Cellulose–kaolin incorporated polymeric hydrogels and its application for dye removal: batch study and mechanism

Continuous growth in textile, paper, rubber, and plastic industries has promoted a significant amount of pollutant dye emanations from wastewater streams, increasing the demand for a sustainable approach to dye removal. In this study, cellulose-incorporated sodium alginate and kaolin hydrogels were used as an adsorbent for the decolorization of carcinogenic Congo red dye. The Fourier transform infrared (FTIR) data of prepared hydrogel suggested that the surface consisted (N–H, C = O, C≡N, C = C) bonds and according to the Point of Zero Charge (PZC) study at 7.783 pH, the surface charge became zero and the thermogravimetric analysis (TGA) data suggested maximum decomposition at 336.083 °C and the residual hydrogel remained was 64.545% of the initial. Scanning electron microscopy (SEM) was done to study the surface morphology properly. The removal efficiency was properly examined with the help of batch study by varying parameters such as adsorbent dosage, initial concentration of pollutant dye, temperature, pH of the dye solution, and agitation speed. The experimental data of the batch study suggested the highest removal of 98.437% for 20 g/L adsorbent dosage at 303 K with dye solution of initial concentration 20 mg/L and at pH 6 after adsorption. The adsorption data revealed more similarity for the Freundlich model ( \({R}^{2}=0.983\) $R^2=0.983$ ) than the Langmuir model. The temperature data seem to be more inclined towards pseudo-second-order kinetics ( \({R}^{2}=0.993\) $R^2=0.993$ ) than pseudo-first-order kinetics. Thermodynamic analysis data gave a negative Gibbs free energy value with a positive value of Enthalpy. The isosteric heat was found to be 24.025 kJ/mole. The above-mentioned studies established the fact that the prepared hydrogels are effective, environment-friendly adsorbents for Congo red dye removal due to their high affinity towards the pollutants present in wastewater. A regeneration study using salt and base established the adsorbents to be efficient enough to run batch experiments multiple times effectively.