Graphene-based composites for heavy metal adsorption: a review on synthesis, mechanisms, and influencing factors

Heavy metal contamination in aquatic ecosystems is a global concern due to its toxicity, persistence, and potential for bioaccumulation. Effective removal is therefore essential. Among other techniques, adsorption is the most reliable and prevalent method of water purification. Graphene-based adsorbents exhibit significant advantages, including high specific surface area, small particle size, excellent mechanical properties, abundant functional groups, and high adsorption efficiency, making them promising materials for heavy metal removal from aqueous solutions. This article reviews recent advances in graphene and its derivative composites for heavy metal adsorption. It discusses structural features, adsorption mechanisms, synthesis methods, and the historical development of these composites. Key factors influencing adsorption capacity-such as temperature, pH, adsorbent dosage, contact time, initial metal concentration, organic ligands, and coexisting ions-are also examined. Additionally, adsorption thermodynamics and regeneration behavior are evaluated, and future research directions for practical applications are outlined.