Mechanism of adsorption of Cu2+ and Zn2+ on the corn silk (Zea mays L.)

In this study the novel biosorbent - raw corn silk (CS) was investigated for Cu2+ and Zn2+ removal from aqueous solutions. The physical and chemical properties of CS were determined by SEM - EDX and ATR - FTIR techniques. The SEM micrographs revealed that surface morphology of CS is suitable for metal adsorption, while FTIR analysis confirmed presence of various active groups (O-H, C-O, C-O C, C=C and amide II) which could interact with metal ions. The adsorption experiments were performed in batch system. Experimental data were fitted by pseudo - first order and pseudo - second order kinetic models as well as Langmuir and Freundlich isotherm models. Biosorption of the both metals follow pseudo second order kinetic model. The best fitting adsorption model is Langmuir model and the maximum biosorption capacities (q(max)) for Cu2+ and Zn2+ at 313 K and pH 5.0 were 15.35 mg g(-1) and 13.98 mg g(-1), respectively. The thermodynamic parameters such as Gibbs free energy change (Delta G), enthalpy change (Delta H) and entropy change (Delta S) were studied at different metal concentration and three temperatures. According to thermodynamic study, the biosorption process for both metals is feasible, endothermic and spontaneous. According to thermodynamic study, the biosorption process for both metals is feasible, endothermic and spontaneous. Ion - exchange is the dominant mechanism in adsorption of Cu2+ and Zn2+ on the CS with a certain degree of complexation. Desorption study was performed in three adsorption/desorption cycles with diluted nitric acid. Results show that after metal adsorption CS can be efficiently recovered and reused for new adsorption process. Obtained results indicated that corn silk could be used as efficient novel biosorbent for Cu2+ and Zn2+ removal from water samples. (C) 2016 Elsevier B.V. All rights reserved.