In situ chemical reduction of the Ta3N5 quantum dots coupled TaON hollow spheres heterojunction photocatalyst for water oxidation

Abstract

Photocatalytic oxygen evolution with a high efficiency was achieved using tantalum nitride (Ta₃N₅) quantum dots (QDs) coupled TaON hollow spheres (Ta₃N₅–TaON). TaON hollow spheres coupled with the surface enriched Ta₃N₅ QDs were prepared by an in situ chemical reduction route in ammonia solution at −45 °C and were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectra, UV-vis diffuse reflectance spectra and photoluminescence spectra. The Ta₃N₅–TaON composites containing 4 mol% Ta₃N₅ QDs showed a high rate of O₂ production at 208.2 μmol h⁻¹ with an apparent quantum efficiency of 67% under 420 nm light. The rate of oxygen formation of the Ta₃N₅–TaON heterojunction was 3.3 times higher than that of the pristine TaON hollow spheres. Furthermore, relative photoelectrochemical properties of Ta₃N₅–TaON composite photoelectrodes were investigated. The resulting 4 mol% Ta₃N₅–TaON heterojunction films exhibited a photocurrent of ca. 2.7 mA cm⁻² under visible light irradiation at 1.0 V vs. SCE in Na₂SO₄ solution. This excellent photocatalytic activity is ascribed to the Ta₃N₅ QDs that alter the energy levels of the conduction and valence bands in the coupled semiconductor system and the slow recombination of photogenerated electron–hole pairs. Moreover, the Ta₃N₅–TaON composite exhibited strong durability which could be attributed to the inhibition of Ta₃N₅ QDs leaching owing to its strong interaction with TaON.