Photophysics and Photocatalysis of Carbon Nitride Synthesized at Different Temperatures

The photophysical properties of carbon nitride (C3N4) 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 C3N4 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 C3N4 under visible (465 nm) light excitation is shorter than that under UV (395 nm) light excitation; second, that the fluorescence lifetime of C3N4 under 465 nm light excitation decreases as increasing its processing temperature; and third, that the fluorescence lifetime of C3N4 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 C3N4 arise from two different transitions of C3N4 and that the origin of the fluorescence emission of C3N4 arises from its singlet exciton. Besides, the photocatalytic H-2 evolutions of C3N4 synthesized at different temperatures under visible light irradiation were also measured and discussed to correlate with the obtained photophysical properties of C3N4.