| Summary: | In this study, two copper(II) complexes, [Cu(C<sub>6</sub>H<sub>8</sub>N<sub>3</sub>S<sub>2</sub>)<sub>2</sub>]Cl<sub>2</sub> (1) and [Cu(C<sub>7</sub>H<sub>10</sub>N<sub>3</sub>S<sub>2</sub>)<sub>2</sub>]Cl<sub>2</sub>·H<sub>2</sub>O (2), were synthesized from 2-(thiophen-2-ylmethylene)hydrazine-1-carbothioamide (L<sub>1</sub>H) and 2-(1-(thiophen-2-yl)ethylidene)hydrazine-1-carbothioamide (L<sub>2</sub>H) respectively and characterized using various spectroscopic techniques and elemental analyses. The as-prepared complexes were used as single-source precursors for the synthesis of oleylamine-capped (OLA@Cu<sub>x</sub>S<sub>y</sub>), hexadecylamine-capped (HDA@Cu<sub>x</sub>S<sub>y</sub>), and dodecylamine-capped (DDA@Cu<sub>x</sub>S<sub>y</sub>) copper sulphide nanoparticles (NPs) via the thermolysis method at 190 °C and 230 °C and then characterized using powder X-ray diffraction (p-XRD), UV-visible spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The p-XRD diffraction patterns confirmed the formation of crystalline rhombohedral digenite Cu<sub>9</sub>S<sub>5</sub> with the space group R-3m. The TEM images showed the formation of nanoparticles of various shapes including hexagonal, rectangular, cubic, truncated-triangular, and irregularly shaped Cu<sub>9</sub>S<sub>5</sub> nanomaterials. The SEM results showed aggregates and clusters as well as the presence of pores on the surfaces of nanoparticles synthesized at 190 °C. The UV-visible spectroscopy revealed a general blue shift observed in the absorption band edge of the copper sulphide NPs, as compared to bulk Cu<sub>x</sub>S<sub>y</sub>, with energy band gaps ranging from 2.52 to 3.00 eV. Energy-dispersive X-ray spectroscopy (EDX) confirmed the elemental composition of the Cu<sub>9</sub>S<sub>5</sub> nanoparticles. The nanoparticles obtained at 190 °C and 230 °C were used as catalysts for the photocatalytic degradation of methylene blue (MB) under UV irradiation. Degradation rates varying from 47.1% to 80.0% were obtained after 90 min of exposure time using only 10 mg of the catalyst, indicating that Cu<sub>9</sub>S<sub>5</sub> nanoparticles have potential in the degradation of organic pollutants (dyes).
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