Use of β-cyclodextrin and starch based polymers for sorption of Congo red from aqueous solutions

Two starch-based and a β-cyclodextrin (β-CD)-based polymers were synthesized using 4,4′-methylene-bis-phenyldiisocyanate (MDI) or hexamethylenediisocyanate (HMDI) as a cross linking agent in dry dimethylformamide and used as a sorbent for the removal of Congo red from aqueous solutions. The cross-linked polymers were characterized by Fourier transform infrared spectroscopy, thermogravimetric and differential scanning calorimetric analysis. The dye adsorption experiments were carried out by using batch and recycling column procedure. The effects of initial pH (pH0), the contact time and the initial dye concentration were changed to obtain the best experimental conditions. The pH0 of the dye solution strongly affected the chemistry of both the dye molecules and polymer 3 in an aqueous solution. The effective pH0 was 7.0 for adsorption on polymer 3. The equilibrium adsorption data were interpreted using Langmuir and Freundlich models. The adsorption of Congo red was better represented by the Freundlich equation.