Origin of enhanced visible-light photocatalytic activity of transition metal (Fe, Cr and Co) doped CeO2: Effect of 3d-orbital splitting

TL;DR

This study uses first-principles calculations to elucidate how transition metal doping (Fe, Cr, Co) in CeO2 introduces mid-gap states that enhance visible-light absorption and photocatalytic activity by modifying the electronic structure.

Contribution

It reveals the mechanism by which 3d-orbital splitting and oxygen vacancies in transition metal-doped CeO2 improve photocatalytic performance, providing insights for designing better photocatalysts.

Findings

Transition metal doping introduces mid-gap t2g and eg states.

Oxygen vacancies cause splitting of t2g levels, affecting light absorption.

Band gap narrowing results in redshift and higher photocatalytic efficiency.

Abstract

Enhanced visible light photocatalytic activity of transition metal-doped ceria (CeO2) nanomaterials have experimentally been demonstrated, whereas there are very few reports mentioning the mechanism of this behavior. Here we use first-principles calculations to explore the origin of enhanced photocatalytic performance of CeO2 doped with transition metal impurities (Fe, Cr and Co). When a transition metal atom substitutes a Ce atom into CeO2, t2g and eg levels of 3d orbits appear in the middle of band gap owing to the effect of cubic ligand field, and the former is higher than latter. Interestingly, t2g subset of FeCe (CoCe and CrCe)-Vo-CeO2 is split into two parts: one merges into the conduction band, the other as well as eg will remain in the gap, because O vacancy defect adjacent to transition metal atom will break the symmetry of cubic ligand field. These eg and t2g levels in the band gap are beneficial for absorbing visible light and enhancing quantum efficiency because of forbidden transition, which is one key factor for enhanced visible light photocatalytic activity. The band gap narrowing also leads to a redshift of optical absorbance and high photoactivity. These findings can rationalize the available experimental results and provide some new insights for designing CeO2-based photocatalysts with high photocatalytic performance.