Adsorption of the dye Acid Blue 158 premetalized with chromium on chitin/chitosan

Removal of the premetalized dyes from the effluents of textile and leather industries is still open. The work aims to investigate functional groups taking part in the sorption of premetalized dye Acid Blue 158:Cr on chitin/chitosan and to investigate the mechanism of the sorption. The process was spontaneous (negative value of the Gibbs function), endothermic (ΔH = 0.2679 kJ/mol) with an affinity between the AB 158:Cr and chitin (ΔS = 1.315 J/mol*K). Langmuir, Freundlich, and Dubinin-Radushkevich isotherms were used to approximate experimental data giving a good correlation. Maximal capacity was evaluated as 46.1 mg/g and 370.4 mg/g for chitin and chitosan, respectively. Kinetics was described with a pseudo-second-order model. It was shown that physical sorption and chemisorption can occur parallelly: chemisorption on amine groups via interaction with chromium and physical sorption on amine group or hydroxyl group via interaction with the azo core of the dye.