<p>This study investigates copper-doped cobalt oxide as an efficient photocatalyst for the degradation of Eosin Yellow (anionic; EY) and Fuchsin Basic (cationic; FB) dyes. Cu-doped Co₃O₄ nanoparticles were synthesized with different copper loadings (2%, 4%, and 6%) and characterized using x-ray diffraction (XRD), Fourier transform infrared (FT-IR) and ultraviolet–visible (UV–vis) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), and x-ray photoelectron spectroscopy (XPS) analyses. XRD confirmed the formation of a face-centred cubic (fcc) spinel structure and FT-IR analysis verified the presence of characteristic functional groups. SEM and TEM analyses revealed randomly agglomerated spherical nanoparticles, with copper uniformly dispersed on the Co₃O₄ surface. UV–Vis measurements showed that the 6% Cu-doped sample exhibited a reduced bandgap of 2.65&#xa0;eV, enhancing light absorption and photocatalytic activity. The photocatalytic efficiency of the synthesized materials was evaluated through the degradation of EY and FB dyes under UV irradiation. Operational parameters, including pH, catalyst dosage, dye concentration, and scavenger effects, were systematically optimized. Among the tested samples, 6% Cu-doped Co₃O₄ demonstrated superior degradation performance compared to pure Co₃O₄ and lower dopant levels. The catalyst also exhibited excellent reusability, retaining high activity over three successive cycles. The enhanced photocatalytic performance is attributed to improved electron–hole separation and efficient reactive oxygen species generation under UV light. These results indicate that Cu-doped Co₃O₄ is a promising photocatalyst for the efficient removal of hazardous organic contaminants from wastewater.</p> Graphical Abstract <p></p>