Sulfur doping effects on the electronic and geometric structures of graphitic carbon nitride photocatalyst: insights from first principles

TL;DR

This study uses first principles calculations to analyze how sulfur doping alters the electronic and geometric structures of graphitic carbon nitride, revealing changes that enhance its photocatalytic properties.

Contribution

It provides a detailed first-principles analysis of sulfur doping effects on g-C3N4, including electronic structure modifications and potential explanations for improved photocatalytic activity.

Findings

Sulfur doping narrows the band gap of g-C3N4.

Doped systems become conductive due to occupied states above the gap.

Electronic structure changes explain enhanced photocatalytic properties.

Abstract

We present here results of our first principles studies of the sulfur doping effects on the electronic and geometric structures of graphitic carbon nitride (g-C3N4). Using the Ab initio thermodynamics approach combined with some kinetic analysis, we reveal the favorable S-doping configurations By analyzing the valence charge densities of the doped and un-doped systems, we find that sulfur partially donates its px- and py- electrons to the system with some back donation to the S pz-states. To obtain accurate description of the excited electronic states, we calculate the electronic structure of the systems using the GW method. The band gap width calculated for g-C3N4 is found to be equal to 2.7 eV that is in agreement with experiment. We find the S doping to cause a significant narrowing the gap. Furthermore, the electronic states just above the gap become occupied upon doping that makes the material a conductor. Analysis of the projected local densities of states provides insight into the mechanism underlying such dramatic changes in the electronic structure of g-C3N4 upon the S doping. Based on our results, we propose a possible explanation for the S doping effect on the photo-catalytic properties of g-C3N4 observed in the experiments.