Photocatalytic Degradation of Methylene Blue Dye by Nickel Sulphide Nanoparticles Derived from Thiosemicarbazone Complexes as Single Source Precursors

Abstract

Nickel sulphide (NiS) with its low band gap and interesting optical properties, is able to absorb visible light, thus possess appreciable photocatalytic properties. However, their synthesis by green and sustainable methods with controlled morphologies, sizes and phases for specific applications remains a major challenge. We herein report the green synthesis of olive oil- (OO) and castor oil-(CO) capped Ni_xS_y nanoparticles by the thermolysis of [Ni(L)₂] (1) and [Ni₂(L)₃(SCN)].6H₂O (2) complexes as single source precursors (SSPs) at 190 °C and 230 °C, (L being furan-2-carbaldehyde thiosemicarbazone). The single crystal X-ray structure of compound (1) has been elucidated. The influence of reaction parameters on the structure, morphology, size, optical and photocatalytic properties of the synthesized nanoparticles Has been examined using various techniques. Results of powder X-ray diffraction (p-XRD) reveal a mixture of hexagonal Ni₁₇S₁₈ and orthorhombic Ni₉S₈ nanomaterials. Energy dispersive X-ray spectroscopy (EDX) confirmed the elemental composition of Ni_xS_y nanoparticles. Transmission electron microscopy (TEM) images revealed spherical and fibrous nanoparticles with sizes ranging between 3.0 and 25.3 nm. Optical properties of Ni_xS_y nanoparticles. The band gap energies obtained from Tauc plots vary between 2.25 and 2.49 eV and 2.29–2.50 eV for NixSy nanoparticles derived from complex (1) and complex (2) respectively and show considerable blue shift from its bulk value due to quantum size confinement effect. The presence of peaks around 1390 and 1561 cm^-1 in the Raman spectra confirm the formation of olive and castor oil capped nickel sulphide nanoparticles (NPs). These results suggest that crystallinity, size, morphology and optical properties of the synthesized Ni_xS_y NPs were affected by thermolysis temperature, capping agent and precursor type. The as-prepared nickel sulphide nanoparticles were used as photocatalysts for the degradation of methylene blue (MB) at a concentration of 10 ppm under UV light irradiation. Nickel sulphide nanoparticles obtained in olive oil at 190 °C using complex (2) as SSP, showed a maximum degradation efficiency of 52.0% after 180 min, suggesting that Ni_xS_y nanoparticles can be used as photocatalysts for the degradation of organic pollutants.

Graphical Abstract