Enhancing the Photocatalytic Activity of Sr4Al14O25: Eu2+, Dy3+ Persistent Phosphors by Codoping with Bi3+ Ions

The photocatalytic activity of Bismuth‐codoped Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺ persistent phosphors is studied by monitoring the degradation of the blue methylene dye UV light irradiation. Powder phosphors are obtained by a combustion synthesis method and a postannealing process in reductive atmosphere. The XRD patterns show a single orthorhombic phase Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺, Bi³⁺ phosphors even at high Bismuth dopant concentrations of 12 mol%, suggesting that Bi ions are well incorporated into the host lattice. SEM micrographs show irregular micrograins with sizes in the range of 0.5–20 μm. The samples present an intense greenish‐blue fluorescence and persistent emissions at 495 nm, attributed to the 5d–4f allowed transitions of Eu²⁺. The fluorescence decreases as Bi concentration increases; that suggest bismuth‐induced traps formation that in turn quench the luminescence. The photocatalytic evaluation of the powders was studied under both 365 nm UV and solar irradiations. Sample with 12 mol% of Bi presented the best MB degradation activity; 310 min of solar irradiation allow 100% MB degradation, whereas only 62.49% MB degradation is achieved under UV irradiation. Our results suggest that codoping the persistent phosphors with Bi³⁺ can be an alternative to enhance their photocatalytic activity.     

Vanadium(V) environments in bismuth vanadates: A structural investigation using Raman spectroscopy and solid state V NMR

The Bi₂O₃---V₂O₅ system was examined using Raman spectroscopy and solid state ⁵¹V wideline, magic-angle spinning (MAS), and nutation NMR spectroscopy. The methods are shown to be complementary in the identification of the various phases and in the characterization of their vanadium site symmetries. Most of the compositions examined (1:1 ≤ Bi:V ≤ 60:1) are multiphasic. Depending on the Bi:V ratio, the following phases have been identified: BiVO₄, Bi₄V₂O₁₁, a triclinic type-II phase, a cubic type-I phase, γ-Bi₂O₃ doped with V(V) (sillenite), and β-Bi₂O₃. Detailed spectroscopic characterization reveals that vanadium is tetrahedrally coordinated in all these compounds, and that the degree of symmetry increases with increasing Bi:V ratio. At the highest Bi:V ratios, the combined interpretation of the Raman and NMR data provides strong evidence for the presence of Bi⁵⁺O₄ tetrahedra.     

Phase relations in the system K2MoO4–KPO3–MoO3–Bi2O3: A new phosphate K3Bi5(PO4)6

Phase equilibrium in the pseudo-quaternary system K₂O–MoO₃–P₂O₅–Bi₂O₃ was studied as three-component solvent K₂MoO₄–KPO₃–MoO₃ containing 15 mol% Bi₂O₃ during slow cooling and spontaneous crystallization. The results of the investigation were shown on a composition diagram, which indicates the crystallization fields of K₂Bi(PO₄)(MoO₄), K₅Bi(MoO₄)₄, BiPO₄ and K₃Bi₅(PO₄)₆. New phosphate K₃Bi₅(PO₄)₆ was characterized by single-crystal X-ray diffraction (space group C2/c, a=17.680(4), b=6.9370(14), c=18.700(4) Å, β=113.79(3)°) and FTIR spectroscopy. The possibility of lone electron pair stereoactivity of bismuth was suggested using the calculations of characteristics of the Voronoi–Dirichlet polyhedra for K₃Bi₅(PO₄)₆ and K₂Bi(PO₄)(MoO₄).     

Thermal synthesis of the (Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>1–x</Subscript>(Er<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>x</Subscript> pigments

The synthesis of new compounds based on Bi₂O₃ is investigated because they can be used as new environmentally friendly inorganic pigments. Chemical compounds of the (Bi₂O₃)_1–x(Er₂O₃)_x type were synthetized. The host lattice of these pigments is Bi2O3 that is doped by Er³⁺ ions. The incorporation of doped ions provides interesting colours and contributes to an increase in the thermal stability of these compounds. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments.     

Microemulsion synthesis, characterization of highly visible light responsive rare Earth-doped bi(2) o(3)

In this paper, Bi₂O₃ and rare earth (La, Ce)‐doped Bi₂O₃ visible‐light‐driven photocatalysts were prepared in a Triton X‐100/n‐hexanol/cyclohexane/water reverse microemulsion. The resulting materials were characterized by X‐ray powder diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) surface area, photoluminescence spectra (PLS) and UV–Vis diffuse reflectance spectroscopy. The XRD patterns of the as‐prepared catalysts calcined at 500°C exhibited only the characteristic peaks of monoclinic α‐Bi₂O₃. PLS analysis implied that the separation efficiency for electron‐hole has been enhanced when Bi₂O₃ was doped with rare earth. UV–Vis diffuse reflectance spectroscopy measurements presented an extension of light absorption into the visible region. The photocatalytic activity of the samples was evaluated by degradation of methyl orange (MO) and 2,4‐dichlorophenol (2,4‐DCP). The results displayed that the photocatalytic activity of rare earth‐doped Bi₂O₃ was higher than that of dopant‐free Bi₂O₃. The optimal dopant amount of La or Ce was 1.0 mol%. And the mechanisms of influence on the photocatalytic activity of the catalysts were discussed.     

Bi2O3 deposited on highly ordered mesoporous carbon for supercapacitors

A simple route has been employed to prepare nanosized Bi₂O₃ deposited on highly ordered mesoporous carbon. The electrochemical measurements reveal that, by loading only 10% Bi₂O₃ on the mesoporous carbon, the specific capacitance of the composite is improved by 62%, with the maximum value reaching 232 F g^?1 at a sweep rate of 5 mV s^?1. The specific capacitance of Bi₂O₃ is calculated and reaches 1305 F g^?1 at 1 mV s^?1. It is found that the mass transfer in the framework of the crystalline oxide is still difficult in spite of its nanosize, as evidenced by the decline of the specific capacitance of the Bi₂O₃ with the increase of the sweep rate. The cyclic life of composite materials is also measured and the capacitance only declines 21% after 1000 cycles.     

Superconductivity Induced by Oxygen Doping in Y2O2Bi

When doped with oxygen, the layered Y₂O₂Bi phase becomes a superconductor. This finding raises questions about the sites for doped oxygen, the mechanism of superconductivity, and practical guidelines for discovering new superconductors. We probed these questions in terms of first‐principles calculations for undoped and O‐doped Y₂O₂Bi. The preferred sites for doped O atoms are the centers of Bi₄ squares in the Bi square net. Several Bi 6p x /y bands of Y₂O₂Bi are raised in energy by oxygen doping because the 2p x /y orbitals of the doped oxygen make antibonding possible with the 6p x /y orbitals of surrounding Bi atoms. Consequently, the condition necessary for the “flat/steep” band model for superconductivity is satisfied in O‐doped Y₂O₂Bi.     

Unconventional Luminescent Centers in Metastable Phases Created by Topochemical Reduction Reactions

A low‐temperature topochemical reduction strategy is used herein to prepare unconventional phosphors with luminescence covering the biological and/or telecommunications optical windows. This approach is demonstrated by using Bi^III‐doped Y₂O₃ (Y_2?xBi_xO₃) as a model system. Experimental results suggest that topochemical treatment of Y_2?xBi_xO₃ using CaH₂ creates randomly distributed oxygen vacancies in the matrix, resulting in the change of the oxidation states of Bi to lower oxidation states. The change of the Bi coordination environments from the [BiO₆] octahedra in Y_2?xBi_xO₃ to the oxygen‐deficient [BiO_6?z] polyhedra in reduced phases leads to a shift of the emission maximum from the visible to the near‐infrared region. The generality of this approach was further demonstrated with other phosphors. Our findings suggest that this strategy can be used to explore Bi‐doped or other classes of luminescent systems, thus opening up new avenues to develop novel optical materials.     

209Bi NQR in Mixed Oxides 2Bi2O3· B2O3, 3Bi2O3· 5B2O3, and Bi2O3· 3B2O3

It was earlier found from nuclear quadrupole resonance (NQR) measurements and computer modeling that -Bi₂O₃, Bi₃O₄Br and mixed oxides Bi₂O₃· 2Al₂O₃, Bi₂O₃· 2Ga₂O₃, Bi₂O₃· 3GeO₂, and 2Bi₂O₃· 3GeO₂exhibit local ordered magnetic fields from 30 to 200 G. It thus follows that these compounds are not diamagnets in a conventional sence of the word. With the aim of revealing previously unknown magnetic properties in bismuth(III) oxide-based Main Group element compounds, the mixed bismuth–boron oxides 2Bi₂O₃· B₂O₃, 3Bi₂O₃· 5B₂O₃, and Bi₂O₃· 3B₂O₃were prepared and studied using ²⁰⁹Bi NQR. The quadrupole interactions of the ²⁰⁹Bi nuclei and their electronic environment were studied, the crystallochemical features of the compounds were discussed, and the conformity of the ²⁰⁹Bi results to the X-ray structure data was verified. The preliminary tests in the field of a permanent magnet showed that the resonance intensities increase in external magnetic fields, indicating that a magnetism of unknown nature develops in the titled compounds. It was found reasonable to continue studies of the magnetic properties of these compounds using single-crystal ²⁰⁹Bi NQR in external magnetic fields.     

Brown pigments based on perovskite structure of BiFeO3−δ

Light brown inorganic pigments based on BiFeO₃ doped by Sr²⁺ cations were prepared by a conventional solid-state reaction at high temperature. This study is focused on the synthesis of Bi_1?x Sr _x FeO_3?δ powders in a range of substitution (x = 0–0.35; with step size 0.05). The main role of strontium is to overcome the defects that come to exist during the evaporation of Bi over material preparation. The substitution of trivalent bismuth ions by divalent strontium ions results in oxygen deficiency in the lattice, which was proved by both thermogravimetric analysis and elemental analysis. The substitution has a positive effect on the thermal stability of samples. The thermal stability of BiFeO₃ is 1046 K, whereas the substitution of 20 mol% of Bi³⁺ by Sr²⁺ ions shifted it to 1403 K and powder with composition Bi_0.65Sr_0.35FeO_3?δ has a thermal stability that is higher than 1434 K. An increasing range of substitution is connected with the change in the pigment color from reddish-brown to orange-brown and back to reddish-brown. The Bi_0.85Sr_0.15FeO_3?δ pigment prepared by calcination at 1273 K offers the most interesting color properties (L* = 45.57; a* = 20.38; b* = 26.23).

     

Thermal analysis of doped Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>

New environmentally inorganic pigments based on Bi₂O₃ doped by metal ions, such as Zr⁴⁺ and Dy³⁺ have been developed and characterized using the methods thermal analysis, X-ray powder diffraction, and spectral reflectance data. The compounds having formula Bi_2−x Dy _x/2Zr_3x/8O₃ (x = 0.2, 0.6, 1.0, and 1.2) were prepared by the solid state reaction. Methods of thermal analysis were used for determination of the temperature region of the pigment formation and thermal stability of compounds. The incorporation of doped ions in Bi₂O₃ changes the color from yellow to orange and also contributes to a growth of their thermal stability. This property gives a direction for coloring ceramic glazes.     

Viscosity and thermal expansion of soda-lime-silica glass doped with Gd2O3 and Y2O3

In order to reveal the effects of rare earth elements on the rheological behavior of silicate melt, the properties of viscosity and thermal expansion of soda-lime-silica glass doped with Gd₂O₃ and Y₂O₃ were investigated by the rotating crucible viscometer and dilatometry. The results show that, introduction of Gd₂O₃ and Y₂O₃ increases the coefficient of thermal expansion and decreases viscosity of soda-lime-silica glass. When the amount of Gd₂O₃ and Y₂O₃ increases from 0 to 1.00 mol%, the coefficient of thermal expansion of soda-lime-silica glass increases firstly from 7.67 to 7.79 and 8.05, and then decreases to 7.78 and 7.66 ( × 10⁻⁶ °C⁻¹) respectively. In the case of melting temperature, its value decreases from 1830K to 1714 K, and then elevates to 1727 K as the content of Gd₂O₃ up to 1.00 mol%, however, as Y₂O₃ content increases from 0 to 1.00 mol% the melting temperature decreases monotonously from 1830K to 1737 K. The viscosity, melting temperature and coefficient of thermal expansion of soda-lime-silica glasses co-doped with Gd₂O₃ and Y₂O₃ are larger, comparing with glasses doped solely with Gd₂O₃ or Y₂O₃. The effect of co-doping with Gd₂O₃ and Y₂O₃ on thermal expansion and viscosity properties of soda-lime-silica glass, which is similar with the mixed-alkali effect in silicate glasses, is also observed.     

Infrared,Raman and XPS spectroscopic studies of Bi2O3–B2O3–Ga2O3 glasses

Glasses with compositions 60Bi₂O₃–(40?x)B₂O₃–xGa₂O₃ (x = 5, 10, 15, 20 mol%) are prepared by conventional melting method. The thermal properties are investigated by differential thermal analysis (DTA) and the structures of the glasses were probed by Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The results show that density, refractive index and optical basicity increase with the increase of Ga₂O₃. The glass transition temperature (T_g), the onset crystallization temperature (T_x), ΔT (T_x?T_g) decrease with the content of Ga₂O₃. The cut-off edges in ultraviolet and infrared shift to longer wavelength with the increase of Ga₂O₃. On the other hand, the addition of Ga₂O₃ causes a progressive coordination number change of the boron atom from 3 to 4. XPS result indicates both Bi⁵⁺ and Bi³⁺ exist in 5 mol% Ga₂O₃ content, while Bi⁵⁺ amounts decrease with the increase of Ga₂O₃ contents. The glass is mainly composed of [BiO₆], [BO₃], [BO₄] and [GaO₄] polyhedra. Glasses are supposed to have layer structure. [BO₃] triangle and [BO₄] tetrahedra may be located between the [GaO₄] tetrahedral and [BiO₆] octahedra to prevent crystallization and to compensate electric charge.     

Maximizing the synergistic effect on accelerated photoelectron transfer of TiO2 by double Z-scheme heterojunctions and specific oxygen vacancies

Photocatalysis is an ideal technology for environmental applications, but its efficiency is severely limited by slow kinetics and low efficiency of carrier separation. Herein, a photocatalyst (TiO₂–Bi₂Ti₂O₇-600 °C) with homotypic growth possessing double Z-scheme heterojunctions was successfully synthesized by the growth of mixed crystalline phase TiO₂ on the surface of Bi₂Ti₂O₇. The carrier separation efficiency of the heterojunctions was enhanced by the photo-ferroelectricity of Bi₂Ti₂O_7. Simultaneously, the interface-fused TiO₂/Bi₂Ti₂O₇ provided stability for carrier transport between heterojunctions. Modern instrumental characterization confirmed that oxygen vacancies mainly exist in Bi–O structural units provided by Bi₂Ti₂O₇ and that the carrier separation efficiency of the double Z-scheme heterojunctions was significantly higher than that of the single Z-scheme heterojunctions. Density-of-states calculations based on the first principle confirmed that the carrier separation efficiency was higher when the oxygen vacancies presented in the Bi–O structural units than they presented in the Ti–O structural units. TiO₂–Bi₂Ti₂O₇-600 °C could accomplish the complete degradation of Rh–B (10 mg/L) in aqueous environment within 80 min, instead of only contributing to the destruction of conjugated chromogenic groups in Rh–B. This photocatalyst with stable structure, multiple carrier transport channels, and sufficient oxygen vacancies enables the photoelectrons to concentrate on the confinement effect, opening a novel avenue for the design strategy of new-generation photocatalysts in environmental wastewater applications.     

The local structure of bismuth germanate glasses and glass ceramics doped with europium ions evidenced by FT-IR spectroscopy

Glasses of the xEu₂O₃·(100 − x)[4Bi₂O₃·GeO₂] system, with 0 ≤ x ≤ 30 mol%, have been characterized by FT-IR spectroscopy measurements in order to obtain information about the influence of Eu₂O₃ on the local structure of the 4Bi₂O₃·GeO₂ glass matrix. FT-IR spectroscopy data suggest that the europium ions play the network modifier role in the studied glasses and both Bi₂O₃ and GeO₂ play the role of network formers. Melting at 1100 °C and the rapid cooling at room temperature permitted to obtain glass samples. In order to improve the local order and to develop crystalline phases the glass samples were kept at 700 °C for 17 h. Both the influences of the europium ions as well as of the heat treatment on the local order of 4Bi₂O₃·GeO₂ glass matrix have been discussed.     

Synergy effects in mixed Bi2O3, MoO3 and V2O5 catalysts for selective oxidation of propylene

In this work, the possible synergy effects between Bi₂O₃, MoO₃ and V₂O₅, and between Bi₂Mo₃O₁₂ and BiVO₄, were investigated. The catalytic activity of the ??mechanical mixture?? of these compounds was measured. The mixture containing 36.96?mol% Bi₂O₃, 39.13?mol% MoO₃ and 23.91?mol% V₂O₅ (21.43?mol% Bi₂Mo₃O₁₂ and 78.57?mol% BiVO₄), corresponding to the compound Bi_1?x/3V_1?x Mo _x O₄ with x?=?0.45 (Bi_0.85V_0.55Mo_0.45O₄), exhibited the highest activity for the selective oxidation of propylene to acrolein. The mixed sample prepared chemically by a sol?Cgel method possessed higher activity than that of mechanical mixtures.     

Preparation and visible light photocatalytic activity of Bi2O3/Bi2WO6 heterojunction photocatalysts

The Bi₂O₃/Bi₂WO₆ heterojunction photocatalysts were prepared by a two-step solvothermal process using Bi(NO₃)₃-ethylene glycol solution as Bi source. The catalysts were characterized by X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-vis diffuse reflection spectroscopy. The heterostructure catalysts are composed of Bi₂O₃ nanoparticles as modifier and 3D Bi₂WO₆ microspheres as substrate. Bi₂O₃ nanoparticles with diameters of about 10-15 nm are tightly grown on the lateral surface of the Bi₂WO₆ microspheres. The hierarchical Bi₂O₃/Bi₂WO₆ microspheres exhibit higher photocatalytic activity than the single phase Bi₂WO₆ or Bi₂O₃ for the degradation of rhodamine B under visible light illumination (λ>420 nm). The enhancement of the photocatalytic activity of the Bi₂O₃/Bi₂WO₆ heterojunction catalysts can be ascribed to their improved light absorption property and the reduced recombination of the photoexcited electrons and holes during the photocatalytic reaction. The effect of loading amount of Bi₂O₃ on the catalytic performance of the heterojunction catalysts was also investigated and the optimal content of Bi₂O₃ is 3 wt%. The Bi₂O₃/Bi₂WO₆ heterojunction photocatalysts are essentially stable during the photocatalytic process.     

Phase relations in the K2W2O7-K2WO4-KPO3-Bi2O3 system and structure of K6.5Bi2.5W4P6O34

The phase relations in the cross-section of the K₂W₂O₇-K₂WO₄-KPO₃ containing 15 mol% Bi₂O₃ were undertaken using flux method. Crystallization fields of K_6.5Bi_2.5W₄P₆O₃₄, K₂Bi(PO₄)(WO₄), Bi₂WO₆, KBi(WO₄)₂ and their cocrystallization areas were identified. Novel phase K_6.5Bi_2.5W₄P₆O₃₄ was characterized by single-crystal X-ray diffraction: sp. gr. P−1, a=9.4170(5), b=9.7166(4), c=17.6050(7) Å, α=90.052(5)°, β=103.880(5)° and γ=90.125(5)°. It has a layered structure, which contains {K₇Bi₅W₈P₁₂O₆₈}_∞ layers stacked parallel to ab plane and sheets composed by potassium atoms separating these layers. Sandwich-like {K₇Bi₅W₈P₁₂O₆₈}_∞ layers are assembled from [W₂P₂O₁₃]_∞ and [BiPO₄]_∞ building units, and are penetrated by tunnels with K/Bi atoms inside. FTIR-spectra of K₂Bi(PO₄)(WO₄) and K_6.5Bi_2.5W₄P₆O₃₄ were discussed on the basis of factor group theory.     

Visible-light photocatalytic activity of the metastable Bi20TiO32 synthesized by a high-temperature quenching method

Metastable Bi₂₀TiO₃₂ samples were synthesized by a high-temperature quenching method using α-Bi₂O₃ and anatase TiO₂ as raw materials. The photocatalytic activity of the as-prepared samples was measured with the photodegradation of methyl orange at room temperature under visible light irradiation. The Bi₂₀TiO₃₂ samples exhibited good absorption in the visible light region with a band gap of about 2.38 eV and the band structure of Bi₂₀TiO₃₂ was studied. Photodegradation against methyl orange was much better than α-Bi₂O₃ prepared by the same way. The photocatalytic activity of Bi₂₀TiO₃₂ samples is supposed to be associated with the hybridized Bi 6s and O 2p orbitals. In addition, the dispersive characteristic of Bi 6s orbital in the hybridized valence band facilitates the mobility of the photogenerated carriers and hampers their recombination.     

Bi/BiVO4&Bi4V2O11复合催化剂的制备及其光催化性能

经由溶剂热反应、光辅助还原过程制备Bi/Bi VO_4Bi_4V_2O_(11)纳米复合光催化材料。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、高分辨率透射电子显微镜(HRTEM)、X射线光电子能谱(XPS)、紫外-可见漫反射光谱(UV-Vis DRS)、N_2吸附-脱附等温线和光致发光(PL)等手段对该复合物进行表征。实验结果表明当金属Bi与BiVO_4Bi_4V_2O_(11)的质量比值为0.8,可见光照射30 min时,Bi/BiVO_4Bi_4V_2O_(11)复合催化剂对罗丹明B(RhB)的降解率可达95.6%。此外,Bi/BiVO_4Bi_4V_2O_(11)对四环素(TC)的降解也表现出增强的光催化性能。Bi/BiVO_4Bi_4V_2O_(11)复合材料提升的光催化性能可能归因于金属Bi的表面等离子体共振(SPR)效应、拓宽的可见光吸收范围和增大的比表面积。此外,提出了复合光催化剂可能的光催化机理。