(Oxy)nitrides are regarded as an emerging class of inorganic materials for photocatalytic water splitting due to their smaller band gap, suitable band structure, stability, and nontoxicity . As BaTaO2N can harvest visible light up to 660 nm and showed an IPCE value of 10%  and generated a current density of 25 mA cm?2  at 1.2 VRHE, the effect of substitutional tantalum on photocatalytic water oxidation activity of BaNbO2N crystals was investigated in this study. The BaNb1-xTax(O,N)3 (x = 0.00, 0.25, 0.50, 0.75, and 1.0) crystals were directly grown by an NH3-assisted flux method at 900°C for 7 h ? 2 times. The diffraction peaks of Ta-substituted BaNbO2N crystals became slightly broader and their positions shifted to higher angle than that of BaNbO2N crystals, indicating the overall lattice contraction. Compared with that of BaNbO2N crystals with more-faceted morphology (d50 = 0.38 ?m), an average size of Ta-substituted BaNbO2N crystals exponentially decreased (d50 = 0.31, 0.28, 0.24, and 0. 17 ?m) and the crystals became less faceted with increased tantalum content. It is thought that the decrease in the tantalum content tends to minimize the surface Gibbs energy of those faces that became the most thermodynamically stable. The BaTaO2N crystals showed an onset of light absorption at ? ? 660 nm, whereas the decrement in the tantalum content shifted an absorption edge toward longer wavelength (? ? 680 nm). However, the intensity of background absorption monotonically increased with decreasing the tantalum content due to the presence of considerable amount of reduced niobium species and anion deficiency. The BaNb1-xTax(O,N)3 (x = 0.25, 0.50, 0.75, and 1.0) crystals loaded with CoOx showed higher photocatalytic activity for O2 evolution compared with CoOx-loaded BaNbO2N crystals due to the shift of valence band to more positive side and the lowered densities of mid-gap states associated with defects.
|Category||Short file description||File description||File Size|