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Background: The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is used to control of agricultural pests (water and soil) and is among the most widely distributed pollutants in the environment. Methods: In this study, Fe2O3/CeO2/Ag composite nanoparticles were synthesized using a simple coprecipitation method. The as-synthesized samples were examined using X-ray diffraction, field emission scanning electron microscopy, and X-ray analysis. The photo catalytic activity of the as-synthesized samples was examined through photo degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) under ultraviolet irradiation. The effects of pH, irradiation time, initial 2,4-D concentration and catalyst dose on the photo catalytic performance of Fe2O3/CeO2/Ag composite nanoparticles were investigated through an optimization process. The photo catalytic reaction kinetic data were analyzed using Langmuir-Hinshelwood model, and the absorption equilibrium was examined by Langmuir and Freundlich isotherm models. Results: The results suggested the second order reaction kinetics as the best model for 2,4-D photo degradation. Moreover, Langmuir isotherm with a higher R2 was reported as the most suitable model. The photo catalytic activities revealed the highest photo degradation percentage for Fe2O3/CeO2/Ag composite nanoparticles with a degradation order as Fe2O3/CeO2/Ag (75.70%)>Fe2O3/CeO2 (36.28%) >CeO2 (26.92)>Fe2O3 (11.96). Conclusions: Based on the determination of nanomaterial efficiency, its components and photo catalytic properties, can be used to remove this contaminant and other toxic compounds.