Synergistic Modulation of Superoxide Radicals and Singlet Oxygen via Band-Engineered CDs-TiO₂ Heterojunctions for Efficient Solar-to-H₂O₂ Conversion

Photocatalytic technology holds immense promise for energy conversion and environmental purification, yet current photocatalysts are often hampered by wide bandgaps, rapid charge carrier recombination, and poor selectivity for reactive oxygen species (ROS). Moreover, the roles of different ROS in photocatalytic reactions remain unclear. To address these challenges, we constructed tunable Z-scheme heterojunctions by coupling anatase TiO₂ nanoparticles (< 5 nm) with four types of absorption-tailored carbon dots (Blue, Green, Orange, and Red). Precise band structure modulation enabled control over charge transfer pathways and ROS generation, thereby achieving enhanced photocatalytic performance at the level of the material's microstructure. By effectively manipulating the charge carrier transfer pathways, these newly formed heterojunctions successfully generate a significant divergence in the concentrations of key reactive oxygen species: the superoxide radicals (·O₂⁻), hydroxyl radicals (·OH), and singlet oxygen (¹O₂). This distinction in ROS generation capabilities is directly manifested in the photocatalytic performance. Specifically, for hydrogen peroxide (H₂O₂) production, the OCDs-TiO₂ composite achieved an impressive H₂O₂ production rate of 292 µmol·g⁻¹·h⁻¹ (12× higher than pure TiO₂) and 90% methyl orange degradation within 30 min(Figure S1.). Mechanistic studies confirm that the synergy of ·O₂⁻ and ¹O₂ is critical for enhanced performance. OCDs-TiO₂ heterojunction maximizes the synergistic generation of superoxide radicals (·O₂⁻) and singlet oxygen (¹O₂). For the first time, we demonstrate the customized fabrication of TiO₂ NPs heterojunctions through precisely regulating their band structure using four types of CDs. It reveals the crucial principle that the bandgap width of CDs determines the charge transfer pathway and resultant ROS concentration, thereby providing a band engineering strategy for optimizing TiO₂ NPs based photocatalysts.