Abstract:

Graphitic carbon nitride (g-CN), as a nonmetal semiconductor material, has been widely used in various fields, such as photocatalysis, electrocatalysis, batteries, light-emitting diodes, and solar cells, owing to its unique electronic and photophysical properties. However, the application of g-CN in practical devices remains limited because of the difficulties in fabricating g-CN films of high quality. In this work, we report a method for preparing a g-CN film with high optical quality on a substrate of indium tin oxide (ITO) glass and/or soda lime (NaCa) glass by using melamine as a precursor. First, we prepared the bulk g-CN from melamine in a muffle furnace via thermal polymerization. Then, we fabricated the g-CN film on the ITO and/or NaCa glass substrate with fine-milled, bulk g-CN in a tube furnace using thermal vapor deposition. With this two-step method, a yellow, transparent g-CN film with high optical quality was successfully fabricated on both the ITO and/or NaCa glass substrates. To check the quality of the film, we used scanning electron microscopy (SEM) to study the morphology of the fabricated g-CN film on the ITO glass substrate. Both the high-resolution and low-resolution SEM image results show that the obtained g-CN film on the ITO glass substrate had a homogeneous and dense structure without a corrugated surface, illustrating that it had good surface roughness. Then, we investigated the thickness and surface roughness of the g-CN film via atomic force microscopy (AFM). The AFM results show that the thickness of the g-CN film deposited on the ITO glass substrate was around 300 nm and that the surface roughness of the g-CN film deposited on the ITO glass substrate was less than 40 nm. To verify the chemical composition of the obtained g-CN film on the ITO glass substrate, we performed X-ray photoelectron spectroscopy (XPS) and energy-dispersive spectroscopy (EDS) analyses. Both the XPS and EDS results demonstrate that the chemical composition of the g-CN film deposited on the ITO glass substrate was similar to that of bulk g-CN powder. More importantly, we determined the band structure for the g-CN film deposited on the ITO glass substrate by using a combination of steady-state absorption and high-resolution valence band XPS analysis. It was found that the determined band structure for the g-CN film deposited on the ITO glass substrate was close to that of bulk g-CN powder, also indicating that its chemical composition was similar to that of bulk g-CN. Meanwhile, we also found that the prepared g-CN film on the ITO glass substrate effectively degraded methylene blue dye under Xe lamp irradiation, which was similar to the effect of bulk g-CN powder. All analyses performed demonstrate that the two-step method presented in this study could successfully fabricate a g-CN film with high optical quality. In addition, we also analyzed the fluorescence lifetime of the g-CN film deposited on the ITO glass substrate by using a homemade time-correlated single-photon counting apparatus and found that it was much shorter than that of bulk g-CN.

Key words: Carbon nitride film, Two-step method of vapor deposition, Morphology, Composition, Steady-state absorption, Fluorescence spectroscopy, Time-correlated single-photon counting,