Sodium thiosulfate-assisted synthesis of NiS₂ nanostructure by using nickel(II)-Salen precursor: optical and magnetic properties.

A NiS2 nanostructure with a protective layer of Ni(2+) and SO4(2-) ions around it has been successfully synthesized using the Ni(II)-Salen (Salen = N,N'-bis(salicylidene)ethylenediamine) complex via a simple solvothermal approach in the presence of anhydrous sodium thiosulfate (Na2S2O3) as sulfur source and stabilizer. Unexpectedly, no one kind of pure nickel sulfide nanostructure was prepared using the Ni(II)-Salophen complex or some of the simple mono and bidentate Ni(II) complexes as starting materials and the obtained products were a mixture of nickel sulfides. In the photoluminescence spectrum of the prepared NiS2, two peaks were evident at 400 and 420 nm with emission maxima, and one broad peak with emission minima was located at 800 nm. The as-synthesized NiS2 nanostructure displays a weak ferromagnetic behaviour at room temperature, which has small remanent magnetization and saturation magnetization compared to bulk NiS2. These changes might be attributed to the existence of a protective layer of nickel and sulfate ions around the NiS2 nanostructures that was confirmed by Energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) and Raman spectroscopy. The prepared nanostructure has been characterized structurally, electrochemically, optically and magnetically by available methods like X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy, Fourier transform infrared and Raman spectroscopy, Cyclic voltammetry (CV), Photoluminescence (PL) spectroscopy and vibrating sample magnetometer (VSM).