wohlfarth theory of single-domain particles.

Magnetic properties and microstructure of carbon encapsulated Ni nanoparticles and pure Ni nanoparticles coated with NiO layer

Two kinds of nickel nanoparticles—carbon encapsulated Ni nanoparticles Ni(C) and pure Ni nanoparticles coated with NiO layers Ni(O) are successfully prepared. Structural characterizations (HR-TEM, SAED, and XRD) reveal their distinct morphological properties. Magnetization measurements for the assemblies of two kinds of Ni nanoparticles show a larger coercivity and remanence by a deviation between the zero-field-cooled and the field-cooled magnetization below the irreversibility temperature, T irr, for the assemblies of Ni(O) particles. This deviation may be explained as a typical nanocluster–glass behavior (collective behavior) due to ferromagnetic dipole–dipole interaction effects among the assemblies of Ni(O) particles. However, Ni(C) particles exhibit modified superparamagnetic properties above the average blocking temperature of T B, which is determined to be around 115 K at 1000 Oe. Moreover, a gradual decrease in saturation magnetization is observed, which is attributed to the nanocrystalline nature of the encapsulated particles, coupled with possible carbon solution in Ni nanocrystals.

Magnetic and microstructural properties of the assembly of Ni(C) nanoparticles

Superparamagnetic properties of the assembly of carbon encapsulated Ni nanoparticles (Ni(C) nanoparticles) with an average particle size of 10.5 nm are studied, the blocking temperature (TB) is determined to around 115 K at l000 Gs applied field. Above TB, the magnetization M(H,T) can be described by the standard Langevin function L using the relation M/MS(T=0)=coth(μH/kT)−kT/μH. Magnetization measurements suggest, this assembly of carbon encapsulated Ni nanoparticles have been exhibited typical single-domain, field-dependent superparamagnetic relaxation properties.

Superparamagnetism and Microstructural Properties of Carbon Encapsulated Ni nanoparticle Assemblies

ABSTRACTCarbon encapsulated Ni nanoparticles (Ni(C)) were synthesized by modified arc-discharge reactor under methane atmosphere. The presence of carbon encapsulation is confirmed by HR-TEM imaging, and Nano-diffraction. The average particle radius is typically 10.5 nm with spherical shape. The intimate and contiguous carbon fringe around these Ni nanoparticles is good evidence for complete encapsulation by carbon shell layers.Superparamagnetic property studies were performed using SQUID magnetometer for the assemblies of Ni(C) nanoparticles. The blocking temperature (TB) is determined to around 115K at 1000Oe applied field. Above TB, the magnetization M (H, T) can be described by the classical Langevin function L using the relation, M/Ms(T=0) = coth(μH/kT)- kT/μH. The particle radius can be inferred from Langevin fit (particle moment μ) and blocking temperature theory (TB), which values are a little bigger than HR-TEM observations. It is suggested, these assemblies of carbon encapsulated Ni nanoparticles have been showed typical single-domain, field-dependent superparamagnetic relaxation properties.