Abstract: Disclosed herein is a photocatalytic coating composition that enables control of refractive index, film density and hydrophilicity and gives a film with improved strength and adhesion. The photocatalytic coating composition comprises: (1) an alkali silicate aqueous solution having: (A) a molar ratio of silicon to an alkali (SiO2/(A2O+B) (A: alkali metal, B: NH3)) in the range of 4 to 30; and (B) a silicon concentration in terms of oxide (SiO2 concentration) in the range of 6.8 to 30% by weight; and (2) a photocatalytic compound.

Abstract: An alkali silicate aqueous solution having intermediate characteristics between water glass and colloidal silica and having a high molar ratio (SiO2/(A2O+B))(A: alkali metal, B: NH3), a high silicon content and a high anionic activity. The alkali silicate aqueous solution has the properties: (A) the molar ratio of silicon to an alkali (SiO2/(A2O+B) is in the range of 4 to 30, and (B) the silicon concentration in terms of an oxide (SiO2 concentration) is in the range of 6.8 to 30% by weight. A process for preparing an alkali silicate aqueous solution comprises dealkalizing a starting alkali silicate aqueous solution by means of an electro-dialysis device, and then optionally concentrating the dealkalized solution by a reverse osmosis membrane method.