Electronic and catalytic properties of carbon nitride derivatives tuned by building blocks and linkages

Carbon nitrides, with a diversity of structures and properties, are a class of emerging non-metal and environmentally friendly photocatalysts for hydrogen production. Great efforts have been devoted to improving the catalytic properties of graphitic C 3 N 4 (g-C 3 N 4 ) by element doping, composites construction, and morphology modification. Exploring carbon nitrides derived from different combinations of heptazine or triazine building blocks and linkages can be another effective way to complement or improve the catalytic properties of g-C 3 N 4. By exploring the structures, stabilities, electronic characters, optical properties and catalytic activities, the heptazine-based (h-C 6 N 7 and h-C 9 N 7 ), the triazine-based (t-C 3 N 3 and t-C 2 N), and the mixed based (ht-C 9 N 10 and ht-C 3 N 2 ) carbon nitride derivatives with different linkages are investigated and compared with the conventional g-C 3 N 4. Dynamical and thermodynamical calculations show that planar configurations of the six carbon nitride derivatives are stable, in contrast to the stable corrugated configuration of g-C 3 N 4. The higher delocalization of electrons in heptazine-based derivatives leads to smaller band gaps compared with triazine-based derivatives. The electron delocalization, band edge positions, and optical properties are regulated by the combination of building blocks or the introduction of the acetylenic linkages. Compared with g-C 3 N 4, the electron mobility of h-C 6 N 7 is improved by two orders of magnitude and that of t-C 3 N 3 is improved by one order of magnitude. The driving forces of all the six carbon nitride derivatives are larger than overpotentials for oxygen evolution reaction (OER), and h-C 6 N 7, ht-C 9 N 10 with lower overpotentials can be good candidates for OER. Insight into the structures and properties of carbon nitride derivatives obtained in this work is expected to provide a guideline for further applications of carbon nitride materials.