Effect of electrolyte additives on sol-precipitated nano silica particles

The effect of mono-valent electrolyte additives on nanosized silica particles, synthesized via the sol-precipitation method, was investigated. Without additives, the particle size varied from about 35 nm to hundreds of nm depending on the TEOS, water, and ammonia concentrations. The addition of a small amount of electrolytes (below the optimal concentration) reduced the particle size up to 17.5 nm, due to an enhanced particle surface electric charge, thereby inhibiting particle growth. Meanwhile, a further increase in the additive concentration (above the optimal concentration) significantly increased the particle size, due to neutralization of the particle charge, thereby promoting particle growth. Among the present additives, sodium iodine had the most effect on reducing the particle size, while cesium chloride had the least.