Determination of bismuth oxide in and on high-purity bismuth

Bismuth is dissolved in mercury on shaking with ammonium nitrate solution in a nitrogen atmosphere; bismuth oxide is insoluble and so can be separated by flotation and dissolved in nitric acid for spectrophotometric determination as tetraiodobismuthate(III). The method is applied to various bismuth samples containing about 0.01% Bi₂O₃, the relative standard deviation being 7–11%.     

Structural and optical properties of barium titanate modified bismuth borate glasses

Glass samples with composition (70B₂O₃–29Bi₂O₃–1Dy₂O₃) modified with Barium titanate (BT), where BT is added in different successive weight percents, have been synthesized by conventional melt quenching technique. X-ray diffraction studies were performed in order to confirm the amorphous nature of the samples. The density of the samples has been found to decrease with an increase in the BT content, whereas an opposite trend has been observed in the molar volume. The analysis of FTIR and Raman spectra of the samples depicts that the glass network is built up of mainly BiO₆, BiO₃, BO₃ and BO₄ units. Its detailed analysis also revealed that the glass structure depends upon the amount of BT in the glass matrix and hence it acts as a modifier in the glass network. Introduction of BT into the glass matrix leads to the conversion of BO₃ trigonal units into BO₄ tetrahedral units, which results in a decrease in the degree of disorder in the glass network and makes the glass system more stable. The values of Urbach energy obtained for the prepared samples also confirmed the decrease in disorder in the glass network. The optical absorption measurements carried out for well-polished samples show a decrease in optical band gap energy with an increase in BT content whereas the molar refractivity shows the reverse trend. The Hydrogenic excitonic model applied to the studied glasses suggested that the present glass system favors direct transitions. The metallization criterion of the presently studied samples suggests that the prepared glasses may be potential candidates for nonlinear optical applications.     

Morphology modulated growth of bismuth tungsten oxide nanocrystals

Two kinds of bismuth tungsten oxide nanocrystals were prepared by microwave hydrothermal method. The morphology modulation of nanocrystals synthesized with precursor suspension's pH varied from 0.25 (strong acid) to 10.05 (base) was studied. The 3D flower like aggregation of Bi₂WO₆ nanoflakes was synthesized in acid precursor suspension and the nanooctahedron crystals of Bi_3.84W_0.16O_6.24 were synthesized in alkalescent precursor. The dominant crystal is changed from Bi₂WO₆ to Bi_3.84W_0.16O_6.24 when the precursor suspension changes from acid to alkalescence. The growth mechanisms of Bi₂WO₆ and Bi_3.84W_0.16O_6.24 were attributed to the different solubility of WO₄²⁻ and [Bi₂O₂]²⁺ in precursor suspensions with various pH. For the decomposition of Rhodamine B (RhB) under visible light irradiation (λ>400 nm), different morphology of Bi₂WO₆ crystal samples obtained by microwavesolvothermal process showed different photocatalytic activity.     

电化学方法制备超细氧化铋粉末

超细氧化铋用途广泛。目前超细氧化铋的制备一般通过四个途径;一、机械粉碎法,可以获得粒径1μm的细粉,但在粉碎的过程中易混入杂质;二、熔融喷雾法,该法可以在短时间(45—48s)内获得超细Bi2O3,但均匀性差,氧化不易完全,生产过程有粉尘污染;三、通过水解氧化铋的     

Oxygen surface exchange kinetics of erbia-stabilized bismuth oxide

The surface oxygen exchange kinetics of bismuth oxide stabilized with 25 mol% erbia (BE25) has been studied in the temperature and pO₂ ranges 773–1,023 K and 0.1–0.95 atm, respectively, using pulse-response ¹⁸O–¹⁶O isotope exchange measurements. The results indicate that BE25 exhibits a comparatively high exchange rate, which is rate determined by the dissociative adsorption of oxygen. Defect chemical considerations and the observed pO₂^1/2 p{{hbox{O}}_2}^{1/2} dependence of the rate of dissociative oxygen adsorption suggest electron transfer to intermediate superoxide ions as the rate determining step in surface oxygen exchange on BE25.     

On the structure of evaporated bismuth oxide thin films

The bismuth oxide films evaporated from bulk Bi₂O₃ are shown to vary in stoichiometry. The as-evaporated low rate (1–5 Å/sec) films are microcrystalline and bismuth rich, relative to Bi₂O₃, and their optical absorption edge broadens and shifts to lower energies. High rate (15–25 Å/sec) films are morphous and oxygen-rich with an absorption edge shifted to higher energies. Thermal decomposition of the Bi₂O₃ during evaporation produces the variations in film stoichiometry. The high temperature δ-Bi₂O₃ observed in the as-evaporated low rate films and thermally treated amorphous films indicates the melt and the films are structurally similar. Thermal treatment of the low rate films results in the formation of the β-form. Comparison of X-ray and stoichiometry results suggests that β-Bi₂O₃ be expressed as β-Bi₂O_±3x, where x is the deviation from trioxide stoichiometry.     

Mixed oxide semiconductors based on bismuth for photoelectrochemical applications

The structural and photoelectrochemical properties of mixed oxide semiconductor films of Bi-Nb-M-O (M = Al, Fe, Ga, In) were studied in order to explore their use as photoanodes in photoelectrochemical cells. These films were prepared on AISI/SAE 304 stainless steel plates by sol–gel dip-coating. The films were characterized by scanning electron microscopy—energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), and their photoelectrochemical properties were studied by open circuit potential (OCP) measurements, linear sweep voltammetry (LSV), and cyclic voltammetry (CV). SEM micrographs show homogeneous and rough films with agglomerates on the surface. EDS analyses show that the films are composed of Bi, Nb, and M, and the agglomerates are mainly composed of Bi. XRD analyses show a predominant crystalline phase of bismuth(III) oxide (Bi₂O₃) and a secondary phase composed of Bi-M mixed oxides. It is noteworthy that there was no identified niobium-based crystalline phase. XPS results reveal that the films are composed by Bi(III), Nb(V), and M(III). CV results show that the electrochemical behavior is attributed only to the semiconductor films which indicate a good coating of the stainless steel support. OCP measurements show that all the films have n-type semiconductor properties and exhibited photoresponse to the visible light irradiation. LSV results show that the application of a potential higher than +0.1 V enhances the photocurrent which can be attributed to an improved charge carrier separation. The results indicate that these materials can be used in photoelectrochemical cells.     

Nanostructured composite materials of cerium oxide and barium cerate

Nanosized powders with a composition of (1-x)Ce_0.8Sm_0.2O_2-δ-xBace_0.8Sm_0.2O_3-δ (x = 0, 0.3, and 1) were obtained by self-ignition combustion synthesis (SICS) from the appropriate nitrates and various organic fuels (glycine, glycerol, citric acid, and a mixture of citric acid and ethylene glycol). The most finely dispersed powders formed when the concentration of the perovskite phase in the system decreased or when glycerol or citric acid-enthyleneglycol mixture was used as a fuel during SICS. A procedure for the preparation of powders and nanostructured ceramics was developed and their electric properties were studied.     

Emission of active oxygen forms from a deposited bismuth oxide

The specific features of the emission of singlet oxygen from deposited bismuth oxide were examined. It was established how the rate of the emission of singlet oxygen depends on the concentration of deposited bismuth oxide. The largest amount of singlet oxygen was emitted from the sample with a crystalline structure. It was shown that only singlet molecular oxygen is emitted from deposited bismuth oxide.     

Determination of chloride ion in bismuth oxide by capillary electrophoresis

A procedure is developed for determining chloride ion in bismuth(III) oxide by capillary electrophoresis with indirect photometric detection after precipitating the major component of the sample as bismuthyl acetate. The mixture containing chromate ion and diethanolamine is used as a separating electrolyte. The detection limit for chloride ions in the developed procedure is 5 × 10^?4%, the relative standard deviation is 15%. The absence of a systematic error is confirmed by atomic absorption and laser mass spectrometry.     

Interaction of bismuth(III) oxide with formic acid solutions

The interaction of bismuth(III) oxide with formic acid solutions at 22 and 55°C was studied using X-ray powder diffraction, thermogravimetry, electron microscopy, IR spectroscopy, and chemical analysis. Solubility curves were found to comprise two branches due to formates of compositions Bi(COOH)₃ and BiOCOOH forming in the system. Thermal decomposition of bismuth formates is shown to be a promising route for the synthesis of metallic bismuth, as well as of tetragonal (β) and monoclinic (α) bismuth oxides.     

CdBiO2NO3, a new layered bismuth oxide nitrate

Step-wise reaction of CdO, Bi₂O₃, and Cd(NO₃)₂^·4H₂O leads to formation of a novel bismuth oxide nitrate, CdBiO₂NO₃, which completes the family of bismuthite-like M^IIBiO₂NO₃ oxide nitrates. The new compound is tetragonal, I4/mmm, a = 3.9486(1)Å, c = 14.2235(2)Å; its crystal structure resembles those of PbBiO₂NO₃ and CaBiO₂NO₃, except for, probably, different positioning of the nitrate group. The compound is stable until ∼425 °C when it decomposes, in one step, into CdO and a mixture of Bi–Cd oxides. Cd-based analogs of isostructural PbLnO₂NO₃ (Ln – lanthanides) oxide nitrates are unlikely to exist. We discuss the similarities and differences in the structures of layered oxyhalides and oxynitrates of bismuth and rare-earths.     

Chemically reacting bismuth and nitrous oxide in a heat pipe oven

The chemical reactions between bismuth and oxidants in a heat pipe oven are described. Strong chemiluminescence (A²Π_{$\text{1}\text{2}$} → X²Π_{$\text{1}\text{2}$}) was observed in the reaction with N₂O and the vibrational temperature of the A²Π_{$\text{1}\text{2}$} state was measured to be 3150 ± 300 K.     

Sol-gel route for obtaining bismuth high T c superconducting oxide compounds

Bismuth high T _c superconducting oxide compounds were obtained by sol-gel method using acetate precursors. A study of the decomposition of quasi-amorphous acetates has been carried out to establish the conditions of superconducting phase formation. A comparison of the acetate sol-gel route with the oxalate coprecipitation method (previously used by the authors) reveals comparable results. Both methods require much shorter periods of thermal treatment for the formation of superconducting phases, as compared with the solid state reactions. The sol-gel route leads to better results from this point of view.     

Chemical and photochemical functionality of the first molecular bismuth vanadium oxide

Anionic metal oxide clusters, so-called polyoxometalates, can be developed as molecular model compounds to mimic the chemical and photochemical reactivity of solid-state metal oxides on the molecular level. Inspired by the well-known visible-light photocatalyst BiVO(4) , the first molecular bismuth vanadium oxide has been synthesized to investigate the chemical and photochemical similarities between the solid-state and molecular compounds. The cluster H(3) [(Bi(dmso)(3) )(4) V(13) O(40) ]?ca. 4?DMSO was obtained from simple precursors in almost quantitative yield. Structural analysis showed that the cluster shell is based on the unusual all-vanadium ε-Keggin framework [ε-V(12) O(40) ](15-) , which is stabilized by coordination of four Bi(III) centers. The acidic character of the three cluster protons was demonstrated by titration studies. The cluster shows promising photocatalytic properties in visible-light photooxidation reactions and has high activity (turnover number >1200), high quantum yield (Φ=7.6?%), and good recyclability, which make it a promising first example of a new class of heterometallic polyoxometalates.