Long-lived triplet state carbon nitride (urea-CNx) catalyzed metal-free photo-ATRP with oxygen acceleration

Abstract

In this study, a long-lived triplet state urea-functionalized carbon nitride (urea-CN_x) was successfully synthesized. It possesses a significant specific surface area, an extended excited state lifetime, and a wide band gap and can be used as recyclable and efficient photocatalyst. Urea-CN_x was applied for metal-free photo atom transfer radical polymerization (photo-ATRP) of methyl methacrylate as a heterogeneous catalyst without any co-catalysts and it exhibited impressive catalytic activity. It combines both photosensitization and catalytic effects within the ATRP system. The ATRP process utilizing methyl methacrylate as the monomer yields polymers with well-matched molecular weights and narrow PDI (Đ = 1.38) when exposed to blue light irradiation. Good time control and high end group fidelity were demonstrated through intermittent on–off light experiments, precise polymerization of various monomers, and synthesis of block copolymers. The oxygen-tolerant photo-ATRP polymerization was proposed to operate via a reactive oxygen species (ROS)-mediated oxidative quenching pathway mechanism, which was found to significantly enhance the reaction rate of the radical polymerization system. Remarkably, even after 10 cycles, the catalytic efficiency of urea-CN_x catalyzed oxygen-tolerant photo-ATRP remained largely unaffected. The system's advantageous features include being completely metal-free, requiring no co-catalysts, and its good sustainability and “oxygen acceleration” behavior. These features provide a new idea and reliable experimental basis for exploring greener, simpler and more economical photo-ATRP polymerisation processes and applications.