Removal of azo dyes from aqueous solutions using calix[4]arene and β-cyclodextrin

A calix[4]arene-based oligomer 5 and a β-cyclodextrin polymer 6 were synthesized by the condensation of p-tert-butylcalix[4]arene and β-cyclodextrin, respectively, with hexamethylene diisocyanate. In their batch sorption of selected azo dyes, the β-cyclodextrin polymer 6 was found to be a better azo dye sorbent than the p-tert-butylcalix[4]arene-based oligomer 5. In addition, oligomer 4 containing pendant calix[4]arene units with crown-6 functionalities on the lower rim was synthesized and its complexation of the azo dyes was investigated by liquid–liquid extraction. The calix[4]crown-6 oligomer 4 showed the highest affinity for the azo dyes.