Colloidal Nickel Research Articles

Dry Sol–Gel Polycondensation of Hydrosilanes to Organosilicas Catalyzed by Colloidal Nickel Nanoparticles

The dry sol-gel polycondensation at toluene in ambient air atmosphere of p-X-C6H4SiH3 (X = H, CH3, CH3O, F, Cl) to silica p-X-C6H4SiO15 in high yield, catalyzed by colloidal nickel nanoparticles in-situ generated from nickelocene(II), nickel(II) acetate, and bis(1,5-cyclooctadiene)nickel(0), is described. Similar catalytic activities were observed for the catalysts. Similarly, the dry sol-gel polyco-condensation p-X-C6H4SiH3 (X = CH3, CH3O, F, Cl):C6H4SiH3 (9:1 mole ratio) at toluene in ambient air atmosphere of was performed to yield co-silicas (p-X-C6H4SiO1.5)9(p-X-C6H4SiO1.5)1 in high yield using nickelocene. The co-gels with higher molecular weights and TGA residue yield were obtained when compared to the homogels. The highest yield, molecular weight, polydispersity index, and TGA residue yield were obtained for p-Cl-C6H4SiH3. Some degree of unreacted Si-H bonds still remained in the gel matrix because of steric bulkiness. All the insoluble gels adopt an amorphous structure with a smooth surface. A plausible mechanism for the dry sol-gel reaction was suggested.

Electrodeposition of macroporous magnetic metal films using colloidal nickel phosphate templates

Two-dimensional (2D) and three-dimensional (3D) macroporous nickel based films with randomly distributed spherical pores (diameter 90–210 nm) were synthesized by a simple templated electrodeposition route. Porous templates on Sn doped In 2O 3 (ITO) coated glass were constructed via electrophoretic deposition (EPD) of colloidal nickel phosphate particles prepared by a homogeneous precipitation method. The infilling of metal was sequently carried out in an electrodeposition bath, and porous films were obtained by dissolving the templates in ammonium sulfate solution. By adjusting the deposition charge, the thickness of the porous films could be controlled from 100 nm to tens of microns. Room temperature magnetic properties of the porous films were studied, remarkably enhanced coercivity and squareness than that of corresponding plain films were observed.

Quasi-homogeneous catalytic hydrogenation over monodisperse nickel and cobaltnanoparticles

Here, nearly monodisperse nanoparticles of nickel and cobalt with spherical morphologieswere successfully synthesized using a solvothermal process. Hydrogenation of nitrobenzenewas selected as a model reaction, and the nickel colloids exhibited excellent catalyticactivity and stability. The ferromagnetic property of the nickel nanoparticles provided aconvenient route for separating the catalyst from the reaction system in an appliedmagnetic field. The nickel colloids demonstrate the character of quasi-homogeneouscatalysts because they have the advantages of both homogeneous and heterogeneouscatalysts, such as high activity and easy separation for re-use, suggesting that they may besuitable for industrial application.

Catalytic Solid-Phase Seeding of Silicon Nanowires by Nickel Nanocrystals in Organic Solvents

Colloidal nickel (Ni) nanocrystals were used to direct the synthesis of crystalline silicon (Si) nanowires in an organic solvent. The reaction temperatures ranged from 400 degrees C to 520 degrees C with pressures from 14.3 to 23.4 MPa, conditions that are well above the critical point of the solvent. The Ni nanocrystals play two roles in the synthesis: (1) Ni catalyzes the decomposition of the silicon precursors, i.e., arylsilanes, alkylsilanes, and trisilane, to silicon; (2) Ni nanocrystals induce silicon crystallization through the solid-phase alloying of Si in the Ni seeds. We call this nanowire growth mechanism supercritical fluid-solid-solid (SFSS) synthesis.

Investigation of interference mechanism of cobalt chloride on the determination of bismuth by electrothermal atomic absorption spectrometry

The interferences of cobalt chloride on the determination of bismuth by electrothermal atomic absorption spectrometry (ETAAS) were examined using a dual cavity platform (DCP), which allows the gas-phase and condensed phase interferences to be distinguished. Effects of pyrolysis temperature, pyrolysis time, atomization temperature, heating rate in the atomization step, gas-flow rate in the pyrolysis and atomization steps, interferent mass and atomization from wall on sensitivity as well as atomization signals were studied to explain the interference mechanisms. The mechanism proposed for each experiment was verified with other subsequent sets of experiments. Finally, modifiers pipetted on the thermally treated sample+interferent mixture and pyrolyzed at different temperatures provided very useful information for the existence of volatilization losses of analyte before the atomization step. All experiments confirmed that when low pyrolysis temperatures are applied, the main interference mechanisms are the gas-phase reaction between bismuth and decomposition products of cobalt chloride in the atomization step. On the other hand, at elevated temperatures, the removal of a volatile compound formed between analyte and matrix constituents is responsible for some temperature-dependent interferences, although gas-phase interferences still continue. The experiments performed with colloidal palladium and nickel nitrate showed that the modifier behaves as both a matrix modifier and analyte modifier, possibly delaying the vaporization of either analyte or modifier or both of them.

Stable Nanoporous Metallic Nickel Colloids

Nanoporous metallic nickel colloids (∼8.3 nm, see Figure) are produced by the thermal decomposition of nickel‐doped poly(vinyl alcohol) films. A small amount of carbon remaining on the surface protects the particles against further degradation. Adsorption isotherms indicate the colloids have both mesopores and micropores.

Reactions of Aluminium Tribromide with Tetrakis(triphenylphosphine)nickel(0) and Tetrakis(triethylphosphite)nickel(0) Complexes

Reactions of aluminium tribromide with the Ni(0) phosphine and phosphite complexes are studied by EPR method. AlBr3was found to cause the oxidation of the transition metal in the (PPh3)4Ni complex to the univalent state with the formation of the tetracoordinated (PPh3)3NiBr complex. With an excess of AlBr3, the phosphine ligands are eliminated from the coordination sphere of Ni(I), and the coordinatively unsaturated complexes are destroyed to give the colloidal nickel. In the reaction of (P(OEt)3)4Ni with AlBr3, Ni(0) is also oxidized to Ni(I), but the acido ligand is not eliminated even with a 15-fold excess of the Lewis acid. The activity of catalytic systems on the basis of the Ni(0) phosphine complexes and the Lewis acids in the low-molecular oligomerization reactions of olefines is determined by the cationic coordinatively unsaturated Ni(I) complexes formed in these systems.

Stability of Dispersions of Colloidal Nickel Ferrite Spheres

The stability of suspensions of nickel ferrite spheres is investigated for different compositions of the dispersion medium, in the absence and in the presence of an external magnetic field. The time-dependence of the optical absorbance of the suspensions is the quantity used for experimentally determining the stability. Two approaches have been used for the calculation of the interaction energy of the particles: first, the classical DLVO theory, in which the net interaction is considered as the superposition of electrostatic double-layer repulsion and van der Waals attraction; and second, the so-called extended-DLVO model, in which short-range hydrophobic (hydrophilic) attractions (repulsions) are also considered. Calculation of all these interactions required the determination of (i) the diffuse double-layer potential of the ferrite particles (that was approximated by the zeta potential, as deduced from electrophoresis measurements); (ii) the Hamaker constant of the particles in aqueous media; and (iii) the acid/base components of the surface free energy of the solids. The quantities in (ii) and (iii) above were obtained from contact-angle measurements for selected liquids on layers of the magnetic oxide. When a magnetic field is applied, another interaction, of magnetic origin, has to be accounted for. It was found that the suspensions are more stable the farther their pH is from the isoelectric point, and the lower the ionic strength of the medium is, in full agreement with the predictions of both the classical and extended-DLVO models. The application of the external magnetic field was found to provoke significant changes in the rate of variation of absorbance with time: The results are coherent with an increased velocity of particle aggregation due to magnetic attractions between the magnetized colloids. The DLVO theory (in any of its versions) including magnetic interactions can explain this behavior, since the calculated force between particles is more attractive when the field is present.

Nickel nanoparticles and solids using organic solvents

Nickel colloids were prepared by codeposition of the metal with several organic solvents: acetone, ethanol, 2-propanol, 2-methoxyethanol and 1,2-dimethoxyethane at 77 K. The stabilities of the colloids and fine powders were measured. The metallic films and active solids were obtained by evaporation under vacuum at room temperature. The Ni-2-methoxyethanol colloids are stable over three months at room temperature, and the UV-VIS absorption spectra of the most stable colloids were obtained.

Size-selective electrochemical preparation of surfactant-stabilized Pd-, Ni- and Pt/Pd colloids.

A detailed study concerning the size-selective electrochemical preparation of R4N+Br- -stabilized palladium colloids is presented. Such colloids are readily accessible using a simple electrolysis cell in which the sacrificial anode is a commercially available Pd sheet, the surfactant serving as the electrolyte and stabilizer. It is shown that such parameters as solvent polarity, current density, charge flow, distance between electrodes and temperature can be used to control the size of the Pd nanoparticles in the range 1.2-5 nm. Characterization of the Pd colloids has been performed using transmission electron microscopy (TEM), small angle X-ray scattering (SAXS) and X-ray powder diffractometry (XRD) evaluated by Debye-function-analysis (DFA). Possible mechanisms of particle growth are discussed. Experiments directed towards the size-selective electrochemical fabrication of (n-C6H13)4N+Br- -stabilized nickel colloids are likewise described. Finally, a new strategy for preparing bimetallic colloids (e.g., Pt/Pd nanoparticles) electrochemically is presented, based on the use of a preformed colloid (e.g., (n-C8H17)4N+Br- -stabilized Pt particles) and a sacrificial anode (e.g., Pd sheet).

Studies on the Chemical Synthesis of Nanosized Nickel Powder and its Stability

The synthesis of nanosized nickel colloids is investigated by using nickel chloride as the precursor, hydrazine as the reducing agent and palladium as the nucleation agent. High purity nickel can be obtained when the reaction temperature is above 80°C. At a lower reaction temperature, nickel hydroxide is also present in the precipitate form. Starting concentration of nickel ion is a dominant factor in affecting colloidal sizes, while other parameters such as reaction temperature and quantity of poly(vinyl pyrrolidone) (PVP) exhibit only minor effects. Although PVP has some dispersion power, it is not capable of preventing nickel colloids from gradual agglomeration. Our study shows that the subsequent addition of poly(acrylic acid) (PAA) after synthesis can help to stabilize the nickel suspension. This stabilized suspension can then be de-stabilized by changing pH to lower than 4 and vice versa. This reversible stabilization–de-stabilization process is likely due to the behaviour of PVP–PAA complex in the aqueous solutions.

Aqueous solutions of colloidal nickel: Radiation-chemical preparation, absorption spectra, and properties

Radiation-chemical reduction of Ni2+ ions in aqueous solutions of Ni(ClO4)2 containing sodium formate or isopropyl alcohol was studied, γ-Irradiation of deaerated solutions in the presence of polyethyleneimine, polyacrylate, or polyvinyl sulfate gives stable metal sols containing spherical particles 2–4 nm in diameter. The optical absorption spectra of nickel nanoparticles exhibit a band with a maximum at 215±5 nm (e215=4.7·103 L mol−1 cm−1) and a shoulder at 350 nm. A mechanism for the radiation-chemical reduction of Ni2+ ions by hydrated electrons and organic radicals (CO2- radical anions in the case of HCOONa and Me2C·OH radicals in the case of PriOH). The redox potentials of the Ni2+/Ni0 and Ni+/Ni0 pairs (Ni0 is a nickel atom) are approximately −2.2 and −1.7 V, respectively. The nanoparticles are readily oxidized by O2, H2O2, and other oxidants. The reactions of these species with silver ions yield relatively stable nanoaggregates containing both nickel and silver in addition to silver nanoparticles.

Surface Spectroscopic Study of the Stabilization Mechanism for Shape-Selectively Synthesized Nanostructured Transition Metal Colloids

Nanoscale palladium and nickel colloids prepared in the presence of certain tetra-n-octylammonium carboxylates contain a high proportion of nonequilibrium trigonal cross section particles. Specifically, those carboxylates which bear a hydroxy function at the α-position, e.g., tetra-n-octylammonium glycolate, exert a strong influence on the shape of the metal colloids. It is shown by an in situ FTIR study of the preparation of colloidal nickel from bis(cyclooctadiene)nickel in the presence of tetra-n-octylammonium glycolate that the interaction of the α-hydroxy carboxylate with the surface of the colloidal metal particle is likely to be the morphology-determining factor in the shape-selective preparation of these metal particles.

Surface Spectroscopic Study of Carbon Monoxide Adsorption on Nanoscale Nickel Colloids Prepared from a Zerovalent Organometallic Precursor

Solutions of bis(cyclooctadiene)nickel react in the presence of polyvinylpyrrolidone in dichloromethane to give stable colloidal suspensions of nickel with a mean particle size of 20 Å (10 wt % Ni/PVP) and 30 Å (15 wt % Ni/PVP). The PVP-stabilized metal particles in organic suspension adsorb CO in both bridged and linear geometries. Spectra obtained at partial coverages of CO show a coverage dependent frequency shift, which is interpreted in terms of vibrational coupling between adsorbed CO molecules, consistent with an ordered surface for the colloidal nickel particles.

Preparation and properties of uniform amorphous and crystalline colloidal nickel sulfide

Amorphous spherical particles of nickel sulfide of 10 nm in diameter were synthesized by the controlled double-jet precipitation (CDJP) technique using nickel sulfate and sodium sulfide. Cubic crystalline particles of 200 nm were obtained by aging dispersions of amorphous particles at 80 °C for more than a week, as long as the pH was kept between 3 and 3.5. Electrokinetic mobilities of these particles are reported, as well as color properties of their dispersions in liquids and in poly(vinyl alcohol) films are described.

Epoxy and hydroxy functional polyolefin macromonomers

Methods for preparing saturated polyolefin oligomers with Si(SINGLE BOND)H, epoxy groups, and with dihydroxy groups have been developed. Anionic polymerization of butadiene, then termination of the chains with chlorodimethylsilane leads to controlled molecular weight oligomers with silane functionality, and wherein the microstructure can be tailored. Hydrogenation of these materials proceeds smoothly using colloidal nickel catalysts to yield the corresponding saturated materials, which are stable to conditions used for melt polyesterifications. Hydrosilation of allyl glycidyl ether with the Si(SINGLE BOND)H end groups produces epoxy functional oligomers, and subsequent hydrolysis of the epoxy rings yields oligomers with a dihydroxy group at one end. Melt copolymerization of the olefin macromers with 1,4-butanediol and 1,4-dimethylcyclohexanedicarboxylate in the presence of titanium isopropoxide affords poly(ester-g-olefin) graft copolymers. These copolymers are under study as model interfacial agents for polyester/polyolefin blends and as suspension agents for polyester particles in nonpolar media. © 1996 John Wiley & Sons, Inc.

Epoxy and hydroxy functional polyolefin macromonomers

Methods for preparing saturated polyolefin oligomers with Si(SINGLE BOND)H, epoxy groups, and with dihydroxy groups have been developed. Anionic polymerization of butadiene, then termination of the chains with chlorodimethylsilane leads to controlled molecular weight oligomers with silane functionality, and wherein the microstructure can be tailored. Hydrogenation of these materials proceeds smoothly using colloidal nickel catalysts to yield the corresponding saturated materials, which are stable to conditions used for melt polyesterifications. Hydrosilation of allyl glycidyl ether with the Si(SINGLE BOND)H end groups produces epoxy functional oligomers, and subsequent hydrolysis of the epoxy rings yields oligomers with a dihydroxy group at one end. Melt copolymerization of the olefin macromers with 1,4-butanediol and 1,4-dimethylcyclohexanedicarboxylate in the presence of titanium isopropoxide affords poly(ester-g-olefin) graft copolymers. These copolymers are under study as model interfacial agents for polyester/polyolefin blends and as suspension agents for polyester particles in nonpolar media. © 1996 John Wiley & Sons, Inc.

Polynuclear nickel hexacyanoferrates: monitoring of film growth and hydrated counter-cation flux/storage during redox reactions

Abstract An electrochemical quartz crystal microbalance (EQCM) was employed to monitor directly the growth of nickel(II) hexacyanoferrate(III) (NiHCNFe) films on gold substrates during electrodeposition as well as a result of sol-gel aggregation in colloidal nickel ferricyanide solutions used for modification. Frequency changes due to mass changes of the gold/crystal working electrode were correlated with cyclic voltammetric (CV) data. Evidence is also provided for the sorption of counter-cations (Li+, Na+ and K+), and associated water molecules, during redox reactions of the film. There is a strict relationship between the amount of alkali metal ions incorporated into the film during reduction, or excluded from the film during oxidation, and the frequency changes during EQCM measurements. The amount of solvent (H2O) transferred and sorbed in the NiHCNFe film reflects the degree of hydration of the investigated counter-ions. Anions also seem to participate in NiHCNFe electrochemistry, but their role is much less pronounced.

Colloidal nickel boride on rare earth oxides for hydrogenation of olefins

An extremely active and colloidal nickel boride was prepared by using rare earth oxide as a support in the presence of polyethylene glycol (PEG) at room temperature which could act as a catalyst in the hydrogenation of olefinic compounds, such as 4-(4'-hydroxyphenyl)-3-buten-2-one.

Ligand stabilized nickel colloids

Ligand stabilized 4 nm nickel colloids are prepared by reduction of Ni(acac)2 with Et2AlH in diethyl ether in the presence of PPh3; they can be isolated in solid state and redispersed in any concentration in polar solvents such as pyridine, due to their ligand shell mainly consisting not of PPh3 molecules but, instead, of PPh moieties which are generated from PPh3 during reaction with Et2AlH with formation of free benzene.