The nanocrystalline nickel phosphide (Ni 2 P) was synthesized through a chemical transformation process using nickel oxalate as a new precursor, and its highly efficient activation of peroxymonosulfate (PMS) for the degradation of organic dyes in water was demonstrated for the first time. The Ni 2 P with the charged nature of nickel (Ni δ+ ) and phosphorus (P δ-) provides the tunable surface Ni valence and electron-rich P center, where Ni δ+ synergically cooperating with surface oxidation layers facilitates the redox cycle of Ni 3+ /Ni 2+ while P δachieves the electron transfer regulation. Such unique dual active sites greatly boost the PMS activation to realize the pollutant degradation with high efficiency and fast kinetics. The Ni 2 P could completely remove 100 mg L −1 of methylene blue (MB) in 12 min, yielding a high reaction rate constant of 0.342 min −1 , which is 43 and 29 times as high as that of nickel oxalate and oxalate-derived nickel oxide, respectively. Both the sulfate and hydroxyl radicals are primary reactive species dominating catalytic activity in the Ni 2 P/PMS system. This work would provide a new method for the rational design of transition metal phosphide for PMS activation.

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