Formation of nickel magnetic nanoparticles and modification of nickel phthalocyanine matrix by sodium doping

Data for the vapor-phase doping (300°C) of nickel phthalocyanine (NiPc) by sodium taken in different concentrations (x), as well as structural analysis data for Na _{x = 0.2}NiPc, Na _{x = 1}NiPc, and Na _{x = 3}NiPc samples, have been reported. The structure of the samples and their atomic configuration versus the doping level have been studied by transmission electron microscopy, Raman scattering, X-ray diffraction, X-ray absorption spectroscopy, and extended X-ray absorption fine structure (EXAFS) spectroscopy. The structural parameters of Ni–N, Ni–C, and Ni–Ni bonds have been determined, and it has been found that, at a low level of doping by sodium, local structural distortions are observed in some molecules of the NiPc matrix near nickel atoms. The fraction of these molecules grows as the doping level rises from x = 0.2 to x = 1.0. It has been shown that doping changes the oscillation mode of light atoms, which indicates a rise in the electron concentration on five- and six-membered rings. At a high level of sodium doping (x = 3.0), nickel nanoparticles with a mean size of 20 nm and molecule decomposition products have been observed in the NiPc matrix. It has been found that the fraction of nickel atoms in the Na _{x = 3}NiPc nanoparticles as estimated from EXAFS data is sufficient for the room-temperature magnetic properties of the samples to persist for a long time.     

Adsorption-resistant properties of copper phthalocyanine dispersed in a polymer matrix

The conduction mechanism in copper phthalocyanine (CuPc)-polymer composite thin films and their sensitivity to nitrogen dioxide are investigated. It is established that a hopping conduction mechanism in the regime of single electron hops prevails in these materials at 290–350 K, and the magnitude and rate of the adsorption-resistance sensitivity to NO₂ is higher than in pure CuPc. Fiz. Tverd. Tela (St. Petersburg) 40, 773–775 (April 1998)     

Study of the composite based on iron-containing nanoparticles dispersed in the polyethylene matrix

A composite representing a system of iron-based nanoparticles about 5 nm in size embedded in a high-pressure polyethylene matrix has been studied. The technology of preparation of this material has been described. The transmission electron microscopy, X-ray powder diffraction, and nuclear gamma-resonance spectroscopy data presented have been used to establish the volumes of the metal and oxide phases of a nanoparticle and the composition of its oxide shell.     

Synthesis of colloids based on gold nanoparticles dispersed in castor oil

New colloidal solutions of gold nanoparticles (AuNP), using castor oil as a nontoxic organic dispersant agent, were prepared via three different methods. In all three cases, tetrachloroauric(III) acid was employed as the gold source. The colloids were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). The AuNP produced by the three methods were quasispherical in shape, however with different average sizes. The individual characteristics of the nanoparticles presented in each colloidal system were also confirmed by observation of absorption maxima at different wavelengths of visible light. Each method of synthesis leads to colloids with different grades of stability with respect to particle agglomeration.     

Stabilization of superparamagnetic nickel nanoparticles in a sepiolite matrix

Superparamagnetic nickel-rich nanoparticles at room temperature have been obtained in a silicate matrix (sepiolite) by a chemical route. During the synthesis process, the control of the acid treatment of the matrix allows nickel cations being incorporated in different locations, into the octahedral site of the structural channels or being deposited onto the sepiolite surface. Thus, two different types of nickel nanoparticles have been obtained depending on the nature of the acid attack: small (~7 nm) and embedded superparamagnetic, or large (~27 nm) deposited single domain nickel nanoparticles for strong or weak acid attack, respectively. Moreover, the embedded nanoparticles have been revealed to possess a remarkable stability against complete oxidation. According to the usage of characterization techniques (transmission electron microscopy, X-ray diffraction and magnetic measurements), embedded nanoparticles seem to be coated with a non-ferromagnetic coating that hinders the oxygen diffusion.     

Synthesis and electrochemical investigation of highly dispersed ZnO nanoparticles as anode material for lithium-ion batteries

Highly dispersed ZnO nanoparticles were prepared by a versatile and scalable sol-gel synthetic technique. High-resolution transmission electronic microscopy (HRTEM) showed that the as-prepared ZnO nanoparticles are spherical in shape and exhibit a uniform particle size distribution with the average size of about 7 nm. Electrochemical properties of the resulting ZnO were evaluated by galvanostatic discharge/charge cycling as anode for lithium-ion battery. A reversible capacity of 1652 mAh g^?1 was delivered at the initial cycle and a capacity of 318 mAh g^?1 was remained after 100 cycles. Furthermore, the system could deliver a reversible capacity of 229 mAh g^?1 even at a high current density of 1.5 C. This outstanding electrochemical performance could be attributed to the nano-sized features of highly dispersed ZnO particles allowing for the better accommodation of large strains caused by particle expansion/shrinkage along with providing shorter diffusion paths for Li⁺ ions upon insertion/deinsertion.     

Synthesis of carbon-encapsulated nickel nanoparticles

Carbon-encapsulated metal nanoparticles (CEMNs) were obtained by the catalytic decomposition of hydrocarbons (CH₄, C₂H₆, C₂H₄) on nanocrystalline nickel. Nanocrystalline nickel was obtained by precipitation from nickel nitrate solution, followed by calcination and reduction under hydrogen. A small amount of structural promoters (aluminium and calcium oxide) was added to avoid recrystallisation of fine nickel particles at elevated temperatures. Reduction and carburisation of the samples was carried out in a differential reactor with mass control. The rate of decomposition of methane, ethane and ethylene on nanocrystalline nickel was measured and the apparent activation energy of the process was determined. The obtained samples were characterised using the XRD, SEM and HRTEM methods.     

Fabrication and structural characterization of nanocomposites consisting of Ni nanoparticles dispersed in polyimide films

Formation and structure of composite layer consisting of polyimide films containing Ni nanoparticles were investigated. The preparation method relies on KOH treatment on polyimide film to form carboxyl acid groups and adsorption of Ni ions by ion exchange followed by hydrogen reduction. The amount of Ni ions adsorbed in polyimide films were found to be systematically controlled by changing initial KOH concentration, subsequent ion exchange time, pH and temperature. Cross-sectional TEM observation revealed that Ni nanoparticles with 3-5 nm in diameter were homogeneously dispersed in the surface modified polyimide layer after heat treatment above 250 ^°C in H₂ atmosphere. The size and distribution of the Ni nanoparticles were strongly dependent on the heat treatment temperature, indicating that this method allows microstructural tuning of metal/polymer nanocomposites.     

Studies on CdS nanoparticles dispersed in silica matrix prepared by sol-gel technique

SiO₂/CdS-nanoparticle composite films (SiO₂:CdS=85:15, 80:20, 75:25 and 70:30) were prepared by the sol-gel route. The films were characterized by studying microstructural (XRD and TEM) and optical (transmittance and photoluminescence) properties. Band gaps of these films annealed at different temperatures (373-473 K) for different times (10-120 min) indicated that the signature of nanocrystallinity is retained throughout the range of our experimental conditions. A thermal diffusion process controlled growth in the crystallite size with increasing annealing time and temperature. The average radii of the nanoparticles varied as the cube root of the annealing time but showed exponential dependence on the inverse of annealing temperature. Photoluminescence (PL) studies of the composite films indicated excitonic transitions. Theoretical analysis of the line shapes of the PL peaks recorded at 300 K and 80 K could be accounted for by the combined effects of size distribution and phonon broadening. It was observed that the deformation potential (E _d) effectively controlled the line shapes of the PL measurements. Received 24 May 2002 Published online 27 January 2003 RID="a" ID="a"e-mail: msakp@mahendra.iacs.res.in     

The effect of oxidation on the structure of nickel nanoparticles

The structural properties of nickel nanoparticles which are prepared by means of DC sputtering in argon and subsequently oxidized in ambient air are reported. Ex situ structural and chemical investigations utilizing (high resolution) transmission electron microscopy and electron energy loss spectroscopy reveal that the particles consist of a metallic core surrounded by an oxide shell. The lattice constant of the nickel core is found to increase significantly with decreasing particle size. This widening of the nickel lattice is attributed to an interfacial stress that originates from the lattice mismatch between nickel and nickel oxide. Received 21 December 2000     

Fe2O3 nanoparticles dispersed unsaturated polyester resin based nanocomposites: effect of gamma radiation on mechanical properties

ABSTRACT

In this work, unsaturated polyester resin (UPR) matrix based nanocomposite was fabricated using synthesized Fe₂O₃ nanoparticle as reinforcement and methyl ethyl ketone peroxide as curing agent by solution casting method. The Fe₂O₃ nanoparticles were synthesized using the sol–gel method and the formation of nanoparticle was confirmed by X-ray diffraction, Scanning electron microscope, Energy dispersive spectrometry analysis. Interactions between metal oxide nanoparticles and polymer molecules in fabricated nanocomposite were investigated by Fourier transform infrared spectrometer analysis. Pure UPR and Fe₂O₃/UPR composite were irradiated with various gamma radiation doses (0–15?kGy). At the 0?kGy (without radiation), the nanoparticles loaded composite showed better mechanical properties (increased in tensile strength and Young’s modulus and decreased in elongation) compared to that of pure UPR sheet. At the 5?kGy radiation dose, the tensile strength and Young’s modulus were further increased; whereas, the elongation was decreased in both samples.     

Size analysis and magnetic structure of nickel nanoparticles

The size distribution of an assembly of fcc nickel nanoparticles is studied by measuring the temperature dependent magnetization curves fitted by a uniform model and a core-shell model, both based on the Langevin function for superparamagnetism with a log-normal particle volume distribution. The uniform model fits lead to a spontaneous magnetization M_s much smaller than the M_s for bulk nickel and to particle sizes larger than the ones evaluated by transmission electron microscopy; the core-shell model fits can result in a correct size distribution but the M_s in the core becomes significantly greater than the M_s for bulk nickel. It is concluded that there is a core-shell magnetic structure in nickel particles. Although the enhanced M_s in the core may be related to the narrowing of the energy bands of 3d electrons in small fcc nickel particles, the modeling values of M_s are over large compared with previous calculations on nickel clusters of different structures, which implies possible existence of an exchange interaction between the core and the shell, which is not considered in the simple core-shell model.     

Synthesis of nanoparticles and its effect on properties of elastomeric nanocomposites

Calcium carbonate (CaCO₃) nanoparticles (9, 15, and 21 nm) were synthesized by solution spray of CaCl₂ and NH₄HCO₃ with sodium lauryl sulfate (SLS) as a stabilizing agent, and their effect was studied on polybutadiene rubber (PBR) with variations in wt% loading (4, 8, and 12%). The results of PBR nanocomposites were compared with commercial CaCO₃ (40 μm) and fly ash (75 μm) filled PBR microcomposites. Properties such as tensile strength, young modulus, elongation at break, glass transition temperature, decomposition temperature, and abrasion resistances were determined. Profound effect in properties was observed, because nanometric size of CaCO₃ particles synthesized using solution spray technique. Maximum improvement in mechanical and flame retarding properties was observed at 8 wt% of filler loading. This increment in properties was more pronounced in 9-nm size CaCO₃. The results were not appreciable above 8 wt% of nanofillers because of agglomeration of nanoparticles. In addition, an attempt was made to consider modeling Young’s modulus of PBR–nano CaCO₃ which was predicted by modified Halpin–Tsai equation. It was observed that the predication by the Guth equation and modified Halpin–Tsai equation agreed very well with experimental, whereas the Halpin–Tsai equation can only applied to predict the modulus of rubber nanocomposites in the range of low addition of nanofiller, which agrees the Nielsen equation.     

Synthesis,structure, and magnetic properties of iron and nickel nanoparticles encapsulated into carbon

Nanocomposites based on iron and nickel particles encapsulated into carbon (Fe@C and Ni@C), with an average size of the metal core in the range from 5 to 20 nm and a carbon shell thickness of approximately 2 nm, have been prepared by the gas-phase synthesis method in a mixture of argon and butane. It has been found using X-ray diffraction, transmission electron microscopy, and Mössbauer spectroscopy that iron nanocomposites prepared in butane, apart from the carbon shell, contain the following phases: iron carbide (cementite), α-Fe, and γ-Fe. The phase composition of the Fe@C nanocomposite correlates with the magnetization of approximately 100 emu/g at room temperature. The replacement of butane by methane as a carbon source leads to another state of nanoparticles: no carbon coating is formed, and upon subsequent contact with air, the Fe₃O₄ oxide shell is formed on the surface of nanoparticles. Nickel-based nanocomposites prepared in butane, apart from pure nickel in the metal core, contain the supersaturated metastable solid solution Ni(C) and carbon coating. The Ni(C) solid solution can decompose both during the synthesis and upon the subsequent annealing. The completeness and degree of decomposition depend on the synthesis regime and the size of nickel nanoparticles: the smaller is the size of nanoparticles, the higher is the degree of decomposition into pure nickel and carbon. The magnetization of the Ni@C nanocomposites is determined by several contributions, for example, the contribution of the magnetic solid solution Ni(C) and the contribution of the nonmagnetic carbon coating; moreover, some contribution to the magnetization can be caused by the superparamagnetic behavior of nanoparticles.     

Optical properties of nanocomposites based on polymers and metal nanoparticles

The optical properties of nanocomposites of metal nanoparticles and polymers of two types have been studied. Gold and silver nanoparticles were obtained by laser ablation of corresponding metal targets in acetone and chloroform. The thus formed colloidal solutions were used to prepare nanocomposites of these nanoparticles in polymer matrices of polymethylmethacrylate (PMMA) and fluorine-containing polymer LF-32. The polymer matrix is found to promote aggregation of the metal nanoparticles under study into elongated chains. In turn, metal nanoparticles affect the polymer matrix. In the case of PMMA, suppression of the vibrational peaks of polymer in the low-frequency region of its Raman spectrum occurs. In the case of LF-32, gold and silver nanoparticles amplify the Raman signal of the polymer matrix. In addition, the Raman spectra of nanocomposites indicate aggregation of disordered carbon around the nanoparticles obtained by laser ablation in organic solvents. The possibilities of studying the ultrafast (about 1 ps) optical response of the nanocomposites obtained in order to use it in photonics elements are discussed.     

Synthesis of nanocomposites based on nanotubes and silicates

In situ synthesis of nanocomposites based on carbon nanotubes and zeolite/montmorillonite was carried out in a hot filament CVD reactor where the precursors (methane and hydrogen) are activated by carbonized tungsten filaments heated up to 2200 °C. In nanocomposites formed both on zeolite and montmorillonite we observed cross-linking of the catalytic particles by nanotubes and creation of carbon nanotube bridges and three-dimensional networks. The length of nanotube bridges was in a range from several nm to nearly 10 μm. A high density of carbon nanotubes was observed in the whole volume of zeolite. The high catalytic efficiency of zeolite is most likely caused by its structure that allows anchoring of Fe³⁺ catalytic particles in the pores and prevents their migration from the sample. At the ends of the nanotubes grown on zeolite we observed particles of the catalyst. In montmorillonite, the particles catalyzing the growth of carbon nanotubes may be present not only on the external surface but also in the interlayer voids of the mineral. Its catalytic efficiency is enhanced as proved by the higher amount of CNTs and their bundles. In the course of CNTs synthesis probably also clumps of Fe³⁺ catalytic particles arise, which may be the reason for formation of bundles of nanotubes.     

Effect of finely dispersed platinum on the structure of luminescence spectra of the adsorbates of magnesium phthalocyanine on silicon dioxide

The luminescence and excitation spectra and kinetic characteristics of the luminescence of the adsorbates of magnesium phthalocyanine (MgPhc) on SiO₂ and the effect on them of surface hydration and finely dispersed platinum are studied. It is found that a structure that improves hydration of the adsorbent surface appears on the platinized surface in the luminescence and excitation spectra. It is assumed that the spectral structure is due to the complexes of MgPhc formed with water molecules, the hydroxyl cover of the surface, and the surface centers of SiO₂ modified by a Pt-catalyst. Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 552–555, July–August, 1999.