Modulating the Optical Properties of Carbon Quantum Dots Through Cerium Doping to Boost the Photocatalytic Efficiency of Titanium Dioxide Composites

In this study, cerium-doped carbon quantum dots (Ce-CDs) are first synthesized by hydrothermal decomposition of organic compounds mixed with different contents of cerium nitrate hexahydrate. The analysis results indicate that cerium doping effectively reduces the CD core's oxygen- and nitrogen-related structural defects. As the doping concentration increases, the incorporation of cerium further induces different defects in carbon quantum dots. Ultraviolet photoemission spectroscopy and Low Energy Inverse Photoemission Spectroscopy show Ce-CDs have similar band gap energy but different Fermi levels. Second, Ce-CDs are combined with TiO₂ to prepare TiO₂/Ce-CDs composites, which demonstrate strong optical properties and enhanced photocatalytic performance due to the structural modification of Ce-CDs. These composites improve visible light photocatalytic performance by improving the charge separation of electron-hole pairs. The main active species include hydroxyl radicals on the TiO₂ surface and superoxide anions on Ce-CDs. The best performance is observed in the TiO₂/0.5Ce-CDs composite, with a reaction rate constant as high as 0.087 min⁻¹ under visible light. This study demonstrates the potential of Ce doping on carbon quantum dots and their advanced photocatalytic applications.