Coconut Shell-Derived rGO for Efficient Adsorption of Heavy Metals and Organic Dyes from Wastewater

The increasing contamination of water resources by toxic heavy metals and organic dyes necessitates the development of efficient, low-cost, and sustainable treatment technologies. In this study, reduced graphene oxide (rGO) was synthesized from coconut shell-derived graphene oxide using a modified Hummers method and evaluated as an adsorbent for the removal of cadmium (Cd²⁺), nickel (Ni²⁺), lead (Pb²⁺), and methylene blue (MB) from aqueous solutions. The successful transformation of graphene oxide (GO) to rGO was confirmed through structural and morphological characterization techniques, including SEM and TEM analyses, which revealed a transition from a wrinkled, porous structure to a more compact and graphitized morphology. Batch adsorption experiments demonstrated that rGO exhibited significantly enhanced adsorption performance compared to GO for all investigated pollutants. The maximum adsorption capacities of rGO were found to be 110 mg/g for Cd²⁺, 102 mg/g for Ni²⁺, 95 mg/g for Pb²⁺, and 108 mg/g for MB, indicating its high efficiency as a multifunctional adsorbent. The improved adsorption behavior was attributed to increased surface area, enhanced structural ordering, and the restoration of π-conjugated domains, which facilitate strong interactions such as surface complexation for metal ions and π–π stacking for organic dyes. The adsorption trend for heavy metals followed the order Cd²⁺ > Ni²⁺ > Pb²⁺, reflecting the influence of ionic properties on adsorption mechanisms. The results highlight the capability of rGO to simultaneously remove both heavy metals and organic contaminants from wastewater. Overall, this study demonstrates that coconut shell-derived rGO is a promising, sustainable, and high-performance material for environmental remediation, offering a viable solution for advanced wastewater treatment applications.