ABSTRACT
Why Coat Titania with Silica? . . . . . . . . . . . . . . . . 689
How to Coat Titania with Silica . . . . . . . . . . . . . . . 691
Iler DS Deposition Process . . . . . . . . . . . . . . . . . . . 692
Solution Chemistry of Aqueous
Sodium Silicate . . . . . . . . . . . . . . . . . . . . . . . . . 692
Adsorption of Aqueous Silica onto
Titania — pH and Concentration . . . . . . . . . . . 693
Concentration of 1024 mol/dm3
Aqueous Silica . . . . . . . . . . . . . . . . . . . . . . . . 693
Concentration of 1023 mol/dm3
Aqueous Silica . . . . . . . . . . . . . . . . . . . . . . . . 695
Concentration of 1:25 1022 mol/dm3 Aqueous Silica . . . . . . . . . . . . . . . . . . . . . . . . 695
Adsorption Isotherm at pH 9:5 . . . . . . . . . . . . 695 Interaction of Aqueous Silica with Titania . . . . . 696
Microelectrophoresis . . . . . . . . . . . . . . . . . . . . 696
Gas Adsorption . . . . . . . . . . . . . . . . . . . . . . . . 698
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . 699
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
The dense silica (DS) process involves the exposure of titania particles to aqueous silica solutions of increas-
ing silica concentration. The process is examined in this chapter by relating silica adsorption on titania
surfaces to solution pH and concentration and to the various monomeric, multimeric, and polymeric
species present in aqueous “solutions” of silica. Microelectrophoresis and gas adsorption studies reveal
that adsorption of monomeric silica occurs via hydrated cation sites that constitute only approximately
40% of titania surfaces. These “anchoring” sites provide a base for complete surface coverage and
buildup of silica multilayers (coatings), a buildup that occurs when the silica concentration is increased suf-
ficiently at the chosen pH (around 10 in the DS process) to induce polymerization.
