Mixed Oxide Semiconductor Research Articles

Experimental and Theoretical Studies of Photocatalytic Water Splitting on Mixed Oxide Semiconductors

Experimental and Theoretical Studies of Photocatalytic Water Splitting on Mixed Oxide Semiconductors

Direct water splitting into H 2 and O 2 under visible light irradiation with a new series of mixed oxide semiconductor photocatalysts

The research on a new series of solid photocatalysts with different crystal structures was reviewed. The first system is A 2B 2O 7 pyrochlore-crystal type: Bi 2MNbO 7 (M=Al, Ga, In and Y, rare earth, and Fe), which is cubic system and space group Fd3m. The second system is ABO 4 stibotantalite-crystal type: BiMO 4 (M=Nb 5+, Ta 5+), in which both the triclinic system with space group P1 in the case of M=Ta and the orthorhombic system with space group Pnna in the case of M=Nb. The third system is ABO 4 wolframite-crystal type: InMO 4 (M=Nb 5+, Ta 5+), which is monoclinic system and space group P2/a. Although these photocatalysts crystallize in the different crystal structure, they contain the same octahedral TaO 6 and/or NbO 6 in the different photocatalysts. The band structure of the photocatalysts is defined by Ta/Nb d-level for a conduction band and O 2p-level for a valence band. The band gaps of the photocatalysts were estimated to be between 2.7 and 2.4 eV. Metal doped InTaO 4 photocatalysts were also investigated. Under visible light ( λ>420 nm) or ultra-violet irradiation, the H 2 and/or O 2 evolutions were observed from pure water as well as aqueous CH 3OH/H 2O and AgNO 3 solutions. The photocatalytic activity increases significantly by loading co-catalysts such as Pt, RuO 2 and NiO x on the surface of the photocatalysts. Finally, direct water splitting into H 2 and O 2 under visible light irradiation was firstly established using newly synthesized NiO x (partly oxidized nickel) promoted In 0.9Ni 0.1TaO 4 photocatalyst.

Micro-structural characterization of annealed cadmium–zinc oxide thin films obtained by spray pyrolysis

The structural properties of annealed (ZnO) x (CdO) 1− x thin films are studied by x-ray diffraction methods. The films were obtained by spray pyrolysis using different values for the nominal composition ( x), and then they were annealed at 450 °C from 0 to 120 min. The structural analysis confirms previous results on the formation of a homogeneously mixed oxide semiconductor, but in which crystalline and amorphous phases co-exist for both CdO and ZnO. In this work, we show that for annealed films there is a strong interaction between the amorphous, the hexagonal ZnO and the cubic CdO phases regarding the lattice constants and the crystallite growth rate. In the annealed films, for x≤0.5 the optical behavior is mainly controlled by the CdO phase, so that there is a reduction of the effective band-gap of the material when the CdO crystallite size is increased, possibly due to grain size effects. On the other hand, for x>0.5 the band-gap behavior is mainly determined by the variation of the ZnO crystallite lattice parameters and the relative volumetric concentration of amorphous and crystalline ZnO in the film.

Selection of optimal mixing ratios to obtain suitable photoelectrodes from mixed semiconductors using band gap calculations

We present results from the application of a computational package Selection of Semiconductor Composition for Photoelectrochemical Solar Cells (SSCPECS) developed to assist in the selection of stoichiometric compounds of mixed materials and the best mixing ratio for narrowing the extent of further experimental investigations. These calculations can provide an estimate of the mixing ratio for obtaining a desired band gap and thereby assist in developing appropriate electrodes for photovoltaic (dry and wet) solar cells. The package has been applied to 28 different semiconductors and insulators. Applications to mixed oxide semiconductor systems PbO 2TiO 2 and PbOSnO establish its applicability for the purpose mentioned above. The computer program is based on the Charge-Self-Consistent Band Structure (CSCBS) method and the calculated band gaps for pure and mixed semiconductors are quite reasonable. The software package is available on request.