Zhigang Zou

A novel hydrogen-evolving photocatalyst InVO4 active under visible light irradiation

Abstract InVO4, with band gap of about 2.0 eV, was found to be a new visible light responding photocatalyst for water decomposition. The photocatalyst showed activity to visible light in a wide wavelength range up to 600 nm. Although the native photocatalyst could evolve H2 from pure water under visible light irradiation (λ>420 nm ) , the photocatalytic activity increases significantly by loading NiO as a co-catalyst. Correlation of the photocatalytic properties with crystal and electronic structure of the compound is discussed in connection with the recently reported 4d and 5d transition metal photocatalysts InNbO4 and InTaO4.

Electronic structures of promising photocatalysts InMO4 (M=V, Nb, Ta) and BiVO4 for water decomposition in the visible wavelength region

The compounds InMO4 (M=V, Nb, Ta) and BiVO4 are promising photocatalysts which are able to induce hydrolysis of water molecules under visible light irradiation. By first principles calculations, supported by experiments, we inspect their peculiar electronic structure in an attempt to rationalize the link between the bulk crystal architecture of the materials and the related electronic properties. We find that the bottom of the conduction band of InMO4 systems consists of a large contribution (about 20%) due to 5s orbitals of In atoms. Another dominant component comes from d orbitals of V, Nb, and Ta. On the other hand, the top of the valence band of the BiVO4 shows a contribution from 6s orbitals of Bi of about 18% as well as a dominant component due to 2p states of O. We can infer that the photocatalytic activity could be improved by the large mobility coming from the s orbital component as well as by tuning the electron affinity (position of the bottom of the conduction band) and ionization potential (t...

Photocatalytic water splitting into H2 and/or O2 under UV and visible light irradiation with a semiconductor photocatalyst

Abstract We report three new series of solid photocatalysts with different crystal structure: Bi2MNbO7 ( M = Al 3+ , Ga 3+ and In3+); A2B2O7 pyrochlore-type with cubic system and space group Fd3m; InMO 4 ( M = Nb 5+ , Ta 5+ ) : ABO4 wolframite-type with monoclinic system and space group P2/a and BiMO 4 ( M = Nb 5+ , Ta 5+ ) : ABO4 stibotantalite-type with triclinic system and space group P1(M=Ta) and orthorhombic systems with space group Pnna (M=Nb), respectively. Although the photocatalysts crystallize in the different crystal structure, they contain the same octahedral TaO6 and/or NbO6 in the different photocatalysts. The band structure of the photocatalysts is defined by Ta / Nb d -level and O 2p-level. The band gaps of the photocatalysts were estimated to be between 2.7 and 2.4 eV . Under visible light (λ>420 nm ) or ultra-violet irradiation, these photocatalysts were found to split water into H2 and/or O2. The photocatalytic activity increases significantly by loading co-catalysts on the surface of the photocatalyst, such as NiO and Pt.

Photoelectrochemical decomposition of water on nanocrystalline BiVO4 film electrodes under visible light

The nanocrystalline BiVO4 film electrode on conducting glass showed an excellent efficiency (IPCE = 29% at 420 nm) for the decomposition of water under visible light.

A novel series of water splitting photocatalysts NiM2O6 (M=Nb,Ta) active under visible light

Abstract A novel series of water splitting solid photocatalysts NiM 2 O 6 ( M = Nb , Ta ) were synthesized by the solid-state reaction method. The NiNb2O6 photocatalyst crystallizes in the Columbite-type structure, orthorhombic with space group pbcn, while NiTa2O6 belongs to the tri-Rutil-type structure, tetragonal system with space group P42/mnm. Both photocatalysts showed high activity to evolve H2 from an aqueous methanol solution under ultra-violet light irradiation. The new photocatalysts can also split water to generate H2 from pure water under visible light irradiation (λ>420 nm ) without any co-catalyst. The band gaps of NiNb2O6 and NiTa2O6 were estimated to be 2.2 and 2.3 eV , respectively. The difference in the band gaps of the photocatalysts is supposed to come from their different conduction band levels formed by Nb 4d in NbO6 and Ta 5d in TaO6.

Photocatalytic hydrogen and oxygen formation under visible light irradiation with M-doped InTaO4 (M = Mn, Fe, Co, Ni and Cu) photocatalysts

In 0.8 M 0.2 TaO 4 (M = Mn, Fe, Co, Ni, Cu) photocatalysts crystallize in the same crystal structure: wolframite type, monoclinic crystal structure with space group P2/c. The rate of H 2 evolution from an aqueous methanol solution under UV irradiation significantly changed with the variation of doping atoms, and In 0.8 Ni 0.2 TaO 4 showed the highest activity. Under visible light irradiation (λ > 420 nm), H 2 and O 2 were evolved from an aqueous methanol and silver nitrate solution, respectively, using the photocatalysts, In 0.8 M 0.2 TaO 4 (M = Mn, Fe, Co, Ni, and Cu).

Photocatalytic and photophysical properties of a novel series of solid photocatalysts, BiTa1−xNbxO4 (0⩽x⩽1)

Abstract BiTa 1−x Nb x O 4 (0⩽x⩽1) solid photocatalysts were prepared by solid-state reaction and characterized by powder X-ray diffraction and Rietveld structure refinement. The structure of BiTa 1− x Nb x O 4 ( x =0.0 and 0.5) is triclinic. However, the structures of x =0.2, 0.8 and 1.0 are orthorhombic. The H 2 evolution was obtained from an aqueous CH 3 OH/H 2 O solution and from pure H 2 O with BiTa 1−x Nb x O 4 (0⩽x⩽1) under UV irradiation. The orthorhombic photocatalysts exhibit much higher activity than that of triclinic photocatalysts. The orthorhombic photocatalyst at x =0.2 showed the highest activity. An UV–vis diffuse reflectance spectroscopy measurement revealed that the band gap of orthorhombic photocatalysts is more narrow than that of triclinic photocatalysts.

Photophysical and photocatalytic properties of new photocatalysts MCrO4 (M=Sr, Ba)

Abstract BaCrO 4 and SrCrO 4 photocatalyst powders were prepared by the solid state reaction method. They were characterized by powder X-ray diffraction, UV–Vis diffuse reflection spectroscopy and photocatalytic activity measurements in case of sacrificial reagents CH 3 OH and AgNO 3 under UV and visible light irradiation ( λ >420 nm), respectively. The band gaps of BaCrO 4 and SrCrO 4 were determined as 2.63 and 2.44 eV. Due to the decrease of the ionic radius of the cation, the photocatalyst SrCrO 4 showed much lower photocatalytic activity than BaCrO 4 in evolving H 2 from CH 3 OH/H 2 O solution. The difference in their photocatalytic activity is ascribed to the special electronic structures of BaCrO 4 and SrCrO 4 .

A new spinel-type photocatalyst BaCr2O4 for H2 evolution under UV and visible light irradiation

The photophysical and photocatalytic properties of BaCr2O4 synthesized with normal spinel-type crystal structure were studied. It was found that H2 could be photocatalytically evolved from the aqueous CH3OH solution suspended with Pt(0.2 wt%)/BaCr2O4 powder under irradiation of both ultraviolet (UV) and visible lights. The wavelength dependence of H2 evolution under visible light irradiation showed a maximum activity for k > 540 nm. A possible electronic band structure and corresponding photoexcitation modes of BaCr2O4 under irradiation of UV and visible lights were proposed in regard to the complicated photophysical and photocatalytic properties. 2003 Elsevier Science B.V. All rights reserved.

Optical and structural properties of the BiTa1−xNbxO4 (0≦x≦1) compounds

Abstract Polycrystalline samples of BiTa1−xNbxO4 (0≦x≦1) were synthesized by a solid state reaction and characterized by powder X-ray diffraction. Rietveld structure refinement revealed that the variation of x in BiTa1−xNbxO4 (0≦x≦1) could cause the change in crystal structure. The structure of BiTa1−xNbxO4 (x=0.0 and 0.5) is triclinic system with space group P1. However, the structure of x=0.2, 0.8 and 1.0 is orthorhombic system with space group Pnna. Ultraviolet–visible diffuse reflectance spectroscopy measurement revealed that the band gap of triclinic compounds is wider than that of orthorhombic compounds.