Nanomaterial-based remediation of industrial wastewater: trends, mechanisms, and challenges in heavy metal removal

Heavy metal ions are ubiquitous in water resources, toxic, and tend to bioaccumulate. Therefore, they represent a serious threat to the environment and to human health. The use of conventional treatment processes such as coagulation-flocculation, membrane separation, chemical precipitation and ion exchange processes has limitations, especially at low metal concentrations, when the effectiveness and economic viability of such processes are reduced. Recently, nanomaterials have been identified as promising remediation materials for the removal of heavy metals, due to their special physicochemical properties, including high surface area, controlled morphology and increased surface reactivity. Nanomaterials have been known to show significant efficiency for the adsorption of toxic metal ions, catalytic degradation and transformation of toxic metal ions. Additionally, their scope of application has grown with functionalization and hybridization, giving them higher selectivity, stability and regeneration capacity in complex aqueous matrices. However, there are still some issues related to the implementation in large-scale municipal wastewater treatment plants, environmental compatibility and sustainability. This review critically discusses the process, synthesis, and mechanism of heavy metal ion removal from wastewater by nanomaterials. It targets adsorption behaviour, regeneration properties and multifunctional performances that will help to pinpoint knowledge gaps and support the design of sustainable water treatment solutions based on nanotechnology.