Band Engineering of Carbon Nitride Monolayers by N-type, P-type, and Isoelectronic Doping for Photocatalytic Applications

TL;DR

This study uses first principles calculations to explore how doping carbon nitride monolayers with various elements can optimize their electronic and optical properties for efficient solar water splitting in photocatalytic applications.

Contribution

It demonstrates how n-type, p-type, and isoelectronic doping can tune the band structure and enhance photocatalytic efficiency of two-dimensional carbon nitrides.

Findings

Doping with Si and Ge narrows band gaps by 0.5-1.0 eV.

Doped structures show increased optical absorption in visible spectrum.

Pristine materials have bandgaps unsuitable for water splitting.

Abstract

Since hydrogen fuel involves the highest energy density among all fuels, production of this gas through the solar water splitting approach has been suggested as a green remedy for greenhouse environmental issues due to extensive consumption of fossil fuels. Low dimensional materials possessing a large surface-to-volume ratio can be a promising candidate to be used for the photocatalytic approach. Here, we used extensive first principles calculations to investigate the application of newly fabricated members of two dimensional carbon nitrides including tg-C3N4, hg-C3N4, C2N, and C3N for water splitting. Band engineering via n-type, p-type, and isoelectronic doping agents such as B, N, P, Si, and Ge was demonstrated for tuning the electronic structure; optimizing solar absorption and band alignment for photocatalysis. Pristine tg-C3N4, hg-C3N4, and C2N crystals involve bandgaps of 3.190 eV, 2.772 eV, and 2.465 eV, respectively, which are not proper for water splitting. Among the dopants, Si and Ge dopants can narrow the band gap of carbon nitrides about 0.5 - 1.0 eV, and also increase their optical absorption in the visible spectrum. This study presents the potential for doping with isoelectronic elements to greatly improve the photocatalytic characteristics of carbon nitride nanostructures.