Exchange of Na+ for the silanolic protons of silica

Interaction of polysilicic acid with monolayers of substances containing quaternary ammonium groups

“…Since the pKa of polysilicic acid is about 6.5 [23,24], the concentration of silicate ions is high at pH > 6.5, so that the interaction with the monolayer, if ionic, may be expected to occur at these pH values. The experimental curves show that this is indeed so.…”

Monodisperse, high refractive index, highly charged ZnS colloids self assemble into crystalline colloidal arrays

“…The TEOS reacted particle surface groups titrate over a broad pH range with a pK a $ 6, within the range of pK a discussed for silica surfaces [58][59][60]. ZnS particles simultaneously reacted with TEOS and the phosphonate silane coupling agent (ZnSTP) show a distinctly higher Zeta potential until pH > 9.…”

Surface Hydroxyl Site Densities on Metal Oxides as a Measure for the Ion-Exchange Capacity

“…Two types of acid hydroxyl groups have been assumed for the exchange of Na ϩ with silanolic protons on silica (45). Polyfunctionality of ion exchange resins has been explained by assuming a total of three types of carboxyl sites with different reactivities due to different internal pore environments (46 -48).…”