Removal of heavy metals in aquatic environment by graphene oxide composites: a review

As the most important graphene derivate, graphene oxide (GO) is a high-efficient adsorbent for the removal of heavy metals in aquatic environment due to its abundant oxygen functional groups, enormous specific area, and strong hydrophilia. However, there are some drawbacks, such as easily aggregating and difficult separation, restricting the environmental application of GO. GO is not a suitable adsorbent by itself. Hence, some materials were used to synthesize GO composites, and GO composites are commonly characterized by high adsorption capacity to overcome the above drawbacks. This review discusses five main GO composites-GO-chitosan, GO-alginate, GO-SiO₂, NZVI-rGO, and magnetic GO composites-and summarizes the synthesis methods of GO composites and its application for the removal of heavy metals in aquatic environments. The influencing factors, adsorption capacities, and mechanisms related to the removal of heavy metals by GO composites are highlighted. Lastly, the application potentials and challenges of GO composites for aqueous environmental remediation are discussed. Graphical abstract.