Selective removal of mercury(II) from water using a 2,2-dithiodisalicylic acid-functionalized graphene oxide nanocomposite: Kinetic, thermodynamic, and reusability studies

Abstract

2,2-Dithiodisalicylic acid-functionalized magnetic graphene oxide (Fe3O4@DTSA_GO) was used for the selective removal of Hg(II) from aqueous solution. The equilibrium was reached after 10 min and the maximum Hg(II) adsorption capacity of the Fe3O4@DTSA_GO nanocomposite was 283.5 mg g−1. The Hg(II) adsorption ability increased with the pH value of the aqueous solution. Isotherm and kinetic studies revealed the Sips isotherm model and pseudo-second kinetic model to provide the best fit to the experimental results. The positive value of ΔH° indicated endothermic interactions between Hg(II) and Fe3O4@DTSA_GO, while the negative ΔG° revealed a spontaneous reaction and the positive ΔS° an increase of the randomness at the solid–solute interface during the adsorption process. The selective removal of Hg(II) by the nanocomposite confirmed the presence of higher-affinity binding sites for Hg(II) than for Cd(II), Co(II), Zn(II), and Ni(II) ions. Furthermore, the Fe3O4@DTSA_GO nanocomposite exhibited excellent preferential adsorption for Hg(II) spiked in drinking water samples. EDTA 0.01 N was found to be an efficient elution agent for nanocomposite regeneration, with which over 84% of the adsorbed Hg(II) was recovered after five adsorption/desorption cycles.