Nitrogen-doped carbon dots as photocatalysts for organic synthesis: Effect of nitrogen content on catalytic activity

Regulating the doping of carbon dots (CDs) and the generation of reactive oxygen species (ROS) is essential to selectively control their application in photocatalytic organic reactions. This study successfully synthesized five newly developed nitrogen-doped carbon dots (CDs 1-5) with varying nitrogen content, which have the ability to generate ROS when exposed to light radiation, specifically superoxide anion radicals (O-2(-)) and singlet oxygen (O-1(2)). The utilization of the aforementioned nitrogen-doped CDs as photocatalysts enables the realization of their potential in facilitating efficient photocatalytic organic conversion. Simultaneously, it was observed that the photocatalytic efficiency exhibited a gradual decrease when the nitrogen content in the CDs increased. In order to provide more evidence for this claim, we employed a set of five CDs in the context of photocatalytic dehalogenation of alpha-bromoacetophenone, photocatalytic oxidative coupling reaction of amines to imines, photooxidation reaction of sulfides to sulfoxides, and cross-dehydrogenation coupling (CDC) reaction, in which it was further observed that there was a steady decrease in the yields of photocatalytic organic reactions as the nitrogen content in CDs increased. Notably, CDs 1 exhibited the best photocatalytic efficiency, thereby reinforcing the hypothesis that a higher nitrogen content corresponds to a decreased catalytic efficiency. This study not only investigates the impact of the nitrogen content on the catalytic performance of CDs, but also offers valuable insights for the future utilization of CDs for photocatalytic organic reactions in water.