Selective removal of lead ions from aqueous solutions using 1,8-dihydroxyanthraquinone (DHAQ) functionalized graphene oxide; isotherm, kinetic and thermodynamic studies

Abstract

An anthraquinone – graphene structure was fabricated and applied for the removal of lead(II) from aqueous solution. The equilibrium occurred in about 10 min revealing the high adsorption rate at the beginning of the process. The maximum Pb(II) adsorption capacity of the Fe₃O₄@DHAQ_GO nanocomposite was about 283.5 mg g⁻¹ that was observed at 323 K and pH 5.5. The Pb(II) adsorption ability increased with the increasing pH. The isotherm and kinetic studies indicated that the Sips isotherm model and the linear form of the pseudo-second kinetic model had a better fit with the experimental results. The positive value of ΔH⁰ indicated endothermic interactions between Pb(II) and Fe₃O₄@DHAQ_GO. The negative ΔG⁰ indicated that the reactions are spontaneous with a high affinity for Pb(II). The positive ΔS⁰ values indicated increasing randomness at the solid–solute interface during the adsorption process. The selective removal of Pb(II) by the nanocomposite confirms the presence of higher-affinity binding sites for Pb(II) than Cd(II), Co(II), Zn(II), and Ni(II) ions. Furthermore, the Fe₃O₄@DHAQ_GO nanocomposite revealed an excellent preferential adsorbent for Pb(II) spiked in drinking water samples containing natural ion matrices. EDTA-2NA 0.01 N was found to be a better elution agent than HCl 0.1 M for the nanocomposite regeneration. After five adsorption/desorption cycles using EDTA-2NA 0.01 N, more than 84% of the adsorbed Pb(II) was still desorbed in 30 min. Capturing sub-ppm initial concentrations of Pb(II) and the capability to selectively remove lead from drinking water samples make the Fe₃O₄@DHAQ_GO nanocomposite practically convenient for water treatment purposes. High adsorption capacity and facile chemical synthesis route are the other advancements.