Application of Eriobotrya japonica (Thunb.) Lindley (Loquat) seed biomass as a new biosorbent for the removal of malachite green from aqueous solution

A new biosorbent, Eriobotrya japonica (loquat) seed biomass, has been investigated in order to remove malachite green (MG) from aqueous solutions. The factors affecting the biosorption process such as adsorbent dosage, pH of the solution and contact time were studied. The results showed that as the dose of loquat seed increased, the percentage of MG biosorption decreased accordingly. The experimental data suggested that the maximum pH for efficient biosorption of MG was 5.0. The biosorption process was relatively fast and equilibrium was achieved after about 60 min. Freundlich and Langmuir adsorption isotherm models were used for adsorption equilibrium data and based on the Langmuir isotherm plots the maximum bisorption capacity (Q_max) value was calculated to be 57.47 mg/g at 20°C. The biosorption kinetics was determined by fitting pseudo-first-order and pseudo-second-order kinetic models to the experimental data, with the second-order model providing the best description of MG biosorption onto loquat seed. Various thermodynamic parameters such as free energy change ΔG⁰, enthalpy of sorption ΔH⁰ and entropy ΔS⁰ were estimated. The positive value of ΔH⁰ and negative values of ΔG⁰ show the sorption process is endothermic and spontaneous. The positive value of ΔS⁰ shows the increased randomness at the solid–liquid interface during the biosorption of dyes onto loquat seed.