Biosorption of methylene blue from aqueous solution by natural Osmanthus fragrans powder

Abstract

The potential of Osmanthus fragrans powder as a natural biosorbent was investigated for the removal of methylene blue (MB) from aqueous solution. The effects of various experimental conditions including contact time, adsorbent dose, initial MB concentration, solution pH, salt ionic strength, and temperature on the adsorption properties of O. fragrans powder were discussed. The adsorption kinetic data were modeled using pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics equations, indicating that the pseudo-second-order and intraparticle diffusion models could better describe the adsorption kinetics. Furthermore, adsorption equilibrium data were analyzed by Langmuir and Freundlich models, suggesting the Langmuir model presented a better correlation with the experimental data. The maximum adsorption capacities (qm) of O. fragrans powder for MB obtained from the Langmuir model were 155.52, 165.02, and 172.71 mg g−1 at different temperatures of 288.15, 298.15, and 308.15 K, respectively. Thermodynamic parameters such as standard free energy changes (ΔG°), standard enthalpy changes (ΔH°), and standard entropy changes (ΔS°) were also calculated. The results showed that the adsorption process was spontaneous and endothermic in nature. In addition, the possible adsorption mechanism of O. fragrans powder as adsorbent was proposed. The present study implies that O. fragrans powder were a promising candidate as novel biosorbents for the removal of MB from aqueous solution.