Strategies for Regulating Reactive Oxygen Species in Carbon Nitride-Based Photocatalysis

Reactive oxygen species (ROS) are increasingly recognized as decisive actors in photocatalytic redox chemistry, dictating both the selectivity and efficiency of target reactions, while most photocatalytic systems generate a mixture of ROS under illumination. Recent studies have revealed that tailoring the generation of specific ROS, rather than maximizing the overall ROS yield, holds the key to unlocking high-performance and application-specific catalysis. In this context, the selective production of specific ROS has emerged as a critical requirement for achieving target-oriented and sustainable photocatalytic transformations. Among the various photocatalytic materials, polymeric carbon nitride (PCN) has garnered considerable attention due to its metal-free composition, visible-light response, tunable structure, and chemical robustness. More importantly, the tunable band structure, surface chemistry, and interfacial environment of PCN collectively make it an excellent scaffold for the controlled generation of specific ROS. In recent years, numerous strategies including molecular doping, defect engineering, heterojunction construction, and co-catalyst integration have been developed to precisely tailor the ROS profile derived from PCN-based systems. This review provides a comprehensive overview of ROS regulation in PCN-based photocatalysis, with a focus on type-specific strategies. By classifying the discussion according to the major ROS types, we highlight the mechanisms of their formation and the design principles that govern their selective generation. In addition, we discuss representative applications in which particular ROS play dominant roles and emphasize the potential of PCN systems in achieving tunable and efficient photocatalytic performance. Finally, we outline key challenges and future directions for developing next-generation ROS-regulated PCN photocatalysts, particularly in the context of reaction selectivity, dynamic behavior, and practical implementation.