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 nonmetal and environmentally friendly photocatalysts for hydrogen production. Great efforts have been devoted to improving the catalytic properties of graphitic C3N4 (g-C3N4) 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-C3N4. By exploring the structures, stabilities, electronic characters, optical properties and catalytic activities, the heptazine-based (h-C6N7 and h-C9N7), the triazine-based (t-C3N3 and t-C2N), and the mixed based (ht-C9N10 and ht-C3N2) carbon nitride derivatives with different linkages are investigated and compared with the conventional g-C3N4. 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-C3N4. 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-C3N4, the electron mobility of h-C6N7 is improved by two orders of magnitude and that of t-C3N3 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-C6N7, ht-C9N10 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. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

Carbon nitrides are emerging environmentally friendly photocatalysts for hydrogen production, and efforts have been made to improve their catalytic properties through element doping, composites construction, and morphology modification. Different combinations of building blocks and linkages in carbon nitride derivatives result in varied stabilities, electronic characters, and catalytic activities.