Papers by Keyword: Stöber Method

Abstract: The nanosized silica (SiO₂) with the size less than 100 nm have successfully been prepared by hydrolysis and condensation of tetraethyl orthosilicate (TEOS) via a modified Stöber method at room temperature. The experiment was conducted by controlling the amount of the catalyst used, i.e., ammonium hydroxide (NH₄OH). The morphology observation of the synthesized silica nanoparticles was conducted by using a transmission electron microscope (TEM). It was found that the size of the silica depending on the amount of the catalyst used, with homogenous size ranging from 10 to 360 nm. The doping of silver nanoparticles was done by mixing the synthesized silica with the silver ions (Ag⁺) solutions. Then the sample was annealed for 75 min which results in the nucleation of the silver nanoparticles less than 20 nm onto the silica surfaces, depending on the temperature used.

Abstract: Monodisperse micron-grade silicon dioxide spherical particles have been prepared by using Stöber method. Effects of the solvents, the concentration of ammonia, TEOS and water on the particle sizes and the particle diameter distribution of silicon dioxide were investigated by scanning electron microscopy (SEM). The results show that the monodisperse micron-grade silicon dioxide spherical particles could be obtained in isopropanol solvent under a suitable reaction condition. The particle sizes increase with the decreasing of TEOS concentration. When the concentration of ammonia and water is increased, the silica particle size will increase. The particle diameter distribution narrows with the increment of the ammonia concentration and decrement of water concentration.

Abstract: To obtain large-sized, monodispersed spherical particles of silica by Sol-Gel, the classic Stöber method was optimized. Effects of the type of solvents，reaction temperature and reaction time on the particle sizes and the particle diameter distribution of silicon dioxide were investigated by scanning electron microscopy (SEM). The results show that the monodisperse silicon dioxide spherical particles with 1.0μm diameter could be obtained in isopropanol solvent under a suitable reaction condition. When the reaction temperature is increased, the silica particle size will decrease. The particle sizes increase first and decrease later as the reaction time passing. The addition method of TEOS has great effects on the morphology and size of silicon dioxide spherical particles.

Abstract: Ferrite particles were prepared by hydrothermal process at high temperature. The characterization of ferrite was examined by XRD, Mössbauer spectrum, and SEM. The XRD and Mössbauer spectrum confirmed that ferrite particles have a Fe₃O₄ inverse spinel structure, the SEM results show that each Fe₃O₄ particles were composed of many smaller magnetite nanoparticles. The as-synthesized Fe₃O₄ particles were modified by sodium citrate then further coated with SiO2 layer through the modified stöber method. The composited Fe₃O₄@SiO₂ microspheres exhibited outstanding monodispersity and magnetic property.

Abstract: Silver chloride (AgCl) nanoparticles with the average size of about 45 nm have successfully been doped onto the iron oxide-silica coreshell surfaces by a simple room temperature wet chemistry method under ambient atmosphere. The Stöber process has been used to make the coreshell structure, followed by adsorption of Ag⁺ species on silica surface prior to the addition of hydrochloric acid (HCl) and polyvinylpyrrolidone (PVP). The concentration of HCl acid that was used to induce the growth of AgCl particles was varied from 0.12 mM to 12x10³ mM of concentrations. Results showed that at a very high concentration of HCl (12x10³ mM), large AgCl agglomerates (0.3-0.6 microns) with irregular cubic-like morphology were obtained while at a very low, 12 mM HCl concentration, 30-50nm AgCl particles having a uniform cubic morphology were observed. Concentrations below 12 mM result in irregular and nearly spherical morphology of AgCl particles with a smaller size (28-60 nm). UV-Vis absorption of the composite materials showed absorption in the visible wavelength indicating that Ag nanoclusters might coexist together with AgCl particles.

Abstract: Antibacterial silver can be used against such micro-organisms as bacteria and molds. When Ag nanoparticles are attached to an inorganic carrier, e.g., silica long-term antimicrobial functionality can be gained. Such Ag-SiO₂ particles are potential for water purification or bactericidal applications. In this work, submicron sized silica particles doped with Ag were prepared by the modified Stöber method. The as-prepared powder was air-dried and annealed for 75 minutes at 573, 673, 773, 873, 973, 1073, 1173, or 1273 K in air. The powders were studied by DSC/TGA, XRD, SEM, TEM and UV-vis methods. The as-prepared powder consisted of round silica particles having size around several hundred nanometers. XRD and SEM studies confirmed that the powder consisted of metallic silver nanoparticles on the submicron silica surface after annealing at 873 K or higher. According to the SEM study the silver particles had an average particle size between 19-400 nm depending on the annealing temperature. DSC was used to determine the phase transformation temperatures. After annealing the Ag-SiO₂ powder at 873 K the TEM study suggested that the silver had crystalline structure. The XRD studies confirmed that silver appeared as a FCC crystal structure. The UV-vis measurements of Ag-SiO₂ powder annealed at and below 773 K showed a steady increase in absorption with decreasing wavelength without absorption peaks. Annealing at 873 K and above resulted in a strong peak in between 404 nm and 416 nm. This peak can be attributed to the surface plasmon resonance of silver nanoparticles.

Abstract: Silica-coating of AgI nanoparticles with a Stöber method was carried out to find out reaction conditions for control of the shell thickness. The AgI nanoparticles were prepared from AgClO4 and KI with the use of 3-mercaptopropyltrimethoxysilane (MPS) as a silane coupling agent and dimethylamine (DMA) catalyst for alkoxide hydrolysis. The silica-coating was performed at 4.5×10-6-4.5×10-5 M MPS, 11-20 M water, 0.002-0.1 M DMA and 0.005-0.04 M tetraethylorthosilicate at AgI concentrations of 0.1-1 mM. Consequently, AgI-silica core-shell particles could be prepared with the use of 4.5×10-5 M MPS, 20 M water, 0.01 M DMA and 1 mM AgI. Silica shell thickness could be varied from 15 to 28 nm with an increase in the TEOS concentration from 0.005 to 0.04 M.

Abstract: A room temperature route for doping silica particles with Cu nanoparticles to achieve hybrid structures is introduced. First, silica nanoparticles were synthesized according to the well-known Stöber method by hydrolysis and condensation of TEOS in a mixture of ethanol with water, using ammonia as catalyst to initiate the reaction. These SiO2 nanoaprticles were dried at 100 oC. We measured the size of these nanoparticles with transmission electron microscopy (TEM). Second, Cu-SiO2 nanoparticles were synthesized by reaction with CuCl2 and SiO2 nanoparticles in presence of catalyst at room temperature for 12 hrs. Results show silica nanoparticles of about 70 nm size with regularly deposited Cu nanoparticles. Cu-SiO2 nanoparticles were investigated with TEM images, energy dispersive X-ray analysis (EDX) spectrum and so on.