Abstract

The visible-light-induced photocatalytic water oxidation activity without cocatalyst has been demonstrated for the first time on tantalum (oxy)nitride nanocrystals synthesized by a Ca-assisted nitrogen-rich molecular approach. Monodisperse TaON and Ta3N5 nanocrystals were synthesized by using suitable urea /Ta ratios in the presence of Ca2+ions. The as-synthesized (oxy)nitrides are in the form of spherically-shaped and well-defined nanocrystals with an average diameter of ca. 7 nm. Both nanocrystals showed absorption edges in the visible region. The band gap energies of TaON and Ta3N5 nanocrystals were determined from the Tauc’s plots of the UV ­ Vis diffuse reflectance spectra to be 2.27 and 2.08 eV for indirect allowed transitions,respectively. The O2 evolution rate was increased and reached the maximum in the following order: 2.01, 3.32, and 4.66 mol·h¹1 for the samples synthesized with Ca2+/urea molar ratio of 0.10, 0.50, and 0.25, respectively, due to the decrease in the optical band gap. ©2016 The Ceramic Society of Japan. All rights reserved.

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