N-doped carbon nanotubes encapsulating Ni-0 nanoparticles (Ni@N-C) were fabricated via thermal reduction of dicyandiamide and NiCl2 center dot 6H(2)O, and used to remove Cr-VI in polluted water. The resultant products present an excellent catalytic activity for Cr-VI reduction using formic acid under relatively mild conditions. The Cr-VI 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 Cr-VI and formic acid, solution pH and temperatures, as well as inorganic anions in solution on Cr-VI reduction efficiency were also evaluated in view of scalable industrial applications. Owing to the synergistic effects amongst tubes-coated Ni-0, doped nitrogen, oxygen containing groups, and the configuration of carbon nanotubes, Ni@N-C catalysts exhibit excellent catalytic activity and recyclable capability for Cr-VI reduction. Carbon shell can efficiently protect inner Ni-0 core and N species from corrosion and subsequent leaching, while Ni-0 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 Ni-0 nanoparticles with high Cr-VI removal efficiency and magnetic recyclability as low-cost catalysts for industrial applications. (C) 2018 Elsevier B.V. All rights reserved.