Aqueous-phase synthesis of Ni₂P within clay nanotube lumens for efficient catalytic nitroarene hydrogenation

The widespread application of transition metal phosphides (TMPs) is often constrained by the use of hazardous and costly phosphorus precursors as well as energy-intensive synthetic routes. To address these limitations, we report a green aqueous-phase synthesis of nickel phosphide (Ni₂P) nanomaterials using sodium phosphathynolate (NaOCP) as a safe phosphorus source and nickel (II) chloride as the metal precursor. The resulting Ni₂P nanoparticles exhibit long-term stability, as indicated by the well-maintained X-ray diffraction patterns after 30 days of storage under ambient conditions. This synthetic approach was further extended to fabricate a spatially confined Ni₂P@HNTs nanocomposite through in situ growth inside the lumen of halloysite nanotubes (HNTs). The confined environment led to a significant reduction in Ni₂P particle size (from ∼80 nm to ∼3 nm) and promoted uniform dispersion. Both Ni₂P and Ni₂P@HNTs show high catalytic activity in the transfer hydrogenation of nitroarenes, delivering up to 98% yield with broad substrate scope. Notably, the Ni₂P@HNTs composite displays enhanced stability and recyclability compared to unsupported Ni₂P in the reduction of both nitrobenzene and substituted nitroarenes. This work establishes NaOCP as the phosphorus precursor for the aqueous synthesis of robust TMPs and demonstrates the efficacy of clay nanotube confinement in designing high-performance catalytic systems.