Defective polymeric carbon nitride: Fabrications, photocatalytic applications and perspectives

Polymeric carbon nitride (CN) as a metal-free photocatalyst with suitable band gap has attracted increasing attention. However, pristine CN has a limited visible-light absorption range and also suffers a high recombination rate of photo-excited charge carriers, resulting in low photocatalytic activity. With the development of modern material characterization technology and electronic structure calculation technology, it is found that vacancy defects in CN play a more decisive role in determining the kinetics, energetics and mechanism of photocatalytic reactions. Therefore, much effort has been made in the past years to enhance the visible light activity of CN through defects control. This review provides the recent progresses and technologies on fabricating defective CN, in which the bottom-up and top-down preparation strategies are systematically summarized. In the meantime, the advancement of defective CN photocatalysts toward versatile applications such as water oxidation, hydrogen production, CO2 reduction, nitrogen fixation, H2O2 and organic synthesis, and pollutants removal are fully discussed. Finally, the existing opportunities and challenges of CN photocatalysts designed with vacancies defects are proposed to highlight the development direction of this field. This paper can lay a theoretical basis and guidance for the preparation of defective graphitic carbon nitride.