Biosorption of Cu2+, Co2+ and Ni2+ from aqueous solution by modified corn silk: Equilibrium, kinetics, and thermodynamic studies

A novel biosorbent modified corn silk by dilute nitric acid (HNO3-MCS) was prepared as a solid phase extractant and applied for removing of Cu2+, Co2+ and Ni2+ in water prior to their determination. Characterizations of HNO3-MCS have been explored by means of FT-IR spectra, surface charge analysis and thermogravimetric analysis (TGA). The abundant oxygen-containing functional groups on the surface of HNO3-MCS are beneficial to the adsorption of Cu2+, Co2+ and Ni2+. Maximum adsorption for Cu2+, Co2+ and Ni2+ was observed at pH 6.0. Two adsorption isotherms of HNO3-MCS for Cu2+, Co2+ and Ni2+ were built, and the adsorption isotherm is well fitted to a linear form of the Langmuir equation. The maximum adsorption capacities of Cu2+, Co2+ and Ni2+ on HNO3-MCS were 96.15 mg/g, 90.09 mg/g and 76.92 mg/g at 25 °C, respectively. The kinetic data fit well the pseudo-second-order and intra-particle diffusion models. Thermodynamic parameters are calculated and show that adsorption of heavy metals on HNO3-MCS is spontaneous and endothermic in nature. The adsorption mechanism analysis revealed that the primary adsorption mode was coordination. The obtained adsorbents could effectively remove Cu2+, Co2+ and Ni2+ from aqueous solution and could be used repeatedly for more than eleven cycles.