Graphene Oxide–Chitosan Composite for Efficient Adsorptive Removal of Cu(II), Co(II), and Ni(II) from Simulated E-Waste Effluents

Electronic waste (E-waste) is a major source of copper, cobalt, and nickel, metals commonly present in batteries, displays, and computer components. Their uncontrolled release into water systems contributes to metal accumulation and environmental contamination. In this study, a graphene oxide-chitosan (GOCS) composite was synthesized as an eco-friendly biosorbent and applied for the removal of Cu-(II), Co-(II), and Ni-(II) ions from simulated E-waste effluents. The composite was prepared using a modified Hummers' method and characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and Brunauer-Emmett-Teller surface area analysis. Structural characterization revealed an amorphous, nonporous composite in which CS reduced the surface area of graphene oxide but introduced abundant functional groups. Despite its low surface area, the composite exhibited high adsorption efficiencies, recording 99.98% for Cu-(II) at pH 7 in 30 min, 92.55% for Co-(II) at pH 9 in 120 min, and 72.36% for Ni-(II) at pH 5 in 180 min. Complementary molecular dynamics simulations confirmed the stability of the graphene oxide-chitosan-metal systems and identified nitrogen atoms of chitosan as primary coordination sites, consistent with experimental findings. Binding free energy analysis further supported the stronger affinity toward Cu-(II). Collectively, these results demonstrate that the adsorption efficiency of GOCS composites arises from the combined effects of pH-dependent functional group speciation, hard-soft acid-base binding preferences, and chitosan-induced pore blocking. These synergistic mechanisms underscore their potential as sustainable adsorbents for wastewater derived from electronic waste.