Control Particle Growth Research Articles

Influence of Polyvinyl Alcohol and Alpha-Methacrylic Acid as Capping Agents on Particle Size of ZnS Nanoparticles

ZnS nanoparticles were synthesized successfully by wet chemical route using two capping agents, polyvinyl alcohol (PVA) and alpha-methacrylic acid (MA) to control particle growth. Optical property and the morphology of the synthesized ZnS nanoparticles revealed the influence of the capping agents in the formation of nanosize ZnS semiconductor. Particle sizes estimated from X-Ray Diffraction (XRD) analysis are 3.75 nm and 2.60 nm for ZnS/PVA and ZnS/MA respectively. The estimated energy band gap of the capped ZnS nanoparticles showed blue shift of 0.60 eV and 1.00 eV for ZnS/PVA and ZnS/MA respectively. The vibrational modes associated with OH-stretching and –COOH from the Fourier transform infrared spectroscopy (FTIR) measurements confirm the presence of the capping agents.

Quantitative nanoscopic impedance measurements on silver-ion conducting glasses using atomic force microscopy combined with impedance spectroscopy

Nanoscopic impedance measurements were carried out on silver ion conducting glasses by coupling an impedance spectrometer with an atomic force microscope. When ac voltages were applied to a conducting AFM tip being in contact with the glass surface, silver nanoparticles were formed during the cathodic half cycle, which were not completely reoxidized in the anodic half cycle. We describe two protocols allowing for a controlled particle growth. The electrochemical oxidation/reduction processes led to low tip/sample interfacial impedances, and the formed silver particles acted as nanoelectrodes sensing the spreading resistance of the glass below the particles. We made a quantitative check of the spreading resistance formula under the assumption that spreading of the electric field is governed by the lateral diameter of the particles and found good agreement between the mean value of the local conductivities obtained at different tip positions and the macroscopic conductivity.

A novel chelating acid-assisted thermolysis procedure for preparation of tin oxide nanoparticles

Pure tin dioxide (SnO 2) nanoparticles were synthesized via thermolysis of tin phthalate and tin oxalate in the presence of oleic acid (OA) as solvent. Oleic acid (OA) was employed as an organic solvent, which can be applied to control particle growth and to stabilize the particles. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. The orthorhombic phase SnO 2 nanoparticles with average size about 12 nm were synthesized through thermolysis of tin phthalate in the presence of oleic acid.

ChemInform Abstract: Transition from Five-Fold Symmetric to Twinned FCC Gold Particles by Thermally Induced Growth.

Stable gold clusters around 1 nm in size have been prepared by evaporation of the metal into an organosilicon polymer solution. A controlled particle growth of the entrapped gold particles was achieved by annealing in helium at ∼410 °C. Above 460 °C the growth rate is dramatically increased, concurrent with the onset of pyrolysis of polysilazane to form a porous solid. X-ray diffraction and simulation calculations using Debye functions of model clusters of different sizes and both crystallographic and noncrystallographic symmetry were used to characterize these particles. The exclusive presence of noncrystallographic (decahedral and icosahedral) multiply twinned particles (MTPs) in the as-prepared material is confirmed by EXAFS. The high precision of the XRD experiments and theoretical data fits gives detailed insight into the thermally induced growth process, during which the MTPs progressively disappear and are replaced by singly twinned fcc particles of larger size. This transition occurs in the range ...

Spectra study and size control of cobalt nanoparticles passivated with oleic acid and triphenylphosphine

Abstract This paper compares the performance of two surfactants—triphenylphosphine (TPP) and oleic acid (OA) as a pair of capping agents in the synthesis of magnetic Co nanoparticles (NPs). Magnetic colloids of cobalt NPs are prepared by reducing solute cobalt chloride in the presence of stabilizing agents at a high temperature and characterized by TEM. Infrared spectra reveal that a chemical bond can be formed between O of C O band and Co atoms while a coordinate bond forms between P and Co atoms around the NPs on the surface. OA binds strongly to the particle surface during synthesis that hinders the particle from growing; the TPP reversibly coordinates neutral metal surface sites that favor rapid growth. We studied the influence of changing the TPP / OA concentration ratio on the particle size distribution and crystallinity of Co NPs. Our results indicate the presence of TPP / OA is able to control particle growth, stabilize the colloidal suspension and prevent the final product from oxidation by air.

Luminescence Study of ZnS Quantum Dots Prepared by Chemical Method

We report synthesis of ZnS quantum dots by chemical method at room temperature. In this technique, ZnS quantum dots are produced by simple chemical reactions where zeolite, acts as matrix, plays the key role in controlling particle growth during synthesis. Quantum dots exhibit luminescence properties such as Zn2+ related emission, efficient low voltage electroluminescence, and super linear voltage-brightness EL characteristics. This study demonstrates the technological importance of semiconductor nanosystems prepared by low cost chemical route.

Size- and shape-controlled synthesis of monodisperse Co nanoparticles from cobalt acetate by thermal decomposition

Monodisperse cobalt nanoparticles with relatively high coercivities were synthesized by thermal decomposition of cobalt acetate for the application of ultra-high density magnetic recording media. Without using any reducing agents, Co nanoparticles of 13.9–21.3 nm in size were prepared using various protecting agents and a high boiling point solvent trioctylamine. The Co nanoparticles prepared with the mixture of oleic acid, oleylamine, and polyvinylpyrrolidone (PVP) showed clear crystalline structure of face centered cubic, and their coercivity was measured to be 27.2 kA/m. PVP was effective in controlling particle growth while hindering agglomeration between the particles. The as-prepared Co nanoparticles with a moderate coercivity can be applicable to patterned media.

Green luminescence of ZnS and ZnS:Cu quantum dots embedded in zeolite matrix

We report the synthesis of ZnS and ZnS:Cu (copper doped ZnS) quantum dots by chemical method at room temperature. In this technique ZnS and ZnS:Cu quantum dots are produced by simple chemical reactions where zeolite acts as matrix and plays the key role in controlling particle growth during synthesis. ZnS exhibits luminescence properties such as Zn2+ related emission. ZnS:Cu possesses Cu related emission, efficient low voltage electroluminescence, and super linear voltage-brightness electroluminescence characteristics. This study demonstrates the technological importance of semiconductor quantum dots prepared by low cost chemical route.

Enhanced Néel temperature in Mn ferrite nanoparticles linked to growth-rate-induced cationinversion

Mn ferrite (MnFe2O4) nanoparticles, having diameters from 4 to 50 nm, were synthesized using a modifiedco-precipitation technique in which mixed metal chloride solutions were added todifferent concentrations of boiling NaOH solutions to control particle growth rate.Thermomagnetization measurements indicated an increase in Néel temperaturecorresponding to increased particle growth rate and particle size. The Néel temperature isalso found to increase inversely proportionally to the cation inversion parameter,δ, appearing inthe formula (Mn1−δFeδ)tet[MnδFe2−δ]octO4. These results contradict previously published reports of trends between Néel temperatureand particle size, and demonstrate the dominance of cation inversion in determining thestrength of superexchange interactions and subsequently Néel temperature in ferritesystems. The particle surface chemistry, structure, and magnetic spin configuration playsecondary roles.

Controlled Particle Growth of Silver Sols through the Use of Hydroquinone as a Selective Reducing Agent

Hydroquinone (HQ) was used as the principal chemical reducing agent to prepare aqueous silver nanocolloids from silver nitrate. The data demonstrate that HQ is unable to initiate the particle growth process on its own, but is able to sustain particle growth in the presence of pre-existing metallic clusters. This unique selectivity is similar to that seen in photographic systems. Data are presented on two different approaches to initiating the HQ growth process. Very low levels of sodium borohydride can be used to form seed particles. Alternatively, the data show that controlled growth can be initiated by exposing the samples to UV radiation, relying on the photoreactivity of hydroquinone to start the process. These results were used to explore the dynamics of very dilute NaBH4 seed particles. They also were used to create nonspherical disk and triangular-plate morphologies directly from solution, without the need for subsequent reformation or template processing.

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.

Formation of group 12 [Zn, Cd] mixed-chalcogen nanoparticles from the reagent Me3Si-SeS-SiMe3

Mixed-chalcogen metal chalcogenide nanoparticles (MSexS1-x; M = Zn, Cd) have been synthesized using Me3Si-SeS-SiMe3 as a delivery source of Se2– and S2– to the metal core. This method demonstrates the ease with which mixed-chalcogen particles can be fabricated at low temperature using colloidal techniques. Reaction with Me3Si-SeS-SiMe3 occurs via a redox pathway resulting in Se–S bond cleavage and ultimately contributing to the nonequivalent Se:S ratio observed in the isolated particles. Subsequent thermolysis of ZnSe0.57S0.43 and CdSe0.28S0.72 in hexadecylamine gives rise to controlled particle growth while maintaining the observed stoichiometry. Particles are characterized by EDX, TEM, and powder X-ray diffraction analysis in conjunction with UV–vis absorption and photoluminescence (PL) spectroscopy.Key words: nanoparticles, semiconductors, mixed-chalcogen, quantum confinement, Group 12.

Accessing Binary CdE [E = S, Se, Te] and Ternary CdxZn1-xE [E = S, Se] Materials in Mesoporous Architectures Using Silylated-Chalcogen Reagents

Binary cadmium chalcogenide materials (CdS, CdSe, and CdTe) have been successfully synthesized at room temperature in the mesoporous environments of MCM-41 and MCF (mesocellular foam) by utilizing silylated-chalcogen reagents [E(SiMe3)2, E = S, Se, Te] as an efficient delivery source of E2-. The encapsulated materials are easily prepared by the initial complexation of anhydrous cadmium acetate to ethylenediamine functionalized mesoporous material. The subsequent addition of E(SiMe3)2 leads to the preferential formation of CdE materials within the host. The observed blue shift in absorption maximum is in agreement with the expected quantum confinement of these materials given the nanometer dimensions of the mesoporous architecture. Mild thermal treatment of CdS and CdSe composites demonstrates the ability to control particle growth under specified thermal conditions, ultimately leading to a red shift in absorption maximum upon increasing thermolysis temperature. The utility of silylated-chalcogen reagents was further demonstrated in the formation of ternary CdxZn1-xE (E = S, Se) encapsulated in MCF. The addition of the molecular precursor, (N,N‘-TMEDA) Zn(ESiMe3)2 (TMEDA = N,N,N‘,N‘-tetramethylethylenediamine), to Cd−MCF yields Cd0.33Zn0.76S− and Cd0.34Zn0.6Se−MCF materials, where the absorption maximum lies between that of the respective parent binary composites. All materials have been characterized by 13C CP-MAS NMR and UV−vis spectroscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray, and nitrogen sorption analysis.

The Microemulsion Synthesis of Hydrophobic and Hydrophilic Silicon Nanocrystals

AbstractSilicon nanocrystals, also called quantum dots, have unique optical properties when in the quantum‐confinement regime. These optical properties make silicon nanocrystals promising materials for a wide variety of applications ranging from optoelectronic devices to fluorophores in biological imaging. A liquid‐phase synthetic approach is reported using surfactant molecules to control particle growth, producing highly monodisperse silicon particles. The surface of the nanocrystals are capped by functional organic molecules that passivate and protect the silicon particles from oxidation, enabling the particles to be used in hydrophobic and hydrophilic applications. The use of hydrophilic silicon quantum dots as optical probes is illustrated by the imaging of Vero cells.

A potential lung perfusion imaging agent of synthetic origin

Abstract99mTc‐labelled macroaggregated albumin (MAA) is the radiopharmaceutical routinely used for perfusion lung scans. However MAA formulations contain excipients of biological origin, that may potentially cause allergic hypersensitivity in patients. The aim of this study was to prepare a non‐biological lung imaging agent, with physiological uptake based on a mechanism of colloid localisation in the pulmonary vasculature. To a frozen stannous fluoride cold kit (RAH Radiopharmacy) was added 99mTc‐pertechnetate (⩽2 GBq) in saline (1–4 ml), and the radioactive contents were mixed by rotation (40 rpm) in a syringe at room temperature for 30–180 min. The preparative conditions were varied to control particle growth by: the addition of metal ions, halide ions, or oxidants; different mixing times; and temperatures. The 99mTc products were analysed for % radiolabelling efficiency (RE), radioactive particle size distribution (RPSD), qualitative and quantitative rat biodistribution studies. Results indicated that all radioactive particles were formed with >99% RE, and 1–47% were >8 µm. The optimum radiotracer formulation containing the highest proportion of the largest particles, was prepared by mixing SnF2 and 99mTc‐pertechnetate with a low [Na+] at room temperature for 50 min. Results from the quantitative organ assays gave 88±1% tracer in the lungs, and less than 10% in the liver and spleen. The images showed excellent, uniform lung uptake with minimal interference from liver and spleen to the lower regions of right and left lobes. In conclusion, the synthetic radiopharmaceutical 99mTc–tin fluoride colloid can be prepared with a large particle size, from a commercially available cold kit in a simple and practical manner, and it has good potential for use as a perfusion imaging agent in lung scans. Copyright © 2006 John Wiley & Sons, Ltd.

Controlled monodisperse Fe nanoparticles synthesized by chemical method

Monodisperse 5 to 20 nm Fe nanoparticles have been directly synthesized by chemical method. Growth processes of Fe nanoparticles were studied by analyzing samples of different reaction stages. The growth process of particles is not simply proportional to the reaction time. In initial reaction, the precursors abruptly decompose to many nuclei and then the nuclei grow up to small particles. Subsequently, the particles trend to uniform in a reasonable reaction condition. It takes some time from nucleation to formation of the monodisperse nanoparticles. Composite addition of surfactants can more efficiently control particle growth. The Fe particles with diameter of 35 nm can be produced by seed mediate method.

Synthesis of Germanium Nanocrystals in High Temperature Supercritical Fluid Solvents

Crystalline germanium (Ge) nanocrystals were synthesized by arrested precipitation in supercritical hexane and octanol at 400∼550 °C and 20.7 MPa in a continuous flow reactor. Two Ge precursors were explored, diphenylgermane (DPG) and tetraethylgermane (TEG), which undergo thermolysis to crystalline Ge under these conditions. Octanol is added to control particle growth, which appears to serve as a capping ligand that binds to the particle surface through an alkoxide linkage. The nanocrystals were characterized by high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), FTIR spectroscopy, and X-ray diffraction (XRD). The average nanocrystal diameter could be changed over a wide range, from ∼2 nm to ∼70 nm, by varying the reaction temperature and precursor concentration. Relatively size-monodisperse nanocrystals could be produced, with standard deviations about the mean diameter as low as ∼10%. UV−visible absorbance and photoluminescence (PL) spectra of Ge nanocrystals in the 3 to 4 nm diameter size range exhibit optical absorbance and PL spectra blue-shifted by approximately 1.7 eV relative to the band gap of bulk Ge, with quantum yields up to 6.6%.

The Self-Preserving Size Distribution Theory: I. Effects of the Knudsen Number on Aerosol Agglomerate Growth

Gas-phase synthesis of fine solid particles leads to fractal-like structures whose transport and light scattering properties differ from those of their spherical counterparts. Self-preserving size distribution theory provides a useful methodology for analyzing the asymptotic behavior of such systems. Apparent inconsistencies in previous treatments of the self-preserving size distributions in the free molecule regime are resolved. Integro-differential equations for fractal-like particles in the continuum and near continuum regimes are derived and used to calculate the self-preserving and quasi-self-preserving size distributions for agglomerates formed by Brownian coagulation. The results for the limiting case (the continuum regime) were compared with the results of other authors. For these cases the finite difference method was in good in agreement with previous calculations in the continuum regime. A new analysis of aerosol agglomeration for the entire Knudsen number range was developed and compared with a monodisperse model; Higher agglomeration rates were found for lower fractal dimensions, as expected from previous studies. Effects of fractal dimension, pressure, volume loading and temperature on agglomerate growth were investigated. The agglomeration rate can be reduced by decreasing volumetric loading or by increasing the pressure. In laminar flow, an increase in pressure can be used to control particle growth and polydispersity. For Df=2, an increase in pressure from 1 to 4 bar reduces the collision radius by about 30%. Varying the temperature has a much smaller effect on agglomerate coagulation.

Study on controlling particle growth in seeded emulsion polymerization with regulated coagulation based on the electrostatic interactions

30wt% solid content, anionic seed copolymer latex P(methyl acrylate-co-methyl methacrylate) was prepared by conventional emulsion polymerization, and then the seeded emulsion polymerization was carried out accompanied with the electrostatic coagulation during the reaction in the presence of counter-ion species, such as cationic monomer and initiator. In this article, effects of cationic monomer (dimethyl aminoethyl methacrylate, DM) content, secondary monomer to seed polymer weight ratio, M/P and amount of emulsifier (polyoxyethylene nonylphenylether with 23 units of ethylene oxide, PEO23) were investigated on the effective particle growth and the stability of final latex. With 10wt% DM in monomer, M/P ratio at 2.0 were recommended. An optimal policy for handling the emulsifier content without the nucleation of secondary particles while achieving the controlled coagulative growth was proposed from the observations of polymer yield and particle size during the polymerization.

Formation of Metal Nanoparticles in Multilayered Poly(octadecylsiloxane) As Revealed by Anomalous Small-Angle X-ray Scattering

Novel hybrid polymeric systems with noble metal nanoparticles located inside specific areas of the material were developed. A self-assembled multilayered polymer, poly(octadecylsiloxane) (PODS), provided a nanostructured matrix for incorporation of gold and platinum compounds and for metal nanoparticle formation. The internal structure of PODS and the nanoparticle size distributions were examined using anomalous small-angle X-ray scattering. The ordering in PODS was largely preserved after interaction with metal compounds and reducing agents. The degree of incorporation of the compounds into PODS depended on the reaction conditions and on the compound type. For the metal-containing PODS isolated from the reaction medium before reduction, the major fraction of the nanoparticles had radii around 2 nm, and the size distributions depended neither on the compound loading nor on the reducing agent. This points to a “cage”-controlled particle growth restricted by the cavity size in the siloxy bilayer. This hypothesis is corroborated by the computed density profiles across the PODS lamella. Incorporation of cetylpyridinium chloride in the hydrophobic layers of PODS promotes formation of nanoparticles also between the hydrophobic tails. This location does not restrict the particle growth so that the nanoparticle sizes strongly depend on the reduction conditions.