Adsorptive removal of rhodamine B from textile wastewater using water chestnut (Trapa natans L.) peel: adsorption dynamics and kinetic studies

Abstract

Water chestnut peel, an agricultural bio-waste, was used as a biosorbent for removal of rhodamine B (RhB), basic textile dye, from an aqueous solution. The effects of various experimental parameters were studied. The equilibrium data correlated well with a Freundlich isotherm (R² = 0.98–0.99) followed by a Halsey isotherm model (R² = 0.98–0.99) which indicated heterogeneity of the adsorbent surface and multilayer adsorption of RhB dye onto the water chestnut peel waste (WCPW). High correlation coefficients (R² = 0.99) together with close agreement between experimental q_e (0.4–1.7 mg g⁻¹) and calculated q_e (0.4–2.5 mg g⁻¹) suggested that the adsorption process followed pseudo-second-order kinetics, with k₂ values in the range of 52–3.4 × 10⁻¹ g mg⁻¹ min⁻¹ at different concentrations. The overall mechanism of adsorption was controlled by both liquid-film and intra-particle diffusions. The negative values of change in Gibb's free energy (−ΔG⁰ = 19.2–29.2 kJ mol⁻¹) and positive values of change in enthalpy (ΔH⁰ = 30.9–117.6 kJ mol⁻¹) revealed the process to be spontaneous and endothermic. WCPW was found to be an effective adsorbent for removal of RhB, a cationic dye, from an aqueous solution.

Keywords:

• water chestnut peel waste
• rhodamine B
• adsorption
• kinetics
• thermodynamics

Acknowledgments

The author M. Nazir is thankful to University Grants Commission (UGC) New Delhi 110025, India for financial assistance.