Enhanced photocatalytic removal of hexavalent chromium and organic dye from aqueous solution by hybrid bismuth titanate Bi4Ti3O12/Bi2Ti2O7

Research on Chemical Intermediates - A hybrid bismuth titanate Bi4Ti3O12/Bi2Ti2O7 obtained via a one-step annealing procedure was employed as photocatalyst to oxidize rhodamine B dyes (RhB) and...     

Thermochemical studies on Bi4Ge3O12 and Bi4Ti3O12 single crystals

The specific heat values of Bi₄Ge₃O₁₂ and Bi₄Ti₃O₁₂ single crystals have been studied using a DSC instrument in the temperature range from 323 to 1273 K. The temperature range at which the anomaly associated with transition from polarized to non-polarized phase in Bi₄Ti₃O₁₂ occurred, has been estimated using the shape of the Bi₄Ge₃O₁₂ heat capacity curve as a “normal” one. The heat effect and the entropy change of the transition were evaluated.     

Mechanism of Formation of Bi4Ti3O12

The mechanism of solid-phase reaction of Bi₄Ti₃O₁₂ formation was studied. Formation of the layered perovskite-like bismuth titanate occurs via intermediates with sequential changes in the coordination polyhedron of bismuth. A correlation is analyzed between the temperature of the onset of activation of the solid-phase reaction and the melting point of the surface (intergrain) phase based on bismuth oxide.     

Bi4Ti3O12 Thin Films from Mixed Bismuth-Titanium Alkoxides

Bi₄Ti₃O₁₂ thin films were obtained by the sol-gel method. The precursor solution was prepared by allowing the two metallic alkoxides, Bi(OC₂H₄OCH₃)₃ and Ti(OC₂H₄OCH₃)₄, to react in 2-methoxy-ethanol to form the mixed alkoxide. This stable sol was deposited by spin-coating onto platinized silicon substrates. X-Ray diffraction patterns indicate that the perovskite initial crystallization temperature is 460°C for powder samples and it ranges between 400 and 500°C, for thin films, as a function of the number of coating layers. Dense, smooth and crack free thin films with grain sizes ranging from 20 nm to 500 nm are obtained, depending on the number of coating layers and on the post-deposition temperature annealing.     

Oxygen-isotope labeled titania: Ti(18)O2

(18)O-isotope labelled titania (anatase, rutile) was synthesized. The products were characterized by Raman spectra together with their quantum chemical modelling. The interaction with carbon dioxide was investigated using high-resolution FTIR spectroscopy, and the oxygen isotope exchange at the Ti(18)O(2)/C(16)O(2) interface was elucidated.     

Atomic Simulations of Aurivillius Oxides: Bi3TiNbO9, Bi4Ti3O12, BaBi4Ti4O15 and Ba2Bi4Ti5O18 Doped with Pb,Al, Ga,In, Ta

The Aurivillius oxides were originally of interest for their ferroelectric properties and have recently been explored in the field of oxide ion conductivity. Atomistic simulation methods have been carried out for Bi₃TiNbO₉, Bi₄Ti₃O₁₂, BaBi₄Ti₄O₁₅ and Ba₂Bi₄Ti₅O₁₈ doped with Pb, Al, Ga, In, Ta to determine defect energy in the materials by employing efficient energy minimization procedures. The calculations rest upon the specification of an interatomic potential model, which expresses the total energy of the system as a function of the nuclear coordinates. The Born model framework, which partitions the total energy into long‐range Coulombic interactions and a short‐range term to model the repulsions and van der Waals forces between electron charge clouds, is employed. This is embodied in the GULP simulation code. Dopant solution energy versus ion size trends are found for both isovalent and aliovalent dopant incorporation at Bi and Ta sites. Trivalent dopants (Al, Ga, In) and Pb are more favorable on the Bi site, whereas Ta dopants preferentially occupy the Ti site.     

Transparent thin films of Bi2WO6, Bi4Ti3O12 and Sr0.75Ba0.25Nb2O6

Transparent thin films were prepared by a sol–gel method starting from precursor formation in solution, subsequent spin coating followed by a heating ramp up to a maximum of 700 °C. Starting from a Bi₂MoO₆ synthesis route, the phase formation and thin film processing of the bismuth containing materials Bi₂WO₆, Bi₃Ti₄O₁₂ and additionally of the tungsten–bronze structure Sr_0.75Ba_0.25Nb₂O₆ were studied. Spin coating was used to adjust the film thickness in a wide range from 6 to 200 nm. All films were obtained as multicrystalline pure phases according to X-ray diffraction analyses. Scanning electron micrographs revealed homogeneous coatings composed of nanoparticles with a crystallite size varying between 20 and 100 nm, furthermore the UV–VIS spectra demonstrated a high transparency of the films, 80–90% at 600 nm.     

Preparation and properties of NH4Ti2P3O12 in the pseudobinary system NH4H2PO4TiO2

Phase equilibria in the system NH₄H₂PO₄TiO₂ were studied and a new compound (NH₄Ti₂P₃O₁₂) with Nasicon-type structure was synthesized. Its stability range was established. X-Ray and thermal properties were investigated and another new compound (Ti₄P₆O₂₃) with the Nasicon-type structure was obtained by heat treatment at 770°C.     

The Formation of Ferroelectric Bismuth Titanate (Bi4Ti3O12) from an Aqueous Metal-Chelate Gel

Bismuth titanate (Bi₄Ti₃O₁₂) was synthesized by an aqueous solution-gel process starting from solutions of bismuth acetate and a peroxocitrato-Ti(IV) complex. To gain insight into the thermal decomposition pattern of the gel several thermal analysis techniques were employed: DTA, TGA-EGA (evolved gas analysis by on-line coupling to a FTIR or mass spectrometer) and HT-DRIFT. Transmission electron micrographs showed that the gel is chemically homogeneous down to ca. 5 nm and that this homogeneity is preserved throughout the heat treatment. High-temperature X-ray diffraction measurements were used to make an in situ study of the phase formation. It has been found that single phase Bi₄Ti₃O₁₂ is formed at 625°C.     

Synthesis of Bi2O3 and Bi4(SiO4)3 Thin Films by the Sol-Gel Method

Bi2O3 thin films were prepared by dipping silica slides in ethanolic solutions of tris(2,2-6,6-tetramethylheptane-3, 5-dionato)bismuth(III) [Bi(dpm)3] [1] and heating in air at temperatures 500°C. Bi4(SiO4)3 homogeneous thin films were obtained from the reaction of the bismuth oxide coating with the silica glass substrate at temperatures higher than 700°C. For heat treatments at temperatures between 600°C and 700°C, Bi2SiO5 coatings were obtained. The composition and microstructure evolution of the films were determined by Secondary Ion-Mass Spectrometry (SIMS), X-Ray Photoelectron Spectroscopy (XPS) and Glancing Angle X-Ray Diffraction (GA-XRD). The synthesis procedure was reproducible and allowed the control of the Bi2O3 phase composition. Moreover, the thin film annealing parameters were correlated with the formation of bismuth silicates, among which Bi4(SiO4)3 (BSO) is very appealing for the production of fast light-output scintillators [2].     

Regulating Spin Polarization through Cationic Vacancy Defects in Bi4Ti3O12 for Enhanced Molecular Oxygen Activation

Molecular oxygen (O₂) activation technology is of great significance in environmental purification due to its eco-friendly operation and cost-effective nature. However, the activation of O₂ is limited by spin-forbidden transitions, and efficient molecular oxygen activation depends on electronic behavior and surface adsorption. Herein, we prepared cationic defect-rich Bi₄Ti₃O₁₂ (BTO-MV2) catalysts containing Ti vacancies (V_Ti) for O₂ activation in water purification. The V_Ti on BTO nanosheets can induce electron spin polarization, increasing the number of spin-down photogenerated electrons and reducing the recombination of electron-hole pairs. An active surface V_Ti is also formed, serving as a center for adsorbing O₂ and extracting electrons, effectively generating ⋅OH, O₂⋅⁻ and ¹O₂. The degradation rate constant of tetracycline achieved by BTO-MV2 is 3.3 times faster than BTO, indicating a satisfactory prospect for practical application. This work provides an efficient pathway to activate molecular oxygen by constructing new active sites through cationic vacancy modification technology.     

Electrochemistry of bismuth interlayers in (Bi2)m(Bi2Te3)n superlattice

Journal of Solid State Electrochemistry - Selective electrochemical transformations of bismuth interlayers in (Bi2)m(Bi2Te3)n superlattices can be of interest as a means of thermoelectric materials...     

A new bismuth iron oxyphosphate,Bi6(Bi0.32Fe0.68)(PO4)4O4

Iron was inserted into the known crystal structure of the bismuth phosphate oxide Bi_6.67(PO₄)₄O₄ to ascertain its location in the vacancies associated with the bismuth ion located at the origin of the unit cell. Single‐crystal X‐ray diffraction refinements converged to a model of composition Bi₆(Bi_0.32Fe_0.68)(PO₄)₄O₄ (hexabismuth iron tetraphosphate tetraoxide), in which Bi and Fe are displaced from the origin giving rise to a random distribution over the 2i sites instead of 1a, the origin of space group P. The isotropic displacement parameter for Bi/Fe has a reasonable value in this model. This structure establishes for the first time that Fe substitutes in the Bi‐deficient site in this series of materials and that Fe and Bi are disordered around the center of symmetry. These results enhance understanding of the crystal chemistry of these main group phosphates that are of interest in ion transport.     

Sulfonato-encapsulated bismuth(III) oxido-clusters from Bi2O3 in water under mild conditions

Treatment of Bi(2)O(3) with the acids; S-(+)-10-camphorsulfonic, 2,4,6-mesitylenesulfonic and sulfamic, under sonication at room temperature in water for 2-4 h, results in the formation and subsequent crystallisation of polynuclear bismuth oxido-clusters; [Bi(18)O(12)(OH)(12)(O(3)S-Cam)(18)(H(2)O)(2)], [Bi(38)O(45)(O(3)S-Mes)(24)(H(2)O)(14)] and [Bi(6)O(4)(OH)(4)(O(3)SNH(2))(6)].     

Synthesis and properties of magnetically separable Fe3O4/TiO2/Bi2O3 photocatalysts

The Fe₃O₄/TiO₂/Bi₂O₃ composites were synthesized by a sol–gel method and used as improved photocatalysts for the degradation of methyl orange (MO) under simulated sunlight at room temperature. The as-prepared Fe₃O₄/TiO₂/Bi₂O₃ composites were characterized by X-ray diffraction, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy (DRS). TEM analysis reveals that the composite has a core–shell structure and diameters of Fe₃O₄ core is about 200 nm. DRS results reveal that all composites showed red shift in optical absorption. TiO₂, Fe₃O₄, and Bi₂O₃ exist mainly as separate phases in the Fe₃O₄/TiO₂/Bi₂O₃ composites based on XPS analysis. The photocatalytic degradation of MO with the prepared photocatalysts was studied under simulated sunlight illumination. Photocatalytic reactivity test indicated that the removal efficiency of MO with the Fe₃O₄/TiO₂/Bi₂O₃ photocatalyst was higher than that of pure TiO₂ and Fe₃O₄/TiO₂. Recovery rate of Fe₃O₄/TiO₂/Bi₂O₃ photocatalysts achieved 80 % after five times reuse.     

Characterization and structure determination of ammonium bismuth oxalate hydrate, Bi(NH(4))(C(2)O(4))(2).xH(2)O

From on-line coupled TGA-MS and TGA-FTIR measurements, in combination with a quantitative chemical analysis, it was deduced that the chemical formula for an unknown bismuth oxalate compound had to be Bi(NH(4))(C(2)O(4))(2).3.71(6)H(2)O. Solution of the crystallographic structure on the basis of X-ray powder data proved this formula to be correct. The diffraction pattern was indexed by a tetragonal unit cell [a and c respectively 11.6896(2) and 9.2357(3) A; M(20) = 195 and F(30) = 302; Z(calc) = 4], from which the space group I4(1)/amd (No. 141) was derived. Direct methods were applied to solve the structure. The initial structural model was subsequently refined by means of the Rietveld method (R(B) = 8.0%, R(wP) = 14.0%). Bi is 8-fold coordinated by oxygen from the oxalate anions. Since these BiO(8) polyhedrons do not share any edges or vertexes, an open framework is formed with water and ammonium molecules between. As a result, water can easily be removed, which is clearly indicated by the instant weight loss in the TGA upon heating. Moreover, as shown by HT-XRD, this process of water exchange is reversible as long as the heating temperature does not exceed 100 degrees C.