Removal of Congo red dye from aqueous solutions by adsorption onto a dual adsorbent (Neurospora crassa dead biomass and wheat bran): optimization, isotherm, and kinetics studies

In this study, the dead biomass of Neurospora crassa along with wheat bran was used as a dual adsorbent for the removal of congo red from aqueous solutions. Decolorization experiments were conducted in batch mode by varying experimental factors such as initial pH, adsorbate concentration, wheat bran dosage, and dead biomass dosage. The experiments were designed to attain the most optimized system. The zero-point charge of the dual adsorbent was 9. The experimental equilibrium data for the decolorization of congo red were evaluated by various isotherm models. Kinetic rate constants were found using different kinetic models. The adsorption mechanisms were described by pore diffusion and Boyd plots. The dye adsorption rate followed pseudo-second-order kinetic model, and the equilibrium data were appropriately fitted to Langmuir adsorption isotherm. The overall rate of adsorption is controlled by both film diffusion and pore diffusion of dye molecules. Thermodynamic studies were performed to determine the change in Gibbs free energy (Delta G), change in enthalpy (Delta H), and change in entropy (Delta S) of the adsorption process. The adsorption was found to be endothermic in nature, and the process was spontaneous and favorable. Desorption studies were conducted using various desorbing agents. The maximum percentage of dye was desorbed using the solvent methanol.