Large-scale synthesis of single crystalline NiHPO₃·H ₂O nanoneedle bundles based on the dismutation of NaH ₂PO₂

In this paper, we report the successful synthesis of well-aligned single crystalline NiHPO₃·H₂O nanoneedle bundles on a large scale via a facile hydrothermal route, employing NiSO₄· 6H₂O and NaH₂PO₂ as the reactants in the presence of NH₃·H₂O, hexamethylenetetramine (HMT), and cetyltrimethylammonium bromide (CTAB). The reaction was carried out at 150 °C for 24 h. Generally, in basic solution, H₂PO₂ ^- is often used as a reductant, but it can also decompose into HPO₃^2- and P^3- ions due to dismutation. Namely, the redox and dismutation reactions are competitive. Since the formation of Ni-HMT-NH₃ complex reduced the potential of the Ni²⁺/Ni pair in our work, the dismutation reaction of H₂PO₂ ^- ions was predominant. This led to the production of NiHPO ₃·H₂O due to the smaller solubility. The as-obtained product was characterized by X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and field emission scanning electron microscopy (SEM). Some factors influencing the morphology of the NiHPO₃·H ₂O nanoneedles were systematically investigated.