2013 Volume 86 Issue 4 Pages 520-525
Previous studies have proposed that silica has micropores or a “gel layer” on its surface; however, previous models of silica dissolution have considered only the top monolayer, and neglected the internal structure of silica. Here, we have developed a dissolution model that takes into account acid dissociation of internal silanol groups. The dissolution rates of silica, the solution pH and the electrophoretic mobilities of the silica particles were measured in basic aqueous media. These parameters were very different depending on the conditions, however all parameters behaved as expected based upon our simple model. In the model, we considered the surface potential and the potential inside the silica particle to quantify the acid dissociation of the top-surface and internal silanols, respectively. The dissolution rates were proportional to the number of top-surface deprotonated silanols, [≡SiO−]top. Internal silanol was not directly involved in the dissolution reaction, however acid dissociation of internal silanol must be considered to evaluate [≡SiO−]top. Electrophoretic mobilities are discussed to confirm the validity of our model.
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