Dopant dependent band gap tailoring of hydrothermally prepared cubic SrTi(x)M(1-x)O(3) (M=Ru,Rh,Ir,Pt,Pd) nanoparticles as visible light photocatalysts

Nanostructured cubic SrTiO(3) particles were hydrothermally synthesized and studied experimentally/theoretically for photoreduction of water. The particles were doped with metal atoms (M=Ru,Rh,Ir,Pt,Pd), which acquired high cyrstallinity after thermal treatment. SrTiO(3):Rh showed the highest rate of H(2) evolution under lambda>420 nm photons. The density functional theory calculations of SrTi(x)M(1-x)O(3) (M=Ru,Rh,Ir,Pt) implied that the photocatalytic activity of SrTi(x)Rh(1-x)O(3) was due to its suitable band energetics, and the induced hybridized Ti/Rh orbitals in the bandgap of SrTiO(3). (C) 2008 American Institute of Physicsclose353

Microwave synthesis of single-crystalline perovskite BiFeO3 nanocubes for photoelectrode and photocatalytic applications

A simple microwave synthesis procedure has been developed for the single-crystalline perovskite nanocubes composed of bismuth ferrite (BiFeO(3)). Typical nanocubes had sizes ranging from 50 to 200 nm. The single-crystalline nature of nanocubes was confirmed by high resolution transmission electron microscopy and selected area electron diffraction pattern. X-ray diffraction pattern showed the rhombohedral phase with R3c space group. The material showed photoinduced water oxidation activity in both photoelectrochemical and photocatalytic modes. It could become a useful material for photoelectrode and photocatalytic applications. (C) 2008 American Institute of Physicsclose878

Theoretical band energetics of Ba(M0.5Sn0.5)O-3 for solar photoactive applications

We report here a comparative study of the theoretically calculated electronic structures of cubic BaSnO3 and cubic Ba(M0.5Sn0.5)O-3 with M=Ti, V, Cr, Zr, Ce, and Pb, the tetravalent metal ions, to explore their possible efficacy for the visible light photocatalysis and solar energy conversion. We performed the calculations within the framework of density functional theory by using WIEN97 code. The 3d orbitals of Ti, V, and Cr, 4d of Zr, and the 4f and 6s orbitals of Ce and Pb, respectively, contributed to the bottom of the conduction band for narrowing of the band gap of cubic BaSnO3. Calculation of the frequency dependent absorption coefficient I(omega) of Ba(M0.5Sn0.5)O-3 indicated that among the transition metal (Ti, V, Cr, and Zr) doped systems, Cr has comparatively higher visible absorption efficiency, whereas among other metal (Pb and Ce) systems, Pb showed significant absorption coefficient in low energy range (E V > Ti among first row transition metals and (ii) Pb > Ce > Zr among rest of tetravalent metals, in decreasing order of photoresponse towards low energy photons (E <= 2.5 eV). (c) 2006 American Institute of Physicsclose242

Difference in electronic structure between tetragonal and cubic SrNbO2N

We report here a comparative study of the electronic structure of earlier known cubic phase and the recently, reported correct tetragonal phase of SrNbO2N. We performed the calculations within the framework of density-functional theory (DFT) by using the WIEN97 code. The valence band consists of N 2p while the conduction band consists of Nb 4d in cubic system; on the contrary, these Nb 4d states show a strong interaction with anion p states in tetragonal system and indicate theoretically, a metallic behavior. The direct forbidden gap of tetragonal system was 0 eV, whereas for cubic system was 0.2 eV; the relative difference in the band gap of two systems is possibly attributed to the high covalency and is possibly acquired due to the presence of the shorter bond length of Nb - N than that of Nb-O in the tetragonal system. The results of electronic structures have been discussed in the light of optical applications of this oxynitride in solar energy conversion. The calculated optical-absorption coefficient I(w) from real and imaginary parts of dielectric function, further clarifies the suitability of the application. (c) 2005 American Institute of Physicsclose5

Photocatalytic Ohmic layered nanocomposite for efficient utilization of visible light photons

The WO3/W/PbBi2Nb1.9Ti0.1O9 photocatalyst was fabricated by depositing the tungsten clusters over the p-type perovskite base material with the chemical vapor deposition method, and later partly oxidizing the surfaces of these clusters to obtain n-type WO3 overlayers and W metal layer as an Ohmic junction. This NCPC showed unprecedented high activity for the photocatalytic oxidation of water, photocurrent generation, and acetaldehyde decomposition under visible light irradiation (lambda >= 420 nm). (c) 2006 American Institute of Physicsclose313

Indium induced band gap tailoring in AgGa(1-x)In(x)S(2) chalcopyrite structure for visible light photocatalysis

Indium was substituted at gallium site in chalcopyrite AgGaS(2) structure by using a simple solid solution method. The spectroscopic analysis using extended x-ray absorption fine structure and x-ray photoelectron spectroscopy confirmed the indium substitution in AgGaS(2) lattice. The band gap energy of AgGa(1-x)In(x)S(2) (x=0 - 1) estimated from the onset of absorption edge was found to be reduced from 2.67 eV (x=0 ) to 1.9 eV (x=1 ) by indium substitution. The theoretical and experimental studies showed that the indium s orbitals in AgGa(1-x)In(x)S(2) tailored the band gap energy, thereby modified the photocatalytic activity of the AgGa(1-x)In(x)S(2). (c) 2008 American Institute of Physicsclose217

Band gap tuning of lead-substituted BaSnO3 for visible light photocatalysis

The Pb substitution effect was investigated experimentally and theoretically on the crystal structure of BaSnO3 and on the photo-oxidation activity of H2O. The chemically doped Pb in BaSnO3 induced a concentration-dependent redshift of the experimental band gap (BG). The BaPb0.8Sn0.2O3 system produced 32 mu mol/h of O-2 under lambda >= 420 nm photons, but no O-2 for BaSnO3. The DFT calculations of BaPbxSn1-xO3 (x=0,0.5,1) by using generalized approximation, implying the BG alteration and the photocatalytic activity of BaPbxSn1-xO3, are due to the induced Pb 6s orbital in the BG of BaSnO3. Thus Pb modified the insulating nature of BaSnO3 to semiconducting and semimetallic. (c) 2007 American Institute of Physicsclose343

Structure and stability of monodisperse 1.4-nm ZnS particles stabilized by mercaptoethanol

Extremely small 1.4-nm size mercaptoethanol-stabilized ZnS clusters have been synthesized with narrow size distribution. The structure of these clusters was studied by wide-angle X-ray scattering. The scattering curves were compared with the calculated scattered intensity of a variety of model clusters (ZnS)N and different defect types via Debye functions. In the as-received state the pattern is best described by a fragment of the zinc blende lattice, with N &#8776; 30, and a defective stacking of three to four (111) planes. A large improvement of the simulation is gained by introducing liquidlike disorder to the model structure. This raises the unanswered question of a "real" liquid state of these small clusters at room temperature. The cluster matrix is thermally stable to 583 K. Above this temperature the primary cluster coalesce to form larger particles. Annealed at 1013 K the particles grow to &gt;4.0 nm with a highly defective zinc blende structure