Enhanced electron transfer pathway of zero-valent iron particles immobilized on coconut shell derived carbon for prolonged Cr(VI) removal

Abstract

Immobilizing zero-valent iron (ZVI) with modulated structure and good dispersibility is of great potential for the elimination of Cr(VI) in contaminated water or soil, but exploring how the support facilitate and prolong the removal of Cr(VI) by ZVI in terms of the electron transfer is inadequate. Coconut shell derived carbon could be promising for Cr(VI) removal due to the features of large specific surface area and porosity. Accordingly, ZVI particles are dispersed into low-cost and scalable coconut shell derived carbon (CSC) matrix uniformly in this study, with enhanced contact area and interaction of ZVI with CSC for effective elimination of Cr(VI). The optimal ZVI/CSC-0.65 demonstrates an equilibrium adsorption capacity of 307.8 mg/g and long-life Cr(VI) cleanup ability over 144 h. The interface reaction mechanism between ZVI/CSC and Cr contaminant have been systematically studied by various techniques including XRD, SEM/TEM and XPS, etc. ZVI’s aggregation and passivation in ZVI/CSC-0.65 have been greatly alleviated. Further analysis by Tafel polarization and DFT computation suggests ZVI/CSC-0.65 undergoes fast electron transfer, with a much higher adsorption energy (−2.90 eV) than that of pristine ZVI (−0.63 eV). The Bader charge analysis demonstrates that there is 4.40 |e| charge transferring the ZVI to the carbon, encouraging the Cr(VI) adsorption. A micro-battery based mechanism is proposed which provides an additional electron transfer pathway in ZVI/CSC for long-term Cr(VI) removal.