Study of Isotherm and Kinetics for Remediation of Congo Red Using Nanocomposite Bead

Abstract

Cellulose-based nanocomposite (FeCNB) has been synthesized via sol-gel conversion for adsorptive remediation of Congo red, a carcinogenic and mutagenic azo dye, from water. The bead was characterized by Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDAX) and transmission electron microscopy (TEM). The effect of adsorbent dose, pH, contact time, shaking speed, initial dye concentration and temperature was carried out in a batch adsorption study. The maximum removal of Congo red was found at pH 6.0, corresponding to the adsorbent dose of 1.0 gdm^-3 and 90 min of contact time. The experimental data were analyzed using different isotherm and kinetic models. The data was fitted best to Langmuir isotherm model and pseudo-second-order kinetic model. The maximum adsorption capacity evaluated from Langmuir isotherm is 3.52 mgg^-1 at 303 K. Thermodynamic study was carried out to evaluate the changes in Gibbs free energy (ΔG⁰ ), enthalpy (ΔH⁰ ) and entropy (ΔS⁰ ) of the dye-adsorbent interaction. The negative ΔG⁰ values at all temperatures suggested the spontaneous nature; the positive ΔH⁰ value indicated the endothermic nature and the positive ΔS⁰ indicated the increased randomness of the adsorption process. Desorption study found 0.1 (M) NaOH as the most suitable eluting agent for dye-loaded adsorbent. The adsorbent can be used up to five successive cycles of adsorption-desorption.