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

Abstract

A NiS₂ nanostructure with a protective layer of Ni²⁺ and SO₄²⁻ 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).