Recent advances of carbon-based nano zero valent iron for heavy metals remediation in soil and water: A critical review

Heavy metal pollution in soil and water has presented a new challenge for the environmental remediation technology. Nano zero valent iron (nZVI) has excellent adsorbent properties for heavy metals, and thus, exhibits great potential in environmental remediation. Used as supporting materials for nZVI, carbon-based materials, such as activated carbon (AC), biochar (BC), carbon nanotubes (CNTs), and graphene (GNs) with aromatic rings formed by carbon atoms as the skeleton, have a large specific surface area and porous structure. This paper provides a comprehensive review on the advancement of carbon-based nano zero valent iron (C-nZVI) particles for heavy metal remediation in soil and water. First, different types of carbon-based materials and their combination with nZVI, as well as the synthesis methods and common characterization techniques of C-nZVI, are reviewed. Second, the mechanisms for the interactions between contaminants and C-nZVI, including adsorption, reduction, and oxidation reactions are detailed. Third, the environmental factors affecting the remediation efficiency, such as pH, coexisting constituents, oxygen, contact time, and temperature, are highlighted. Finally, perspectives on the challenges for utilization of C-nZVI in the actual contaminated soil and water and on the long-term efficacy and safety evaluation of C-nZVI have been proposed for further development.