A silica-silver nanocomposite obtained by sol-gel method in the presence of silver nanoparticles

Silver nanoparticles (AgNPs) were obtained by a redox reaction, using a glucose-containing cyclosiloxane as a reduction agent and stabilizer. Then the AgNPs aqueous solution was used as the reaction medium for the sol-gel process, starting from tetraethylorthosilicate (TEOS) as silica precursor. The nanocomposite material resulted (SilAg) after solvent removal, aging and calcination and was investigated by infrared spectroscopy (FT-IR), atomic force microscopy (AFM), scanning electron microscopy coupled with energy dispersive X-ray system (SEM/EDX), transmission electron microscopy (TEM), energy-dispersive X-ray fluorescence spectroscopy (EDXRF), X-ray diffraction (XRD) and dynamic vapor sorption (DVS). The results were compared to model silicas obtained without silver. A higher condensation degree in SilAg was obtained due to the basic medium used in the first step and was confirmed by a sorption capacity lower than for the model silicas. The solid surface area calculated with GAB analysis using DVS data for the water vapors is 210 m² g^?1. The nanocomposite showed good catalytic activity for hydrogen peroxide decomposition.      

Study of the formation and electrochemical properties of nickel oxide-carbon fiber composites obtained in the presence of surfactants

The electrochemical properties of nickel oxide-carbon fiber composites obtained in the presence of SDS and PEG surfactants and chitosan biopolymer by means of cyclic voltammetry have been investigated. The material’s capacity parameters have been determined and the charging times and electrolyte resistance in pores have been calculated. The interrelation between the electrochemical and structural composite parameters are demonstrated.     

Unusual catalytic properties of nanostructured nickel films obtained by laser electrodispersion

Nanostructured nickel films deposited by laser electrodispersion onto a silicon (semiconducting) or thermally oxidized silicon (insulating) substrate show a remarkably high catalytic activity (of the order of 10³–10⁴ (mol product) (mol Ni)^?1 h^?1) in the isomerization of chlorinated hydrocarbons and olefin hydrogenation. The special properties of the laser-deposited films are likely due to the small size (2.5 nm), developed surface, and amorphism of the nickel particles, as well as to highly active, charged particles appearing on the insulating substrate. The latter result from thermal fluctuations of electrons between closely spaced particles. In a film deposited on silicon covered with a natural oxide layer, a significant role is also played by charge redistribution between the substrate and metal particles.     

Voltammetric method for direct determination of nickel in natural waters in the presence of surfactants

Voltammetric procedures for direct Ni(II) determination in natural water samples are described. The procedures are based on nickel deposition to the metallic state and then its oxidation in the presence of dimethylglyoxime with the formation of the complex adsorbed on the electrode. Reduction of the complex is exploited in the detection step. Due to the application of a sufficiently negative deposition potential the interference from surfactants is minimized. The detection limits for Ni(II) are 2x10(-9) and 2x10(-10) mol l(-1) for deposition times of 30 and 120 s, respectively. The influence of foreign ions is also presented.     

Hollow colloidal particles obtained by nano-extrusion in the presence of phospholipids

Using nano- and microsize extrusion, a simple synthetic procedure of preparing hollow monodispersed colloidal particles dispersed in an aqueous phase was developed. Hydrophobic styrene monomer containing 2-hydroxy-2-methyl propiophenone photoinitiator was forced into desired diameter membrane channels and stabilized by the hydrophobic regions of a liposome obtained from 1,2-dilauroyl-phosphocholine phospholipid in an aqueous phase. Such moieties exposed to 254-nm UV radiation polymerize monomers in the hydrophobic zone of the liposome, thus resulting in reinforced hollow vesicles. The size of such particles is controlled by the size of the membrane channels in the extruder and may vary from a few nanometers to micrometers, thus allowing the synthesis of monodisperse hollow colloidal spheres.     

Features of the sol-gel process of formation of nanostructured gadolinium oxide

The process of dehydration of Gd(OH)₃·nH₂O obtained by the sol-gel method from a solution of Gd(NO₃)₃, to Gd₂O₃ in the temperature range of 50–700°C was explored. The hydrogel and Gd₂O₃ structurization is shown to depend on the additives (AF-12 and 2-propanol). The final average particle size of Gd₂O₃ after annealing at 700°C is 20±2 nm, depending on the conditions of the synthesis. The resulting oxide particles are larger than the particles of yttrium oxide Y₂O₃ (17±2) obtained under the same conditions of the process due to the higher basicity of gadolinium and its higher coordination number with respect to the OH groups. This promotes the formation of crystalline phases of Gd(OH)₃ at lower temperature, 50–250°C, while maintaining a favorable structural short-range order in passing through an amorphous state to a crystalline Gd₂O₃.     

Control of structure and particle size of iron oxide on carrier oxide by the sol-gel method using organic polydentate ligands

It was tried to control the structure and particle size of iron oxide supported on a carrier by regulating the hydrolytic polymerization of aquo iron complexes with organic polydentate ligands. The iron oxide/carrier composites were prepared by calcining carrier oxides impregnated with organic ligands and Fe(NO₃)₃·9H₂O. When ligands were diacetone alcohol and ethanol, the structure of the iron oxide was exclusively corundum. But, with ligands such as ethylene glycol, citric acid and galacturonic acid, the structure of the iron oxide changed from corundum to spinel as the amount of ligands used increased. With both series of ring and straight chain saccharides, size of the iron oxide particles changed depending on saccharides used. It was thus concluded that the structure and particle size of iron oxide supported on a carrier can be regulated by using organic polydentate ligands.     

Physical and chemical properties of nano-sized aluminum hydroxide and oxide particles obtained by the electrochemical method

The structure and properties of nanoparticles of aluminum hydroxides and oxides obtained by electrochemical, chemical, and combined methods were studied by transmission electron microscopy, X-ray diffraction, thermal analysis, and atomic emission spectroscopy. The influence of synthesis conditions on the structure and morphology of nanoparticles was studied. It was shown that the effect of an electrochemical field allows monophasic systems to be obtained with a narrower range of particle sizes than in the case of chemical deposition.     

Porosity of aluminium oxide-based binary systems obtained by sol-gel method

A comparative study of binary oxide systems Al₂O₃-SnO₂; Al₂O₃-GeO₂ and Al₂O₃-B₂O₃ obtained by the sol-gel method has been made. Particular attention was paid to changes in the texture as a function of the type of the second component and its concentration in the binary system. Additionally, we describe changes in the porosity of the above systems after annealing in hydrogen atmosphere. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of the nanostructured luminophor Y2O3-Eu-Bi by the sol-gel method

The sol-gel method of the formation of the nanostructured luminophor based on Y₂O₃ doped by Eu³⁺ and Bi³⁺ was studied. The mechanism of the dehydration and dehydroxylation of gels and xerogels of the mixed hydroxides, particle sizes, structure, and luminescent properties of the synthesized products based on Y₂O₃ depend on the chemical nature of a precipitating agent (NaOH or NH₄OH) and a washing agent (water and alcohol).     

Behaviour of phenol red pH-sensors in the presence of different surfactants using the sol-gel process

Phenol red was immobilised into a polysiloxane matrix using a sol-gel process to form pH optical sensors. The sol-gel was obtained by hydrolysis of tetraethoxysilane (TEOS) in the presence of phenol red (PR) and the appropriate surfactant. Different surfactants, namely cetyltrimethylammonium bromide (CTAB), dodecyldimetyl amino-oxide (GLA) and Triton X-100 (TX-100), were employed. Interestingly, the use of surfactants significantly improved the mesostructure of the silica and increased the porosity of the system. The two response pH ranges were shifted to pH 0.0–3.0 and pH 10.5–1.5M [OH^?] compared with those of the free PR (pH 0.0–3.0 and pH 6.5–9.5). It is found that the pH response and the pKa shift of the phenol red were dependent, not only on the silica matrix but also on the ionic properties of surfactants. In the case of ionic surfactants such as CTAB or GLA, there was further shift to more acidic and more basic pH, whereas in the case of non-ionic surfactants such as TX-100 no significant change of the pH curve was observed.     

Structural features of finely dispersed pseudoboehmite obtained by a sol-gel method

Simulation of diffraction patterns, radial distribution function analysis, and electron microscopy are applied to study the features of the structure of nanosized pseudoboehmite obtained by the sol-gel method. It is found to consist of plate-like particles with a thickness of one lattice constant in the [010] direction. Such a structure of the pseudoboehmite particles results in the absence of the 020 diffraction peak in the diffraction pattern.     

Interactions and dispersion stability of aluminum oxide colloidal particles in electroless nickel solutions in the presence of comb polyelectrolytes

The effect of comb polyelectrolytes on the dispersion stability of colloidal alumina particles in DI water and commercial electroless nickel (EN) solutions was investigated. Adsorption of polyelectrolytes and major EN components onto colloidal alumina was assessed by TGA, chemical analysis, and zeta potential measurements. Zeta potential measurements were made during titrations of comb-polyelectrolyte-stabilized dispersions with EN solutions to full ionic strength for the first time. The compilation of titration curves made with varying amounts of comb polyelectrolytes provides high resolution and novel insight into the particle/surfactant/EN systems. Continuous decrease in particle/EN components surface interactions with the increase in comb polyelectrolyte coverage is observed. Laser diffraction measurements reveal steric stabilization of nano- and submicronmeter alumina dispersions in both DI water and EN solutions with >7 wt% and >2 wt% comb polyelectrolyte, respectively.     

Thermostability of glucose oxidase in silica gel obtained by sol-gel method and in solution studied by fluorimetric method

The thermostability of glucose oxidase entrapped in silica gel obtained by sol-gel method was studied by thermostimulated fluorescence of FAD at pH 5 and 7 and compared with that of the native enzyme in the solution and at the presence of ethanol. The unfolding temperatures were found to be lower for the enzyme immobilised in gel as compared with the native enzyme but higher as for the enzyme at the presence of ethanol. In gel, the thermal denaturation of glucose oxidase is independent on pH while in solution the enzyme is more stable at pH 5. The investigation the enzyme in different environment by steady-state fluorescence of FAD and tryptophan, synchronous fluorescence and time-resolved fluorescence of tryptophan indicates that the state of the molecule (tertiary structure and molecular dynamics) is different in gel and in solution. The ethanol produced during gel precursor hydrolysis is not the main factor influencing the thermostability of the enzyme but more important are interactions of the protein with the gel lattice.     

On the pseudocapacitive behavior of nanostructured molybdenum oxide

Nanostructured molybdenum oxide having a particle size in the range of 30–80 nm was prepared by potentiodynamic electrodeposition method, and the effects of H₂SO₄ concentration on its capacitive behavior were studied by cyclic voltammetry, galvanostatic discharge, and electrochemical impedance spectroscopy. Poor to fair capacitive behaviors were witnessed depending on the electrolyte concentration and conditions of charge/discharge. Increasing acid concentration to 0.02 M had favorable effect, while beyond that, the effect was detrimental. Capacitance around 600 F g⁻¹ was recorded in the potential range of 0 to −0.55 V vs. Ag/AgCl.     

Narrow size distribution polystyrene latexes prepared in the presence of amphoteric sulfobetaine surfactants

Polystyrene latexes with a narrow size distribution (Dw/Dn < 1.05) were prepared with a large range of particle sizes (from 40 to 800 nm) in the presence of various amphoteric sulfobetaine surfactants. The influence of the nature of the surfactant and of the ionic strength, the pH and solid content were studied. The results are discussed and compared with those obtained using sodium dodecyl sulfate or in the absence of surfactants.     

Preparation,structure and properties of silicate-phosphate glasses obtained by means of sol-gel method

Gels, densified amorphous materials and thin layers in SiO₂-P₂O₅, SiO₂-P₂O₅-Al₂O₃ and SiO₂-P₂O₅-Na₂O systems were obtained from alcohol solutions. Detailed DTA, XRD and FTIR investigations were carried out for dried gels and heat-treated samples. It has been found, among others, that the addition of aluminium to the silicate-phosphate glasses eliminates the doubly bonded oxygen (P=O) and leads to the formation of a continuous framework connected with [SiO₄], [PO₄] and [AlO₄] tetrahedra.There were measured the chemical and electrical properties of glasses covered with silicatephosphate gel layers. It has been found that the chemical resistance of the covered glasses is higher than that of the basic, sodium-calcium-silicate glass. Moreover, the silicate-phosphate layers modify the surface electrical conduction of the basic glasses. The layers of systems SiO₂-P₂O₅ and SiO₂-P₂O₅-Al₂O₃ show the electrical conduction considerable higher than the basic glass. The layers containing sodium, depending on its concentration, behave similarly to the basic glass or show lower electrical conductivity.     

Syntheses of rare-earth metal oxide nanotubes by the sol-gel method assisted with porous anodic aluminum oxide templates

In this paper, we report a versatile synthetic method of ordered rare-earth metal (RE) oxide nanotubes. RE (RE=Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) oxide nanotubes were successfully prepared from corresponding RE nitrate solution via the sol-gel method assisted with porous anodic aluminum oxide (AAO) templates. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM, and X-ray diffraction (XRD) have been employed to characterize the morphology and composition of the as-prepared nanotubes. It is found that as-prepared RE oxides evolve into bamboo-like nanotubes and entirely hollow nanotubes. A new possible formation mechanism of RE oxide nanotubes in the AAO channels is proposed. These high-quantity RE oxide nanotubes are expected to have promising applications in many areas such as luminescent materials, catalysts, magnets, etc.