To study the effects of organic compounds on the formation of silica, the polymerization of silicic acid in sodium silicate solutions in the presence and absence of sodium salicylate and disodium phthalate was investigated. The monosilicic acid concentration showed minor differences among the three different solutions. However, the concentration of polysilicic acid particles larger than 0.45 μm varied significantly among the three solutions, suggesting that the two organic compounds accelerate the growth of polysilicic acid. In particular, the concentration of polysilicic acid particles larger than 0.45 μm increased sharply in accordance with phthalate concentration, which is further evidence that phthalate accelerates the growth of silica. SEM images and size distribution measurements revealed that phthalate accelerates the aggregate of small silica particles to form larger silica pieces. FT-IR spectra of the silica formed during the polymerization of silicic acid showed the presence/or adsorption of salicylate and phthalate in the silica particles/or on the silica surfaces. The bidentate adsorption of salicylate or phthalate to two different polysilicic acid particles may accelerate the P–P reaction to aggregate the individual silica particles and rapidly form large size of silica.
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