Adsorption of Cu2+, Zn2+and Pb2+ ions on a novel graphene-containing nanocomposite: An isotherm study

Abstract

The present research is dedicated to the problem of adsorption purification of aquatic media from toxic heavy metal ions. To extract some of these species (Cu2+, Zn2+, and Pb2+) from aqueous solutions, a novel material - polyhydroquinone/graphene nanocomposite – was used as adsorbent. Its adsorption/desorption performance was assessed through isotherm studies. The following process parameters were determined: equilibrium metal concentrations in solution, metal distribution coefficients, percentage desorption, and adjusted metal distribution coefficients. Besides, based on experimental data, adsorption isotherms were constructed, from which it was possible to determine the maximum adsorption capacity of the nanocomposite regarding each heavy metal ion (Pb2+ - 1350 mg-1; Cu2+ - 800 mg g-1, and Zn2+ -300 mg g-1). In order to elucidate adsorption-desorption mechanisms occurring in the considered adsorbate/adsorbent systems and the process nature, the data were fitted to different isotherm models: empirical (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich), and combined (single- and dual-site Langmuir-Freundlich). All the models provided satisfactory fits to the data, thereby making it possible to assume heterogeneity of adsorption sites on the adsorption surface, and the irreversibility of the adsorption process.