Synthesis Of Co Nanoparticles Research Articles

Facile Synthesis of Co Nanoparticles Embedded in N-Doped Carbon Nanotubes/Graphitic Nanosheets as Bifunctional Electrocatalysts for Electrocatalytic Water Splitting.

Developing robust and cost-effective electrocatalysts to boost hydrogen evolution reactions (HERs) and oxygen evolution reactions (OERs) is crucially important to electrocatalytic water splitting. Herein, bifunctional electrocatalysts, by coupling Co nanoparticles and N-doped carbon nanotubes/graphitic nanosheets (Co@NCNTs/NG), were successfully synthesized via facile high-temperature pyrolysis and evaluated for water splitting. The morphology and particle size of products were influenced by the precursor type of the cobalt source (cobalt oxide or cobalt nitrate). The pyrolysis product prepared using cobalt oxide as a cobalt source (Co@NCNTs/NG-1) exhibited the smaller particle size and higher specific surface area than that of the pyrolysis products prepared using cobalt nitrate as a cobalt source (Co@NCNTs/NG-2). Notably, Co@NCNTs/NG-1 displayed much lower potential -0.222 V vs. RHE for HER and 1.547 V vs. RHE for OER at the benchmark current density of 10 mA cm-2 than that of Co@NCNTs/NG-2, which indicates the higher bifunctional catalytic activities of Co@NCNTs/NG-1. The water-splitting device using Co@NCNTs/NG-1 as both an anode and cathode demonstrated a potential of 1.92 V to attain 10 mA cm-2 with outstanding stability for 100 h. This work provides a facile pyrolysis strategy to explore highly efficient and stable bifunctional electrocatalysts for water splitting.

The drastic influence of the NaBH4 reducing agent on the growth of cobalt nanoparticles and their 3D assemblies

Cobalt nanoparticles are synthesized by chemical reduction in reverse micelles using 6 different products of NaBH4 reducing agent. The nanoparticle size polydispersity strongly depends on the NaBH4 used. With the same synthetic approach, only one product yields to uniform size and shape nanoparticles. This result highlights that the NaBH4 plays a key role in the reproducibility of (1) the synthesis of Co nanoparticles characterized by a low size polydispersity, and (2) their 3D assembly. I stress that this finding can strongly affect not only the development of nanoparticles and their 3D assemblies but also our knowledge concerning the nucleation and growth mechanisms at both the atomic and nanoparticle scales, which can be biased, if we do not account this additional key parameter among all the ones involved in the colloidal synthesis.

Chemically embedding Co nanospheres in N-doped carbon nanosheets for enhanced zinc-air batteries

The next-generation oxygen electrochemical catalysts based on non-precious metals have been extensively studied for zinc-air batteries (ZABs). Among them, Co–N–C catalysts have attracted considerable attention due to their excellent oxygen catalytic performance. However, the synthesis of Co nanoparticles with uniform structure and distribution on conductive and stable substrates remains challenging. Herein, we have prepared cobalt nanoparticles chemically embedded in N-doped carbon nanosheets (Co@NCS) by a simple organic-inorganic hybrid molten salts method. Due to the multifunctional environment provided by the mixed salts, the Co@NCS can exhibit efficient oxygen reduction and evolution reaction (ORR/OER) performance, enabling them to be suitable in ZABs. The resulting ZABs has a considerable open-circuit voltage of 1.40 V, a good peak power density of 130.4 mW cm−2 and long cycle stability for 100 h at 10 mA cm−2.

Size control of cobalt nanoparticles by adjusting the linear carboxylic acid ligand chain length

Size control in the synthesis of Co nanoparticles (NPs) through thermolysis of Co2(CO)8 is achieved by adjusting the chain length of linear carboxylic acids used as ligands. As the chain length increases, steric effects reduce the reactivity of the carboxylic acids, thereby slowing the nucleation rate. In the subsequent growth phase, completing deposition of Co precursor onto fewer nuclei yields an increased NP size. Oxidation of Co NPs under ambient atmosphere causes formation of an antiferromagnetic CoO shell that can exchange couple to the Co core, resulting in exchange bias. The superparamagnetic blocking temperature (TB), coercivity (HC), and exchange shift (HEB) strongly depend on the size of the NP, and the most pronounced effects of exchange bias are observed for the smallest Co core size.

Controllable synthesis of Co nanoparticles with the assistance of cucurbit[6]uril and its efficient photoelectrochemical catalysis in water splitting on a g-C3N4 photoanode

An innovative photoanode was developed for efficient PEC water splitting by the deposition of a Co nano-catalyst on the surface of a g-C3N4 film, producing the significant photocurrent density of 393 μA cm−2 at 1.23 V vs. RHE.

Design of Co Nanoparticles‐Encapsulated by Boron and Nitrogen Co‐Doped Carbon Nanosheets as Highly Efficient Electrocatalyst for Oxygen Reduction Reaction

AbstractIn this paper, for the first time, a rationally designed strategy for synthesis of Co nanoparticles encapsulated by boron and nitrogen co‐doped carbon nanosheets (CNs), namely B, N‐Co/CNs, as highly efficient electrocatalyst for oxygen reduction reaction (ORR) is demonstrated. The generated Co nanoparticles not only create well‐defined heterointerfaces with high conductivity to overcome the poor ORR activity but also promote the formation of robust graphitic carbon. The co‐existence of boron and nitrogen atoms can increase the highest occupied molecular orbital energy of sp2 hybridization, activating π electrons in graphitic CNs, thereby enhancing the activity of the catalyst. The B, N‐Co/CNs exhibit a comparable half‐wave potential (E1/2 = 0.83 V) to that of commercial Pt/C catalyst (E1/2 = 0.85 V) with a larger current density for ORR. Importantly, the homemade disposable Zn‐air battery (ZAB) is able to deliver excellent performance, including a peak power density of 93.93 mW cm−2 and a specific capacity of 727.5 mAh g−1, outperforming the Pt/C catalyst. The findings highlight a new guideline for constructing B, N‐Co/CNs catalyst with a rationally designed structure toward superior property for advanced metal‐air cathode materials.

In-situ synthesis of Co nanoparticles encapsulated in mesoporous Co, N-codoped graphene-like carbon hybrid as an efficient oxygen reduction electrocatalyst

Rational design and construction of robust electrocatalysts towards oxygen reduction reaction (ORR) are vital for energy conversion devices. Here, we report a hierarchically engineered Co nanoparticle (NP) encapsulated in Co, N codoped graphene-like carbon sample (Co@NC) via direct pyrolyzing the mixture of glucose, dicyandiamide and cobalt salt. Benefiting from the Co-N4 moiety and high content of doped N species (8.81 at.%) which highly dispersed on the large Co NP modified carbon surface, Co@NC sample delivers remarkable ORR catalytic performance with an onset potential of 0.98 V and a half-wave potential of 0.86 V together with robust durability, which outperforms the benchmark Pt/C catalyst and most of published Co-Nx-C samples in alkali. This facile mass-producible strategy undoubtedly provides an avenue to achieve highly active and durable practical-oriented electrocatalytic catalysts for wide electrochemical energy devices.

Template-guided synthesis of Co nanoparticles embedded in hollow nitrogen doped carbon tubes as a highly efficient catalyst for rechargeable Zn-air batteries

Rational design and construction of highly efficient and durable non-noble-metal bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial to promote the widespread implementation of rechargeable Zn-air batteries. Herein, a bifunctional catalyst comprising Co nanoparticles uniformly embedded in hollow nitrogen doped carbon tubes (Co@hNCTs) is fabricated by a facile tube-directed templating strategy. In this strategy, surfactant-treated polypyrrole (PPy) nanotubes serve as the structure-guiding templates for efficient capture of Co2+, realizing the in-situ growth of zeolitic imidazolate frameworks-67 (ZIF-67) nanocrystals on PPy nanotubes. Sodium laurylsulfonate acts as anionic surfactant to endow PPy nanotubes with functional electronegative surface and strong anchoring effect toward ZIF-67, playing the pivotal role in binding of ZIF-67 nanocrystals with PPy nanotubes potently. Consequently, the developed catalyst presents a superior ORR activity with the half-wave potential of 0.87 V excellent durability with only a 7 mV loss of half-wave potential after 5000 cycles. The catalyst also exhibits superior catalytic performance for OER. When serving as an air electrode in Zn-air batteries, a large power density of 149 mW cm−2 and long-term cyclability for over 500 h are realized in ambient air, implying the great potential in practical application.

MOF-derived Co nanoparticles embedded in N,S-codoped carbon layer/MWCNTs for efficient oxygen reduction in alkaline media

The hydrothermal reaction of cobalt salt in the presence of 4-pyridyl-tetrathiafulvalene-4-pyridyl (4-py-TTF-4-py) and terephthalic acid (PTA) has been employed for the preparation of a novel metal–organic framework (MOF), i.e., (4-py-TTF-4-py)2M2(PTA)4 (M = Co2+). The obtained MOF is then used as a starting material for the synthesis of Co nanoparticles embedded in N,S-codoped carbon layer and supported on multi-walled carbon nanotubes (Co@NSC/MWCNTs) through the high-temperature calcination. Specifically, the calcination leads to the formation of N,S-codoped carbon-coated Co nanoparticles with simultaneous growth on the MWCNTs due to decomposition of the MOF. When used as the electrocatalyst, the Co@NSC/MWCNTs are found to have a higher activity for the oxygen reduction reaction (ORR) and follow a four-electron pathway. The catalytic activity of the Co@NSC/MWCNTs is much higher than that of the pure MWCNTs and the MOFs/MWCNTs. Although the Co@NSC/MWCNTs still exhibit slightly higher overpotential for the ORR, it is indeed more kinetically facile than the commercial Pt/C catalyst, as demonstrated by its higher limiting current density and lower Tafel slope. Additionally, the Co@NSC/MWCNTs also show superior stability and better tolerance to methanol crossover and CO poisoning, compared with those of the commercial Pt/C catalyst. These results strongly suggest that the Co@NSC/MWCNTs could be used as one of the most promising ORR electrocatalysts for the ORR with great potential to replace the Pt/C. The work present here opens up a new route for the design of carbon-integrated ORR electrocatalysts with high performance from a great number of available and yet rapidly growing MOFs.

Green synthesized Co nanoparticles doped amino-graphene modified electrode and its application towards determination of baicalin

The present paper reported an one-pot synthesis of Co nanoparticles doped amino-graphene nanocomposites (Co-amino-Gr), involving in situ generation of Co nanoparticles (NPs). The simultaneous reduction of graphene oxide (GO) and Co2+ to produce Co-amino-Gr had been achieved under mild reaction conditions using an environmentally benign reducing agent, glycine. By combining the merits of amino-Gr and the Co NPs, a highly sensitive electrochemical sensor was erected to detect baicalin based on the Co-amino-Gr nanocomposites. Under optimum conditions, the response peak currents were linear related with baicalin concentrations in the range of 1.0×10−8–8.0×10−7molL−1 with a lower detection limit of 5.0×10−9molL−1 (S/N=3). Additionally, the proposed method was used to detect baicalin in the medicinal capsules with satisfactory results.

Synthesis of Nanostructured Catalytic Materials from Microemulsions

Since the 1980s [1,2], colloidal systems such as microemulsions (ME) have been widely investigated, especially for the synthesis of nanomaterials for various applications.[...]

Clustering and Solvation of Cobalt Nanostructures in Dimethyl Sulfoxide

It has been reported that the molecule dimethyl sulfoxide (DMSO) can be effectively utilized as both a stabilizing ligand and a solvent during cobalt (Co) nanoparticle synthesis. Accordingly, stabilization of the nanostructures is provided by electrostatic contributions from the molecular sulfoxide components. This paper reports the synthesis of Co nanoparticles and nanoclusters (i.e., nanoparticle aggregates) of various sizes in DMSO at 25, 50, and 150 °C. This study illustrates that the size of the resulting Co nanoclusters is a direct function of the synthesis temperature. Moreover, these Co nanoclusters are composed of smaller Co nanoparticles that preferentially aggregate at increased temperatures during synthesis, where the largest nanoclusters are constructed at the highest synthesis temperatures. Furthermore, it is demonstrated that the smaller Co nanoparticles that makeup the larger Co nanoclusters can be liberated in solution upon the addition of various cosolvents.

Electron beam synthesis of 3D metal nanostructures from fluoride precursors

ABSTRACTVarious metal fluoride crystals were subjected to electron beam irradiation at 200 and 300 kV using transmission electron microscopy in order to study in-situ fabrication of 3D metal nanostructures. Lithium fluoride, cobalt fluoride and aluminum fluoride salt fragments were chemically reduced and transformed by the electron beam to the corresponding metals. Using live video recording we observe that LiF crystals decompose in a unique way different to all other metal-halides. Li diffuses rapidly out of the salt crystal and covers its surface and the surrounding C-support film to many microns distance, where at random positions nucleation, growth and annihilation of Li nanorods and some nanospheres is observable. Decomposition of CoF2 also involves non-local synthesis of Co nanoparticles, mostly facetted, however, these are stable, without annihiliation, and their positioning seems to follow some degree of self-organisation. AlF3 transforms locally to Al grains inside the irradiated area only, and grain growth occurs to sizes proportional to the beam intensity. Findings are discussed in terms of displacement energy differences between the materials.

Synthesis of Co Nanoparticles by Pulsed Laser Irradiation of Cobalt Carbonyl in Organic Solution

Interest in producing magnetic nanoparticles with controllable sizes has led to the development of new synthesis methods. In this article, we report the synthesis of sub 4 nm cobalt nanoparticles by using pulsed laser irradiation to decompose cobalt carbonyl in a solution of stabilizing ligands. The physical characteristics of the synthesized nanoparticles were determined by transmission electron microscopy, powder X-ray diffractometry, and SQUID magnometry. It was possible to control the size of the synthesized nanoparticles by varying the reaction conditions such as the ligand concentration and the wavelength of light used. The formation mechanism of the nanoparticles was also investigated by changing these conditions. It is possible that this technique could be applied to the synthesis of a variety of nanomaterials with potential applications such as biomedicine, catalysis, and water purification.

A simple aminoalkyl siloxane-mediated route to functional magnetic metal nanoparticles and magnetic nanocomposites

Magnetic nanoparticles have emerged as an important class of functional nanostructures with applications in various fields of biology and medicine. We have developed a simple synthetic route for functional Co nanoparticles which further allows their direct integration into Co@SiO2 microspheres, a synthesis that could be also applied to Fe nanoparticles. One advantage of the method described herein, compared to other methods for the synthesis of Co nanoparticles and Co@SiO2 nanocomposites, is the direct decomposition of the dicobalt octacarbonyl precursor in the presence of a silane coupling agent, therefore allowing an easy and size-controlled synthesis of siloxane-functionalized nanoparticles and the further preparation of magnetic nanocomposites. As shown by infrared spectroscopy, nanoparticle formation proceeds via an initial homonuclear disproportionation reaction. We could further show that the size of the particles can be controlled by varying the reaction parameters. The size, structure, and magnetic properties of the particles were characterized by transmission electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, Mossbauer spectroscopy, X-ray diffraction, atomic emission spectroscopy, and magnetic measurements.

Size controlled synthesis of Co nanoparticles by combination of organic solvent and surfactant

Co particles were synthesized with mean particle sizes in the range of 3.2–171.4 nm in ambient atmosphere by reduction of cobalt salt with sodium borohydride as the reducing reagent, a combination of alcohols as solvents and a triblock copolymer P123 (EO 20PO 70EO 20) as the surfactant. The particle size and its distribution were controlled by varying the synthesis parameters such as the viscosity of the medium, the amount of alcohols or P123 in the reaction system. FT-IR and X-ray photoelectron spectroscopy (XPS) measurements confirmed the interaction between the oxygen atoms of P123 and Co 2+ or Co 0. Detailed surface analyses by XPS and HRTEM revealed that the synthesized particles consisted of Co 0 metal surrounded by amorphous CoO, Co 2B and chemisorbed P123.

Synthesis of Co Nanoparticles and Their Catalytic Effect on the Decomposition of Ammonium Perchlorate

The monodispersed Co nanoparticles were successfully prepared by means of hydrogen plasma method in inert atmosphere. The particle size, specific surface area, crystal structure and morphology of the samples were characterized by transmission electron microscopy (TEM), BET equation, X-ray diffraction (XRD), and the corresponding selected area electron diffraction (SAED). The catalytic effect of Co nanoparticles on the decomposition of ammonium perchlorate (AP) was investigated by differential thermal analyzer (DTA). Compared with the thermal decomposition of pure AP, the addition of Co nanoparticles (2%-10%, by mass) decreases the decomposition temperature of AP by 145.01-155.72°C. Compared with Co 3O 4 nanoparticles and microsized Co particles, the catalytic effect of Co nanoparticles for AP is stronger. Such effect is attributed to the large specific surface area and its interaction of Co with decomposition intermediate gases. The present work provides useful information for the application of Co nanoparticles in the AP-based propellant.

Synthesis and characterization of magnetic Co nanoparticles: A comparison study of three different capping surfactants

This paper compares the performance of three long-chain acids—oleic and elaidic (both olefinic) and stearic (aliphatic)—as a capping agent in the synthesis of magnetic Co nanoparticles. The particles were formed through thermal decomposition of dicobalt octacarbonyl in toluene in the presence of the long-chain acid, and characterized by TEM, high-resolution TEM, and SQUID measurements. Infrared spectra revealed that some of the added olefinic acid was transformed from cis- to trans-configuration (for oleic acid) or from trans- to cis- (for elaidic acid) to facilitate the formation of a densely packed monolayer on the surface of Co nanoparticles. As compared to aliphatic acids, olefinic acids are advantageous for dense packing on small particles with high surface curvatures due to a bent shape of the cis-isomer. The presence of an olefinic acid is able to control particle growth, stabilize the colloidal suspension, and prevent the final product from oxidation by air. Our results indicate that oleic acid, elaidic acid, and a mixture of oleic/stearic acids or elaidic/stearic acids have roughly the same performance in serving as a capping agent for the synthesis of Co nanoparticles with a spherical shape and narrow size distribution.

The wet chemical synthesis of Co nanoparticles in a microreactor system: A time-resolved investigation by X-ray absorption spectroscopy

In this paper, we report the first results from an in situ XANES experiment using a microreactor system for the wet chemical synthesis of Co nanoparticles. In this system, time resolution (in the order of milliseconds) is obtained by spatial resolution, i.e. by measuring spectra at various points along the microreactor.

Synthesis of cobalt nanoparticles by ion implantation and effects of postimplantation annealing

A study of the synthesis of Co nanoparticles by ion implantation and the effects of postimplantation annealing was carried out. Silica was implanted with 35keV Co+ ion beams to doses ranging from 8×1015to1×1017atoms∕cm2. Nanoparticle size, distribution, and structure were ascertained via transmission electron microscopy measurements, which reveal the presence of spherical nanoparticles in both as-implanted and annealed samples. X-ray photoelectron spectroscopy show the chemical state of the nanoparticles in both as-implanted and annealed samples to be metallic. Temperature-dependent field-cooled and zero-field-cooled, susceptibility measurements indicated superparamagnetic behavior, which is analyzed by accounting for the size dispersion of the nanoparticles. Results showed that the magnetic properties of the specimen can be tailored by implantation conditions. Annealing in vacuum at 900°C for up to 10h leads to an increase of the average nanoparticle size and a broader size distribution. Mie scattering and magnetic force microscopy measurements provide evidence of a strong interaction among the nanoparticles in the annealed samples. The feasibility of obtaining small-dispersion size-controlled synthesis of Co nanoparticles at room temperature is illustrated.