# Insulating titanium oxynitride for visible light photocatalysis

## TL;DR

This study introduces insulating titanium oxynitride Ti₂N₂O as a promising visible-light photocatalyst with a suitable band-gap and favorable electronic properties, potentially easier to synthesize than nitrogen-doped TiO₂.

## Contribution

The paper systematically investigates Ti₂N₂O's electronic structure and proposes it as a novel, efficient photocatalytic material for water splitting under visible light.

## Key findings

- Ti₂N₂O is a semiconductor with a 1.81 eV band-gap.
- Band-gap reduction achieved by raising the valence-band maximum.
- Ti₂N₂O has favorable band-edge alignment for water-splitting.

## Abstract

We propose a systematic approach to obtain various forms of insulating titanium oxynitrides Ti$_{n}$N$_{2}$O$_{2n-3}$ and we conduct a detailed study on its $n=2$ case, Ti$_{2}$N$_{2}$O. We study the energetics and the electronic structures of Ti$_{2}$N$_{2}$O and compare these results with those of pristine and nitrogen-doped TiO$_{2}$ within the framework of the density-functional theory (DFT) and the GW approximation. We find that Ti$_{2}$N$_{2}$O is semiconducting with the calculated band-gap of 1.81 eV, which is significantly smaller than those of pristine TiO$_{2}$ rutile (3.14 eV) or anatase (3.55 eV). Furthermore, the reduction of the band-gap of Ti$_{2}$N$_{2}$O is realized not by lowering of the conduction-band minimum but by rising the valence-band maximum. Therefore the proposed Ti$_{2}$N$_{2}$O has suitable band-edge alignment for water-splitting photocatalysis. Finally, total energy calculations indicate that Ti$_{2}$N$_{2}$O is potentially easier to synthesize than nitrogen-doped TiO$_{2}$. Based on these results, we propose Ti$_{2}$N$_{2}$O as a promising visible-light photocatalytic material.