In situ chemical reduction of the Ta ₃N ₅ quantum dots coupled TaON hollow spheres heterojunction photocatalyst for water oxidation

Photocatalytic oxygen evolution with a high efficiency was achieved using tantalum nitride (Ta ₃N ₅) quantum dots (QDs) coupled TaON hollow spheres (Ta ₃N ₅-TaON). TaON hollow spheres coupled with the surface enriched Ta ₃N ₅ 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 Ta ₃N ₅-TaON composites containing 4 mol% Ta ₃N ₅ QDs showed a high rate of O ₂ 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 Ta ₃N ₅-TaON heterojunction was 3.3 times higher than that of the pristine TaON hollow spheres. Furthermore, relative photoelectrochemical properties of Ta ₃N ₅-TaON composite photoelectrodes were investigated. The resulting 4 mol% Ta ₃N ₅-TaON heterojunction films exhibited a photocurrent of ca. 2.7 mA cm ^-2 under visible light irradiation at 1.0 V vs. SCE in Na ₂SO ₄ solution. This excellent photocatalytic activity is ascribed to the Ta ₃N ₅ 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 Ta ₃N ₅-TaON composite exhibited strong durability which could be attributed to the inhibition of Ta ₃N ₅ QDs leaching owing to its strong interaction with TaON.