ABSTRACT Pure and nickel (Ni) doped cobalt oxide nanoparticles were employed by the co-precipitation method to present the structural, optical, and photocatalytic characteristics of NixCo3-xO4 nanoparticles (x = 0, 0.05, 0.1, and 0.3) for organic pollutant photodegradation. X-ray diffraction (XRD) was employed on NixCo3-xO4 samples with particle sizes ranging from 14 to 22 nm, confirming the occurrence of cubic phase. In addition, particle size was calculated by Debye Scherrer, Williamson-Hall (W-H) and Halder methods, respectively. The Fourier transform infrared (FTIR) analyses of all samples characterised the inherent lattice vibrations of spinel structures octahedral and tetrahedral sites, respectively. FESEM image depicts irregular-shaped clusters and EDX confirmed the presence of Ni, Co and O elements. The mesoporous nature of the pores and high BET specific surface area indicated the presence of several active sites, proving their viability as photocatalysts. UV-Vis spectrophotometer was utilised to measure the optical properties, which included recording absorption spectra and computing optical parameters. The photocatalytic activities of the pure Co3O4 and NixCo3-xO4 photocatalysts were studied by the degradation of a series of four dyes (Congo Red, Tartrazine, Rhodamine B, and Methylene Blue) solution under visible light irradiation. Compared to pure cobalt oxide, Ni-incorporated Co3O4 exhibits a substantially higher photocatalytic efficiency that increases with Ni doping concentration. The photocatalysts displayed superior recycling stability, retaining high performance after three cycles. The photosensing properties were investigated under UV light, and a considerable photocurrent enhancement was observed. As a result, it is illustrated that Ni-doped cobalt oxide NPs are a potential material for the fabrication of photosensitive devices.