Recovery Behavior of the Luminescence Peak from Graphitic Carbon Nitride as a Function of the Synthesis Temperature

Abstract

Graphitic carbon nitride (g-C3N4) is synthesized by thermal decomposition of thiourea and subsequent in situ polymerization of the products in the oxygen-containing ambient at 450–625 °C and studied with scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, and photoluminescence techniques. The synthesized material contains oxygen at a concentration increasing with the processing temperature from 4.8 to 9.8 at %. The photoluminescence peak is found to be red-shifted with the temperature increased to 575 °C becoming then blue-shifted at higher temperatures. The observed red-shift of the photoluminescence peak is supposed to be caused by band-gap narrowing in g-C3N4 doped by oxygen while its recovery behavior is controlled by thermally induced oxygen-assisted disruption of sp2 bonds in C-N π-orbital conjugated system of tri-s-triazine units building polymer sheets in g-C3N4.