Rapid adsorptive removal of Pb2+ ions from aqueous systems using a magnetic graphene oxide calcium alginate composite: optimisation, isotherms, and kinetics

Abstract

Water consumption from polluted sources is a significant cause of human exposure to lead compounds, posing potential risks to humans. This study investigated the synthesis and application of a magnetic graphene oxide calcium alginate composite (MGO@CA) for rapid removal of lead (Pb²⁺) ions from aqueous systems, demonstrating its effectiveness through various adsorption studies and characterisation techniques. We utilised XRD, FTIR, VSM, and SEM to confirm the structural and magnetic properties of the MGO@CA composite, while BET and AFM analyses were performed to assess its surface area and roughness, which are essential for evaluating its adsorption capacity. Characterization results indicated the formation of a composite with functional groups of both graphene oxide and alginate and a rough surface, high surface area, and magnetic properties. The adsorption process was optimised by studying the effect of varying solution pH, adsorbent dosage, contact time, and initial lead concentration. The maximum adsorption capacity for Pb²⁺ ions was determined to be 270.27 mg g⁻¹, as revealed using the Langmuir isotherm model, indicating the high efficiency of the composite in removing lead from water. Different adsorption isotherms and reaction kinetic models were studied for the adsorption process. The obtained adsorption data fit well with both the Langmuir and Freundlich adsorption isotherms, indicating the heterogeneous surface of the composite containing sites with different affinities for Pb²⁺. The adsorption process followed pseudo-second-order reaction kinetics. Furthermore, the adsorbent is regenerable and reusable, maintaining 82.28% of its initial adsorption capacity after 5 cycles. Thus, the MGO@CA adsorbent is remarkably efficient, ecologically sound, readily separable, and thus optimal for rapid and effective elimination of heavy metals from water.