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

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.