Abstract
The perovskite-type oxynitride LaNbN2O is a photocatalyst that can evolve oxygen from aqueous solutions in response to long-wavelength visible light. However, it is challenging to obtain active LaNbN2O because of the facile reduction of Nb5+ during the nitridation of the precursor materials. The present study attempted to synthesize a perovskite-type oxide La0.6Na0.4Zn0.4Nb0.6O3, containing equimolar amounts of La3+ and Nb5+ in addition to volatile Na+ and Zn2+, followed by the nitridation of this oxide to generate LaNbN2O. The obtained oxide was not the intended single-phase material but rather comprised a cuboid perovskite-type oxide similar to La0.5Na0.5Zn0.33Nb0.67O3 along with spherical LaNbO4 particles and other impurities. A brief nitridation was found to form a LaNbN2O-like shell structure having a light absorption onset of approximately 700 nm on the cuboid perovskite-type oxide particles. This LaNbN2O-based photocatalyst, when loaded with a CoOx cocatalyst, exhibited an apparent quantum yield of 1.7% at 420 nm during oxygen evolution reaction from an aqueous AgNO3 solution. This was more than double the values obtained from the nitridation products of LaNbO4 and LaKNaNbO5. The present work demonstrates a new approach to the design of precursor oxides that yield highly active LaNbN2O and suggests opportunities for developing efficient Nb-based perovskite oxynitride photocatalysts.
Highlights
Photocatalytic water splitting is an attractive approach to addressing issues related to energy and the environment by converting renewable solar energy into chemical energy stored in the form of hydrogen [1,2]
This work demonstrates a new approach to the synthesis of LaNbN2 O from a perovskitetype La and Nb mixed oxide
The addition of volatile Na and Zn species caused the original oxide to be partly converted into cuboid perovskite-type oxide particles along with spherical LaNbO4 particles and other byproducts
Summary
Photocatalytic water splitting is an attractive approach to addressing issues related to energy and the environment by converting renewable solar energy into chemical energy stored in the form of hydrogen [1,2] This requires developing efficient semiconductor photocatalysts capable of using visible light, which accounts for close to 54% of solar energy to achieve sufficient solar-to-hydrogen energy conversion efficiencies with reasonable quantum efficiencies [1]. Ti4+ , Nb5+ and Ta5+ , respectively) are promising visible-light-driven photocatalysts These materials exhibit intense visible light absorption, tunable compositions and band structures, and stable crystal structures [3,4,5,6].
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