Decontamination of Congo red dye from aqueous solution using nanoclay/chitosan-graft-gelatin nanocomposite hydrogel

Abstract

In this study, bentonite nanoclay (BNC) impregnated chitosan-g-gelatin (CS-g-GEL/BNC) nanocomposite hydrogels were prepared with multi-features including being cost-effective, high-performance, biodegradable, and easy to separate for Congo red (CR) dye adsorption. Various characterization techniques, including FTIR, XRD, SEM, TGA, and EDX, were used to verify the successful formulation of the prepared hydrogels. The results revealed that the thermal stability of CS-g-GEL/BNC nanocomposite hydrogel was improved compared to CS-g-GEL hydrogel. CR dye also reached its equilibrium adsorption quickly and effectively at 60 min. When bentonite clay nanoparticles content was increased to 10 %, the removal efficiency increased to 70.41 %, which was significantly greater than 43.20 % for CS-g-GEL hydrogel. The maximum removal and adsorption capacity of 93.85 % and 453.87 mg/g was achieved at the optimal conditions of the adsorption process (pH = 9, an adsorbent dosage of 2 g/L, a temperature of 25 °C for 60 min, and a CR concentration of 100 mg/L). The results in thermodynamics indicated spontaneous adsorption from negative Gibbs free energy (ΔG°). Also, the analysis of the thermodynamics of the adsorption process resulted in an adsorption enthalpy (ΔH°) of − 21.8699 kJ/mol, which shows its spontaneous and exothermic nature at temperatures ranging from 25 °C to 45 °C. An equilibrium behavior of adsorption was successfully described using the Langmuir isotherm model. Compared with the pseudo-second-order, intra-particle, and Elovich models, the pseudo-first-order model gave a better description of the adsorption kinetics. CS-g-GEL/BNC nanocomposite hydrogels demonstrated enhanced reusability over five successive cycles, indicating potential application in adsorptive removal from aquatic environments contaminated with anionic dyes.