The photocatalytic degradation of 2-chlorophenol (2-CP) in aqueous solution was studied using Co-doped TiO₂ nanoparticles catalyst. The catalyst samples were synthesized by a sol–gel technique from TiCl₄ with different concentrations of Co(III) dopant and calcination temperatures. The typical composition of the prepared Co-doped TiO₂ was Ti_1−xCo_xO₂, where x values ranged from 0.004 to 0.14. Several analytical tools, such as X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area measurement, X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDAX), were used to investigate the nanoparticles structure, size distribution, and composition. The catalytic activity of the prepared nanoparticles was measured in a batch photoreactor containing appropriate solutions of 2-CP with UV irradiation of 100W. High performance liquid chromatography (HPLC) was used for analyzing the concentration of 2-CP in solution at different time intervals during the photodegradation experiment. Parameters affecting the photocatalytic process such as catalyst crystallinity, light absorption efficiency, concentration of the catalyst and the dopant, solution pH, and 2-CP concentration have been investigated. Results obtained revealed that Co-doped TiO₂ showed high activity for UV-photocatalytic degradation of 2-CP. The surface area of the catalyst was measured to be 39.7m²g⁻¹. The photodegradation process was optimized by using 10mg/L Co-doped TiO₂ with Co doping concentration of 0.036, after 3h irradiation. The efficiency values of the 2-CP photodegradation were 93.4% and 96.4% at solution pH of 9 and 12, respectively. The photodegradation follows a pseudo-first-order reaction and the observed rate constant values change with the 2-CP concentration. The optical absorption properties of the samples were also measured. The presence of Co ions in the TiO₂ structure caused a significant absorption shift towards the visible region. The photodegradation efficiency matched the maximum light absorption efficiency.