A novel method for synthesis of silica nanoparticles

A sequential method has been used, for the first time, to prepare monodisperse and uniform-size silica nanoparticles using ultrasonication by sol-gel process. The silica particles were obtained by hydrolysis of tetraethyl orthosilicate (TEOS) in ethanol medium and a detailed study was carried out on the effect of different reagents on particle sizes. Various-sized particles in the range 20-460 nm were synthesized. The reagents ammonia (2.8-28 mol L(-1)), ethanol (1-8 mol L(-1)), water (3-14 mol L(-1)), and TEOS (0.012-0.12 mol L(-1)) were used and particle size was examined under scanning electron microscopy and transmission electron microscopy. In addition to the above observations, the effect of temperature on particle size was studied. The results obtained in the present study are in agreement with the results observed for the electronic absorption behavior of silica particles, which was measured by UV-vis spectrophotometry.     

A facile method of synthesis of asymmetric hollow silica spheres

This paper presents a "one-step" method to synthesize asymmetric hollow silica spheres. In this method, when positively charged polystyrene particles were blended with mercaptopropyltriethoxysilane and stirred at 50 °C in alkaline ethanol/water medium for a period of time, Janus or lobed asymmetric hollow silica spheres could be directly obtained, just changing the ratio of ethanol to water in the reaction medium. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to characterize the morphology and topography of the asymmetric hollow silica spheres. The formation mechanism was described in detail.     

Transition metal-chelating surfactant micelle templates for facile synthesis of mesoporous silica nanoparticles

Highly ordered mesoporous silica nanoparticles with tunable morphology and pore-size are prepared by the use of a transition metal-chelating surfactant micelle complex using Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ ions. These metal ions formed a metal-P123 micelle complex in an aqueous solution, while the metal ions are chelated to the hydrophilic domain such as the poly(ethylene oxide) group of a P123 surfactant. The different complexation abilities of the utilized transition metal ions play an important role in determining the formation of nano-sized ordered MSNs due to the different stabilization constant of the metal-P123 complex. Consequently, from a particle length of 1700 nm in the original mesoporous silica materials, the particle length of ordered MSNs through the metal-chelating P123 micelle templates can be reduced to a range of 180–800 nm. Furthermore, the variation of pore size shows a slight change from 8.8 to 6.6 nm. In particular, the Cu²⁺-chelated MSNs show only decreased particle size to 180 nm. The stability constants for the metal-P123 complex are calculated on the basis of molar conductance measurements in order to elucidate the formation mechanism of MSNs by the metal-chelating P123 complex templates. In addition, solid-state ²⁹Si, ¹³C-NMR and ICP-OES measurements are used for quantitative characterization reveal that the utilized metal ions affect only the formation of a metal-P123 complex in a micelle as a template.     

Fast and facile synthesis of silica coated silver nanoparticles by microwave irradiation

A novel, fast and facile microwave technique has been developed for preparing monodispersed silica coated silver (Ag@SiO(2)) nanoparticles. Without using any other surface coupling agents such as 3-aminopropyltrimethoxysilane (APS) or polymer such as polyvinyl pyrrolidone (PVP), Ag@SiO(2) nanoparticles could be easily prepared by microwave irradiation of a mixture of colloidal silver nanoparticles, tetraethoxysilane (TEOS) and catalyst for only 2 min. The thickness of silica shell could be conveniently controlled in the range of few nanometers (nm) to 80 nm by changing the concentration of TEOS. Transmission electron microscopy (TEM) and UV-visible spectroscopy were employed to characterize the morphology and optical properties of the prepared Ag@SiO(2) nanoparticles, respectively. The prepared Ag@SiO(2) nanoparticles exhibited a change in surface plasmon absorption depending on the silica thickness. Compared to the conventional techniques based on St?ber method, which need 4-24 h for silica coating of Ag nanoparticles, this new technique is capable of synthesizing monodispersed, uniform and single core containing Ag@SiO(2) nanoparticles within very short reaction time. In addition, straightforward surface functionalization of the prepared Ag@SiO(2) nanoparticles with desired functional groups was performed to make the particles useful for many applications. The components of surface functionalized nanoparticles were examined by Fourier transform infrared (FT-IR) spectroscopy, zeta potential measurements and X-ray photoelectron spectroscopy (XPS).     

A facile, water-based synthesis of highly branched nanostructures of silver

We report a facile and environmentally friendly method of preparing highly branched silver nanostructures. By reducing AgNO 3 with l-ascorbic acid in an aqueous solution, silver particles having a coral-like morphology were formed in a few minutes. A mechanistic study of the growth process revealed that the silver branches grew from a bulbous seed formed through aggregation, and that by changing the concentrations of the reagents, the degree of particle branching could be altered. With their potentially high surface areas, these branched structures could find use as catalysts or as substrates for surface-enhanced Raman scattering applications.     

A facile and controllable one-pot synthesis approach to amino-functionalized hollow silica nanoparticles with accessible ordered mesoporous shells

The development of a practical synthetic method to functionalize hollow mesoporous silica with organic groups is of current intere st for selective adsorption and ene rgy storage applications.Herein,a facile and controllable one-pot approach for the synthesis of monodisperse amino-functionalized hollow mesoporous silica nanoparticles is presented.A novel solid-to-hollow structural transformation procedure of the silica nanoparticles is presented.The structural transformation is easily designed,as obse rved through transmission electro n microscopy,by tailo ring the HCl and N-lauroylsarcosine sodium molar ratio and the water content in the sol-gel.Ordered and radially oriented in situ aminofunctionalized mesochannels were successfully introduced into the shells of the hollow silica nanoparticles.A formation mechanism for the hollow mesoporous silica materials is discussed.     

Supercritical ethanol--a fascinating dispersion medium for silica nanoparticles

For the first time, the dispersion stability of silica nanoparticles has been investigated in high-temperature and high-pressure ethanol by measuring the hydrodynamic diffusion coefficient of the particles by means of dynamic light scattering. The silica nanoparticles remain stable in ethanol within a wide temperature range of 24-304 degrees C at 12.3 MPa, and they start to aggregate at T >or= 305 degrees C. Numerical analysis reveals that the net interparticle repulsive potential barrier decreases dramatically with increasing temperature due to the changes in the properties of the medium. We observed that particles remain highly stable in the nonpolar supercritical ethanol in the temperature regime 241-304 degrees C, where the DLVO potential barrier is only 5-2 k(B)T. The dispersion stability of silica nanoparticles at this low potential barrier in high-temperature and high-pressure ethanol, especially in the supercritical ethanol, is fascinating. The silica-ethanol system might be a unique and special example in the colloidal dispersions. Results suggest that silica nanoparticles may be used as a model colloid to investigate the colloidal transport phenomena in the supercritical ethanol.     

A facile synthesis of azoviolet@Mn3O4 nanoparticles for supercapacitor

Russian Journal of Physical Chemistry A - The azoviolet@Mn3O4 nanoparticles have been successfully synthesized using the azoviolet as a stable absorbed reagent for the supercapacitor. The prepared...     

A novel method for the facile synthesis of depsipeptides

A one pot, high yield synthesis of depsipeptides is described involving room temperature condensation of hindered substrates (N-Boc amino acids and benzyl α-hydroxy esters) in the presence of DCC and a dialkylaminopyridine. In this manner previously inaccessible depsipeptides were prepared.     

A facile one-pot synthesis of ruthenium hydroxide nanoparticles on magnetic silica: aqueous hydration of nitriles to amides

One-pot synthesis of ruthenium hydroxide nanoparticles on magnetic silica is described which involves the in situ generation of magnetic silica (Fe(3)O(4)@SiO(2)) and ruthenium hydroxide immobilization; the hydration of nitriles occurs in high yield and excellent selectivity using this catalyst which proceeds exclusively in aqueous medium under neutral conditions.     

New method for facile synthesis of amphiphilic thiol-stabilized ruthenium nanoparticles and their redox-active ruthenium nanocomposite

The one-phase reduction of RuCl3 with lithium triethylborohydride as a reductant in tetrahydrofuran in the presence of 1-octanethiol, 1-octadecanethiol, 1,1'-binaphthalene-2,2'-dithiol, or oligoethyleneoxythiol gave organic solvent- and water-soluble thiol-stabilized ruthenium nanoparticles. The oligoethyleneoxythiol-stabilized ruthenium nanoparticles were soluble in both water and organic solvents. The ruthenium nanoparticles were stable in the solid state and did not aggregate in solution. Transmission electron microscope images of the ruthenium nanoparticles reveal small dispersed particles with a narrow size distribution. The ligand-exchange reaction of octadecanethiol-stabilized ruthenium nanoparticles (2.0 nm) with phenothiazine-linked decanethiol afforded redox-active phenothiazine-functionalized ruthenium nanoparticles (1.9 nm) that showed a reversible redox peak at +0.51 V (vs Ag/0.1 M AgNO3) in the cyclic voltammogram.     

A facile synthesis of bimodal mesoporous silica and its replication for bimodal mesoporous carbon

Bimodal mesoporous silica material composed of 30-40 nm sized nanoparticles with 3.5 nm sized three-dimensionally interconnected mesopores was synthesized under neutral conditions using sodium silicate as a silica source. Using the bimodal mesoporous silica as a template, bimodal mesoporous carbon having 4 nm sized framework mesopores and approximately 30 nm sized textural pores was synthesized.     

A facile route for shape-selective synthesis of silica nanostructures using poly-L-lysine as template

A facile method for the shape-selective synthesis of silica nanostructures using a reversemicroemulsion -mediated template(RMMT) technique is reported.In this method,positive poly-Llysine (PLL) is selected as template due to its configuration diversity.By adjusting pH and concentration, PLL demonstrates various secondary structures containing random coil,α-helix andβ-sheet,which result in the formation of silica nanorods,silica nanospheres and silica nanotubes in the reversemicroemulsion system,respectively.Thus,the shape-selective synthesis of silica nanostructures might be achieved by using PLL as structural template in the reverse-microemulsion system.     

A facile one-pot synthesis of uniform core-shell silver nanoparticle@mesoporous silica nanospheres

The uniform core-shell silver nanoparticle@mesoporous silica nanospheres have been prepared by a simple one-pot synchronous method, which combines several steps into one, including the generation of silver nanocrystals and mesoporous silica, transfer and aggregation of silver nanoparticles in an incompact silica framework.     

A facile electrochemical method for synthesis of new benzofuran derivatives

Electrooxidation of 3-substituted catechols has been studied in the presence of dimedone in aqueous solution, using cyclic voltammetry and controlled-potential coulometry. The results indicate that the quinones derived from catechols participate in Michael addition reactions with dimedone to form the corresponding benzofuran derivatives (6a-c). We propose a mechanism for the electrode process. The efficient electrochemical synthesis of 6a-c has been performed at carbon rod electrodes in an undivided cell using a constant current.     

A facile and efficient method for the synthesis of solasodine from diosgenin

A facile and high-yielding route for the synthesis of solasodine from diosgenin is devised. Ring opening of steroidal spiroketal under mild conditions with trifluoroacetyl trifluoromethanesulfonate (TFAT) provides an applicable protocol to prepare key intermediates 4 or 3-Ac-solasodine, which can potentially serve as a platform for the selective functionalization of C(3)-OH and N-H of solasodine. The simple operations without purification by column chromatography make this method suitable to scale up.     

A general method for the controlled embedding of nanoparticles in silica colloids

A novel method for the controlled embedding of multiple nanoparticles of various materials, such as gold nanoparticles, quantum dots, and magnetic nanoparticles, in silica colloids is presented. After adsorption of the amphiphilic polymer poly(vinylpyrrolidone) on hydrophobic or hydrophilic stabilized nanoparticles, these are adsorbed on silica spheres and covered by variable-thickness silica shells. This silica coating protects the embedded nanoparticles against chemical transformations, which is of crucial importance for the biocompatibility of particles containing toxic elements. Moreover, it is found that the optical properties of the nanoparticles are retained. Possible applications of multicore particles are briefly discussed.     

A new and simple method for sulfur nanoparticles synthesis

Sulfur nanoparticles were successfully synthesized via novel water-in-oil microemulsion system. The microemulsion system contained cyclohexane as an oil phase, Triton X-100 as a surfactant, butanol as a co-surfactant and sodium polysulfide solution or hydrochloric acid solution as aqueous phase, respectively. The sulfur nanoparticles were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy. The results showed that the as-prepared monoclinic sulfur nanoparticles exhibited high purity and spherical shape with an average size of about 22 nm.     

Carbon nanotubes-supported palladium nanoparticles for the Suzuki reaction in supercritical carbon dioxide: A facile method for the synthesis of tetrasubstituted olefins

A facile and efficient method for the synthesis of tetrasubstituted olefins in supercritical carbon dioxide was developed by using carbon nanotubes-supported palladium nanoparticles (Pd/CNTs) as the catalyst. Compared with common Pd/C, Pd/CNTs could more effectively catalyze the reaction of dibromo-substituted olefins with boronic acids, affording the corresponding tetrasubstituted olefins with moderate to good yields. This environmentally benign route with an easy-to-handle catalyst provides an appealing alternative to the currently available methods.