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

Two insoluble beta-cyclodextrin polymers were synthesized by reacting beta-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 beta-CD molecules through host-guest interactions.