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TEOS concentration effects:

Stober et al. have reported that TEOS has no effect on the final particle size. The larger particles reported by Bogush et al. Will be opposite to the increase in TEOS concentration, and van Helden et al. found that the particle size was reduced. It was found that the size of silicon dioxide nanoparticles increased with the increase of TEOS, ammonia and water concentrations of 7 and 2M, respectively, and the effect was opposite. In this study, it can be observed that when the concentration of ethanol, water and ammonia (Exps.4-6) is 8M, 3M and 14M, respectively, with the increase of TEOS in the concentration range of 0.012-0.12, the size is also increasing. In contrast, when the concentrations of ethanol, water and ammonia (Exps.7-8) were 4M, 14M and 14M, the size of the silica nanoparticles was also decreasing as TEOS increased in the 0.012-0.12 concentration range. This may be due to the high concentration of water, its hydrolysis rate in the orthosilicate is the first order and the first rate constant model is a function of water concentration. Thus, the rate constant must increase with increasing water concentration, which should lead to faster kinetics, resulting in smaller particles. In addition to this, the effect of R = [H2O] /[TEOS] on particle size at different temperatures was studied. The figure shows that as the temperature increases at a higher R 'value, the particle size increases and the particle size decreases as the temperature increases at lower values.

Water and ammonia concentrations:

In general, hydrolysis is a very slow reaction, although the use of acid or alkali as a catalyst. Hydrolysis and condensation of TEOS in ethanol uses ammonium hydroxide as a catalyst. According to Matsoukas and Gulari, by increasing the concentration of ammonia and water, get larger particles. Ammonia as a catalyst, it will increase the rate of hydrolysis and condensation, resulting in faster kinetics. As a result, the concentration of water increases to produce smaller particles. Surprisingly, in this method, a reverse effect was observed. As the concentration of ammonia increases, we find that the size of the silicon dioxide nanoparticles is reduced. As shown in the figure, under the experimental conditions of ethanol, water and TEOS concentrations of 8 M, 3 M and 0.045 M, it is noted that the ammonia concentration is increased in the range of 2.8-28 M and the size of the silicon dioxide particles decreases from 242 to 30.6 nm. Matsoukas and Gulari also mentioned that increased water concentrations also produce smaller particles. On the other hand, Park et al. obtained larger particles at higher water concentrations. According to Park et al., in the presence of high water concentrations, a high rate of nuclear generation produces many submicron particles in the short term. However, the hydrogen bonding of the SiO2 submicron particles is lower than the water concentration, and the water concentration is higher because of the excess water. As a result, agglomeration leads to the formation of large particles. In this study, it can be seen from the figure that the concentration of water is as high as 10 M and its size is increased, and after that it is noted that as the concentration of water increases, the concentration of TEOS and ammonia is 0.045M, 14M under the experimental conditions, the size is reduced.



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