Dye-sensitized graphitic carbon nitride (g-C3N4) for photocatalysis: a brief review

Photocatalytic semiconductors by solar light have received significant attention for their application on photocatalytic H-2 evolution, degradation of pollutants, CO2 reduction, and so on. Among them, graphitic carbon nitride (g-C3N4) has the properties of earth rich, metal-free, high physicochemical stability, and suitable electronic band structure and band gap for many kinds of photocatalyst reactions. However, the energy conversion efficiency still limited due to the low utilization efficiency in the longer wavelength. Dye sensitization is currently one of promising methods to extend the absorption response region of semiconductors, and enhances the separation and transportation of photogenerated electrons and holes between dyes and semiconductors. It may be a good candidate strategy to enhance photocatalysis efficiency, even though lack of stability and repeatability for these composites. In this article, we have summarized dye-sensitized g-C3N4 with different mechanisms for variety of photocatalysis process, the relationship between structure of dyes and photocatalytic activity. Especially, dyes in H-2 evolution process are divided into metal- free organic dyes, phthalocyanines, and porphyrins in detail. Comparing to metal-free organic dyes, the absorption of phthalocyanines and porphyrins can easily move to near-infrared region, which lead to the enhancement of H-2 evolution activity. It may provide a guidance of the structure designing and constructing for highly effective dye-sensitized g-C3N4 photocatalysts for various applications. At last, we shared our opinions on the challenges and perspectives of dyes on g-C3N4 for photocatalyst.