Chemicals

Sodium silicate solution (assay 52.0–57.0 wt %, SiO₂ content 35.0–38.0 wt %, molar ratio (SiO₂/Na₂O): 2.06–2.31) and 2-methyl-2-propanol (Special Grade) were purchased from Wako. Ion-exchange resin (Amberlite IR120B) was supplied by Organo Corp. Two commercial titania sols, one stabilized using nitric acid (TKS-202, 33 wt % TiO₂) and the other in neutral condition (TKS-203, 20 wt % TiO₂), were obtained from Tayca. Methylene blue trihydrate (>98.5 wt %) used as a model substrate was purchased from Kanto Chemical. Azure A (AA) and Azure B (AB), main intermediates generated during decolorization of methylene blue, were supplied by Sigma-Aldrich (as a chloride salt, ∼80%) and Wako, respectively.