Aminofunctionalized acrylamide–maleic acid hydrogels: Adsorption of indigo carmine

Aminofunctionalized acrylamide–maleic acid hydrogels having both amine and acid groups were prepared by transamidation reaction of acrylamide–maleic acid (AAM–MA) hydrogels using ethylenediamine in non-aqueous media. Modified polymers were characterized by determination of amine value (AV), carboxylic acid group content (AGC) and FTIR spectra. The modified hydrogels obtained have the amine value of 2.81 mmol/g. Their swelling properties were changed depending upon the pH value of external medium. The modified hydrogels were used as a new sorbent for removal of indigo carmine from aqueous solution. The effects of pH, time, NaCl concentration and initial dye concentration on the adsorption capacity were investigated. Almost 70–80% of capacity was saturated within approximately 30 min and quite high adsorption capacity was observed. The adsorption capacity increased at acidic pH and also in presence of NaCl in dye solution. The adsorption isotherm models were applied to the experimental data and it was seen that the Langmuir isotherm model was the best fit for these modified AAM–MA hydrogels–indigo carmine system.