Efficient overall water splitting under visible-light irradiation on (Ga(1-x)Zn(x))(N(1-x)O(x)) dispersed with Rh-Cr mixed-oxide nanoparticles: Effect of reaction conditions on photocatalytic activity

The photocatalytic activity of (Ga(1-x)Zn(x))(N(1-x)O(x)) loaded with Rh-Cr mixed-oxide (Rh(2-y)Cr(y)O3) nanoparticles for overall water splitting under visible-light irradiation (lambda > 400 nm) is investigated with respect to reaction pH and gas pressure. The photocatalytic performance of the catalyst is found to be strongly dependent on the pH of the reactant solution but largely independent of gas pressure. The present photocatalyst exhibits stable and high photocatalytic activity in an aqueous solution of pH 4.5 for 72 h. The photocatalytic performance is much lower at pH 3.0 and pH 6.2, attributable to corrosion of the cocatalyst and hydrolysis of the catalyst. The dispersion of Rh(2-y)Cr(y)O3 as a cocatalyst on the (Ga(1-x)Zn(x))(N(1-x)O(x)) surface promotes hydrogen evolution, which is considered to be the rate-determining step for overall water splitting on this catalyst.     

Characterization of ruthenium oxide nanocluster as a cocatalyst with (Ga(1-x)Zn(x))(N(1-x)Ox) for photocatalytic overall water splitting

The formation and structural characteristics of Ru species applied as a cocatalyst on (Ga(1)(-)(x)()Zn(x)())(N(1)(-)(x)()O(x)()) are examined by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. RuO(2) is an effective cocatalyst that enhances the activity of (Ga(1)(-)(x)()Zn(x)())(N(1)(-)(x)()O(x)()) for overall water splitting under visible-light irradiation. The highest photocatalytic activity is obtained for a sample loaded with 5.0 wt % RuO(2) from an Ru(3)(CO)(12) precursor followed by calcination at 623 K. Calcination is shown to cause the decomposition of initial Ru(3)(CO)(12) on the (Ga(1)(-)(x)()Zn(x)())(N(1)(-)(x)()O(x)()) surface (373 K) to form Ru(IV) species (423 K). Amorphous RuO(2) nanoclusters are then formed by an agglomeration of finer particles (523 K), and the nanoclusters finally crystallize (623 K) to provide the highest catalytic activity. The enhancement of catalytic activity by Ru loading from Ru(3)(CO)(12) is thus shown to be dependent on the formation of crystalline RuO(2) nanoparticles with optimal size and coverage.     

Characterization of Rh-Cr mixed-oxide nanoparticles dispersed on (Ga(1-x)Zn(x))(N(1-x)Ox) as a cocatalyst for visible-light-driven overall water splitting

The structure of Rh-Cr mixed-oxide (Rh(2)(-)(y)Cr(y)O(3)) nanoparticles dispersed on (Ga(1)(-)(x)Zn(x))(N(1)(-)(x)O(x)) is characterized by electron microscopy and X-ray spectroscopy. The Rh(2)(-)(y)Cr(y)O(3) nanoparticle is an efficient cocatalyst for photocatalytic overall water splitting on the (Ga(1)(-)(x)Zn(x))(N(1)(-)(x)O(x)) solid solution and is loaded onto the catalyst by impregnation from an aqueous solution containing Na(3)RhCl(6).2H(2)O and Cr(NO(3))(3).9H(2)O followed by calcination in air. Impregnation of the (Ga(1)(-)(x)Zn(x))(N(1)(-)(x)O(x)) with 1 wt % Rh and 1.5 wt % Cr followed by calcination at 623 K for 1 h provides the highest photocatalytic activity. Structural analyses reveal that the activity of this photocatalyst is strongly dependent on the generation of trivalent Rh-Cr mixed-oxide nanoparticles with optimal composition and distribution.     

Photophysical and photocatalytic properties of Ca(1-x)BixVxMo(1-x)O4 solid solutions

New solid solutions with the composition of Ca(1-x)BixVxMo(1-x)O4 prepared by a solid-state method were found as novel photocatalysts with enhanced activity for O(2) evolution from aqueous solutions containing sacrificial reagent AgNO3 under visible-light irradiation (>420 nm). The obtained solid solutions crystallized in tetragonal crystal structures, except one of the end compounds, BiVO4, which crystallized in monoclinic structures. The diffuse reflection spectra of the solid solutions shift monotonically to a long wavelength as the ratio of Bi (V) ions to Ca (Mo) ions increases in the solid solution. The band structure and the dependence of the photocatalytic properties were discussed in relation to the solid-solution compositions and photophysical properties.     

Correlation of crystal structure, dielectric properties and lattice vibration spectra of (Ba(1-x)Sr(x))(Zn(1/3)Nb(2/3))O3 solid solutions

(Ba(1-x)Sr(x))(Zn(1/3)Nb(2/3))O(3) (BSZN) (x = 0.0, 0.50, 0.60, 0.65, 0.70, 1.0) solid solutions were synthesized by a conventional solid-state sintering technique. Vibration spectra (Raman spectroscopy and Fourier transform far-infrared reflection spectroscopy, FTIR) and X-ray diffraction (XRD) were employed to evaluate the crystal structures and phonon modes of these solid solutions. Dielectric constants (ε(r)) and temperature coefficient of capacitances (τ(c)) were examined to reveal the correlation of the dielectric properties and the crystal structures. The results show that with the increase in Sr(2+) content, the lattice structures of ceramics turn gradually from disordered cubic structure to ordered structure because antiphase tilting of the oxygen octahedra occurs where x≥ 0.65, which is the main reason for the phase transitions and variation of crystal structure. The appearance of the phase transitions is associated with variation of the symmetry structure, from cubic (Pm ?3m, where x = 0) to pseudocubic (I4/mcm, where 0.65 ≤x < 1.0) and then to hexagonal (P ?3ml, where x = 1.0). New phonon modes appear at around 250 cm(-1) in Raman spectra where x≥ 0.65, and there is also a different phonon mode appearing at 156 cm(-1) in the FTIR spectra at the same x range. The appearance of the new phonon modes is the characteristic of ceramics whose oxygen octahedra have tilted with Sr(2+) concentration where x≥ 0.65. The Raman shifts are related to the rigidity of the oxygen octahedra, while the widths of peaks are correlated with τ(c). The FTIR spectra were subjected to the Kramers-Kronig analysis, and the imaginary part of the dielectric constant was analyzed in detail.     

Structural and thermochemical chemisorption of CO2 on Li(4+x)(Si(1-x)Al(x))O4 and Li(4-x)(Si(1-x)V(x))O4 solid solutions

Different Li(4)SiO(4) solid solutions containing aluminum (Li(4+x)(Si(1-x)Al(x))O(4)) or vanadium (Li(4-x)(Si(1-x)V(x))O(4)) were prepared by solid state reactions. Samples were characterized by X-ray diffraction and solid state nuclear magnetic resonance. Then, samples were tested as CO(2) captors. Characterization results show that both, aluminum and vanadium ions, occupy silicon sites into the Li(4)SiO(4) lattice. Thus, the dissolution of aluminum is compensated by Li(1+) interstitials, while the dissolution of vanadium leads to lithium vacancies formation. Finally, the CO(2) capture evaluation shows that the aluminum presence into the Li(4)SiO(4) structure highly improves the CO(2) chemisorption, and on the contrary, vanadium addition inhibits it. The differences observed between the CO(2) chemisorption processes are mainly correlated to the different lithium secondary phases produced in each case and their corresponding diffusion properties.     

Site-differentiated solid solution in (Na(1-x)Cu(x))2Ta4O11 and its electronic structure and optical properties

The (Na(1-x)Cu(x))(2)Ta(4)O(11) (0 ≤ x ≤ 0.78) solid-solution was synthesized within evacuated fused-silica vessels and characterized by powder X-ray diffraction techniques (space group: R3c (#167), Z = 6, a = 6.2061(2)-6.2131(2) ?, c = 36.712(1)-36.861(1) ?, for x = 0.37, 0.57, and 0.78). The structure consists of single layers of TaO(7) pentagonal bipyramids as well as layers of isolated TaO(6) octahedra surrounded by Na(+) and Cu(+) cations. Full-profile Rietveld refinements revealed a site-differentiated substitution of Na(+) cations located in the 12c (Wyckoff) crystallographic site for Cu(+) cations in the 18d crystallographic site. This site differentiation is driven by the linear coordination geometry afforded at the Cu(+) site compared to the distorted seven-coordinate geometry of the Na(+) site. Compositions more Cu-rich than x ~ 0.78, that is, closer to "Cu(2)Ta(4)O(11)", could not be synthesized owing to the destabilizing Na(+)/Cu(+) vacancies that increase with x up to the highest attainable value of ~26%. The UV-vis diffuse reflectance spectra show a significant red-shift of the bandgap size from ~4.0 eV to ~2.65 eV with increasing Cu(+) content across the series. Electronic structure calculations using the TB-LMTO-ASA approach show that the reduction in bandgap size arises from the introduction of Cu 3d(10) orbitals and the formation of a new higher-energy valence band. A direct bandgap transition emerges at k = Γ that is derived from the filled Cu 3d(10) and the empty Ta 5d(0) orbitals, including a small amount of mixing with the O 2p orbitals. The resulting conduction and valence band energies are determined to favorably bracket the redox potentials for water reduction and oxidation, meeting the thermodynamic requirement for photocatalytic water-splitting reactions.     

FT-Raman and powder XRD analysis of the Ba(SO(4))(x)(CrO(4))(1-x) solid solution

The Ba(SO(4))(x)(CrO(4))(1-x) solid solution has been described in nature, forming the mineral Hashemite. From the geochemical point of view, however, anionic solid solutions have much interest because they are suitable systems to probe order-disorder phenomena. The solid solution analysed in the present study has, moreover, a special incentive in its possible use for the extraction from water, and immobilisation, of the pollutant Cr(VI) ion. The orthorhombic (space group Pnma) unit cell parameters of the solid solution change linearly with the mole fraction of both anions, decreasing with increase in the sulfate anion concentration. The vibrational spectroscopic study is centred on the behaviour of the anionic symmetric stretching band (nu(1),A(1)), whose characteristics are examined in detail. While the chromate anion band retains its wavenumber along the full compositional range, the sulfate anion band is shifted toward lower wavenumbers with decrease in the corresponding mole fraction. The positional disorder induced by the random anionic substitution results in strong increase of the halfwidth in both bands, which becomes greatest in the central member of the series.     

Influence of disorder-to-order transition on lattice thermal expansion and oxide ion conductivity in (Ca(x)Gd(1-x))(2)(Zr(1-x)M(x))2O7 pyrochlore solid solutions

The effect of simultaneous substitutions of Ca at A site and Nb or Ta at B site in pyrochlore-type solid solutions: (Ca(x)Gd(1-x))(2)(Zr(1-x)M(x))(2)O(7) (x = 0.1, 0.2, 0.3, 0.4, 0.5 and M = Nb or Ta) were studied by powder X-ray diffraction (XRD), FT NIR Raman spectroscopic techniques and transmission electron microscopy. The solid solutions were prepared by the conventional high-temperature ceramic route. The XRD results and Rietveld analysis revealed that the defect fluorite structure of Gd(2)Zr(2)O(7) progressively changed to a more ordered pyrochlore phase by simultaneous substitutions at A and B sites. Raman spectroscopy reveals the progressive ordering in the anion sublattice with simultaneous doping. High-resolution images and selected-area electron diffraction patterns obtained from TEM confirms the XRD and Raman spectroscopic results. High-temperature XRD studies show that the lattice expansion coefficient in these pyrochlore oxides is of the order of 10(-6) K(-1). Lattice thermal expansion coefficient increases with increase of disorder in pyrochlore oxides, and hence the variation of thermal expansion coefficient with composition is also a good indicator of disordering in pyrochlore-type oxides. The ionic conducting properties of the samples were characterised by impedance spectroscopy, and it was found that Nb-doped compositions show a considerable change in conductivity near the phase boundary of disordered pyrochlore and defect fluorite phases.     

Cation ordering in natural and synthetic (Cu(1-x)Zn(x))(2)CO(3)(OH)(2) and (Cu(1-x)Zn(x))(5)(CO(3))(2)(OH)(6)

In the present paper we report combined experimental and theoretical studies of the UV-vis-NIR spectra of the mineral compounds malachite, rosasite, and aurichalcite and of the precursor compounds for Cu/ZnO catalysts. For the copper species in the minerals the crystal field splitting and the vibronic coupling constants are estimated using the exchange charge model of the crystal field accounting for the exchange and covalence effects. On this basis the transitions responsible for the formation of the optical bands arising from the copper centers in minerals are determined and the profiles of the absorption bands corresponding to these centers are calculated. The profiles of the absorption bands calculated as a sum of bands of their respective Cu species are in quite good agreement with the experimental data. In agreement with crystal chemical considerations, the Zn ions were found to be preferentially located on the more regular, i.e., less distorted, octahedral sites in zincian malachite and rosasite, suggesting a high degree of metal ordering in these phases. This concept also applies for the mineral aurichalcite, but not for synthetic aurichalcite, which seems to exhibit a lower degree of metal ordering. The catalyst precursor was found to be a mixture of zincian malachite and a minor amount of aurichalcite. The best fit of the optical spectrum is obtained assuming a mixture of contributions from malachite (0% Zn) and rosasite (38% Zn of [Zn + Cu]), which is probably due to the intermediate Zn content of the precursor (30%).     

Correlation between the band positions of (SrTiO3)1-x.(LaTiO2N)x solid solutions and photocatalytic properties under visible light irradiation

N-doped SrTiO3 and (SrTiO3)1-x.(LaTiO2N)x samples were prepared by the thermal ammonolysis method. The photocatalytic activities of the samples were investigated in a water suspension system. Aqueous methanol solution (50 mL CH3OH + 220 mL H2O) for H2 evolution and aqueous silver nitrate solution (270 mL, 0.01 mol L(-1)) for O2 evolution were used as sacrificial reagents. The oxynitrides showed photocatalytic activities under visible light irradiation. The maximum rates of photocatalytic hydrogen and oxygen evolution under visible light irradiation (lambda > 420 nm) were 10 and 8 micromol h(-1), respectively. The samples were characterized by X-ray diffractometry, UV-Vis spectrophotometry, Fourier transform infrared spectrometry, and laser Raman spectroscopy. The unit cell edge length of (SrTiO3)1-x.(LaTiO2N)x increased linearly and their band gaps reduced from 3.18 to 2.04 eV with increasing x from 0 to 0.30. Moreover, the calculation results of (SrTiO3)0.75.(LaTiO2N)0.25 by density functional theory suggested that the band gap narrowing of the solid solutions came from the hybridization of N2p and O2p orbital. The band positions of the solid solutions were further investigated by Mott-Schottky and the onset potential method. The results suggested that the conduction band of the solid solution was lowered, which led to decrement of the hydrogen evolution rate.     

Ce-doped ZnO (Ce(x)Zn(1-x)O) becomes an efficient visible-light-sensitive photocatalyst by co-catalyst (Cu2+) grafting

We have fabricated an efficient visible-light-sensitive Cu(2+)-grafted Ce-doped ZnO photocatalyst (Cu(2+)-Ce(x)Zn(1-x)O) by adopting a metal ion doping and co-catalyst modification. Impurity states were formed below the conduction band (CB) edge in Ce(x)Zn(1-x)O, and these impurity states induce the visible-light absorption. Ce(x)Zn(1-x)O without a Cu(2+)-co-catalyst showed negligible visible-light activity due to the low reduction power of electrons in impurity levels. Surprisingly, Cu(2+)-modification over Ce(x)Zn(1-x)O drastically increased its visible-light activity. Excited electrons in impurity states can transfer to the Cu(2+)-ions on the surface and form Cu(2+)/Cu(+) redox couples, which cause the efficient oxygen reduction through a multi-electron reduction process. One of the striking features of the present study is that the metal doped semiconductors which were inactive due to their impurity states become efficient visible-light photocatalysts upon co-catalyst modification. The successful strategy used here for designing a highly active visible-light photocatalyst would provide numerous opportunities to develop an efficient metal-ion based visible-light photocatalyst.     

Local structure of actinide dioxide solid solutions Th(1-x)U(x)O2 and Th(1-x)Pu(x)O2

Extended X-ray absorption fine structure (EXAFS) has been utilized to investigate the local atomic structure around Th, U, and Pu atoms in polycrystalline mixed dioxides Th(1-x)M(x)O2 (with M = U, Pu) for x ranging from 0 to 1. The composition dependence of the two first-coordination-shell distances was measured throughout the entire composition range for both solid solutions. The first-shell distances vary slightly across the solid-solution composition with values close to those of the pure dioxide parents, indicating a bimodal cation-oxygen distribution. In contrast, the second-shell distance varies strongly with composition, with values close to the weighted amount average distances. Nevertheless, in both systems, the lattice cell parameters, deduced from the first- and second-shell bond determined by EXAFS, are very close to those measured from X-ray diffraction (XRD). They vary linearly with composition, accurately following Vegard's law.     

Core-shell microspherical Ti(1-x)Zr(x)O2 solid solution photocatalysts directly from ultrasonic spray pyrolysis

A series of Ti(1-x)Zr(x)O(2) solid solutions photocatalysts (x = 0.000, 0.045, 0.090, 0.135, and 0.180) was directly obtained by an ultrasonic spray pyrolysis method. Compared with previous methods for solid solutions, our preparation was very fast. The resulting samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, nitrogen adsorption, and UV-vis diffuse reflectance spectroscopy. The characterizations revealed core-shell spherical structures of the resulting solid solutions. We evaluated photocatalytic activities of the solid solutions on degradation of rhodamine B in aqueous solution under simulated solar light. It was found that Ti(0.91)Zr(0.09)O(2) solid solution exhibited the highest photocatalytic activity among all the as-prepared samples. Its activity was much higher than that of P25. The formation mechanism of core-shell spherical structures was proposed. Moreover, we successfully extended this method to prepare microspheres of ceria and ceria-zirconia solid solutions. We think this general method may be easily scaled up for industrial production of microspherical solid solutions photocatalysts and catalysts.     

Effects of thermal annealing on the structural and optical properties of Mg(x)Zn(1-x)O nanocrystals

Mg(x)Zn(1-x)O ternary alloy nanocrystals with hexagonal wurtzite structures were fabricated by using the sol-gel method. X-ray diffraction patterns, UV-vis absorption spectra, and photoluminescence spectra were used to characterize the structural and optical properties of the nanocrystals. For as-prepared nanocrystals, the band gap increases with increasing Mg content. Weak excitonic emission with strong deep-level emission related to oxygen vacancy and interface defects is observed in the photoluminescence spectra at room temperature. Thermal annealing in oxygen was used to decrease the number of defects and to improve the quality of the nanocrystals. In terms of XRD results, the grain sizes of nanocrystals increase with increasing annealing temperature and the lattice constants of alloy are smaller than those of pure ZnO. The band gap becomes narrower with increasing annealing temperature. For Mg(x)Zn(1-x)O nanocrystals (x=0.03-0.15) annealed at temperatures ranging from 500 to 1000 degrees C, intense near-band-edge (NBE) emissions and weak deep-level (DL) emissions are observed. Consequently, the quality of Mg(x)Zn(1-x)O nanocrystals can be improved by thermal annealing.     

Vibrational modes and structural characteristics of (Ba(0.3)Sr(0.7))[(Zn(x)Mg(1-x))(1/3)Nb(2/3)]O3 solid solutions

(Ba(0.3)Sr(0.7))[(Zn(x)Mg(1-x))(1/3)Nb(2/3)]O(3) (BSZMN) (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) solid solution ceramics were synthesized by the conventional solid-state sintering technique. Vibration spectra (Raman spectroscopy and Fourier transform far-infrared reflection spectroscopy, short for FTIR) and X-ray diffraction (XRD) were employed to evaluate the correlation between crystal structures and vibration modes of these solid solutions as a function of Mg(2+) ions replaced by Zn(2+) ions. It is verified that these ceramics present a phase transition, i.e., the crystal structure changes from hexagonal phase (P ?3m1, where x≤ 0.4) to the pseudocubic phase (I4/mcm, where x≥ 0.8) with increasing Zn(2+) content. The phase transition is a gradual process, the sample where x = 0.6 is of the transition phase, i.e., at x = 0.6, phase transition begins to appear from hexagonal phase to pseudocubic phase but is not complete. The phase transition is also verified by the FTIR spectra. Tilting of oxygen octahedra is the main reason for the phase transition. The phonon modes of the vibration spectra were assigned, the position and width were determined, and the correlation of phonon vibrations with the microstructure for the different atoms substituted in B'-site was found.     

Unusual physical and chemical properties of Cu in Ce(1-x)Cu(x)O(2) oxides

The structural and electronic properties of Ce(1-x)Cu(x)O(2) nano systems prepared by a reverse microemulsion method were characterized with synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and density functional calculations. The Cu atoms embedded in ceria had an oxidation state higher than those of the cations in Cu(2)O or CuO. The lattice of the Ce(1)(-x)Cu(x)O(2) systems still adopted a fluorite-type structure, but it was highly distorted with multiple cation-oxygen distances with respect to the single cation-oxygen bond distance seen in pure ceria. The doping of CeO(2) with copper introduced a large strain into the oxide lattice and favored the formation of O vacancies, leading to a Ce(1-x)Cu(x)O(2-y) stoichiometry for our materials. Cu approached the planar geometry characteristic of Cu(II) oxides, but with a strongly perturbed local order. The chemical activities of the Ce(1-x)Cu(x)O(2) nanoparticles were tested using the reactions with H(2) and O(2) as probes. During the reduction in hydrogen, an induction time was observed and became shorter after raising the reaction temperature. The fraction of copper that could be reduced in the Ce(1-x)Cu(x)O(2) oxides also depended strongly on the reaction temperature. A comparison with data for the reduction of pure copper oxides indicated that the copper embedded in ceria was much more difficult to reduce. The reduction of the Ce(1-x)Cu(x)O(2) nanoparticles was rather reversible, without the generation of a significant amount of CuO or Cu(2)O phases during reoxidation. This reversible process demonstrates the unusual structural and chemical properties of the Cu-doped ceria materials.     

Phase evolution, phase transition, raman spectra, infrared spectra, and microwave dielectric properties of low temperature firing (K(0.5x)Bi(1-0.5x))(Mo(x)V(1-x))O4 ceramics with scheelite related structure

In the present work, the (K(0.5x)Bi(1-0.5x))(Mo(x)V(1-x))O(4) ceramics (0≤x ≤ 1.00) were prepared via the solid state reaction method and sintered at temperatures below 830 °C. At room temperature, the BiVO(4) scheelite monoclinic solid solution was formed in ceramic samples with x < 0.10. When x lies between 0.1-0.19, a BiVO(4) scheelite tetragonal phase was formed. The phase transition from scheelite monoclinic to scheelite tetragonal phase is a continuous, second order ferroelastic transition. High temperature X-ray diffraction results showed that this phase transition can also be induced at high temperatures about 62 °C for x = 0.09 sample, and has a monoclinic phase at room temperature. Two scheelite tetragonal phases, one being a BiVO(4) type and the other phase is a (K,Bi)(1/2)MoO(4) type, coexist in the compositional range 0.19 < x < 0.82. A pure (K,Bi)(1/2)MoO(4) tetragonal type solid solution can be obtained in the range 0.82 ≤ x ≤ 0.85. Between 0.88 ≤ x ≤ 1.0, a (K,Bi)(1/2)MoO(4) monoclinic solid solution region was observed. Excellent microwave dielectric performance with a relative dielectric permittivity around 78 and Qf value above 7800 GHz were achieved in ceramic samples near the ferroelastic phase boundary (at x = 0.09 and 0.10).     

Composition dependence of the photocatalytic activities of BiOCl(1-x)Br(x) solid solutions under visible light

We prepared BiOCl(1-x)Br(x) (x=0-1) solid solutions and characterized their structures, morphologies, and photocatalytic properties by X-ray diffraction, diffuse reflectance spectroscopy, scanning electron microscopy, Raman spectroscopy, photocurrent and photocatalytic activity measurements and also by density functional theory calculations for BiOCl, BiOBr, BiOCl(0.5)Br(0.5). Under visible-light irradiation BiOCl(1-x)Br(x) exhibits a stronger photocatalytic activity than do BiOCl and BiOBr, with the activity reaching the maximum at x=0.5 and decreasing gradually as x is increased toward 1 or decreased toward 0. This trend is closely mimicked by the photogenerated current of BiOCl(1-x)Br(x) , indicating that the enhanced photocatalytic activity of BiOCl(1-x)Br(x) with respect to those of BiOCl and BiOBr originates from the trapping of photogenerated carriers. Our electronic structure calculations for BiOCl(0.5)Br(0.5) with the anion (O(2-), Cl(-), Br(-)) and cation (Bi(3+)) vacancies suggest that the trapping of photogenerated carriers is caused most likely by Bi(3+) cation vacancies, which generate hole states above the conduction band maximum.     

DFT investigation of the tri(amino)amine N(NH(2))(3)(2+) and the tri(azido)amine N(N(3))(3)(2+) dications and related mixed amino(azido)ammonium ions (N(3))(x)N(NH(2))(4-x)(+) (x = 0-4)(1)

Structures of the tri(amino)amine N(NH(2))(3)(2+) and the tri(azido)amine N(N(3))(3)(2+) dications were calculated at the density functional theory (DFT) B3LYP/6-311+G level. The tri(amino)amine dication (NH(2))(3)N(2+) (1) was found to be highly resonance stabilized with a high kinetic barrier for deprotonation. The structures of diamino(azido)amine dication (NH(2))(2)N(N(3))(2+) (2), amino(diazido)amine dication (NH(2))N(N(3))(2)(2+) (3), and tri(azido)amine dication (N(3))(3)N(2+) (4) were also found to be highly resonance stabilized. The structures and energetics of the related mixed amino(azido)ammonium ions (N(3))(x)N(NH(2))(4-x)(+) (x = 0-4) were also calculated.