Pure phase Ni12P5 anchored on N, P-codoped carbon nanosheet: A stable and highly efficient catalyst to reduce toxic organic compounds for continuous-flow application

The removal of toxic organic compounds from aqueous media through reduction reactions using nonnoble catalysts has attracted much attention in recent years. In this study, a simple method for the synthesis of pure-phase Ni12P5 nanoparticles supported on N, P-codoped carbon (NPC) sheets was developed, in which a nickel phosphine complex was selected as the precursor due to its high Ni/P ratio, air stability and easy preparation. By controlling the pyrolysis temperature, NixPy@NPC700 with a high dispersity and exposed active sites can be obtained, which was characterized by XRD, HRTEM, EDS, XPS, Raman and NH3-TPD. The catalytic performance of the composite in the reaction of 4-nitrophenol (4-NP) was assessed under mild conditions, exhibiting excellent catalytic activity with a low apparent activation energy Ea (29.87 KJ·mol−1). In addition, the catalyst can be recycled without obvious loss of activity for up to ten successive cycles. The outstanding hydrogenation activity is ascribed to the exposed Ni12P5(3 1 2) crystal plane of NixPy@NPC700, which is attributed to the lower energy barrier required to form a hydrogen splitting state according to DFT calculations. Moreover, NixPy@NPC700 was creatively coated in a Teflon tube with Nafion as the adhesive and constructed as a fixed-bed device. The continuous-flow catalytic reaction shows that the catalyst can maintain a satisfactory efficiency for approximately 6 h in the reduction of 4-NP and methyl orange (MO). These findings suggest that NixPy@NPC700 is an ideal catalyst for industrial applications for the chemical reduction of toxic compounds from wastewater.