Ca-assisted nitrogen-rich molecular approach for the synthesis of monodisperse tantalum oxide and (oxy)nitride nanocrystals for visible light–induced water oxidation

抄録

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 µmol·h⁻¹ 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.