Persistent organic pesticides (POPs), particularly chlorinated pesticides, represent a critical environmental threat due to their chemical stability, bioaccumulation potential, and resistance to conventional water-treatment methods. Herein, a rapid and cost-effective photocatalytic strategy is developed for the degradation of seventeen structurally diverse POPs in water under ultraviolet (UV) irradiation at ambient temperature. A magnetic heterostructured nanocomposite consisting of activated carbon, derived from sugarcane bagasse, and bentonite, coupled with a magnetite/cerium oxide (Fe3O4/CeO2) nanocomposite, is fabricated via a facile ball-milling approach and tested. The material exhibits a strong light absorption, high adsorption capability, high surface activity, and excellent magnetic recoverability. Comprehensive characterization is performed using ultraviolet-visible (UV-vis) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) surface analysis. Under optimized conditions (0.1 g L−1 catalyst, 20 °C, UV 365 nm, 20 min), removal efficiencies exceeding 90% are achieved for δ-benzene hexachloride (δ-BHC), heptachlor, dichlorodiphenyl trichloroethane (DDT), endrine aldehyde, and methoxychlor, while 73.9–86.6% degradation is recorded for α-BHC, β-BHC, γ-BHC, aldrin, heptachlor epoxide, dichlorodiphenyldichloroethylene (DDE), endrin, dieldrin, dichlorodiphenyldichloroethane (DDD), and endosulfan sulfate. The developed AC/Bentonite/Fe3O4/CeO2 nanocomposite demonstrates some key advantages including high adsorption affinity, fast reaction kinetics, broad pollutant applicability, magnetic separability, and significantly shorter treatment time compared with many of those previously reported using cerium-based photocatalysts. These results highlight the potential of this sustainable catalyst system for efficient remediation of POP-contaminated water.