Enhanced copper(II) biosorption on SiO2-alginate gel composite: A mechanistic study with surface characterization

Abstract

A new SiO2-alginate biocomposite was synthesized with improved mechanical properties, showing chelation capability of divalent metal ions, especially Cu(II), through its carboxylic acid ends. The biocomposite was characterized using scanning electron microscopy (SEM), Fourier-transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) techniques. The adsorption of copper(II) onto both H- and Ca-forms of sorbent was investigated as a function of pH and contact time, and adsorption data were modeled with the aid of Langmuir and Freundlich isotherms. The release of Ca(II) ions accompanying copper(II) binding was evaluated by selective surface complexation concept involving ion-exchange. The IR spectra gave detailed information on complexation of carbonyl group with copper ions and on the relative contribution of SiO2 involved in copper uptake. The adsorption edge of copper was within the pH range 4.0-5.5, and the sorbent capacity was determined as 1.85 and 1.10 mmolg(-1) for H- and Ca-forms, respectively.