Highly efficient and acid-corrosion resistant nitrogen doped magnetic carbon nanotubes for the hexavalent chromium removal with subsequent reutilization

Highly efficient and acid-corrosion resistant for carbon adsorbent in hexavalent chromium removal is a significant property in the practical application. In this study, nitrogen doped carbon nanotubes with encapsulated Fe and Fe3C were synthesized through a facile pyrolysis procedure using melamine and ferric chloride as precursors, displaying an excellent efficiency and stability for hexavalent chromium removal. High maximum removal capacities with 35.26 and 970.87 mg g−1 were obtained in neutral and acid solutions, respectively, due to the adsorption process, reduction reaction between Fe0 or Fe2+ nanoparticles and Cr(VI) ions. The unexpected high stability in acid solution (pH at 1) after five recycles was observed for the first time, ascribed to N doping and the tubular structure with encapsulated ferric carbide, which could be resistant to the acid corrosion. After a simple treatment, the used adsorbent could be re-utilized as catalysts for the electrochemical reduction of CO2 with high faradic efficiency (over 90% total efficiency and about 50% for CO production at −0.6 V), demonstrating a promising potential for reutilizing the used carbon adsorbents.