Effects of Metal-Cation Doping on Photocatalytic H2 Evolution Activity of Layered Perovskite Oxynitride K2LaTa2O6N

Abstract

Aliovalent cation doping into a heterogeneous photocatalyst affects several of its physicochemical properties, including its morphological characteristics, optical absorption behavior, and charge carrier dynamics, causing a drastic change in its photocatalytic activity. In the present work, we investigated the effects of aliovalent cation doping on the visible-light H₂-evolution photocatalytic activity of the Ruddlesden–Popper layered perovskite oxynitride K₂LaTa₂O₆N. The photocatalytic activity toward H₂ evolution from an aqueous NaI solution was found to be enhanced by an increase in the specific surface area of the K₂LaTa₂O₆N photocatalyst, which could be realized upon doping with lower-valence cations (e.g., Mg²⁺, Al³⁺, and Ga³⁺). Among the dopants examined at 1 mol % doping, Ga resulted in the highest activity. The activity of the Ga-doped specimen was further improved with increasing Ga concentration, where the maximal activity was obtained at 10 mol %, corresponding to an apparent quantum yield of 2.7 ± 0.4% at 420 nm from aqueous methanol. This number is the highest reported for a layered oxynitride photocatalyst. In the Ga-doped K₂LaTa₂O₆N, a trade-off was observed between the Ga concentration and the photocatalytic activity. Although doping with Ga reduced the particle size of K₂LaTa₂O₆N and suppressed undesirable charge recombination, it led to an enlarged bandgap, unsuitable for visible-light absorption.