Response surface methodological evaluation of the adsorption of textile dye onto biosilica/alginate nanobiocomposite: thermodynamic, kinetic, and isotherm studies

Abstract: The present investigation was carried out to synthesize biosilica/calcium alginate (CA) nanobiocomposite and evaluate the efficiency of as-prepared adsorbent for removing Direct Blue 71 (DB71) from aqueous solutions. Response surface methodology based on central composite design was applied to optimize the process. Accordingly, the maximum color removal of 81.49% was achieved at an initial DB71 concentration of 21 mg/L, adsorbent dosage of 2.4 g/L, contact time of 42 min and initial pH of 5. The negative values of Gibbs free energy (ΔG°) and enthalpy change (ΔH°), which were obtained during the thermodynamic study, revealed spontaneous and exothermic nature of the adsorption process, respectively. The adsorption of DB71 onto the nanobiocomposite followed pseudo-second-order kinetic model (R² = 0.977) and Langmuir isotherm model (R² = 0.994). The maximum adsorption capacity of biosilica/CA nanobiocomposite for the adsorption of DB71 was found to be 21.32 mg/g. The value of mean free energy (12.91 kJ/mol) indicated chemical adsorption of DB71 onto the adsorbent.