From urea to high-efficiency photocatalyst: The impact of confined-degree and silica support on structure engineering of carbon nitride

Background

The synthesis of g-C₃N₄ (CN) through confined pyrolysis of urea is a widely employed method. However, the impact of confined-degree on the nano- and molecular-structure of CN has been scarcely addressed.

Methods

We investigated this influence by varying the confined-degree of the covered crucibles used for urea pyrolysis. Additionally, a silica nanosheet (SiNS) support was incorporated to achieve high dispersion and easy use.

Significant findings

With increasing confined-degree, the crystallinity and porosity of the synthesized CN nanosheets initially decreased and then increased, whereas the size and dispersion exhibited an opposite tendency. The introduction of SiNS primarily enhanced the yield (excepting CN/SiNS-1), reduced the size (excepting CN/SiNS-4), and improved the dispersion of the supported CN nanosheets. Furthermore, larger CN nanosheets with greater dispersion enhanced the separation efficiency of photoinduced carriers, whereas smaller nanosheets with higher crystallinity displayed a more negative conduction band minimum potential (E_CBM), offering more reactive oxygen species. Therefore, the optimal CN/SiNS-4 composite exhibited significant photocatalytic activity for degrading Rhodamine B in 25 min, with an apparent rate constant of 0.189 min⁻¹, owing to the nanostructure dependent photoreactivity of the well-dispersed and small-sized CN nanosheets, and the strong adsorption capacity of SiNS and urea-derived CN.