Deciphering the Role of Carbon Doping in Regulating the Intrinsic Charge Carrier Kinetics of Carbon-Rich Polymeric Carbon Nitride Materials through Femtosecond Transient Absorption Spectroscopy

Carbon-rich polymeric carbon nitride (PCN), achieved through the controlled incorporation of carbon into its framework, exhibits significantly enhanced photocatalytic hydrogen evolution activity. While the performance benefits of carbon doping are well recognized, the mechanistic underpinnings of how carbon doping regulates charge carrier kinetics in carbon-rich PCN remain unclear. In this study, we synthesized a series of carbon-rich PCN samples (PCN-BAX) with gradient carbon doping levels and systematically investigated their charge carrier kinetics using femtosecond transient absorption (fs-TA) spectroscopy. The successful modulation of carbon doping levels in PCN-BAX was confirmed through Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), elemental analysis (EA), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), thermogravimetric analysis (TGA), and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS) measurements. fs-TA analysis revealed a decay component (∼30 ps) in the intrinsic charge carrier kinetics of carbon-rich PCN samples, in which its amplitude increases with the increase in carbon doping content. This finding highlights the critical role of carbon doping in regulating intrinsic charge carrier kinetics of carbon-rich PCN materials, providing key insights for optimizing PCN-based photocatalytic systems.