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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]

Extensive studies on photoluminescence (PL) were devoted to the well-known “ RE BaB 9 O 16 ” family, while the structure remained unsolved until the recent work on the structure determination of its new analogue Ba 6 Bi 9 B 79 O 138 . Accordingly, a re-visit to “ RE BaB 9 O 16 ” with the new formula was rationally performed by the syntheses and Tb 3+ -PL study on Ba 6 La 9 B 79 O 138 ( BLBO ) and Ba 6 Y 9 B 79 O 138 ( BYBO ). Powder XRD patterns of Ba 6 ( RE 1− x Tb x ) 9 B 79 O 138 ( RE = La and Y, 0 ≤ x ≤ 1) show a linear shrinkage or expansion of the unit cell in BLBO : x Tb 3+ and BYBO : x Tb 3+ , respectively. The ratio of Tb 3+ cyan/green (C/G) emission was proposed to evaluate the evolution principle of the RE -site symmetry in both series of phosphors. The C/G value remains unchanged in BLBO : x Tb 3+ , while it is sensitive to the Tb 3+ -to-Y 3+ substitution in BYBO : x Tb 3+ . For example, C/G keeps almost constant (∼0.30) when 0.10 ≤ x ≤ 0.5; a dramatic increase of C/G (from 0.33 to 0.67) occurs in the range of 0.50 ≤ x ≤ 0.90, accompanied with a RE -site symmetry transition from centrosymmetric to noncentrosymmetric; the value of C/G remains unchanged thereafter. The Ce 3+ -to-Tb 3+ sensitization effect is applied in Ba 6 ( RE 0.3− y Ce y Tb 0.7 ) 9 B 79 O 138 ( RE = La or Y, 0 ≤ y ≤ 0.3), and the samples with y = 0.2 possess the strongest green emission. [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]

Photocatalytic reduction of nitrate ( NO 3 − ) is a green and potentially inexpensive technique for reducing NO 3 − pollution in ground water. TiO 2 -based photocatalysts have been studied extensively for this purpose. In the present study, the semiconducting catalyst CuFe 0.7 Cr 0.3 S 2 was applied to NO 3 − reduction. Loading this catalyst with metal co-catalysts (Ru, Au, Cu, Ag, Pt, and Pd) greatly increased the rate of NO 3 − reduction and the N 2 selectivity. In addition, there was a synergistic enhancement of the photocatalytic performance when the catalyst was loaded two co-catalysts. For example, the catalyst loaded with Pd and Au at mass fractions of 0.75% and 3%, respectively, could photocatalyze the complete reduction of NO 3 − in a 100 ppm N aqueous solution with 100% N 2 selectivity in less than 5 h with UV irradiation. However, with an inner irradiation from a full-arc Xe lamp, the NO 3 − conversion rate reduced to 0.065 mg N/h, probably because of the low density of the photoexcited electrons. The results show the potential of metal sulfides for photocatalytic reduction of NO 3 − , and the possibility of use of visible light. [ABSTRACT FROM AUTHOR]