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Completely B-site-ordered Ba2InTaO6 has been prepared previously by prolonged heating at 1500 °C; here, we significantly lowered the annealing temperature to 1130 °C under H2/Ar dynamic flow and obtained a partially ordered (ca. 74 %) double perovskite, as determined by Rietveld refinement of the powder X-ray diffraction data. As a wide-band-gap semiconductor, Ba2InTaO6 possesses photocatalytic activity for overall water splitting under UV irradiation, though the gas evolution rates of 12.9 and 6.6 μmol/h/g for H2 and O2 generation, respectively, are low. With the assistance of methanol as a sacrificial reagent, the H2 evolution rate increases to 50.5 μmol/h/g, which indicates that the surficial charge recombination rate is really high. We applied the typical cocatalyst-loading method to this material, and with 1 wt.-% PtO x and NiO x, the H2 production rates in pure water were further improved to 16.0 and 18.4 μmol/h/g, respectively. Attempts to dope Ba2InTaO6 with first-row transition metals (Ti, V, Cr, Mn, Fe, Co, and Ni) led to a general enhancement of the light-harvesting ability; however, the experimental water-splitting activity did not improve. We believe that the doped cations most likely behaved as recombination centers for photogenerated charges. Considering its structural similarity to the well-known catalyst InTaO4:Ni, Ba2InTaO6 possesses the potential to extend its photocatalytic activity to the visible-light region but needs further enhancement. [ABSTRACT FROM AUTHOR]

Metal borates are well-known optical materials while their semiconducting behavior, i.e. photocatalytic property, was less studied. Inspired by the recent publications on gallium borates with good photocatalytic performances, we investigated photocatalytic water reduction activity of another gallium borate, PbGaBO 4 , comprising edge-sharing GaO 6 -chains. Both conventional and solution assisted solid state reaction methods were employed for the preparation. Phase purity and the crystallinity of both samples were identified by powder X-ray diffraction and scanning electron microscopy. The UV–Vis reflectance spectra suggested the wide bandgap characteristic (4.10 eV) and theoretical calculations pointed out that the 6s and 5p orbitals of Pb 2+ contribute to both the bottom of CB and the top of VB. However the ionic bonding of Pb O in PbGaBO 4 led to a slight hydrolysis during the photocatalysis process, which can be suppressed by loading cocatalysts of Pt and RuO x . In addition, such a surficial modification significantly improved the photocatalytic water reduction ability, with an optimal H 2 evolution rate of 41.9(9) μmol/h/g under UV-light irradiation. [ABSTRACT FROM AUTHOR]

Tb 3+ -substituted SrWO 4 Scheelite compounds are well-known green phosphors. Herein this work, we prepared three partial solid state solutions of Sr 1−1.5 x Tb x □ 0.5 x WO 4 (□ = vacancy, 0.01 ⩽ x ⩽ 0.24) and Sr 0.64− y Tb 0.24 Li 2 y □ 0.12− y WO 4 (0 ⩽ y ⩽ 0.12) and Sr 0.70−2 z Tb 0.20+ z Li z □ 0.10 WO 4 (0 ⩽ z ⩽ 0.10). Rietveld refinements on selected samples were performed to confirm the existence of A -site vacancies. In addition, the continuous variation of either Tb 3+ or vacancy concentrations offers an opportunity to study the structure–property correlation. A decrease of Sr–O average distance and an elongation of W–O bond length were detected in Sr 1-1.5 x Tb x □ 0.5 x WO 4 , which result in a slight red-shifting of WO 4 2− CT absorption band. The optimal concentration for green emission of Sr 1−1.5 x Tb x □ 0.5 x WO 4 (0.01 ⩽ x ⩽ 0.24) was found to be 0.12. The occurrence of concentration quenching effect is not only due to the increase of the Tb 3+ concentration, vacancies in the structure also play an important role. With Li + -co-doping, the emission shows a great enhancement not only due to the modification of the A -site coordination but also the diminishing of the A -site vacancy. [ABSTRACT FROM AUTHOR]

Abstract: Three new borates MB12O14(OH)10 (M=Mn, Fe, Zn) have been synthesized by boric acid flux methods, which are isotypic to NiB12O14(OH)10. Single-crystal XRD was performed to determine the crystal structures in detail. They all crystallize in the monoclinic space group P21/c. The size of MO6 (M=Mg, Mn, Fe, Co, Ni, Zn) octahedron shows a good agreement with the Shannon effective ionic radii of M2+. Magnetic measurements indicate MnB12O14(OH)10 is antiferromagnetic without a long-range ordering down to 2K. The values of its magnetic superexchange constants were evaluated by DFT calculations, which explain the observed magnetic behavior. The UV–vis diffuse reflectance spectrum of ZnB12O14(OH)10 suggests a band gap ∼4.6eV. DFT calculations indicate it has a direct band gap 4.9eV. The optical band gap is contributed by charge transfers from the occupied O 2p to the unoccupied Zn 4s states. [Copyright &y& Elsevier]

BiMn x Fe 3- x O 6 ( x = 1) represents a new type of oxide structure containing Bi 3+ and competing magnetic super-exchanges. In literature, multiple magnetic states were realized at low temperatures in BiMnFe 2 O 6 , and the hypothetical parent compounds (BiMn 3 O 6 , BiFe 3 O 6 ) were predicted to be different in magnetism. Herein, we performed a careful study on the syntheses of BiMn x Fe 3- x O 6 at ambient pressure, and the solid solution range was determined to be 0.9 ≤ x ≤ 1.3 by Rietveld refinements on high-quality powder X-ray diffraction data. Due to the very similar cationic size of Mn 3+ and Fe 3+ , and possibly the structural rigidity, there was no significant structure change in the whole range of solid solution. The magnetic behavior of BiMn x Fe 3- x O 6 ( x = 1.2, 1.22, 1.26, 1.28 and 1.3) was generally similar to BiMnFe 2 O 6 , while the relative higher concentration of Mn 3+ led to the decreasing of the antiferromagnetic ordering temperature. [ABSTRACT FROM AUTHOR]

PKU-5 (Al 4 B 6 O 15 ) is potentially a solid acid catalyst, and it possesses an interesting open-framework composed of [AlO 6 ] and [B 2 O 5 ] groups. PKU-5 shows a high thermal stability, while no physical and chemical properties were investigated thus far, because of the difficulty in its synthesis. Cr-stabilized PKU-5 with the formula (Al 1− x Cr x ) 4 B 6 O 15 (0.08 ≤ x ≤ 0.14) can be easily prepared by annealing Cr-doped PKU-1 precursors. XRD and TEM experiments demonstrate Cr 3+ has been successively incorporated into the framework of PKU-5. NH 3 -TPD measurements indicate that the partial substitution of Al 3+ by Cr 3+ leads to a small change of acid sites in total amounts and distributions. Cr-PKU-5 shows a good catalytic activity for methanol dehydration from 300 to 450 °C. Other operation conditions, such as the Cr 3+ content, space velocity of methanol were also discussed in detail to evaluate its catalytic performance. [ABSTRACT FROM AUTHOR]

Abstract: New “114” oxides Ca1−x Eu x BaZn2+x Ga2−x O7 (x≤0.24) were synthesized by solid state reaction. Rietveld refinements were performed on high quality powder XRD data in the space group P63 mc. Zn2+ and Ga3+ co-occupy T1 and T2 positions, which are both in tetrahedral coordinated environment. Comparing the host compound, O3 moves towards T2 cation as much as 0.08Å when x=0.24. It is the most observable structural change during the substitution. By comparing the structures of CaBaZn2Ga2O7 (P63 mc) and CaBaCo4O7 (Pbn21), we find that smaller cations in tetrahedral sites would lead to a lower symmetry in “114” oxides. Luminescent spectra show the noncentrosymmetric coordination of Eu3+, and the f–f excitations are comparable to CT-excitation. No concentration quenching was observed up to x=0.24. The optical band gaps were estimated to be 3.8eV for Ca1−x Eu x BaZn2+x Ga2−x O7 (x=0, 0.16). [Copyright &y& Elsevier]

Abstract: CdB10O14(OH)4·H2O has been synthesized under boric acid flux condition and characterized by single-crystal X-ray diffraction, infrared spectra, and UV–vis reflectance spectroscopy. It crystallizes in the monoclinic space group P21/n with a =7.7277(8), b =18.95(2), c =9.8616(10)Å, β=91.454(1)°, V =1443.7(3)Å. The structure consists of [B10O16(OH)4] layers of 9-membered borate rings enclosing Cd2+ cations. Adjacent borate layers are interconnected via hydrogen bonding to form a 3D network. It possesses an unprecedented decaborate fundamental building block B10O20. The structure details are discussed together with Sr[B6O9(OH)2]·3H2O, Pb[B8O11(OH)4], Pr[B8O11(OH)5], and Nd[B9O13(OH)4]·H2O, which have correlated FBBs. The band structure calculations show its direct energy band gap of ∼4.68eV, in consistent with the estimated value (4.77eV) from UV–vis. In addition, dielectric constants and refractive indexes are also calculated. [Copyright &y& Elsevier]

Supported metal catalysts have been applied in many current industrial processes. The morphology of metal particles coated on support has been proven to affect the performance of catalysts greatly. In this study, a simple photodeposition process will be introduced to coat palladium onto titanium dioxide with an emphasis on the morphology control and size distribution of palladium particles. The effect of pH on the morphology of palladium particles was systemically investigated. It is found that the deposited palladium particles can be controlled to have narrow particle size distribution and homogeneous dispersion by a simple pH-controlled process during photodeposition. Experimental results demonstrate that the adsorption competition between OH- and PdCl42- or it’s hydrolytic anions can efficiently keep local concentration of palladium ions on titanium dioxide extremely low to control the morphology of deposited palladium particles on titania. The as-prepared Pd/TiO2 particles are found to be crystallitic stable indicated by TEM, XRD and XPS measurements. [Copyright &y& Elsevier]