Although nanotechnology has offered effective and efficient solutions for environmental remediation, the full utilization of sustainable energy and the avoidance of secondary pollution are still challenges. Herein, we report a two-step modification strategy for TiO2 nanoparticles by first forming a thin, surface-adherent polydopamine (PDA) shell onto the nanoparticles and then assembling core-shell nanoparticles as a photodegradation coating. The composite coating modified from TiO2 could not only realize the highly efficient utilization of photons from the visible region but also avoid the secondary pollution of nanoparticles during application. Additionally, improvements in the adsorption ability after modification greatly facilitated the photocatalytic process of the modified materials. A preliminary in vivo study on Daphnia magna and a wastewater treatment experiment suggest that treatment with the composite coating can effectively eliminate fluorene and significantly reduce its lethality. We believe the two-step modification scheme can open new avenues for the facile modification of nanomaterials for designed purposes, especially in the field of environmental remediation.