Eosin-Y and sulfur-codoped g-C3N4 composite for photocatalytic applications: the regeneration of NADH/NADPH and the oxidation of sulfide to sulfoxide

Graphitic carbon nitride (g-C3N4) is a promising two-dimensional semiconducting material that has shown potential for various applications in the field of photocatalysts due to its thermal stability and excellent electronic properties. However, pristine g-C3N4 has a wide optical band gap, which limits the active absorption of solar light in the spectral region below 420 nm. One way to improve the optical character is by doping with a sulfur heteroatom to make sulfur-doped g-C3N4 (S-g-C3N4), which has a smaller band gap relative to the pristine g-C3N4. Herein, we have developed a new type of S-g-C3N4 composite incorporating eosin-Y (EY–S-g-C3N4) by employing the co-polymerization approach between eosin-Y (EY) and S-g-C3N4. In this composite, eosin-Y moieties act as external photosensitizing groups. The optical characteristics of EY–S-g-C3N4 were investigated using density functional theory, various optical spectroscopies, and various imaging techniques. From those characterizations, it was found that the appearance of the charge-transfer state in the low band gap regime improved the light-harvesting ability relative to the g-C3N4 and S-g-C3N4. The use of the EY–S-g-C3N4 photocatalyst for the regeneration of NADH and NADPH showed quite excellent efficiencies of 64.38% and 81.14%, respectively. In addition, it showed the high conversion efficiency of sulfide to sulfoxide with an yield of 99.6%. This research highlights the potential application of the EY–S-g-C3N4 composite in the field of organic transformation based on photoinduced conversion.