Nitrogen-doped porous carbon spheres for highly efficient capacitive deionization

•N-doped carbon spheres were obtained via microwave synthesis and ammonia treatment.•N doping enhances the specific surface area and facilitates the charge transfer.•The capacitive deionization performance of N-doped carbon spheres was investigated.•N-doped carbon spheres exhibit a high NaCl removal with good regeneration ability.

Nitrogen-doped porous carbon spheres (NPCSs) were prepared through a fast microwave-assisted approach using sucrose as the precursor in a microwave system and subsequent thermal treatment in ammonia atmosphere at different temperatures. The morphology, structure and electrochemical performance of the NPCSs were characterized by scanning electron microscopy, nitrogen adsorption-desorption, X-ray photoelectron spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy, and their electrosorption performance in NaCl solution was studied. The results show that NPCSs treated at 1000 °C exhibit an extremely high electrosorption capacity of 14.91 m g g−1 when the initial NaCl concentration is 1000 mg l−1, which shows great improvement compared with their undoped counterpart. The nitrogen doping is suggested to be a very effective method to improve the electrosorption performance, and the NPCSs should be a very promising candidate as electrode material for CDI application.