Thermolysis-derived copper sulphide nanoparticles as visible-light photocatalysts for the degradation of methylene blue

Copper sulphide (Cu2−xS) photocatalyst have been synthesized by thermolysis from [Cu(L)2(H2O)2](NO3)2.H2O (1) and [Cu(L)(SCN)2(H2O)2]. 6H2O (2) complexes as single source precursors (SSPs) using olive oil (OO) and castor oil (CO) as eco-friendly capping agents at 190 and 230 °C. The as-prepared Cu2−xS nanoparticles (Nps) were characterized using powder X-ray diffraction (p-XRD), scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), energy-dispersive X-ray (EDX), Fourier transform infrared (FT-IR), UV–Visible, and Raman spectroscopy, and employed for the visible-light-driven degradation of cationic methylene blue (MB) dyes. p-XRD revealed a monoclinic Djurleite (Cu1.94S) phase at 190 °C when complex (2), (irrespective of the capping agent) was used as precursor, while orthorhombic Djurleite (Cu1.97S) phase was observed when the reaction temperature and precursor type were varied. EDX confirmed the elemental composition of Cu2−xS nanoparticles. TEM images showed the formation of nanoparticles of various shapes including spherical, elliptical, and irregularly shape, with particle sizes ranging from 5 to 142 nm. Optical properties of Cu2−xS nanoparticles showed band gaps ranging between 2.17 and 2.48 eV and 2.20–2.46 eV for Castor and Olive oil-capped NPs respectively, (larger than the bulk material value of 1.3 eV), due to quantum size confinement effect. Raman spectroscopy confirms the formation of castor and olive oil-capped Cu2−xS nanoparticles. Under optimized conditions, Cu2−xS demonstrated excellent photocatalytic performance, achieving 56.7 and 59.8% degradation efficiency of methylene blue (MB) within 120 min under visible light for CuS2 and CuS6 derived from complex (2) at 190 °C in olive oil or castor oil respectively. These results clearly highlight the effect of reaction parameters on the properties of Copper Sulphide NPs which render them potential candidates for environmental remediation applications.