Nanoparticles Of Co Research Articles

High-pressure electrical resistivity and Mössbauer spectroscopic studies on narrow band Co0.8Fe0.2S2 nanoparticles up to 8 GPa

Pyrite-structured Co0.8Fe0.2S2 colloid nanoparticles, synthesized using solution method with particle distribution around 3–4 nm determined by transmission electron microscope, were studied under high pressure up to 8 GPa using 57Fe Mössbauer spectroscopy and electrical resistivity techniques. Drastic decrease in TC by magnetic measurements indicated nanosize of the particle. Higher quadrupole splitting (QS) at ambient condition was due to large lattice strain and electric field gradient generated by higher surface to volume ratio of these nanosized particles. Under pressure, Mössbauer parameters – isomer shift and QS – showed an expected trend up to ∼5.6 GPa. Above 6.4 GPa, the QS remained constant up to 8 GPa with decreased value. Even after decompression, the high-pressure phase is retained. The variation of pressure coefficient of electrical resistivity from −0.021/GPa to −0.151/GPa across 6.8 GPa suggested a second-order phase transition. The coincidence of observed value with that of the bulk suggested that the particle size does not impart much influence on transition pressure. This is the first report on nanoparticles of Co0.8Fe0.2S2 under pressure.

Synthesis and Characteristics of Superparamagnetic Co0.6Zn0.4Fe2O4 Nanoparticles by a Modified Hydrothermal Method

Nanoparticles of Co0.6Zn0.4Fe2O4, with narrow size distribution, regular morphology, and high saturation magnetization, have been synthesized. The synthesis, involved a very rapid mixing of reducible metal cations with sodium borohydride, is carried out in a colloid mill and followed by a separate hydrothermal process. The microstructure and magnetic properties of the synthesized nanoparticles are characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). The effects of different synthesis conditions (synthesis temperature and reaction time) on the characteristics of the ferrite nanoparticles are discussed. The changes in cation contribution are revealed by the Raman study. The magnetic measurements explore that all the as‐synthesized samples are superparamagnetic in nature. The corresponding superparamagnetic behavior is explained by paramagnetic Langevin theory. Note that, the superparamagnetic Co0.6Zn0.4Fe2O4 ferrite nanoparticle, with excellent performance, can be synthesized at 160°C for a short reaction time (4 h).

The impact of pre-reduction thermal history on the metal surface topology and site-catalytic activity of [formula omitted] Fischer–Tropsch catalysts

For ex-nitrate Co/SiO2 Fischer–Tropsch synthesis (FTS) catalysts, the influence of the early thermal treatments during catalyst synthesis on the ultimate catalytic properties is studied without overlapping of particle size effects (d(Co)>15nm). The bulk and surface properties of the Co3O4 crystallites in the oxidic catalyst precursors depend on the previous thermal history and are decisive for the oxide reduction kinetics. Even after a homogeneous reduction treatment (673K, H2 flow), catalysts with different pre-reduction thermal histories showed dissimilar TOF (per surface Co0 atom) under FTS conditions (493K, 2.0MPa). As revealed by CO-TPSR and CO-FTIR, the different surface-specific activitites relate to differences in the surface topology of the Co0 nanoparticles which likely result from the varying reduction kinetics. By tracking the effects of the earlier thermal treatments on the properties of the Co species, this work evidences that the pre-reduction thermal history not only determines metal dispersion and reducibility, but also the ultimate TOF. Such “memory effect” underscores the significance of a rational design of the entire synthesis and activation procedures to achieve Co-based Fischer–Tropsch catalysts with improved activity.

Structure and magnetic properties of Co–Ni–Li ferrites synthesized by citrate precursor method

Nanoparticles of Co0.5Ni0.5−2xLixFe2+xO4 with x ranging from 0.00 to 0.25 in steps of 0.05 were prepared by using citrate precursor method. The microstructure and the magnetic properties of the as-prepared nanosamples and the effect of increasing Li1+ ions on their physical properties were studied. X-ray diffraction (XRD), transmission electron microscopy (TEM), particle size analyzer (PSA), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM) were used to investigate the samples. The XRD analysis confirmed the cubic spinel phase formation of the prepared samples, while TEM images and PSA ensure the nanostructural features of them. The FTIR spectra reveal the presence of two prominent absorption bands v1 and v2 in the range of 600 and 400cm−1 which are usually attributed to the tetrahedral and octahedral complexes of the spinel lattice, respectively. The change of v2 gradually towards lower frequency and the slightly change of v1 were explained depending on the effect of increasing Li1+ content on the bond length of B-site metal ions and the spin canting of A-site metal ions, respectively. Saturation magnetization and remnant magnetization were found to increase with adding Li1+ ions up to x=0.15 and then to decrease again, while coercivity decreases monotonically by increasing Li1+ ions. The change in magnetic properties by adding Li1+ ions is explained as to be dependent on many factors such as crystallite size, measured density, porosity, expected cation distribution, A–B exchange interactions, and magnetocrystalline anisotropy.

ZrO2 Doped with Cobalt Nanoparticles to Detect UV Radiatiion

ABSTRACTThis paper reports the synthesis and characterization of the ZrO2:Co nanosystem, by incorporation of Co nanoparticles (CoNP) into tetragonal and monoclinic zirconia. ZrO2 was synthesized by a sol-gel process, while cobalt nanoparticles were obtained through a colloidal method by chemical reduction of a metal precursor. CoNP were incorporated by two different approaches: during the synthesis of the ZrO2 and by classical impregnation of CoNP on zirconium oxide. The size of Cobalt nanoparticles was controlled through the concentration of reducing agent (NaBH4) and passivanting agent (1-dodecanethiol). According to SEM and TEM analysis, the diameter of the zirconium oxide particles depends on the CoNP concentration added; the particle size for pure zirconia treated at 500°C is 200 nm and 180 nm for ZrO2:Co. X-Ray diffraction showed presence of the tetragonal and monoclinic zirconia, but the abundance of each one depends on the Co nanoparticles and thermally treatment.

Structural, electrical and magnetic properties of Co0.5Zn0.5AlxFe2−xO4 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) prepared via sol–gel route

Nanoparticles of Co0.5Zn0.5AlxFe2−xO4 (x=0, 0.2, 0.4, 0.6, 0.8 and 1.0) were synthesized by sol–gel method and the influence of Al3+ doping on the properties of Co0.5Zn0.5Fe2O4 was studied. X-ray diffraction studies revealed the formation of single phase spinel type cubical structure having space group Fd-3m. A decreasing trend of the lattice parameter was observed with increasing Al3+ concentration due to the smaller ionic radii of Al3+ ion as compared to Fe3+ ion. TEM was used to characterize the microstructure of the samples and particle size determination, which exhibited the formation of spherical nanoparticles. The particle size was found to be increases up to ∼45nm after annealing the sample at 1000°C. Electrical resistivity was found to increase with Al3+ doping, attributed to the decrease in the number of Fe2+–Fe3+ hopping. The activation energy decreased with increasing Al3+ ion concentration, indicating the blocking of conduction mechanism between Fe3+–Fe2+ ions. The value of saturation magnetization decreased, when Fe3+ ions were doped with Al3+ ions in Co0.5Zn0.5Fe2O4; however, the coercivity values increased with increasing Al3+ ion content.

Magnetization enhancement in nanocrystalline Co0.4Zn0.6Fe2O4 by 200 MeV Ag15+ ion irradiation

The effects of 200 MeV Ag15+ ion irradiation on the magnetic behavior of nano particles of Co0.4Zn0.6Fe2O4 have been studied using the field, temperature and time-dependent magnetization measurements. Rietveld profile refinement of the XRD patterns confirms the formation of a cubic spinel structure of the specimens retaining the spinel structure upon irradiation. The Ag15+ ion irradiation of the sample causes an appreciable enhancement in the saturation magnetization, coercivity, and remanent magnetization. These observations can be attributed to a slight increase in the particle size due to the heat evolved during the irradiation, cation redistribution, and irradiation-induced modifications on the surface states of the nanoparticles.

Preparation of Co/SiO2 Using Several Glycols for Enhanced Fischer-Tropsch Synthesis Activity and Dispersion of Co0 Nanoparticles with Unique Co0 Particle Size Effect

Co/SiO2 catalysts with highly dispersed Co0 and reducible Co were prepared by impregnation using an aqueous solution of Co nitrate containing ethylene glycol or its homologs. Addition of glycols enhanced FTS activity by a factor of 4. Particle size of Co0 decreased from 30 to below 6 nm, while TOF of the catalysts was independent of the Co0 particle size.

Boron Compounds as Stabilizers of a Complex Microstructure in a Co‐B‐based Catalyst for NaBH4 Hydrolysis

AbstractCo⋅B‐based materials are widely used as catalysts for hydrogen generation through sodium borohydride self‐decomposition. In the mid 1990 s, the aqueous and organic chemistry involved in Co⋅B synthesis and handling was studied. Nevertheless, the exact microstructure of these catalysts has remained unsolved. Herein we present an exhaustive study which shows a new and complete microstructural view of a Co⋅B‐based material together with the chemistry of the cobalt and boron involved. By using nanoscale‐resolution microscopy and spectroscopy techniques, we have elucidated the role of boron compounds as stabilizers in a complex microstructure, which also explains its high catalytic performance and long‐term stability. The catalyst is proposed to be made up of 1–3 nm hcp Co0 nanoparticles embedded in amorphous CoxB (x=1, 2, 3), CoxOy, Co(BO2)2, and B2O3 phases alternatively or all together. All of these amorphous phases protect the nanocrystalline metallic core from growth and oxidation.

Bismuth effect in the structural, magnetic and dielectric properties of CoZn ferrite

Nano particles of Co0.5Zn0.5BixFe(2−x)O4, with x varying from 0.0 to 0.3 in steps of 0.1 were synthesized using the chemical co-precipitation method. The powder X-Ray diffraction pattern confirms the formation of spinel phase for all prepared samples. The lattice parameters are calculated by powder X-Ray diffraction, and it is observed that the values of the lattice parameter are less than those of bulk materials. The saturation magnetization is found to decrease with the increase of concentration of Bi ion up to x = 0.2 and then increases for x = 0.3. The hysteresis loop for concentration x = 0.0, 0.1 and 0.3 shows almost zero coercivity and remanance at 300 K, implying that the samples behave as superparamagnetic at this temperature; whereas for the concentration at x = 0.2 the coercivity was found to be 32 Oe at 300 K. The dielectric measurements were carried out in the Co0.5Zn0.5BixFe(2−x)O4 system over the temperature range from 300 to 700 K as a function of frequency, from 5 to 5 MHz. The variation of dielectric constant and dielectric loss factor for the prepared samples are explained on the basis of Maxwell–Wagner interfacial polarization.

Magnetic and Mössbauer Effect Study of (Co0.5Zn0.4Cu0.1Fe2O4)(1−x)(Al2O3/PVA)x (x = 0 and 0.30) Synthesized by Sonochemical Route

Nanoparticles of Co0.5Zn0.4Cu0.1Fe2O4 were prepared by a combination of sonochemical and standard coprecipitation methods. The as-prepared samples were heat treated at four different temperatures to obtain particles of different sizes. The formation of the nanocrystalline phase has been confirmed by X-ray diffractograms (XRDs). The sizes of the nanoparticles have been estimated from the (311) peak of the XRD patterns using the Debye−Scherrer formula. The nanoparticles of some selected samples were coated with two different nonmagnetic matrices, viz., alumina (Al2O3) and poly(vinyl alcohol) (PVA). Results of high-resolution transmission electron microscopy observations of some samples are in agreement with those extracted from the XRD data. The inclusion of sonochemical technique in the coprecipitation method reduces the distribution of sizes of nanoparticles. The static magnetic properties have been measured with maximum applied field of 2 T, and the dynamic magnetic properties have also been observed at ...

Characterization of Co0.5Mn0.5Fe2O4 nanoparticles

Magnetic nanoparticles of Co0.5Mn0.5Fe2O4 have been synthesized using sol–gel combustion method in which citric acid was used as the complexing agent. The structural, thermal and magnetic properties of synthesized powder particles have been studied as a function of calcination temperature. It is observed that the coercivity attains maximum around the particle size of 32nm. The presence of functional group was identified by Fourier transform infrared (FTIR) spectroscopic studies. The saturation magnetisation values increase with the size of the particles and then coercivity of the nanoparticles varies significantly as calcination temperature increases.

Photochemical and Electrochemical Encoding of Erasable Magnetic Patterns

General patterns: A photoisomerizable nitrospiropyran monolayer associated with a gold surface enables the photolithographic patterning of the surface with nitromerocyanine domains. The selective association of Co2+ ions on the nitromerocyanine domains (red) allows the electrochemical generation of magnetic Co0 nanoparticles (NPs) on these domains. The magnetic information can be electrochemically erased and restored.

A study on carbon nanotubes prepared from catalytic decomposition of C2H2 or CH4 over the pre-reduced LaCoO3 perovskite precursor

A large amount of carbon nanotubes with uniform diameter were produced from catalytic decomposition of C2H2 or CH4 over perovskite oxide LaCoO3 catalyst precersor. The result of XRD measurement indicated that after reduction of LaCoO3 at 700 ○C cobalt existed chiefly as Co0 particles supported and separated by La2O3. La2O3 can prevent Co0 from agglomeration. The size of Co0 nanoparticles determined the diameter of carbon nanotubes. The morphologies and microscopic structure of carbon nanotubes were examined by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Raman. Reduction of LaCoO3 in H2 and thermal oxidation of carbon nanotubes in air were made by thermogravimetric experiments (TG). XPS and Raman results revealed that the carbon nanotubes made from CH4 are probably more graphitized than those made from C2H2.