Photophysics and Photocatalysis of Carbon Nitride Synthesized at Different Temperatures

The photophysical properties of carbon nitride (C 3 N 4 ) are very basic and important in the understanding of its photocatalytic activity. Herein, we measured the UV–vis diffuse reflectance (UVDR) and fluorescence spectra of C 3 N 4 prepared at different temperatures and studied their fluorescence decay kinetics under different wavelengths and different fluences of light excitation. We found, first, that the fluorescence lifetime of C 3 N 4 under visible (465 nm) light excitation is shorter than that under UV (395 nm) light excitation; second, that the fluorescence lifetime of C 3 N 4 under 465 nm light excitation decreases as increasing its processing temperature; and third, that the fluorescence lifetime of C 3 N 4 under 395 nm light excitation decreases with the increase of the light excitation fluence. These findings revealed that the two distinct absorption bands in the UVDR spectrum of C 3 N 4 arise from two different transitions of C 3 N 4 and that the origin of the fluorescence emission of C 3 N 4 arises from its singlet exciton. Besides, the photocatalytic H 2 evolutions of C 3 N 4 synthesized at different temperatures under visible light irradiation were also measured and discussed to correlate with the obtained photophysical properties of C 3 N 4 .