Synthesized Cobalt Nanoparticles Research Articles

An Assessment of the In Vitro Antioxidant Activity of Cobalt Nanoparticles Synthesized From Millettia pinnata, Butea monosperma, and Madhuca indica Extracts: A Comparative Study.

Objective This study aimed to synthesize cobalt nanoparticles (CoNPs) via the green synthesis method using Millettia pinnata(M. pinnata), leaf (MPL), Butea monosperma(B. monosperma)flower (BMF), and Madhuca indica(M. indica)flower (MIF) as eco-friendly reducing agents. It further aimed to compare the effectiveness of these plant extracts in CoNPs production and evaluate the antioxidant activities of the synthesized nanoparticles (NPs), establishing a link between the phytochemical constituents of the extracts and the antioxidant capacity of CoNPs for potential applications in drug development and environmental sustainability. Materials and methods CoNPs were synthesized using aqueous extracts of MPL, BMF, and MIF. These extracts act as stabilizing and self-reducing agents. Initially, the presence of CoNPs was detected visually by observing a color change. To confirm this observation, UV-visible spectroscopy and Fourier transform infrared (FTIR) spectroscopy were employed. UV-visible spectroscopy helps in analyzing the absorption of light by the CoNPs, while FTIR spectroscopy is used to identify the functional groups present in the NPs. Subsequently, the antioxidant activity of the synthesized CoNPs was assessed using the 1,1-diphenyl-2-picryl hydroxyl (DPPH) radical-scavenging assay. This assay measures the ability of antioxidants to neutralize free radicals by determining the reduction in the DPPH radical's absorption. To ensure the reliability of the results, the experiments were conducted in triplicate. Statistical analysis was then performedto compare the antioxidant effectiveness of the different plant extracts used in synthesizing the CoNPs. This analysis helps in determining any significant differences in antioxidant activity among the extracts. Results UV-visible spectral analysis confirmed the successful synthesis of CoNPs, revealing characteristic absorption peaks. For M. pinnata leaf extract (MPLE), the maximum peak was observed at ~272 nm, while B. monosperma flower extract (BMFE) exhibited a peak at ~276 nm, and M. indica flower extract (MIFE) revealed a maximum peak at ~320 nm. FTIR analysis further validated the presence of organic molecules from plant components on the outer layer of CoNPs, indicating successful capping and stabilization by phytochemicals from the extracts. The spectra displayed various peaks at different wavenumbers: MPLE showed prominent peaks at 3335 cm-1, BMFE showed distinct peaks at 3314 cm-1, and MIFE exhibited significant peaks at 3261 cm-1. Among the three types of CoNPs tested, those synthesized using MIFEexhibited the highest inhibition of 87.67% at a concentration of 60 µL. This higher inhibition was compared to those synthesized using BMFEand MPLE. This study suggests that the CoNPs synthesized on MIFEcan serve as an antioxidant agent because of their remarkable free radical-scavenging activity. Conclusions The study highlights the potential of CoNPs synthesized using MIFE as they exhibited superior antioxidant activity compared to those synthesized with BMFE and MPLE. Therefore, the study underscoresthe promise of MIFE as a valuable natural resource for producing CoNPs abundant in antioxidants. Furthermore, it emphasizes the importance of implementing environmentallyfriendly synthesis techniques to produce nanomaterials that are both safe for the environment and biologically effective.

Green synthesized cobalt nanoparticles from Trianthema portulacastrum L. as a novel antimicrobials and antioxidants

Trianthema portulacastrum is a dietary and medicinal plant that has gained substantial importance due to its pharmacological properties. This plant was used for its various healing properties since the ancient period in ayurvedic system of medicine. The green synthesis technique is an eco-friendly as well as cost effective technique which can produce more biocompatible nanoparticles when compared with those fabricated by physio-chemical methods. Therefore, nanoparticles produced by green synthesis are credible alternatives to those which are produced by conventional synthesis techniques. This research mainly aims to produce nanoparticles with the methanolic leaf extract of T. portulacastrum. The optimized nanoparticles were further analyzed for anti-fungal, anti-bacterial and antioxidant properties. Disk diffusion assay was used for the determination of the antimicrobial property and on the other hand, DPPH radical scavenging assay as well as hydrogen peroxide scavenging activity proved the antioxidant property of the formulation. The study revealed that Escherichia coli (gram negative strain) shows greater zone of inhibition when compared with Bacillus subtilis (gram positive bacteria). The nanoparticles have also been reported to show significant anti-fungal activity against the strains of Aspergillus niger and Fusarium oxysporum which proves its desirability for its further use against both bacterial as well as fungal infections. The novel formulation can be explored dually as antimicrobial and antioxidant agent.

Solid-State Synthesis of Cobalt/NCS Electrocatalyst for Oxygen Reduction Reaction in Dual Chamber Microbial Fuel Cells.

Due to the high cost of presently utilized Pt/C catalysts, a quick and sustainable synthesis of electrocatalysts made of cost-effective and earth-abundant metals is urgently needed. In this work, we demonstrated a mechanochemically synthesized cobalt nanoparticles supported on N and S doped carbons derived from a solid-state-reaction between zinc acetate and 2-amino thiazole as metal, organic ligand in presence of cobalt (Co) metal ions ZnxCox(C3H4N2S). Pyrolysis of the ZnxCox(C3H4N2S) produced, Co/NSC catalyst in which Co nanoparticles are evenly distributed on the nitrogen and sulfur doped carbon support. The Co/NSC catalyst have been characterized with various physical and electrochemical characterization techniques. The Co content in the ZnxCox(C3H4N2S) is carefully adjusted by varying the Co content and the optimized Co/NSC-3 catalyst is subjected to the oxygen reduction reaction in 0.1 M HClO4 electrolyte. The optimized Co/NSC-3 catalyst reveals acceptable ORR activity with the half-wave potential of ~0.63 V vs. RHE in acidic electrolytes. In addition, the Co/NSC-3 catalyst showed excellent stability with no loss in the ORR activity after 10,000 potential cycles. When applied as cathode catalysts in dual chamber microbial fuel cells, the Co/NCS catalyst delivered satisfactory volumetric power density in comparison with Pt/C.

Green Synthesis, Characterization and Antibacterial Activity of Cobalt Nanoparticles from Parkia biglobosa Aqueous Stem Extract

In this research article, Cobalt nanoparticles were green synthesized, Characterized and applied in antimicrobial study of some selected pathogens. The formation of cobalt nanoparticles was confirmed by first, its colour change from light brown to dark brown within 10 minutes. From the UV-Vis spectral analysis, it was observed that highest absorption peak appeared at 400nm reflecting the surface Plasmon resonance of Cobalt NPs from Parkia biglobosa stem which is characteristic of Cobalt Nanoparticles. From the FT-IR studies, the absorption peaks were seen at 3787.71 cm-1, 3660.31 cm-1, 3436.44 cm-1, 1638.75 cm-1, 1384.50 cm-1, 1090.80 cm-1and 798 cm-1. Investigation revealed a medium sharp peak absorption at 1090.80 cm-1which may be attributed to the stretching of aliphatic hydrocarbon (C–H). A peak at 1384.50 cm-1corresponds to C=C stretching while the absorption bands at 1638.75 cm-1and 3436.44 cm-1may be assigned to N-H and O-H stretching vibration modes respectively. Similarly, peaks were seen at 3787.71 cm-1 and 3660.31 cm-1 corresponding to O-H belonging to water and alcohol respectively. Furthermore, the very strong band at 798 cm-1emanates from C-O-C symmetric stretching and C-O-H bending vibrations of protein in the Cobalt nanoparticles. The surface morphology of the bio fabricated Cobalt nanoparticles, has revealed by SEM image, is spherical in shape having smooth surface and well dispersed with close compact arrangement. From the microbial study carried out, the surfaces of the cobalt nanoparticles might have interacted directly with the bacterial outer membrane, causing the membrane to rupture thereby killing the microbes. The antibacterial activity demonstrated by the cobalt nanoparticles in this study could be attributed to their small size and high surface to volume ratio, which therefore enables them to interact closely with bacterial membranes. From the minimum inhibitory concentration (MIC) study conducted, it showed clearly that the green synthesized cobalt nanoparticles inhibited the growth of the pathogens investigated.

Potential application of in-situ synthesized cobalt nanoparticles on chitosan-coated cotton cloth substrate as catalyst for the reduction of pollutants

In current study, nanostructured cobalt particles were supported over chitosan coated cotton cloth (Co/CH-CC) and used for the reduction of congo red (CR) dye which is carcinogenic in nature and a toxic nitroaromatic 2-nitrophenol (2-NP). Cobalt nanoparticles were in-situ synthesized after the metal ions loading by a CH-CC and followed by reduction with sodium borohydride (NaBH 4) which is a strong reducing agent. The formation of cobalt nanoparticles has been assessed by SEM and EDX. The size of cobalt nanoparticles was found to be 90 ± 22 nm. The Crystallinity of cotton cloth (CC), chitosan coated cotton cloth (CH-CC) and Co/CH-CC confirmed by using XRD technique. The reductions of the CR and 2-NP were analysed using sodium borohydride as reducing agent and Co/CH-CC as a catalyst. The results showed that cobalt nanoparticles are excellent catalyst for reduction of hazardous dyes as ∼96% of CR dye was degraded in 21 min, which was confirmed by analysing its absorption peak using UV–Vis spectrophotometer. The reduction reactions of CR dye and 2-NP followed the first order kinetics, and the rate constants were found to be 0.1099 min−1 and 01437 min−1, respectively. The results in this study indicate a good catalytic potential of the Co/CH-CC for other similar reactions.

Physicochemical and mechanical properties of electrospun polyurethane composite patch integrated with green synthesized cobalt nanoparticles for cardiac applications

Cardiac patches are used to recover the damaged cardiac tissues. In this research, cardiac patch was fabricated using electrospinning method and evaluated for its physicochemical properties. The patch was made from polyurethane (PU) added with cobalt nanoparticles (CoNPs) which is synthesized through green route via green tea containing polyphenols. The 0.5 mg/mL, 1.0 mg/mL and 1.5 mg/mL cobalt salt concentrations mixed with green tea solution produced different nanoparticles morphology. Further, synthesized CoNPs with cobalt salt concentration of 1.5 mg/mL was incorporated in the PU using electrospinning method. The developed patches with higher CoNPs ratio exhibited smaller diameter compared to PU as observed using SEM. PU- CoNPs patch rendered hydrophilic surface with lower ratio of CoNPs. On the other hand, higher ratio of CoNPs exhibited enhanced strength compared to the pristine PU. Patches with the improved physicochemical properties and mechanical strength can be exploited for cardiac applications.

Fast and efficient removal of Pb(II) ion and malachite green dye from wastewater by using magnetic activated carbon-cobalt nanoparticles.

A high-surface-area and inexpensive activated carbon has been produced from lemon peel using chemical activation with H3PO4 at 500 °C in a N2 atmosphere. Afterwards, the synthesized cobalt nanoparticles using coprecipitation method were adsorbed on the activated carbon surface, and as a result magnetic activated carbon was obtained. Sample characterization has been assessed via X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption-desorption and magnetic properties. It was found that magnetic activated carbon-cobalt nanoparticles (MAC/Co) synthesized had a high saturation magnetization. The MAC/Co revealed super-paramagnetic behaviors at room temperature, and have been readily isolated from solution by using an exterior magnet. Next, adsorption behavior of malachite green and Pb(II) onto the generated MAC/Co has been examined. Sorption kinetics and equilibrium have been studied using batch procedure. The kinetic and isothermal adsorption results were matched completely with the Elovich and Langmuir models, respectively. Based on the Langmuir model, the highest adsorption capacities of malachite green dye and Pb(II) ion respectively were 263.2 and 312.5 mg g-1 at room temperature. Based on the results, the MAC/Co is a probable economic and effective adsorbent that can be employed as a new adsorbent to remove malachite green dye and Pb(II) from wastewater.

Cobalt Nanoparticles on Plasma-Controlled Nitrogen-Doped Carbon as High-Performance ORR Electrocatalyst for Primary Zn-Air Battery.

Metal–air batteries and fuel cells have attracted much attention as powerful candidates for a renewable energy conversion system for the last few decades. However, the high cost and low durability of platinum-based catalysts used to enhance sluggish oxygen reduction reaction (ORR) at air electrodes prevents its wide application to industry. In this work, we applied a plasma process to synthesize cobalt nanoparticles catalysts on nitrogen-doped carbon support with controllable quaternary-N and amino-N structure. In the electrochemical test, the quaternary-N and amino-N-doped carbon (Q-A)/Co catalyst with dominant quaternary-N and amino-N showed the best onset potential (0.87 V vs. RHE) and highest limiting current density (−6.39 mA/cm2). Moreover, Q-A/Co was employed as the air catalyst of a primary zinc–air battery with comparable peak power density to a commercial 20 wt.% Pt/C catalyst with the same loading, as well as a stable galvanostatic discharge at −20 mA/cm2 for over 30,000 s. With this result, we proposed the synergetic effect of transitional metal nanoparticles with controllable nitrogen-bonding can improve the catalytic activity of the catalyst, which provides a new strategy to develop a Pt-free ORR electrocatalyst.

Synthesis of Eco-friendly Cobalt Nanoparticles Using Celosia argentea Plant Extract and Their Efficacy Studies as Antioxidant, Antibacterial, Hemolytic and Catalytical Agent

The aim of the present study was to synthesize safe and economical cobalt nanoparticles by using secondary metabolites from Celosia argentea plant extract and to further evaluate their antioxidant, antibacterial and hemolytic activities. Catalytic activity of these green synthesized nanoparticles was evaluated for the degradation studies of cationic methylene dye in the presence and absence of anionic surfactant (sodium dodecyl sulfate). Different parameters affecting the dye degradation procedure were investigated and optimized. Fourier transform infrared spectroscopy studies identified the functional groups present in bioactive compounds which were responsible for the reduction and stabilization of the cobalt nanoparticles. The green synthesized cobalt nanoparticles were characterized by X-ray diffraction, scanning electron microscope and energy-dispersive X-ray spectroscopy. Cobalt nanoparticles (CoNPs) exhibited good antioxidant activity against 2,2-diphenyl-1-picrylhydrazyl radical, and its scavenging power was found to be increased with increasing concentration. CoNPs also displayed good antimicrobial activity against tested microbes. Moreover, they showed very less toxicity and efficient activity toward dye degradation.

Green Fabrication of Cobalt NPs using Aqueous Extract of Antioxidant Rich Zingiber and Their Catalytic Applications for the Synthesis of Pyrano[2,3-c]pyrazoles.

In this study, biological synthesis of cobalt nanoparticles was developed in the presence of ginger extract as the reducing and capping agent through the simple and convenient co-precipitation method. The as-synthesized cobalt nanoparticles were characterized by X-ray diffraction (XRD), scanning Electron Microscopy (SEM), spectra energy dispersive analysis of Xray (EDS), Fourier transform infrared (FT-IR), and vibrating sample magnetometer (VSM) techniques. According to the vibrating sample magnetometer, cobalt nanoparticles show paramagnetic behaviour at room temperature. Furthermore, the effect of ginger extract concentration on the UV-Vis absorbance of Co nanoparticles was investigated. Based on the UVVis absorbance spectra, increasing ginger extract concentration causes particle size to decrease. In addition, the catalytic performance of the synthesized cobalt nanoparticles was investigated in the preparation of pyrano[2,3-c]pyrazoles via one-pot four-component reactions of aryl aldehydes, hydrazine hydrate, malononitrile and diethyl acetylenedicarboxylate. The prepared pyrano[2,3-c]pyrazole derivatives were obtained in high yields within short reaction times and the nanocatalyst was easily separated using an external magnet and reused for several times with no significant loss of its activity.

Effects of Functionalization of Carbon Nanotubes on Activity and Selectivity of Co/CNT Catalysts in Fischer-Tropsch Synthesis

The Fischer–Tropsch Synthesis (FTS) activities of cobalt-based catalysts supported on carbon nanotubes (CNTs) and functionalized carbon nanotubes (FCNTs) are investigated in this work. The cobalt-based catalysts are synthesized by the reverse micro-emulsion technique using a non-ionic surfactant, and characterized by the Brunauer-Emmett-Teller, X-ray diffraction, H2 chemisorption, temperature program reduction, and transmission electron microscopy techniques. The activities of the synthesized catalysts are evaluated in terms of the FTS production rate (g produced hydrocarbons /g.cat./h) and selectivity (percentage of the CO converted to hydrocarbon products). According to the TEM results, the synthesized cobalt nanoparticles have a narrow size distribution and are mostly confined inside the functionalized CNTs (FCNTs) . These nanoparticles are highly reducible as evidenced by the reduction peaks of the FCNT catalyst shifting to low temperatures. In comparison to non-functionalized CNT, FCNT increases the FTS rate and CH4 selectivity and decreases the C5+ selectivity as a catalytic support. In addition, the FCNT support preserves the high dispersion and reducibility of cobalt, which can be attributed to the hydrogen spill-over effect of the functional groups present on the CNT surface.

Co Nanoparticles Confined in 3D Nitrogen-Doped Porous Carbon Foams as Bifunctional Electrocatalysts for Long-Life Rechargeable Zn-Air Batteries.

Proper design and simple preparation of nonnoble bifunctional electrocatalysts with high cost performance and strong durability for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is highly demanded but still full of enormous challenges. In this work, a spontaneous gas-foaming strategy is presented to synthesize cobalt nanoparticles confined in 3D nitrogen-doped porous carbon foams (CoNCF) by simply carbonizing the mixture of citric acid, NH4 Cl, and Co(NO3 )2 ·6H2 O. Thanks to its particular 3D porous foam architecture, ultrahigh specific surface area (1641 m2 g-1 ), and homogeneous distribution of active sites (C-N, Co-Nx , and Co-O moieties), the optimized CoNCF-1000-80 (carbonized at 1000 °C, containing 80 mg Co(NO3 )2 ·6H2 O in precursors) catalyst exhibits a remarkable bifunctional activity and long-term durability toward both ORR and OER. Its bifunctional activity parameter (ΔE) is as low as 0.84 V, which is much smaller than that of noble metal catalyst and comparable to state-of-the-art bifunctional catalysts. When worked as an air electrode catalyst in rechargeable Zn-air batteries, a high energy density (797 Wh kg-1 ), a low charge/discharge voltage gap (0.75 V), and a long-term cycle stability (over 166 h) are achieved at 10 mA cm-2 .

Green Synthesized Cobalt Nano Particles for using as a Good Candidate for Sensing Organic Compounds

Green Synthesized Cobalt Nano Particles for using as a Good Candidate for Sensing Organic Compounds

Green Synthesized Cobalt Nano Particles for using as a Good Candidate for Sensing Organic Compounds

Green Synthesized Cobalt Nano Particles for using as a Good Candidate for Sensing Organic Compounds

Mechanochemical Preparation of Cobalt Nanoparticles through a Novel Intramolecular Reaction in Cobalt(II) Complexes

A novel solid state reaction involving a series of cobalt(II) hydrazine-azides has been used to prepare metallic cobalt nanoparticles. The reactions of [Co(N2H4)(N3)2], [Co(N2H4)2(N3)2], and [Co(N2H4)(N3)Cl]·H2O via NaOH, KOH as reactants were carried out in the solid state. These complexes undergo an intramolecular two-electron oxidation-reduction reaction at room temperature, producing metallic cobalt nanoparticles (Co1–Co6). The aforementioned complexes contain cobalt(II) that is an oxidizing agent and also hydrazine ligand as a reducing agent. Other products produced include sodium azide and ammonia gas. The cobalt metal nanoparticles were characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The synthesized cobalt nanoparticles have similar morphologies; however, their particle size distributions are different.

Cobalt(III) ammine complexes as precursors in the synthesis of cobalt nanoparticles

Cobalt nanoparticles have been prepared by the chemical reduction of [Co(NH3)6]Cl3, [Co(NH3)5Cl]Cl2, and [Co(NH3)5ONO]Cl2 in alcoholic solution. The reaction of these complexes with hydrazine as a reducing agent were carried out at 70 °C and pH = 10–12. The metallic nanoparticles were characterized by using X-ray powder diffraction, IR spectroscopy, scanning electron microscopy, and vibrating sample magnetometer. The synthesized cobalt nanoparticles have different morphologies and nanosheet distributions. The Co1 has a sheet thickness ranging from 15 to 40 nm and shows an aggregated dendrite structure. On the other hand, Co2 has a cactus like morphology with a nanosheet thickness ranging from 15 to 35 nm. The Co3 nanoparticles were pompon-like microspheres in shape and aggregated powders with a nanosheet thickness ranging from 10 to 45 nm. This work presents a novel approach for the preparation of metallic nanoparticles via metal complexes.

Eco-friendly microbial route to synthesize cobalt nanoparticles using Bacillus thuringiensis against malaria and dengue vectors

The developments of resistance and persistence to chemical insecticides and concerns about the non-target effects have prompted the development of eco-friendly mosquito control agents. The aim of this study was to investigate the larvicidal activities of synthesized cobalt nanoparticles (Co NPs) using bio control agent, Bacillus thuringiensis against malaria vector, Anopheles subpictus and dengue vector, Aedes aegypti (Diptera: Culicidae). The synthesized Co NPs were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Field-emission scanning electron microscopy (FESEM) with energy dispersive X-ray spectroscopy, and Transmission electron microscopy (TEM). XRD analysis showed three distinct diffraction peaks at 27.03°, 31.00°, and 45.58° indexed to the planes 102, 122, and 024, respectively on the face-centered cubic cobalt acetate with an average size of 85.3nm. FTIR spectra implicated role of the peak at 3,436cm(-1) for O-H hydroxyl group, 2924cm(-1) for methylene C-H stretch in the formation of Co NPs. FESEM analysis showed the topological and morphological appearance of NPs which were found to be spherical and oval in shape. TEM analysis showed polydispersed and clustered NPs with an average size of 84.81nm. The maximum larvicidal mortality was observed in the cobalt acetate solution, B. thuringiensis formulation, and synthesized Co NPs against fourth instar larvae of A. subpictus and A. aegypti with LC50 values of 29.16, 8.12, 3.59mg/L; 34.61, 6.94, and 2.87mg/L; r (2) values of 0.986, 0.933, 0.942; 0.962, 0.957, and 0.922, respectively.

Synthesis of Cobalt Nano Particles on Silica Support Using the Strong Electrostatic Adsorption (SEA) Method

Supported cobalt is one of the common catalysts used in Fischer-Tropsch synthesis (FTS). Strong electrostatic adsorption (SEA) was employed to synthesize cobalt nano particles supported on silica. Cobalt nitrate was used as the catalyst precursor and non-porous silica spheres, which were synthesized using the modified Stöber method, were used as a catalyst support. Point of zero charge (PZC) for silica was determined using equilibrium pH at high oxide loading (EpHL) method. The optimum pH was determined by measuring cobalt uptake versus pH. High cobalt uptake at basic pH and low cobalt uptake at acidic pH indicates electrostatic interaction between the cobalt complexes in the precursor solution and the hydroxyl group on the support’s surface. Catalysts prepared at optimum pH were characterized using TPR, XPS and TEM. TPR shows reduction peak at high temperature (587°C) indicating strong interaction between cobalt and silica support. XPS shows presence of Co2+ species on the surface. TEM images of the Co/SiO2 at 5 wt% and 10 wt% cobalt loadings show fairly well-dispersed cobalt oxide nano particles on the spherical silica support with narrow particle size distribution. The findings suggest that SEA was deemed a suitable method to prepare supported cobalt catalysts.

Effect ofAr+andH+etching on the magnetic properties ofCo∕CoOcore-shell nanoparticles

The ex situ preparation of chemically synthesized cobalt nanoparticles leads unavoidably to particles coated with organic surfactants and a thin CoO shell. Argon ion $({\mathrm{Ar}}^{+})$ etching is a method often used to remove the surfactant and the oxide shell. Ex situ prepared nanoparticles of $9.7\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ diameters were investigated as a function of the sputtering time, by means of soft x-ray absorption spectroscopy at the C and O K edges and at the Co ${\mathrm{L}}_{2,3}$ edges. Low-energy $(500\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ ${\mathrm{Ar}}^{+}$ ion etching was effective in removing the organic coating layer of the nanoparticles, while much higher energy and longer sputtering times were required to affect the CoO shell. On the other hand, only a short time using low-energy hydrogen ion $({\mathrm{H}}^{+})$ etching was necessary to completely reduce the oxide shell. Magnetic circular dichroism of soft x-rays was used to measure the magnetic properties of the etched samples. We found that the orbital to spin magnetic moment ratio, ${\ensuremath{\mu}}_{l}∕\ensuremath{\mu}_{s}{}^{\mathrm{eff}}$, increases as a function of the ${\mathrm{Ar}}^{+}$ etching time. Such an increase may be ascribed to the incomplete removal of the CoO shell as well as to surface strain, increased roughness, and an effective reduction of the particle size induced by the high-energy ion etching. A much smaller effect was observed for the low-energy $(500\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ and short time ${\mathrm{H}}^{+}$ etched samples, where the magnetic moment ratio after the reducing procedure ${\ensuremath{\mu}}_{l}∕\ensuremath{\mu}_{s}{}^{\mathrm{eff}}=0.12$ is comparable to values obtained for bulk cobalt.

Synthesis of cobalt nanoparticles in polymeric membrane and their magnetic anisotropy

We systematically synthesized cobalt nanoparticles in the perfluorinated sulfo-cation membrane (MF-4SK) in aqua solution using ion-exchange method. The average radius of cobalt nanoparticles in the polymer film is determined to be 3.5±1.0 nm by TEM. FMR measurements show that the angle dependence of resonance field ( H r ) follows the characteristics of flat-plate magnetic film and the easy axis lies along the surface of the polymer film. The experimental results suggest that the magnetic anisotropy comes from magnetized polymer film containing Co nanoparticles.