Charge carrier kinetics of carbon nitride colloid: a femtosecond transient absorption spectroscopy study

Carbon nitrides (CN) have been widely used in photocatalytic applications. However, the charge carrier kinetics of CN after light excitation remains unclear. Herein, we prepared a stable and transparent CN colloid in an aqueous tetraethylammonium hydroxide solution and investigated its carrier kinetics using both femtosecond transient absorption and picosecond time-resolved fluorescence spectroscopy. We found that a new and positive absorption band appears in the femtosecond transient absorption spectrum of the CN colloid, which could be attributed to the absorption of the photogenerated electron/hole pairs (or the electronic excited state) of the CN colloid after light excitation. Moreover, we found that the charge carrier kinetics obtained from the femtosecond transient absorption measurements is dramatically different from that obtained from the picosecond time-resolved fluorescence measurements, indicating that the photophysical process of the CN colloid after light excitation is complicated. With the results obtained from both the femtosecond transient absorption and picosecond time-resolved fluorescence measurements, we proposed a schematic to understand the photophysics and charge carrier kinetics of the CN colloid. We believe that the current study is also significant for researchers to understand the photophysics and charge carrier kinetics of bulk CN.