Selective Adsorption of Pb(II) from Aqueous Medium by Cross-Linked Chitosan-Functionalized Graphene Oxide Adsorbent

Abstract

Functionalization of graphene oxide (GO) was achieved by synthesizing aminopropylsilane graphene oxide (APSGO) by a condensation reaction. Cross-linked chitosan (CHI) adsorbent grafted with aminopropylsilane graphene oxide was synthesized in acidic medium by sol–gel in the presence of glutaraldehyde. Reported adsorbent, with a high surface concentration of active sites (−NH2/═NH) and low swelling properties (due to incorporation of silica and formal cross-linking), was assessed for Pb(II) adsorption in aqueous medium. The spherical and rough surface of the pristine beads was altered after Pb2+ adsorption. The selective removal of Pb2+ using cross-linked CHI-APSGO adsorbent was attributed to its larger hydrated radius than other metal ions (Cu2+, Ni2+, and Cr3+). In a batch process and under different operating conditions, the effect of time, temperature, pH, adsorbent dose, and adsorbate concentration were also analyzed. Thermodynamic parameters (ΔG°, ΔH°, and ΔS°) confirmed an endothermic and spontaneous process, while the equilibrium adsorption obeyed Langmuir and Freundlich isotherms. The adsorption capacity of CHI-APSGO adsorbent (566.2 mg/g at pH 5.0) was comparatively higher than other adsorbents cited earlier. Desorption studies also revealed effective utilization of cross-linked CHI-APSGO material for selective removal of Pb2+ from wastewater.