Structural band-gap tuning in g-C$_3$N$_4$

TL;DR

This study reveals a linear relationship between the structural parameters and the band gap of g-C3N4, enabling tuning of its optical properties for improved photocatalytic hydrogen production.

Contribution

It demonstrates, through combined experimental and ab initio methods, that structural modifications can precisely tune the band gap of g-C3N4, a novel insight for material optimization.

Findings

Linear correlation between band gap and structural aspects

Wave function overlap influences unoccupied p_z states

Structural tuning affects light absorption frequency

Abstract

g-C$_3$N$_4$ is a promising material for hydrogen production from water via photo-catalysis, if we can tune its band gap to desirable levels. Using a combined experimental and ab initio approach, we uncover an almost perfectly linear relationship between the band gap and structural aspects of g-C$_3$N$_4$, which we show to originate in a changing overlap of wave functions associated with the lattice constants. This changing overlap, in turn, causes the unoccupied $p_z$ states to experience a significantly larger energy shift than any other occupied state ($s$, $p_x$, or $p_y$), resulting in this peculiar relationship. Our results explain and demonstrate the possibility to tune the band gap by structural means, and thus the frequency at which g-C$_3$N$_4$ absorbs light.