Ni0 encapsulated in N-doped carbon nanotubes for catalytic reduction of highly toxic hexavalent chromium

Abstract

N-doped carbon nanotubes encapsulating Ni0 nanoparticles (Ni@N-C) were fabricated via thermal reduction of dicyandiamide and NiCl2·6H2O, and used to remove CrVI in polluted water. The resultant products present an excellent catalytic activity for CrVI reduction using formic acid under relatively mild conditions. The CrVI reduction efficiency of Ni@N-C was significantly affected by the preparation conditions including the mass of nickel salt and synthesis temperatures. The impacts of several reaction parameters, such as initial concentrations of CrVI and formic acid, solution pH and temperatures, as well as inorganic anions in solution on CrVI reduction efficiency were also evaluated in view of scalable industrial applications. Owing to the synergistic effects amongst tubes-coated Ni0, doped nitrogen, oxygen containing groups, and the configuration of carbon nanotubes, Ni@N-C catalysts exhibit excellent catalytic activity and recyclable capability for CrVI reduction. Carbon shell can efficiently protect inner Ni0 core and N species from corrosion and subsequent leaching, while Ni0 endows the Ni@N-C catalysts with ferromagnetism, so that the composites can be easily separated via a permanent magnet. This study opens up an avenue for design of N-doped carbon nanotubes encapsulating Ni0 nanoparticles with high CrVI removal efficiency and magnetic recyclability as low-cost catalysts for industrial applications.