Intercalation of D & C Red No. 6 in Hydrotalcite

Abstract

D & C Red No. 6 (Rithol Bubin B), a pigment which is a Na salt of an anionic azo compound, was intercalated into mixed hydroxide layers of synthetic hydrotalcites with composition of [Mg_xAl_1-x (OH) ₂] ^x+ (A^n-) _x/n· yH₂O (0.2≤x≤0.33), where A^n-is an anion such as Cl^-, OH^- or CO₃^2- located in the interlayer gallery and which can be replaced with the dye anion by ion-exchange. The ion-exchanged form of hydrotalcites was prepared by three methods : (1) by ion-exchanging a Cl-form of hydrotalcite with the dye anion in an aqueous solution, (2) by reacting a decomposed form of hydrotalcite calcined at 500°C with the dye anion in an aqueous solution and (3) by coprecipitating a dye-combined form of hydrotalcite directly from a mixed solution of metal salts, dye anion and NaOH. The alignment of interlayer dye anions which have planar configuration was determined by the method of preparation. Method (2) gave a flat setting parallel to the host layer, method (3) gave a perpendicular setting and method (1) gave mixed layers of the two settings. The perpendicular alignment allowed a higher dye anion content of up to 47 % compared to 30% for the parallel one. The hue of the coloured interlayer composite was a little more blue as compared to the original pigment. The dye elution was as low as 5 mg/L in 1% NaCl aqueous solution.