Sustainable durio zibethinus-derived biosorbents for congo red removal from aqueous solution: Statistical optimization, isotherms and mechanism studies

This investigation reports on the biosorption mechanism of Congo Red dyes (CR) in aqueous solution using acid-treated durian peels, prepared for this study. The biosorbent nature was char-acterized using the Scanning Electron Microscopy (SEM), Fourier Transform infrared spectroscopy (FT-IR) and Brunaure-Emmet-Teller (BET). The effect of process parameters within operational range of pH (2–9), contact time (10–200 min), initial concentration (25–400 mg g⁻¹) and temperature (25–65^◦C) for the optimum removal of CR dyes was investigated using central composite design (CCD) under response surface methodology (RSM), and revealed that the optimum condition of biosorption was achieved around a pH of 5.5, contact time of 105 min at initial concentration of 212.5 mg L⁻¹ within 45^◦C temperature, which corresponds to 95.2% percent removal of CR. The experimental data fitted better to the second order polynomial model, with a correlation coefficient R² value of 0.9917 and the Langmuir isotherm model with biosorption capacity of 107.52 mg g⁻¹. Gibbs free energy indicated that the adsorption of CR dyes was spontaneous. The mechanism of the adsorption of CR dyes revealed that the biosorption of CR dyes investigated under different operational conditions show that under acidic pH, the adsorption efficiency of the acid treated durian peels is enhanced for the adsorption of CR dye molecules.