Enhancement of adsorption of Congo red dye onto novel antimicrobial trimellitic anhydride isothiocyanate-cross-linked chitosan hydrogels

The removal of the dyes from industrial wastewater is one of the main environmental requirements. In this work, three trimellitic anhydride isothiocyanate-cross-linked chitosan hydrogels, previously reported as novel antimicrobial agents, have been investigated for the first time as adsorbents for anionic Congo red (CR) dye from its aqueous solution. The hydrogels behave as polycationic materials. Their adsorption capacity for the CR dye increased significantly with increasing the temperature, with decreasing the solution pH and with an increase in their contents of cross-linking. Their adsorption fitted to the pseudo-second-order kinetic model. The adsorption isotherms conform to the Langmuir model with a maximum sorption capacity of 63.05 mg g⁻¹ and removal efficiency of 96.59%. The results proved that the sorption process is remarkably controlled by chemisorption phenomenon. Based on the data of adsorption thermodynamics, the adsorption is an endothermic process. The regeneration and the reuse of the hydrogels were possible. Thus, incorporation between chitosan and the functional groups of the cross-linker into the same structure is efficiently enhanced the features of chitosan. It is a good manner for achieving appropriate systems as efficient adsorbents that can be considered as favorable candidates in the field of acidic dye removal.