Hierarchical tantalum-based oxide and (oxy)nitride with hollow urchin-like nanostructures have been synthesized for the first time by an in situ self-assembly wet-chemical route in addition with post-thermal nitridation. Notably, a single-phase metastable γ-TaON with hollow urchin-like spheres among the tantalum (oxy)nitrides was obtained during the phase transformation process from an orthorhombic Ta2O5 to a typical monoclinic β-TaON, corresponding the order of phase formation: Ta2O5 → γ-TaON → β-TaON → Ta3N5. The combined effect of the crystal and electronic structures and hierarchical morphology on the tunable photocatalytic and photoelectrochemical performances of the tantalum-based photocatalysts was systematically investigated. Efficient photocatalytic hydrogen production as high as 381.6 μmol h−1 with an apparent quantum efficiency of 9.5% under 420 nm irradiation (about 47.5 times higher than that of the conventional TaON) was achieved over this metastable γ-TaON architecture. Furthermore, the hierarchical γ-TaON photoanode exhibited a photocurrent density of ∼1.4 mA cm−2 at 0.8 V vs. SCE in Na2SO4 solution under visible light irradiation. This excellent photocatalytic activity is ascribed to the unique urchin-like nanostructure with large specific surface area, the metastable crystal structure and appropriate electronic structure as well as the efficient charge carrier separation.
An Lin,Han Xin,Li Yaogang,Hou Chengyi,Wang Hongzhi,Zhang Qinghong
Abstract In recent years, tantalum oxynitride (TaON) semiconductor as one of the most efficient photocatalysts has been studied intensively owing to the appropriate potentials for overall solar water splitting. In this work, ZnS/CdS/γ-TaON composite photocatalysts with wide light response were successfully prepared by nitridation of Ta 2 O 5 at 800 °C in a wet NH 3 flowing and subsequently deposition CdS and ZnS quantum dots. The powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflection spectroscopy (DRS), N 2 adsorption–desorption isothermals, X-ray photoelectron spectroscopy (XPS), and so on. The photocatalytic property for hydrogen production was also studied. The results indicated that CdS and ZnS quantum dots with a diameter of 3–8 nm were uniformly dispersed on the surface of γ-TaON, which enlarged the spectral response of the ZnS/CdS/γ-TaON photocatalysts. And the optimized H 2 evolution rate of ZnS/CdS/γ-TaON composite (839.6 μmol h −1 g −1 ) is about 14 times higher than that of CdS/γ-TaON in the absence of any noble-metal cocatalyst and 47 times higher than that of Pt loaded γ-TaON sample. The enhanced photocatalytic activity is attributed to the higher separation efficiency of electrons and holes with the heterogeneous junction between ZnS, CdS, and γ-TaON. Besides, the presence of γ-TaON and ZnS also prevent the photocorrosion of CdS. The results provide a new insight for developing the TaON-based nanocomposite photocatalysts with enhanced stability and excellent photocatalytic H 2 production activity.
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