Synthesis and properties of g-C₃N₄ bulk and nanosheets derived from thiourea

Graphitic carbon nitride (g-C₃N₄) has attracted significant interest due to its stability, low-cost elements, and potential applications in photocatalysis. In this study, g-C₃N₄ bulk was synthesized by thermal polycondensation of thiourea at temperatures ranging from 480 to 550 °C. The influence of calcination temperature on the structural and optical properties of g-C₃N₄ was investigated using XRD, FTIR, SEM, UV-Vis diffuse reflectance, and photoluminescence (PL) analyses. Results showed that g-C₃N₄ synthesized at 520 – 550 °C exhibited high crystallinity with typical (002) and (100) diffraction peaks. FTIR spectra confirmed the presence of triazine units in the structure. Nanosheets of g-C₃N₄ were obtained via thermal oxidation of the bulk in static air, resulting in a porous and expanded morphology. Compared to the bulk, the nanosheets displayed a reduced bandgap energy (from 2.750 eV to 2.625 eV) and blue-shifted PL emission, indicating enhanced separation of photo-induced charge carriers. Lorentz fitting of PL spectra revealed three primary emission centers, related to different transition states. These findings suggest that the synthesized g-C₃N₄ nanosheets possess improved optical properties and could be promising materials for visible-light-driven photocatalytic applications. This work also demonstrates a facile, environmentally friendly route to synthesize g-C₃N₄ materials from thiourea, suitable for scale-up.