Advanced Bi<Subscript>2</Subscript>O<Subscript>2.7</Subscript>/Bi<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> composite film with enhanced visible-light-driven activity for the degradation of organic dyes

Bi₂O_2.7/Bi₂Ti₂O₇ composite photocatalyst films are synthesized by sol–gel dip-coating. The ratio of adding Bi and Ti precursors can be controlled during the preparation process. The phase structure is confirmed by X-ray diffraction. The UV–visible diffuse reflectance spectrum shows that the composite catalysts present light absorption in the visible region. The obtained Bi₂O_2.7/Bi₂Ti₂O₇ composite films possess superior photocatalytic degradation of rhodamine B, owing to the visible light response of Bi₂O_2.7 and the separation of photogenerated electrons and holes between the two components. As a result, the Bi₂O_2.7/Bi₂Ti₂O₇ (Bi/Ti = 1:1) displays the highest photocatalytic activity under visible light or UV light irradiation for the degradation of different organic dyes, including methyl blue, methyl orange and acid orange 7.     

Synergistic effect of additives on electrochemical properties of MnO<Subscript>2</Subscript> cathode in aqueous rechargeable batteries

The synergistic effect of bismuth oxide (Bi₂O₃) + titanium disulphide (TiS₂) additives in different proportions into the MnO₂ cathode material is physically modified and tested in a Zn-MnO₂ battery with aqueous LiOH electrolyte. It is found that these foreign cations stabilized the MnO₂ structure upon multiple cycling and the synergistic effect between two additives enhanced the rechargeability. This class of additive modified MnO₂ may be of interest for high-energy density and safer batteries for applications such as electric vehicles. The cyclability of the material suitable for electric vehicle (EV) applications is established in this report. The incorporation of Bi₂O₃ (3 wt.%) and TiS₂ (2 wt.%) additives into the MnO₂ cathode was found to improve the cell performance, this is partly due to the suppression of proton insertion. The results on cyclic voltammetric and charge–discharge studies describing the redox mechanisms in LiOH electrolyte and the role of additives on those redox reactions are discussed and compared with that of traditional KOH electrolyte.     

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.     

Formation and thermal properties of nanocrystalline Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript>

Mechanism by which nanocrystalline Bi₄Ti₃O₁₂ is formed in thermal treatment of coprecipitated hydroxides was studied. It was shown that the onset of the active formation is correlated with the melting point of the surface phase based on bismuth oxide. The technological synthesis parameters of Bi₄Ti₃O₁₂, at which crystallite sizes in the range 35–60 nm are provided, were determined.     

Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/BiFeO<Subscript>3</Subscript> heterostructure: preparation,characterization, and photocatalytic activity

Bi₂O₃/BiFeO₃ composite was successfully fabricated by a conventional sol–gel method and structural properties were characterized based on X-ray diffractometer, scanning electron microscope, transmission electron microscope, energy-dispersive X-ray analyzer, nitrogen adsorption–desorption measurement, and UV–visible diffuse reflectance spectroscopy. Bi₂O₃/BiFeO₃ had a good absorption for visible light, which was benefit to photocatalytic activity. The highest degradation efficiency was obtained when the content of Bi₂O₃ in Bi₂O₃/BiFeO₃ was 63.9%. Effect of experimental conditions was investigated, and the highest photocatalytic activity of Bi₂O₃/BiFeO₃ was observed at photocatalyst dosage of 0.5 g/L, initial BPA concentration of 10 mg/L, and solution pH of 6.3. Bi₂O₃/BiFeO₃ photocatalyst exhibited enhanced photocatalytic activity for BPA, and the reaction rate constant over Bi₂O₃/BiFeO₃ composite was 2.23, 3.65, and 8.71 times higher than that of BiFeO₃, Bi₂O₃ and commercial TiO₂ (P25), respectively. Bi₂O₃/BiFeO₃ showed high photocatalytic activity after three cycles, suggesting that it was a stable photocatalyst. The possible photocatalytic mechanism has been discussed on the basis of the theoretical calculation and the experimental results. The hydroxyl and superoxide radicals together with photogenerated holes played significant roles in the photocatalytic reaction.     

Effect of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> addition on structure and magnetic properties of Ni<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanofibers

Ni_0.5Zn_0.5Fe₂O₄ nanofibers with addition of 0–5 wt% Bi₂O₃ were synthesized by calcination of the electrospun polyvinylpyrrolidone/inorganic composite nanofibers at the temperature below the melting point of Bi₂O₃. The effects of Bi₂O₃ addition on the phase structure, morphology and magnetic properties of the nanofibers were investigated by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, selected area electron diffraction and vibrating sample magnetometer. It is found that the nanofiber diameter, crystallite size and magnetic parameters can be effectively tuned by simply adjusting the amount of Bi₂O₃ addition. The average diameter of Ni_0.5Zn_0.5Fe₂O₄ nanofibers doped with different contents of Bi₂O₃ ranges from 40 to 63 nm and gradually decreases with increasing Bi₂O₃ content. The addition of Bi₂O₃ does not induce the phase change and all the samples are a single-phase spinel structure. The amorphous Bi₂O₃ tends to concentrate on the nanoparticle surface and/or grain boundary and can retard the particles motion as well as the grain growth, resulting in a considerable reduction in grain size compared to the pristine sample. The specific saturation magnetization and coercivity of the nanofibers gradually decrease with the increase of Bi₂O₃ amount. Such behaviors are explained on the basis of chemical composition, surface effect, domain structure and crystal anisotropy.     

Synthesis of Bi<Subscript>2</Subscript>O<Subscript>4</Subscript>@TiO<Subscript>2</Subscript> Heterojunction with Enhanced Visible Light Photocatalytic Activity

A novel Bi₂O₄@TiO₂ heterojunction was constructed by a simple two-step method. The charges migration between Bi₂O₄ and TiO₂ via the heterojunction improves the electron/hole separation efficiency. Furthermore, Bi₂O₄@TiO₂ heterostructures exhibit better adsorption capability for methyl orange molecular due to their higher specific surface area than pure Bi₂O₄. As a result, Bi₂O₄@TiO₂ hybrids show an improved visible light photocatalytic activity and photostability for the degradation of methyl orange.     

The Effect of Chromium Oxide on the Conductivity of Ce<Subscript>0.9</Subscript>Gd<Subscript>0.1</Subscript>O<Subscript>2</Subscript>, a Solid-Oxide Fuel Cell Electrolyte

To study the effect of chromium oxide on the electric properties of Ce_0.9Gd_0.1O₂, a solid-oxide fuel cell electrolyte, two approaches were used: (a) the studying of electrochemical properties of the Ce_0.9Gd_0.1O₂- electrolyte after the spontaneous adsorption of chromium-containing molecules from a gas phase and (b) the analyzing of transport properties of the Ce_0.9Gd_0.1O₂-based chromium-containing compositions obtained by the mixing of solid-oxide electrolyte with chromium(III) oxide. It was found that the chromium reduction at the electrolyte surface dominates when chromium is adsorbed from gas phase. Both approaches allow concluding that the chromium presence in Ce_0.9Gd_0.1O₂ deteriorates the electrolyte transport properties at temperatures above 735°С. This is caused by the chromium incorporation into the electrolyte’s fluorite structure, as well as surface microheterogeneity induced by the chromium presence at the Ce_0.9Gd_0.1O₂ surface and the cerium and gadolinium cation redistribution between the grains’ bulk and surface. At intermediate temperatures (below 735°С) the electric conductivity of the Ce_0.9Gd_0.1O₂-based chromium-containing composition exceeds that of the initial solid-oxide electrolyte, which can be due to changes in transport properties of the chromium-containing phases formed at the Ce_0.9Gd_0.1O₂ surface and grain boundaries.     

Electrochemical deposition of Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> for thermoelectric microdevices

The electrolyses of solutions of bismuth oxide and tellurium oxide in nitric acid with molar ratios of Bi:Te=3:3–4:3 lead to cathodic deposits of films of bismuth telluride (Bi₂Te₃), an n-type semiconductor. Current densities of 2–5 mA/cm² were applied. Voltammetric investigations showed that Bi₂Te₃ deposition occurred at potentials more negative than −0.125 V (Ag/AgCl, 3 M KCl). The deposit was identified as bismuth telluride (γ-phase) by X-ray analysis. Hall-effect measurements verified the n-type semiconducting behaviour. The films can be deposited in microstructures for thermoelectric microdevices like thermoelectric batteries or thermoelectric sensors.     

Thermoanalytical study of the synthesis of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> ferroelectric

The study presents results of examination on Na_0.5Bi_0.5TiO₃ (NBT) ferroelectric synthesis through intermediate binary compound Bi₄Ti₃O₁₂ (BIT). The first stage of the study related to obtaining BIT from oxide precursors, i.e. Bi₂O₃ and TiO₂. The second stage included obtaining NBT from Bi₄Ti₃O₁₂, Na₂CO₃ and TiO₂. Two polymorphic modifications of TiO₂ (anatase, rutile) and diversified initial homogenization of raw material batches were applied during examination.     

Composition and structure of solid solutions in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>-V<Stack><Subscript>2</Subscript><Superscript>5+</Superscript></Stack>O<Subscript>5</Subscript> system with the structure sillenite

In the Bi₂O₃-SiO₂-V₂⁵⁺+O₅ system, single crystal solid solutions of the sillenite family of the general composition Bi₂₄(Bi,Si,V)₂O₄₀ are obtained by a hydrothermal method and for the first time characterized by neutron and X-ray diffraction analysis. The tetrahedral position is found to contain vanadium ions with different formal charges (V⁴⁺ and V⁵⁺) responsible for green and orange colors, respectively, of the samples. For the first time, for some sillenites of this system dissymmetrization of the structure (a transition from the I23 space group into P23) is revealed, which is caused by the presence of several atoms in one crystallographic position and also by crystal growth conditions.     

Structure and electrical conductivity of cobalt-doped Bi<Subscript>26</Subscript>Mo<Subscript>10</Subscript>O<Subscript>69</Subscript>

The existence boundaries, structures, and transport parameters of Bi_{1 ? x} Co _x [Bi₁₂O₁₄]Mo₅O_{20 ± δ} and Bi[Bi₁₂O₁₄]Mo_{5 ? y} Co _y O_{20 ± δ} solid solutions, which have a unique columnar structure, were studied. Electrical conductivity in these solid solutions was studied by impedance spectroscopy.     

Entrapment of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in TiO<Subscript>2</Subscript> nanotubes for visible light-driven photocatalysis

In this study, we prepared nanoparticles of the visible light-responsive photocatalyst, Bi₂O₃ entrapped in anatase TiO₂ nanotubes (Bi₂O₃-in-TNTs) via a vacuum-assisted precursor-filling process followed by annealing. Owing to the unique tubular electronic structure of TiO₂ nanotubes, the interior of the nanotube is in an electron-deficient state, which was confirmed by XPS spectra and H₂-TPR. Electrochemical impedance studies showed that the Bi₂O₃-in-TNTs demonstrated a more efficient separation of photogenerated carriers than when Bi₂O₃ nanoparticles were deposited on the outer wall of TiO₂ nanotubes (Bi₂O₃-out-TNTs). Due to the confinement effect of TiO₂ nanotubes, which inhibits photogenerated carriers’ recombination, the Bi₂O₃-in-TNTs exhibited a better photocatalytic performance for the photo-degradation of methyl orange under visible light compared to Bi₂O₃-out-TNTs.     

Structural features of bismuth borates in the system <Emphasis Type="Italic">n</Emphasis>Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-<Emphasis Type="Italic">m</Emphasis>B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The crystal structures of general composition nBi₂O₃-mB₂O₃ were analyzed and systematized with the use of the structures of borate groups. Based on the CNs calculated by the bond valence method, the shapes of bismuth coordination polyhedra derived from an octahedron were suggested. A correlation was found between the number of BO₃ triangles and BO₄ tetrahedra in borate groups, the average CN of Bi atoms, and the degree of distortion of Bi polyhedra as a function of the m: n ratio, as well as between the polarity of BO₄ tetrahedra and noncentrosymmetry of the structures. The role of Bi³⁺ with the active E pair in the manifestation of specific features of the forms of bismuth polyhedra and the types of connection of boron polyhedra was elucidated.     

Effect of SO<Subscript>2</Subscript> on chlorination of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> + Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> mixtures

The reaction of Bi₂O₃ + Fe₂O₃ mixtures with chlorine and SO₂ at 250–700°C is studied. At 300–500°C, the degree of bismuth chloride sublimation from the oxide mixture increases in the presence of SO₂. Chemical sublimation of FeCl₃ occurs after BiCl₃ is virtually completely recovered from the solid phase.     

Microstructure and Conduction of Composites Bi<Subscript>2</Subscript>CuO<Subscript>4</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> Near the Eutectic Melting Point

Microstructure and conduction of ceramic composites Bi₂CuO₄ + xBi₂O₃ (x = 5, 10, 15, 20 wt %) near the eutectic melting point (770°C) are studied. Bismuth oxide, initially randomly distributed over the ceramics bulk, after quenching from temperatures exceeding the eutectic melting point, becomes localized at triple junctions and grain boundaries in Bi₂CuO₄, which is caused by wetting grain boundaries and forming a liquid-channel structure. The jumpwise change in the composites’ conductivity near 730 and 770°C caused by polymorphic transformation of Bi₂O₃ and the eutectic melting with simultaneous formation of a liquid-channel structure. Transport numbers of the oxygen ion are measured at 770°C by coulomb-volumetric method. The conduction by oxygen ions increases in the composites with decreasing average size of Bi₂CuO₄ crystallites.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 596–601.Original Russian Text Copyright © 2005 by Lyskov, Metlin, Belousov, Tret’yakov.     

Mass spectrometric investigation of vaporization in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The thermodynamics of vaporization in the Bi₂O₃-Fe₂O₃ quasibinary system was studied by high-temperature mass-spectrometry. The partial pressures of the constituents of a saturated vapor over the system at 1100 K were determined. Based on the experimental data, the following parameters were calculated: the activities of the components of the Bi₂O₃-Fe₂O₃ system condensed phase, the standard enthalpies of some heterogeneous reactions, and standard enthalpies of formation and enthalpies of formation for crystalline BiFeO₃ and Bi₂Fe₄O₉ from individual oxides. An optimal temperature for the solid-phase synthesis of bismuth ferrites from simple oxides is recommended.     

Enhanced electrochemical properties of pseudocapacitor with Bi<Subscript>3.64</Subscript>Mo<Subscript>0.36</Subscript>O<Subscript>6.55</Subscript> NPs as electrodes

In this work, Bi_3.64Mo_0.36O_6.55 nanoparticles (NPs) were successfully prepared by a facile hydrothermal method and utilized in pseudocapacitor for the first time. Within a redox potential range from ?1.0 to 0 V vs. Hg/HgO in a 1 M aqueous KOH solution by cyclic voltammetry (CV), chronopotentiometry (CP) and AC impendence, the specific capacitance could reach 998 F g^?1 at 1 A g^?1, which is possibly ascribed to the higher Bi content of Bi_3.64Mo_0.36O_6.55 NPs. Furthermore, the Bi_3.64Mo_0.36O_6.55 NP electrode exhibited good cycle stability maintaining over 85 % after 5000 cycles. These results demonstrated Bi_3.64Mo_0.36O_6.55 NPs might be a promising electrode material for pseudocapacitor.

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Graphical abstract The fabrication of uniform Bi_3.64Mo_0.36O_6.55 nanoparticles with a diameter of 100 nm were succefully reported by a facial hydrothermal method, which exhibits a extraordinary electronic performance with 998 F g^-1 at 1 A g^-1 and cycling stability

     

Conductivity of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-NiO composites

The conductivity and transport number of oxygen ions of Bi₂O₃-(10, 30, 50) vol % NiO composites are measured using the four-probe and coulomb-volumetric methods at various temperatures. It is shown that the Bi₂O₃-50 vol % NiO composite exhibits a high mixed ionic-electronic conductivity in the temperature range from 730 to 800°C.     

Effect of CuO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> on low temperature sintered MnZn-ferrite by sol–gel auto-combustion method

A sol–gel auto-combustion method was investigated to incorporate small amounts of additives of Cu and Bi uniformly into soft magnetic MnZn-ferrite nanoparticles, which were prepared by Fe(NO₃)₃·9H₂O, Mn(NO₃)₂ and Zn(NO₃)₂·6H₂O dissolved in water and citric acid. The powder was characterized by the X-ray diffraction analysis and transmission electron microscope method. The effects of nano-particle sized powders in microstructure development and adding CuO–Bi₂O₃ into MnZn-ferrite on phase formation, densification process as well as magnetic properties were studied by scanning electron microscope and vibrating sample magnetometer techniques. The sample without additive can be sintered well at 930 °C, while the samples with a small amount of the additive can be sintered at less than 900 °C. Obviously, the micron-sized powders exhibited high sintering activity. It was also found that CuO–Bi₂O₃ additive promoted the growth of grains and improved magnetic properties. The permeability and the saturation magnetization were improved substantially by adding CuO–Bi₂O₃ into MnZn-ferrite and the sintering temperature was lowered to 875 °C, which may be associated with the redistribution of cations on the tetrahedral (A) sites and octahedral (B) sites within the spinel lattice.