Preparation of pigments on modified precipitated silicas

Pigments were obtained by attaching C.I. Direct Red 81 dye to a modified silica surface. Two types of precipitated silicas were applied, namely the commercial Syloid 244 and the precipitated EG-SILICA which was prepared according to a novel procedure. The silica surface was modified with silane coupling agents, such as 3-aminopropyltriethoxysilane and N-2-(aminoethyl)-3-aminopropyltrimethoxysilane. The staining process was conducted in an aqueous suspension of silica in the presence of the dye. Various amounts of modifiers were applied in order to determine their effect on the dye adsorption process. The physicochemical, structural and microscopic properties of the modified silicas and of the obtained pigments were examined.