<p>In this study, the Fe₃O₄/BiOI heterojunction photocatalyst was prepared by a traditional two-step hydrothermal method and secanalyzed in depth using various characterization techniques. The results show that nano-sized spherical Fe₃O₄ particles are firmly adsorbed on the surface of micron-sized spherical BiOI particles. The formation of this heterojunction not only enhances the light absorption and utilization capacity of BiOI across the full solar spectrum but also promotes the migration and separation of photogenerated carriers, thereby inhibiting the recombination of photogenerated holes and electrons. Photocatalytic degradation experiments on rhodamine B (RhB) dye indicate that the photocatalytic activity of the Fe₃O₄/BiOI sample is 17.2 times that of pure Fe₃O₄ and 2.6 times that of pure BiOI, respectively. In this process, photogenerated holes play a key role, while hydroxyl radicals and photogenerated electrons also exert positive effects. Meanwhile, this study conducts an in-depth discussion on the mechanism underlying the enhanced photocatalytic activity of the Fe₃O₄/BiOI heterojunction. The coupling of magnetic Fe₃O₄ not only enhances the photocatalytic activity of BiOI but also enables its rapid separation and recovery from water bodies. This strategy provides a new direction for the development of high-performance full-spectrum responsive nanophotocatalysts and their large-scale practical applications.</p>