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

Graphitic carbon nitride (g‐C 3 N 4 ) 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‐C 3 N 4 doped by oxygen while its recovery behavior is controlled by thermally induced oxygen‐assisted disruption of sp 2 bonds in C‐N π‐orbital conjugated system of tri‐s‐triazine units building polymer sheets in g‐C 3 N 4 .