<p>This study investigates the synthesis and photocatalytic performance of CeO₂/porphyrin nanocomposites, created by self-assembling porphyrin monomers onto CeO₂ nanoparticles, which were green-synthesized using <i>Cleistocalyx operculatus</i> leaf extract. The resulting CeO₂/porphyrin composite showed enhanced photocatalytic efficiency for degrading organic pollutants, such as methylene blue and rhodamine B, compared to individual CeO₂ nanoparticles and free porphyrin aggregates. CeO₂ nanoparticles were characterized by SEM, XRD, FTIR, EDX, and UV-Vis, confirming successful synthesis and their crystalline integrity. The porphyrin TCPP (Tetrakis(4-carboxyphenyl)porphyrin) was integrated via a reprecipitation method, and SEM and XRD analysis verified the uniform incorporation of TCPP onto CeO₂ nanoparticles, preserving the nanofiber morphology and a crystalline structure with an average size of 9 nm. The CeO₂/TCPP composite exhibited extended visible light absorption, as shown in UV-Vis diffuse reflectance spectra, indicating its potential for photocatalytic applications under visible light. Photocatalytic tests under simulated sunlight demonstrated a significant improvement in performance, with a 95.9% degradation of Rhodamine B after 120 minutes, particularly at a CeO₂:TCPP ratio of 10:1. This research highlights the effective synergy between CeO₂ and porphyrin materials, providing a novel approach for developing efficient, green-synthesized nanocomposites for environmental remediation under visible light, marking a significant contribution to photocatalytic technology.</p>