Thermodynamics, kinetics and isotherm studies on the removal of anionic Azo-dye (Congo red) using synthesized Chitosan/Moringa oleifera gum hydrogel composites

Low cost and biocompatible hydrogels were synthesized using chitosan (CS) and Moringa oleifera (MO) gum biopolymers through Maillard reaction with glutaraldehyde as crosslinker. These CS/MO hydrogels were characterized using FT-IR spectroscopy and thermo gravimetric analysis (TGA). Equilibrium swelling behavior at different pH, temperature and salt solutions indicated almost equal swelling at all pH values, while higher swelling was observed at high temperature and low salt concentrations. Congo red dye, an azo dye, is potentially carcinogenic and can have different molecular structure at different pH. For its removal, variables including initial dye concentration, temperature, pH and contact time were optimized in order to achieve best adsorption capacity. The kinetics and isotherm studies suggested that the process of Congo red sorption on hydrogels was better fitted through pseudo second-order and Langmuir isotherm model. Maximum adsorption capacity of 50.25 mg/g was obtained at pH 2 as per Langmuir isotherm that represented a monolayer adsorption mechanism. The thermodynamic evaluation of the system suggested chemical nature of adsorption of dye. Since CS/MO hydrogels showed removal of more than 95% at all pH values along with ease of use, they could exhibit a potential of commercial utility in textile sectors for Congo red dye removal if further studies are conducted.