Excellent catalytic performance toward room temperature reduction of Cr(VI) in water over Ni/N-doped carbon catalysts prepared by sol-gel method in the range of 800–1000 °C

Reduction of toxic Cr(Ⅵ) to Cr(Ⅲ) is an important method to treat Cr(VI) pollution in water remediation. In this study, a series of Ni/N-doped carbon (Ni/NC) catalytic materials were successfully prepared by sol-gel method in which glycerol or ethylene glycol were used as carbon source, and urea was conducted as source of N element. The materials were obtained by heating the precursors in the temperature range of 500–1000 °C in Ar atmosphere. The catalysts prepared in the range of 800–1000 °C could activate formic acid to completely reduce Cr(VI) within 2 min and a high activity parameter of 8.25 s⁻¹ g⁻¹ could be obtained for the catalyst prepared at 800 °C. The activity of the Ni/NC catalyst was still at a high level after five successive cycles. The high catalytic activities were attributed to the structural character where Ni metal grains could be encapsulated by NC to prevent corrosion, the high degree of graphitization which could enhance electron conduction of the catalysts, and synergistic effect between nickel species and NC to promote the production of active hydrogen. Our results provide a reliable way to treat Cr(Ⅵ) contamination in water.