Synthesis and growth of germanium oxide nanoparticles in AOT reversed micelle

Germanium oxide (GeO₂) nanoparticles with a narrow size distribution have been synthesized by a reverse micelle technique. The cubic GeO₂ particles with particle size of 15 nm were obtained as the reaction solution was left standing for 24 h, the particle size and shape can be controlled by changing the molar ratio of surfactant/water (R_w) and the aging time. The effect of R_w and aging time on the particle size was discussed.     

Preparation of nanosize SnO2 particles in an aerosol reactor by pyrolysis of tetra-n-butyl tin

Possibility of preparing nanosize SnO₂ particles from alkyl metal by pyrolysis was tested. SnO₂ particles with a diameter of 10 to 45 nm were obtained from tetra-n-butyl tin (TNBT) in a tubular aerosol reactor. Crystalline SnO₂ particles began to be formed over 500 °C. The size of SnO₂ particles was increased with increasing concentration of precursor and decreasing reaction temperature. The number density in the reactor was in the order of 10¹⁴/ml. IR spectrum showed that the alkyl group was completely removed and the color became bright white as the reaction temperature was increased. Oxygen concentration was found to be around 80% for complete removal of alkyl group.     

Preparation of nanometer-sized SnO2 by the fusion method

Nano-sized SnO₂ particles were prepared by the fusion of SnCl₂·2H₂O with sodium nitrate. X-ray diffraction and TEM were used to study the samples. According to XRD and TEM results, the average particle size/crystal sizes of SnO₂ increase from 2.9 nm/2.5 nm to 8.6 nm/8.4 nm. The experiments reveal that the effects of synthesis temperature and synthesis time on the crystalline size are significant but the influence of reaction mixture composition on the particle size is rather small. Nano-sized SnO₂ with advisable crystalline size can be obtained by the control of reaction mixture composition, synthesis temperature and synthesis time.     

A novel microwave synthesis of nanocrystalline SnO2 and its structural optical and dielectric properties

Nanocrystalline SnO₂ particles with the rutile structure have been successfully synthesized by a novel microwave irradiation method. This process requires less reaction time and low temperature. Transmission electron microscopy studies show that SnO₂ particles are in spherical shape with size about 25–30 nm. Selected area electron diffraction pattern confirms single crystalline nature of the SnO₂. UV–Vis spectrometer was carried out to study the optical properties and estimated band gap energy of SnO₂ particles is 3.55 eV. In Fourier transform infrared study, a defined peak at around 615 cm^?1 is observed due to Sn–O vibration. Frequency dependent dielectric anomaly is observed in SnO₂ nanoparticles at low temperature. It is found that the value of dielectric constant of SnO₂ particles at 10 kHz is found to be 777.5. It systematically decreases with increasing frequency whereas increases with increasing temperature. Further, the prepared samples were characterized by Photoluminescence spectroscopy and energy dispersive spectroscopy.     

Synthesis of high tap density spherical micro-size silver particles by liquid-phase reduction using response surface methodology

Mono-disperse and spherical micro-size silver particles with high tap density were prepared by using silver nitrate as metal source, ascorbic acid as reductant, sulfuric acid as dispersant and polyethylene glycol 4000 (PEG4000) as surfactant. The aim of this paper was to study the simultaneous effects of surfactant dosage (PEG4000/AgNO₃ mass ratio), silver nitrate concentration [AgNO₃], deionized water dosage in reductant solution, stirring rate and their interactions on properties of silver particles. For optimizing these parameters, irregular fractional factorial design of experiments was used. As-prepared silver particles were characterized by X-ray diffraction, scanning electron microscopy, laser particle size analyzer and tap density (tap density refers to the stacking density of particles after vibration compaction) meter. The results showed that silver particles were spherical, mono-disperse and with high tap density (>5.0 g/mL), average particle size of about 2–3 μm and narrow particle size distribution. By surveying the experiment results and analysis of variance, two mathematical models were obtained and optimized parameters were determined. Analysis of the variance demonstrated that the interaction of [AgNO₃] and stirring rate were the most significant factor affecting particle size and PEG4000/AgNO₃ mass ratio and [AgNO₃] were main significant factors affecting tap density. The predicted particle size and tap density were respectively 2.5 μm and 5.065 g/mL while the experimental results were 2.52 μm and 5.108 g/mL, which indicated that the models were in good agreement with the experimental data.     

微乳液法纳米SnO2材料的合成、结构与气敏性能

本文研究了由阴离子表面活性剂组成的微乳液在纳米SnO     

The formation of layers of porous crystalline tin dioxide from a composite on the basis of multiwalled carbon-nanotube arrays

A new method for the synthesis of porous crystalline tin-dioxide (SnO₂) layers from composites on the basis of multiwalled carbon nanotubes (MWCNTs) and nonstoichiometric amorphous tin oxide (MWCNT/SnO _x ) is proposed. An MWCN/SnO _x composite layer produced by magnetron sputtering is annealed in air atmosphere at 500°C for 30 min. A homogeneous porous layer comprised of crystalline SnO₂ spherical particles with a size of about 0.1 μm is obtained as a result. In the process of annealing, nearly all the amount of carbon is removed in the form of gaseous oxides (only a small amount remains in the upper part of the porous SnO₂ layer). The structural defectiveness of nanotube walls, which increases because of the magnetron deposition of tin, plays a crucial role in the carbon oxidation and destruction of MWCNTs.     

Preparation and spectroscopy study of monodispersed metal oxide nanocrystals

SnO₂ nanocrystals with an average particle size of 3.5 nm are obtained by heating the mixture of hydrous SnO₂ nanoparticles and SrCO₃ particles. SrCO₃ can be removed from the product by washing with diluted HNO₃ acid. A series of SnO₂ nanocrystal samples with different particle size are prepared by heating at different temperature. All the samples obtained are characterized by XPS and Raman spectra. XPS result shows that the binding energy of Sn3d_5/2 decreases as the particle size increases. There is a surface-related Raman peak observed, which increases in intensity when the SnO₂ particles size decreases. The size-related change of the surface structure is responsible for the properties of nanocrystals.     

Synthesis of hydrous SnO2 and SnO2-coated TiO2 powders by the homogeneous precipitation method and their characterization

Hydrous SnO₂ and SnO₂-coated TiO₂ powders were synthesized by the homogeneous precipitation method using urea and the products were characterized by X-ray diffraction, thermogravimetry, differential thermal analysis, scanning electron microscopy and energy- dispersive X-ray microanalysis. Electrical conductivities were measured with an impedance analyser. Hydrous SnO₂ powder prepared under conditions without SO ₄ ^2– ions was a bulky product containing 75 wt% of water. The addition of SO ₄ ^2– ions to the solution changed bulky hydrous SnO₂ to a dense product; approximately spherical particles were obtained with an average particle size of 0.14 ± 0.03 m. with 13.5 wt % of absorbed water. Antimony-doped hydrous SnO₂ prepared under conditions with SO ₄ ^2– ions consisted of approximately spherical particles with an average particle size of 0.17 ± 0.04 m with 15.0 wt % of absorbed water. Hydrous SnO₂-coated TiO₂ powders with a good dispersion state and with various Sn/Ti ratios were prepared under conditions with SO ₄ ^2– ions. All the as-prepared coated powders were white, but the products doped with Sb³⁺ ions were turned to pale blue by heat treatment at 600° C for 1 h and their electrical conductivities increased by orders of about 3.0 in comparison with those of the other two.     

Tin dioxide nanoparticles: Reverse micellar synthesis and gas sensing properties

Tin dioxide (SnO₂) nanoparticles have been synthesized by reverse micellar route using cetyltrimethyl ammoniumbromide (CTAB) as the surfactant. Monophasic tin dioxide (SnO₂) was obtained using NaOH as the precipitation agent at 60 °C, however, when liquor NH₃ was used as precipitating agent then crystalline SnO₂ nanoparticles are obtained at 500 °C. SnO₂ prepared using NaOH show crystallite size of 4 and 12 nm after heating at 60 and 500 °C respectively using X-ray line broadening studies. Transmission electron microscopy (TEM) studies show agglomerated particles of sizes 70 and 150 nm, respectively. The grain size was found to be 6-8 nm after heating the precursor obtained (using liquor NH₃) at 500 °C by X-ray line broadening and the TEM studies. Dynamic light-scattering (DLS) studies show the aggregates of SnO₂ nanoparticles with uniform size distribution. Mössbauer studies show an increase of s-electron density at the Sn sites compared to bulk SnO₂ and a finite quadrupole splitting indicative of lowering of symmetry around tin atoms. The gas sensing characteristics have also been investigated using n-butane which show high sensitivity and fast recovery time.     

Microwave-assisted sol–gel process for production of spherical mesoporous silica materials

Spherical mesoporous SiO₂ and SiO₂–TiO₂ particles were synthesized by sol–gel method using W/O emulsion under microwave irradiation. In SiO₂ system, W/O emulsion was prepared by mixing partially hydrolyzed Si(OC₂H₅)₄ aqueous solution including C₁₈TAC as template with n-hexane solution including polyglycerol polyricinalate as emulsifier. In SiO₂–TiO₂ system, Ti(OC₂H₅)₄ capped by acetylacetone was added to the aqueous phase. In both cases, spherical products were synthesized by heating of W/O emulsion for 30 min under microwave irradiation. The specific surface area and pore size of spherical products were 800 m²/g and 1.6 nm, respectively, which indicates that the spherical products are mesoporous. These results suggest that sol–gel reaction in water phase proceeds rapidly because microwave quickly and selectively heats up the aqueous solution.     

Template-free fabrication of SnO2 hollow spheres with photoluminescence from Sni

SnO₂ hollow spheres with interstitial Sn²⁺ defect were fabricated by the hydrothermal method without any surfactant or polymer, whose shell is constructed by two layers of tetragonal prism nanorod arrays. The growth mechanism of the hollow spheres was investigated and attributed to the nucleation and arrangement of SnO₂ tetragonal prism nanorods on the surface of the hydrothermal reaction formed NO bubbles in the aqueous solution. After illumination by 275 nm wavelength light, narrow peak emissions centered at about 587-626 nm have been found in the photoluminescence spectrum, which have been ascribed to the interstitial Sn²⁺ defect in the SnO₂ hollow spheres.     

表面活性剂对纳米SnO2负极材料形貌结构及电化学性能的影响

为了提高SnO_2负极材料的电化学性能,本文以锡酸钠为原料、聚乙烯吡咯烷酮(PVP)、尿素、十二烷基硫酸钠(SDS)分别作为表面活性剂,采用水热法制备了具有纳米结构的SnO_2负极材料.利用扫描电子显微镜(SEM)、X射线衍射(XRD)、电化学测试仪测试了材料的形貌、结构和电化学性质.结果表明,使用不同表面活性剂,可获得不同形貌的纳米结构,并且对材料的电化学性能有较大的影响.当尿素作表面活性剂时,获得了分散较好的球形材料,在0.01~3.0 V,以200 mA/g进行充放电测试,首次放电容量2 256.6 mAh/g,经过50次循环后,放电容量保持在440 mAh/g,表现了较好的循环性能.     

A Study on the Role of Ethylene Glycol/Alcohol Ratio on Synthesis of Nano-Size SnO2

Nano-sized SnO₂ particles have been synthesized using sol-gel method. For this purpose, hydro-alcoholic solution consisting of SnCl₄ · 5H₂O, citric acid, and ethylene glycol (Et.G) are used as initial materials. The tin oxide powder obtained at different Et.G/Et ratios is characterized using powder x-ray diffraction (XRD) and transmission electron microscope (TEM) spectroscopic techniques. The results show that their structural depend strongly on Et.G/Et ratio. The XRD patterns show SnO₂-cassiterite phase in the nanopowders and the preferred orientation of the powder along (101) plane prevails upto Et.G/Et = 1 ratio, which shifts to (110) plane for Et.G/Et = 2 ratio. TEM investigation revealed that the average particle size is in the range of 20 to 32 nm. Electron diffraction pattern of nanopowders obtained at different Et.G/Et ratios shows that distribution of spherical particles increase and crystallite size those reduces with an increase in Et.G/Et ratio from .5to 2 due to the effect of ethylene glycol as polymerizing agent in sol-gel process. The possible explanation for this is given in the present investigation.     

The effect of SnO2 on the improvement of mechanical properties of MgO–MgAl2O4 composites

Incorporation of SnO₂ into MgO–spinel (M–S) increased mechanical properties significantly. Relationships between the parameters improving mechanical properties and microstructural variables were examined. Basic parameters improving the mechanical properties of M–S–SnO₂ composites were identified as follows: (a) when microcracks come across with either Mg₂SnO₄ particles or pores; crack branching and deviation of interlinked microcracks or crack arresting occurred more effectively than those of spinel particles, (b) fracture type was converted to intergranular fracture with incorporation of spinel into MgO, and transgranular fracture with addition of SnO₂ to M–S; additionally with the incorporation of additives, (c) critical defect size, (d) work of fracture values increased, and (e) MgO grain size decreased. R_st thermal shock parameter values of M–S–SnO₂ composites were markedly higher than those of M–S materials, associated with low strength loss, high thermal shock damage resistance and thus longer service life of M–S–SnO₂ composites for high-temperature industrial applications.     

Effect of non-ionic surfactant concentration and type on the formation and stability of W/O/W multiple emulsions: Microscopic and conductometric evaluations

Abstract

W/O/W multiple emulsions with sodium salicylate as a model drug were prepared and evaluated for the effect of surfactant concentration and type on stability using microscopic and conductometric methods. Primary (W/O) emulsions were prepared with lipophilic surfactants (2-31% W/W relative to the oily phase). W/O/W emulsions were formed by mixing the primary emulsions with solutions containing 0.5 to 2% W/V hydrophilic surfactants. Optimum concentration of the lipophilic surfactant was 26% W/W. The optimum hydrophilic surfactant concentration was 1% W/V. Best stability was achieved with HLB 3.7 lipophilic and HLB 15.6 hydrophilic surfactants.     

Synthesis of spherical Al2O3 and AlN powder from C@Al2O3 composite powder

A novel approach has been taken to produce (1) spherical Al₂O₃ particles by decarbonisation and (2) spherical AlN particles by nitridation and subsequent decarbonisation of C@Al₂O₃ composite particles. C@Al₂O₃ composite particles have been prepared by heterogeneous nucleation and crystallisation of Al(NO₃)₃ on surfactant encapsulated carbon nano particles followed by evaporative decomposition of the nitrate. Overpressure (0.4 MPa) of nitrogen and a temperature range (1723–1873 K) have been used for nitridation. Whiskers as well as spherical particles of AlN have been observed in the final product. The final product has been characterised by X-Ray Diffraction, Scanning Electron Microscope and Carbon–Hydrogen–Nitrogen content analysis by Elemental Analyser and the mechanism of the nitridation reaction has been analysed. The average size of the spherical AlN particles consisting of crystallites in nano-dimensions (30–50 nm) could be varied from 100 nm to 8 μm by changing the composition of the sol.     

Design and development of multiple emulsion for enhancement of oral bioavailability of acyclovir

The objective of this investigation was to design and develop water-in-oil-in-water type multiple emulsions (w/o/w emulsions) entrapping acyclovir for improving its oral bioavailability. Multiple emulsions (MEs) were prepared and optimized using Span-80 and Span-83 as lipophilic surfactant and Brij-35 as hydrophilic surfactant. The physio-chemical properties of the w/o/w emulsions - particle size, viscosity, phase separation (centrifugation test) and entrapment efficiency were measured and evaluated along with macroscopic and microscopic observations to confirm multiple nature, homogeneity and globule size. Stability study, in vitro and ex vivo release studies were performed followed by in vivo studies in rats. Stable w/o/w emulsions with a particle size of 33.098 ± 2.985 µm and 85.25 ± 4.865% entrapment efficiency were obtained. Stability studies showed that the concentration of lipophilic surfactant was very important for stability of MEs. Drug release from the prepared formulations showed initial rapid release followed by a much slower release. In vivo studies in rats indicated prolonged release and better oral bioavailability as compared to drug solution. The overall results of this study show the potential of the w/o/w emulsions as promising drug delivery systems for acyclovir.     

Synthesis of fine sodium-free silica powder from sodium silicate using w/o emulsion

Fine silica powders were synthesized from sodium silicate at room temperature using w/o emulsion containing water, nonionic surfactant of Triton N-57, and cyclohexane. Submicron and sodium-free silica particles could be prepared at low cost using inexpensive starting material of aqueous sodium silicate solution and ion exchange of ammonium sulfate. The particle size and size distribution of the silica powders were affected by the factors of reaction time, and concentrations of surfactant and sodium silicate solutions. The particle size of silica powders could be controlled by the same factors to be ranged from submicron to micron sizes. The particle size of SiO₂ decreased with reaction time and concentration of surfactant, but increased with concentration of sodium silicate. The preparation conditions were experimentally determined for obtaining the silica powder with submicron size, narrow size distribution, sphere in shape, and high purity without sodium contamination.     

The Coherent Scattering Cross-section of a Slightly Rough Sphere

In the case of scalar waves and impenetrable material, the coherent scattering cross-section of a nearly spherical particle is calculated, where the surface irregularities are described statistically by a correlation function. The results are valid up to the second order of hk (k is the wavenumber,h² the mean-square deviation from a smooth sphere), but for any value of the size parameter f = kR₀ (RR₀ is the radius of the sphere). The limits for small particles (f 1) and for large particles (f d 1) are derived, and it is shown that for f d 1 the scattering pattern outside the diffraction peak coincides with the result obtained by means of the Rayleigh-Rice approach, i.e. by applying scattering results for planar rough areas locally to the curved surface of the scattering body.