Encapsulated Ni Nanoparticles Research Articles

Ultra-thin N-doped-graphene encapsulated Ni nanoparticles coupled with MoO2 nanosheets for highly efficient water splitting at large current density

Ultra-thin N-doped-graphene encapsulated Ni nanoparticles coupled with MoO2 nanosheets are prepared for HER and OER. As used for overall water splitting, it can work for 196 h at 1000 mA cm−2.

Encapsulated Ni@La2O3/SiO2 Catalyst with a One-Pot Method for the Dry Reforming of Methane

Ni nanoparticles encapsulated within La2O3 porous system (Ni@La2O3), the latter supported on SiO2 (Ni@La2O3)/SiO2), effectively inhibit carbon deposition for the dry reforming of methane. In this study, Ni@La2O3/SiO2 catalyst was prepared using a one-pot colloidal solution combustion method. Catalyst characterization demonstrates that the amorphous La2O3 layer was coated on SiO2, and small Ni nanoparticles were encapsulated within the layer of amorphous La2O3. During 50 h of dry reforming of methane at 700 °C and using a weight hourly space velocity (WHSV) of 120,000 mL gcat−1 h−1, the CH4 conversion obtained was maintained at 80%, which is near the equilibrium value, while that of impregnated Ni–La2O3/SiO2 catalyst decreased from 63% to 49%. The Ni@La2O3/SiO2 catalyst exhibited very good resistance to carbon deposition, and only 1.6 wt% carbon was formed on the Ni@La2O3/SiO2 catalyst after 50 h of reaction, far lower than that of 11.5 wt% deposited on the Ni–La2O3/SiO2 catalyst. This was mainly attributed to the encapsulated Ni nanoparticles in the amorphous La2O3 layer. In addition, after reaction at 700 °C for 80 h with a high WHSV of 600,000 mL gcat−1 h−1, the Ni@La2O3/SiO2 catalyst exhibited high CH4 conversion rate, ca. 10.10 mmol gNi−1 s−1. These findings outline a simple synthesis method to prepare supported encapsulated Ni within a metal oxide porous structure catalyst for the dry reforming of methane reaction.

Ultrasmall Rh nanoparticles decorated on carbon nanotubes with encapsulated Ni nanoparticles as excellent and pH-universal electrocatalysts for hydrogen evolution reaction

Synthesis of Rh-based material with low loading as efficient and pH-universal electrocatalyst for hydrogen evolution reaction (HER) remains challenging. Here, ultrafine and well-dispersed Rh nanoparticles (NPs) (1.92 nm in diameter) were synthesized and fixed on nitrogen (N)-doped carbon nanotubes with encapsulated nickel NPs (Rh/Ni@NCNTs) by a simple and sustainable strategy without any organic solvents, capping agents, and reducing agents. Rh/Ni@NCNTs with a low Rh loading of 2.84 wt% exhibited an outperforming catalytic activity with overpotentials of 14, 26, and 45 mV at 10 mA cm−2 in 1.0 M KOH, 1.0 M PBS, and 0.5 M H2SO4, respectively. Moreover, Rh/Ni@NCNTs displayed a high turnover frequency (TOF) of 1.67 s−1 at 100 mV in alkaline solution. The high HER performance should be attributed to the catalytically active nature of metal Rh, unique structure characteristics of Ni@NCNTs induced positive synergistic effects with the anchored Rh NPs, and metal Ni promoted N-rich feature of Rh/Ni@NCNTs. The NCNTs with ultrathin wrinkle graphitic carbon walls could efficiently wrap the as-synthesized ultrasmall Rh NPs, prohibiting their aggregations and leading to high stability and durability of Rh/Ni@NCNTs. The present study may open a new frontier for preparing high-dispersed and high-active HER catalyst.

MOFs-induced encapsulation of ultrafine Ni nanoparticles into 3D N-doped graphene-CNT frameworks as a recyclable catalyst for Cr(VI) reduction with formic acid

Recently, nitrogen-doped carbon encapsulating with transition metal hybrids has attracted extensive interests in catalysis because of its unique microstructure and promising properties. In this work, three dimensional N-doped graphene-CNT frameworks with well encapsulated ultrafine Ni nanoparticles (Ni@N-CNTs/N-G) were developed by a facile two-stage encapsulation strategy by combining Ni-MOFs with melamine as the precursor. In terms of Cr(VI) reduction by using formic acid (HCOOH) as the reductant, N-CNTs/N-G matrix not only protected the encapsulated Ni nanoparticles from poisoning or leaching in strong acid media, but also provided enhanced active sites for Cr(VI) by its rich mesopores and high N content. Among all the products obtained after thermal treatments at different temperatures, Ni@N-CNTs/N-G-800 (pyrolyzed at 800 °C) exhibited superb reduction performance with the efficiency of approximately 99.6%, ascribing to the synergistic effects including the porous 3D framework with large specific surface area, high N-doping level, and large amount of ultrafine Ni nanoparticles. More importantly, its catalytic activity and microstructure rarely changed after 10 times of recycling, suggesting that Ni@N-CNTs/N-G-800 processes excellent stability. This study provides a new strategy of synthesizing transition metal-based catalyst, which can broaden the applicability of MOF materials for heavy metal pollution cleanup.

Methanation of Carbon Dioxide over Zeolite‐Encapsulated Nickel Nanoparticles

AbstractEfficient methanation of CO2 relies on the development of more selective and stable heterogeneous catalysts. Herein, we present a simple and effective method to encapsulate Ni nanoparticles in zeolite silicalite‐1. In this method, the zeolite is modified by selective desilication, which creates intraparticle voids and mesopores that facilitate the formation of small and well‐dispersed nanoparticles upon impregnation and reduction. Transmission electron microscopy and X‐ray photoelectron spectroscopy analyses confirm that a significant part of the Ni nanoparticles are situated inside the zeolite rather than on the outer surface. The encapsulation results in increased metal dispersion and, consequently, high catalytic activity for CO2 methanation. With a gas hourly space velocity of 60 000 mL gcatalyst−1 h−1 and H2/CO2=4, the zeolite‐encapsulated Ni nanoparticles result in 60 % conversion at 450 °C, which corresponds to a site‐time yield of approximately 304 mol molNi−1 h−1. The encapsulated Ni nanoparticles show no change in activity or selectivity after 50 h of operation, although postcatalysis characterization reveals some particle migration.

Nitrogen Doped Carbon Nanosheets Coupled Nickel–Carbon Pyramid Arrays Toward Efficient Evolution of Hydrogen

The implementation of water electrolysis cells to produce hydrogen for practical usage requires highly efficient and cost‐effective electrode materials that can replace the exorbitant Pt based catalysts. Herein, the outstanding hydrogen evolution performance of a nonprecious material based electrocatalyst obtained through the pyrolysis of bilayer thin films of metal–organic framework and graphitic carbon nitride supported on a 3D Ni foam is demonstrated. The obtained electrocatalyst exhibits a pyramid structure composed of nickel and carbon, coupled with nitrogen doped carbon nanosheets on the outer layer. It requires a negligible overpotential (≈0 mV) to initiate hydrogen evolution reaction (HER) in alkaline media. The overpotentials needed to deliver current densities of 10 and 100 mA cm−2 are 8 and 28 mV, respectively. Moreover, the as‐prepared electrode also exhibits prominent stability in prolonged constant potential electrolysis of water. Density functional theory calculations reveal the active sites originated from the combination of nitrogen doped carbon nanosheets (NC) and the encapsulated Ni nanoparticles. Furthermore, the obtained hydrogen electrode is one of the most active catalysts toward HER, even comparable with the benchmarking platinum carbon catalyst. It has the potential to be fabricated and employed as the working electrode for large‐scale electrolytic generation of hydrogen from water.

Nanoreactor of Nickel-Containing Carbon-Shells as Oxygen Reduction Catalyst.

A Pt-free nanoreactor, consisting of N-doped hollow carbon nanocapsules with encapsulated Ni nanoparticles, is developed for high-performance oxygen reduction reaction (ORR) catalyst. The nanoreactor effect improves its catalytic activity for ORR mainly in a 4e- pathway. The presence of Ni nanoparticles within the nanoreactor significantly enhances the stability with a current retention of 90% after 40 h.

Highly stable Ni–Al2O3 catalyst prepared from a Ni–Al layered double hydroxide for ethanol decomposition toward hydrogen

The preparation, characterization, activity, and stability of a Ni–Al2O3 catalyst derived from reduction of a Ni–Al layered double hydroxide precursor (LDH, Ni6Al2(OH)16(CO3)0.75(OH)0.25·4H2O) are reported in this paper. In-situ X-ray adsorption spectroscopy shows that reduction of Ni from the LDH precursor to form a highly loaded 80% Ni–Al2O3 catalyst (Ni–Al2O3–LDH) is faster than reduction of a 10% impregnated Ni–Al2O3 alumina (Ni–Al2O3–I) catalyst. The reduced Ni–Al2O3–LDH catalyst exhibits highly dispersed Ni nanoparticles (3–5nm) distributed on top, partially embedded nanoparticles, and some encapsulated in the Al2O3 matrix. The nanoparticles impregnated on alumina (Ni–Al2O3–I) are larger (∼7–15nm) and appear on top of the alumina support. Conversion vs time on stream (TOS) results during ethanol decomposition at 250°C on Ni–Al2O3–LDH exhibits only a slight deactivation during 100h TOS, while the Ni–Al2O3–I catalyst shows rapid deactivation with no conversion after 2h TOS. X-ray photoelectron spectroscopy shows that the carbon content increases up to 48% after 100h TOS on the Ni–Al2O3–LDH catalyst, while a similar increase occurs after 2h TOS on the Ni–Al2O3–I catalyst. TEM shows that after 100h TOS either a thin layer of amorphous carbon or carbon nanotubes forms on Ni on top of the alumina matrix and on partially embedded Ni nanoparticles on the Ni–Al2O3–LDH catalyst. Total surface area of the Ni–Al2O3–LDH catalyst increased during TOS, which may be suplying fresh surface Ni from the encapsulated Ni nanoparticles that sustain the high activity.

Synthesis of Nickel-Encapsulated Carbon Nanocapsules and Cup-Stacked-Type Carbon Nanotubes via Nickel-Doped Fullerene Nanowhiskers

Nickel- (Ni) doped C60nanowhiskers (NWs) were synthesized by a liquid-liquid interfacial precipitation method using a C60-saturated toluene solution and isopropanol with Ni nitrate hexahydrate Ni(NO3)2·6H2O. By varying the heating temperature of Ni-doped C60NWs, two types of one-dimensional carbon nanostructures were produced. By heating the NWs at 973 and 1173 K, carbon nanocapsules (CNCs) that encapsulated Ni nanoparticles were produced. The Ni-encapsulated CNCs joined one dimensionally to form chain structures. Upon heating the NWs to 1373 K, cup-stacked-type carbon nanotubes were synthesized.

Silica Encapsulated Ni Nanoparticles: Variation of Optical and Magnetic Properties with Particle Size

Ni nanoparticles embedded in SiO2 matrix were prepared by sol-gel process. The molar percentages of Ni were varied from 2 to 20% of total SiO2 present in the matrix. Transmission electron microscope (TEM) images revealed that particle sizes varied from 8.0-15.7 nm at an annealing temperature of 773 K with variation of concentration. The optical absorption spectra revealed that the surface plasmon resonance (SPR) peak in the UV region of the spectrum shifted with the particle diameter (D) from that at 247.3 nm for D = 8.0 nm to 250.7 nm for D = 15.7 nm. In hysteresis loop measurements the magnetizations (M) of the nanocomposites also increased with higher Ni content in the matrix and did not saturate in the measuring limit of the magnetic filed (H) of 4 KOe. The anhysteric curves for different samples were analyzed with the law of approach to saturation (LAS). The zero field cooled (ZFC) and field cooled (FC) magnetization measurements at 50 Oe showed increasing broadening of the ZFC curve with the higher Ni content. To calculate the average blocking temperature ((T(B a distribution of the blocking temperatures (T(B)) was assumed to initiate theoretical fittings and it was found to be increasing with the Ni concentration in the matrix.

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.

Investigations on magnetic properties and structure for carbon encapsulated nanoparticles of Fe, Co, Ni

In the present work, experiments aim at the encapsulation of foreign materials within hollow graphitic cage have been carried out for iron group metals (Fe, Co, Ni) using a modified arc-discharge (carbon arc) reactor. HRTEM (high resolution transmission electron miscroscope), and XRD (X-ray diffractometer) studies, for three carbon encapsulated materials, showing nanoparticles of both a metallic phase (α-Fe, γ-Fe; hcp-Co, fcc-Co; fcc-Ni) and also a carbide phase (M 3C, M=Fe, Co, Ni) are encapsulated in graphitic carbon. The magnetic measurement for the three as-made nanoparticles, indicating that the values of saturation magnetic moment of three nanoparticle are 37.6, 55.5 and 15.7% of the bulk ferromagnetic elements counterparts, respectively. The different comparison values ( M r/ M s) of remanent magnetization ( M r) and saturation magnetization ( M s) suggest, the encapsulated Fe and Co nanoparticles are shown to be ferromagnetic with a ratio of remnant to saturation magnetization M r/ M s∼0.3; whereas, the encapsulated Ni nanoparticles exhibits superparamagnetic behavior at room temperature.