Removal of carcinogenic direct azo dyes from aqueous solutions using calix[n]arene derivatives

Calix[n]arenes having different internal cavities sizes were synthesized. The ability of these sorbents to extract carcinogenic direct azo dyes from water by a solid-liquid extraction process was studied and compared to results obtained with the unsubstituted calix[n]arene. The carboxylic acid derivative of calix[6,8]arene showed the highest affinity towards the azo dyes. The sorption capacity of dyes on the calix[n]jarenes was dependent on the presence of sulfonate groups on the anionic dyes. The optimum pH value for dye sorption was observed at pH 3.5 to 8.5 for all calixarene derivatives. The proposed sorption mechanism involves several kinds of interactions: electrostatic repulsion between carboxylic acid groups of calix[n]arenes and sulfonate groups of azo dyes, hydrogen bonding and formation of an inclusion complex through host-guest interactions. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.