Photocatalytic dye degradation using modified g-C₃N₄

Dye wastewater is a highly toxic organic pollutant that is not easily degraded. For that reason, it causes serious environmental damage to nature and ecosystems. Therefore, the degradation research of organic matter by using photocatalysts is attracting attention because of their low cost and environmental friendliness. Graphitic carbon nitride (g-C₃N₄), a photocatalyst, has the advantages of being inexpensive, chemically and thermally stable, and easy to prepare. On the other hand, g-C₃N₄ possesses a small surface area, narrow visible light absorption, and a quick-recombination photogenerated electron–hole pair. Photocatalysts are also known to incorporate heteroatoms within their structures and to develop various characteristics depending on the atoms incorporated. In this research, we aim to enhance the dye degradation performance by synthesizing g-C₃N₄, incorporating heteroatoms.

The photocatalyst was obtained by mixing urea, a carbon nitride source, and a heteroatom source, followed by thermal treatment. Bulk g-C₃N₄ (CN-U), N-deficient g-C₃N₄ (CN-N), Br-doped g-C₃N₄ (CN-Br), S-doped g-C₃N₄ (CN-S), and O-doped g-C₃N₄ (CN-O) were prepared. Photocatalytic degradation was carried out under visible light irradiation using a Xenon lamp equipped with a cutoff filter. Methyl orange (MO) and methylene blue (MB) were selected as decolorizing targets. They were characterized in a variety of ways to clarify their photocatalytic properties.

A series of characterization results showed that the typical structure of g-C₃N₄ was maintained. It has been shown that doping carbon nitride with heteroatoms changes the optical properties of carbon nitride. Furthermore, we confirmed that doping carbon nitride with heteroatoms prevents the recombination of photogenerated electron–hole pairs. From the results of the dye degradation experiment, for MO, CN-N degraded the most. For MB, CN-U and CN-N degraded the most. We think this is due to the improved optical properties resulting from the incorporation of heteroatoms.