A calix[4]arene oligomer and two beta-cyclodextrin polymers: Synthesis and sorption studies of azo dyes

Two insoluble β-cyclodextrin polymers were synthesized by reacting β-cyclodextrin with hexamethylene diisocyanate (HMDI) or 4,4-methylene bis phenyldiisocyanate (MPDI) as a crosslinking agent and a calix[4]arene-based oligomer was prepared by the condensation of p-tert-butylcalix[4]arene with HMDI and utilized to remove selected water-soluble azo dyes from aqueous solution. Oligomer 2 was found to be a poor sorbent for the azo dyes. The influence of several parameters (pH, contact time, and NaCl concentration) on the sorption capacity was evaluated using the batch and recycling column methods. The proposed sorption mechanism involved several kinds of interactions: physical adsorption, hydrogen bonding and formation of an inclusion complex due to the β-CD molecules through host-guest interactions.