► Iodine-doped TiO2 using silica-coated Fe3O4 as the magnetic core. ► Photocatalysts for phenol degradation. ► Increasing the molar ratio of Ti/Fe will increase the catalytic activity. ► Increasing the molar ratio of Ti/Fe will decrease the saturation magnetization. ► An optimum molar ratio of I/TiO2 is 1:10. A series of iodine-doped titanium dioxide (I-TiO2) photocatalysts was synthesized by using silica-coated Fe3O4 (SF) as the magnetic core (abbreviated here as ITSF), in order to facilitate the efficient recovery of these photocatalysts. Transmission electron microscopy and X-ray diffraction results indicated that the ITSF nanoparticles had a ternary structure with a core of Fe3O4, a SiO2 mesosphere and an I-TiO2 crust with a mixture of anatase and rutile phases. Magnetic measurements with a vibrating sample magnetometer showed that the ITSF core–shell structures exhibited favorable superparamagnetic behaviors and the magnetic saturation value decreased after coating with the non-magnetic I-TiO2 layer. The photocatalytic activity of the particles was tested by degrading an aqueous phenol solution under visible-light illumination. The photocatalytic activity of the multi-functional hybrid magnetite nanoparticles was enhanced with increasing content of TiO2, while the magnetism of the composite particles decreased. Moreover, an optimum molar ratio of 1:10 I/TiO2 was determined for the efficient degradation of phenol. The study showed that the presence of SF magnetic core would be helpful in the separation and recovery of I-TiO2 photocatalysts.