Ki Do Kim

PREPARATION OF SILICA NANOPARTICLES: DETERMINATION OF THE OPTIMAL SYNTHESIS CONDITIONS FOR SMALL AND UNIFORM PARTICLES

Abstract Silica nanoparticles were prepared from tetraethylortho-silicate (TEOS) dissolved in ethanol by using a semi-batch process in order to control the particle properties. In this work, the statistical experimental method was also used to compare the properties (particle size and SD) of the SiO 2 particles according to the four parameters ( R =[H 2 O]/[TEOS]), concentration of ammonia (NH 3 ), the feed rate of reactant, reaction temperature]. We have obtained monodispersed silica particles having size ranging from 10 to 350 nm by our experiment. It was found that the optimal synthesis conditions for the preparation of SiO 2 nanoparticles with narrow size distribution in semi-batch process were as follows; ( R =[H 2 O]/[TEOS], 30–55; concentration of ammonia (NH 3 ), 0.2–0.35 mole l −1 ; feed rate of reactant, 13–17 cm 3 min −1 ; reaction temperature, 55–65°C). The above-mentioned optimal conditions were used to prepare the particles with minimum particle size (30 nm) and its SD ( 2 nanoparticles was increased in the following order; reaction temperature, ( R =[H 2 O]/[TEOS]); concentration of ammonia (NH 3 ), feed rate of reactant.

Formation of Silica Nanoparticles by Hydrolysis of TEOS Using a Mixed Semi-Batch/Batch Method

A new method for preparing silica nanoparticles, which consists of a two-stage semi-batch/batch hydrolysis reaction of tetraethylorthosilicate (TEOS), is presented. A relatively slow rate of hydrolysis of the TEOS occurred during the semi-batch process, which resulted in larger silica particles with a narrower size distribution. This was in direct contrast to the batch process. An example of reduction in particle size for an initial semi-batch and subsequent batch reaction is shown. On completion of the initial semi-batch step, the silica particles had a diameter of 106 nm. As the subsequent batch reaction proceeded, the mean size of the particles decreased to 23 nm. In this work, it was found that the optimal conditions for the silica nanoparticles using this mixed method were as follows; (TEOS: 0.5 M, H2O: 6.0 M, NH4OH: 0.2 M, feed rate: 5.0 ml/min, temperature: 42.5°C). In conclusion, a mixedsemi-batch/batch system suggested a new probability for the synthesis of nanoparticles.

Synthesis of TiO2 nanoparticles by hydrolysis of TEOT and decrease of particle size using a two-stage mixed method

Abstract A new preparation method of particles was introduced, which consisted of a semibatch–batch two-stage reaction to decrease the size of TiO 2 fine particles. Using a semibatch process as a first stage, the particle size grew to a certain level (132 nm). Using a batch process as a second stage, however, the particle size decreased about 42 nm. The particles prepared by using a two-stage (semibatch–batch) method had a smaller mean particle size and smaller standard deviation than those obtained from the single-stage process. In this work, the statistical experimental method was also used to compare the various properties of the TiO 2 particles according to the six parameters [concentration of TEOT during 1st and 2nd stages, reaction temperature during 1st and 2nd stages, the amount of hydroxypropyl cellulose (HPC) during 1st and 2nd stages]. It was found that the optimum conditions for the maximum reduction of TiO 2 particle size using this method were as follows: (1st TEOT (M): 0.091, 2nd TEOT (M): 0.146, 1st temperature (°C): 20.0, 2nd temperature (°C): 38.2, 1st HPC (×10 −2 g/cm 3 ): 0.018, 2nd HPC (×10 −2 g/cm 3 ): 0.290). The experimental results measured by using the above optimum conditions were in agreement with calculated results and produced the smallest size (∼42 nm in diameter) with the value of DPS (−90 nm). In addition, we found that the main parameters affecting the decrease of particle size were concentration of TEOT and the reaction temperature during second stage.

Comparison of the effect of reaction parameters on particle size in the formation of SiO2, TiO2, and ZrO2 nanoparticles

Abstract Monodisperse SiO 2 , TiO 2 , and ZrO 2 nanoparticles were synthesized by hydrolysis of tetraethylorthosilicate (TEOS), tetraethylorthotitanate (TEOT), and zirconium normal propoxide (ZNP), respectively, in a semi-batch reactor, which consisted of a reservoir of starting solutions, a micro feed pump to supply the solutions, a water bath, and a reactor with a stirrer. The effects of three parameters (reaction time, R =(H 2 O/[TEOS or TEOT or ZNP], and feed rate of reactant) on particle size were observed. The main differences in the formation of SiO 2 , TiO 2 , and ZrO 2 nanoparticles were as follows. (1) Mean particle size of SiO 2 increased with increasing the reaction time, whereas the increase of reaction time decreased the particle size of TiO 2 and ZrO 2 . (2) TiO 2 and ZrO 2 particles should be prepared at high water concentration to obtain the nanoparticles and SiO 2 particles have to be synthesized at low water concentration by contraries. (3) In the case of SiO 2 , increasing the feed rate of reactant decreased the particle size, while the particle size of TiO 2 and ZrO 2 increased with increasing the feed rate.

Synthesis and growth mechanism of TiO2-coated SiO2 fine particles

Abstract TiO2-coated SiO2 fine particles were synthesized by the hydrolysis of tetraethylorthosilicate (TEOS) and tetraethylorthotitanate (TEOT) in order to investigate the growth mechanism of TiO2 particles coated on monodispersed silica seed particles using the semi-batch reactor. Firstly, SiO2 seed particles with narrow particle size distribution were prepared by controlled hydrolysis of TEOS solutions. Secondly, SiO2 seed particles were allowed to coat and grow by further addition of TEOT as a precursor of TiO2 particles. Nielsens chronomal analysis and Overbeeks theory were applied to clarify the growth mechanism of TiO2 particles coated on silica seed particles. As a result, it was found that the particle growth mechanism was presumed to be a surface reaction in which the rate determining step was a first-order polynuclear-layer growth mechanism and the growth rate constant, kpwas about 2.95×10−6 cm s−1.

Comparison of particle size and standard deviation of TiO2 particles prepared by batch, semi-batch and continuous reaction method

Abstract A new preparation method for TiO2 nanoparticles was introduced, which consisted of a small reactor for controlling the hydrolysis rate and continuous aging tube for reducing the size and standard deviation of TiO2 particles. In this process, TiO2 nanoparticles were synthesized from the hydrolysis and condensation of TEOT without HPC dispersant. The particles prepared by using a continuous reaction method without dispersant had a smaller mean particle size and a smaller standard deviation than those obtained from batch or semi-batch processes using dispersant. In this work, it was also found that the size of TiO2 particles decreased by applying intermittent flow to the aging tube. By using the above conditions, mean diameters as small as 30 nm were obtained.