Bi4Ti3O12/TiO2 heterostructure: Synthesis,characterization and enhanced photocatalytic activity

A multicomponent oxide, Bi₄Ti₃O₁₂/TiO₂ heterostructure was successfully synthesized via a two-step synthesis route based on an anodic oxidation procedure and a subsequent hydrothermal technique. X-ray diffraction confirmed that the composition of the as-fabricated sample was a Bi₄Ti₃O₁₂/TiO₂ composite. Scanning and transmission electron microscopy observation reveals that the as-synthesized sample consisted of TiO₂ nanotubes decorated with Bi₄Ti₃O₁₂ nanocubes. The photocatalytic property of Bi₄Ti₃O₁₂/TiO₂ heterostructure was evaluated by decomposing methyl orange as a model organic compound. Compared with the unmodified TiO₂ nanotube arrays, Bi₄Ti₃O₁₂/TiO₂ heterostructure exhibits a higher photocatalytic activity in the decomposition of methyl orange under UV light. The prominent photocatalytic activity could be ascribed to the formation of the heterostructure between Bi₄Ti₃O₁₂ and TiO₂ as well as a good dispersity of Bi₄Ti₃O₁₂ nanocubes, which could effectively separate the photogenerated carriers and reduce the electron–hole recombination.     

Rapid microwave-assisted sol-gel synthesis and exceptional visible light photocatalytic activities of Bi12TiO20

Crystalline Bi₁₂TiO₂₀ and Bi₄Ti₃O₁₂ particles were selectively synthesized by rapid microwave-assisted sol-gel method. During the thermal decomposition process of the dried gel, microwave calcination played a key role in producing single phase Bi₁₂TiO₂₀. Our Bi₁₂TiO₂₀ demonstrated one of the highest visible-light photocatalytic activities for MO degradation among the reported bismuth titanate particles with various compositions. Single phase Bi₄Ti₃O₁₂ can also be prepared by either a conventional calcination at high temperature or a combined heat treatment of a conventional heating followed by microwave calcination. The photocatalytic reaction rate constant of the Bi₄Ti₃O₁₂ prepared by microwave calcination was three times higher than that of conventionally calcined Bi₄Ti₃O₁₂, further confirming the advantage of microwave calcination in preparation of highly photocatalytically active bismuth titanate.     

Self-assembly of BixTi1−xO2 visible photocatalyst with core–shell structure and enhanced activity

Mesoporous Bi_xTi_1−xO₂ spheres with core–shell chamber were prepared by alcoholysis under solvothermal conditions. The cross-condensation between Ti–OH and Bi–OH ensured complete incorporation of Bi-dopants into TiO₂ lattice, though Bi atom is much bigger than Ti. Meanwhile, the aggregation of titania building clusters into spheres and their subsequent reactions including dissolution and re-deposition processes lead to the hollow spheres with tunable interior structure. The Bi-doping induced strong spectral response in visible region owing to the formation of narrow intermediate energy band gaps. Meanwhile, multiple reflections within the sphere interior voids promoted the light absorbance. As a result, the as-prepared Bi_xTi_1−xO₂ spheres exhibited much higher activity than the undoped TiO₂, the Bi₂O₃/TiO₂ obtained by impregnating the TiO₂ with Bi(NO₃)₃ solution, and the Bi_xTi_1−xO₂ after being ground during photodegradation of p-chlorophenol under visible light irradiation. Meanwhile, the Bi_xTi_1−xO₂ could be used repetitively for 10 times owing to the high hydrothermal stability and the absence of Bi-leaching.     

Bi and Al co-doped anatase titania for photosensitized degradation of Rhodamine B under visible-light irradiation

Although TiO₂ is a wide band gap semiconductor, it demonstrates photodegradation activity under visible light irradiation after dye sensitization. Compared with esterification between the surface hydroxyl group of TiO₂ and the carboxylic group of dyes, electrostatic interaction between TiO₂ and dye shows better photosensitized performance. In this work, Bi/Al co-doping anatase titania (Ti_1-xBi_2x/3Al_2x/3O₂ (0 ≤ x ≤ 0.3)) is designed to enhance the electrostatic interaction. The effect of Al ions is to enhance the solubility of Bi³⁺ into titania nanocrystals. A new band gap is generated after high concentration of Bi element doping, which not only promotes the absorption of visible light, but also improves the utilization of photogenerated carriers. Based on the results of transmission electron microscopy, light absorption, photodegradation activity and density functional theory calculations, it is found that bismuth dopant is the electron capture site. It first accumulates electrons through photocatalytic degradation reaction to enhance electrostatic adsorption between the catalyst and the positively charged dye molecules, and finally realizes high-efficiency photosensitization degradation of Rhodamine B. In addition, the sensitized titania has excellent photodegradation recyclability.     

Intermediate phases formation during the synthesis of Bi4Ti3O12 by solid state reaction

In this work, the formation of Bi₄Ti₃O₁₂ by solid state reaction from Bi₂O₃ and TiO₂ starting powders has been studied. The Bi₄Ti₃O₁₂ formation occurs through an intermediate Bi₁₂TiO₂₀ sillenite phase formed at temperatures sligthly over 300 °C. This sillenite phase is stable up to ∼750 °C, but in the presence of TiO₂ reacts to form Bi₄Ti₃O₁₂ at temperatures >500 °C. Raman spectroscopy has been used to evidence the amorphization of TiO₂, demonstrating that the Bi₄Ti₃O₁₂ formation occurs through the reaction of sillenite Bi₁₂TiO₂₀ and TiO₂.     

Preparation of Ag@AgCl/g-C3N4/TiO2 porous ceramic films with enhanced photocatalysis performance and self-cleaning effect

We report a novel method to prepare translucent and stable Ag@AgCl/g-C₃N₄/TiO₂ ceramic films having strong photocatalytic activities and self-cleaning capabilities under light irradiation. Colloidal silica was used as an inorganic binder and P25 TiO₂ was added as a hydrophilicity enhancer without which a smooth coating was not achievable. Ag@AgCl of particle size around 30?nm, was synthesized by in-situ oxidation of nano-silver particles in porous g-C₃N₄/TiO₂ films. Optimal conditions for Ag@AgCl/g-C₃N₄/TiO₂ preparation in terms of strongest photocatalysis were established by tests on Rhodamine B degradation under visible and full spectral irradiations. A good adhesion strength of the porous films on glass substrate was achieved. Stability and reusability of the films were assessed by cycling tests. Possible photocatalytic mechanisms are proposed based on the basis of trapping experiments. Systematic characterization of the film suggests that the in-situ oxidation is an effective and practical method to produce nanoscale Ag@AgCl.     

The growth of interfacial compounds between titanium dioxide and bismuth oxide

The growth of interfacial compounds between TiO₂ and Bi₂O₃ during transient liquid phase bonding at 900, 1000 and 1100 °C for various times was investigated. The microstructures and compositions of compounds in joints were analyzed by means of SEM and EPMA. It was found that the compound Bi₄Ti₃O₁₂ forms initially and replaces the Bi₂O₃ interlayer. Bi₂Ti₄O₁₁ then arises at the interface between Bi₄Ti₃O₁₂ and TiO₂ and the metastable Bi₂Ti₂O₇ phase appears last at the interface between Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁. The modes and activation energies of the growth of Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ were determined respectively. Holes in the middle of the joint heated at 1100 °C for 24 h were also found.     

A Novel Method for Preparing V-doped Titanium Dioxide Thin Film Photocatalysts with High Photocatalytic Activity Under Visible Light Irradiation

The liquid phase deposition (LPD) method was successfully used for preparing V-doped TiO₂ thin film photocatalysts. In this simple and easily-controlled process, V-doped anatase TiO₂ thin films were directly deposited on a soda lime glass substrate placed in an aqueous solution containing Ti- and V-fluoro complex ions, followed by annealing. The thin films were analyzed by XRD, XPS, UV-vis. V⁴⁺ ions were introduced into the lattice of TiO₂ through in-situ substituting Ti⁴⁺. The absorption edge of V-doped TiO₂ films shifted to visible light region. The highly efficient photocatalytic activity was verified by the decomposition of methylene blue under visible light irradiation.     

Synthesis,optical, and magnetic properties of six-layered Aurivillius bismuth ferrititanate

This work reports on the preparation, structure, photochemical, and magnetic properties of six-layered Aurivillius bismuth ferrititanates, that is, Bi₇Ti₃Fe₃O₂₁, Bi₇(Ti₂Nb)Fe₃O_21+δ, and Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticles. The samples were prepared through the modified citrate complexation and precursor film process. The XRD Rietveld refinements were conducted to study the phase formations and crystal structure. The morphological and chemical component characteristics were investigated using SEM, TEM, and EDX analyses. Bi₇Ti₃Fe₃O₂₁, Bi₇(Ti₂Nb)Fe₃O_21+δ, and Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticles present an indirect allowed transitions with band energies of 2.04, 2.03, and 2.02 eV, respectively. The hybridized (O2p+Fet_2g+Bi6s) formed the valence band (VB) and electronic components of (Ti–3d+Fe–e_g) formed the conduction band (CB) of this six-layered Aurivillius bismuth ferrititanate. The three samples showed efficient photocatalytic degradation of Rhodamine B (RhB) dyes with the excitation wavelength λ > 420 nm. The optical absorption, photodegradation, and magnetic abilities were improved through microstructural modification on “B” site via partial substitution of Mg²⁺ and Nb⁵⁺ for Ti⁴⁺. The photocatalytic results were discussed based on the layer structure and multivalent Fe ions. Fe^3+/2+ in the perovskite slabs (Bi₅Fe₃Ti₃O₁₉)²⁻ could act as the catalytic mediators in the photocatalysis process. As a photocatalyst, Aurivillius Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticle is advantageous due to its photocatalytic and magnetically recoverable abilities.     

Na0.5Bi0.5TiO3 phase relations: Thermodynamics and phase equilibria in the systems Bi2O3 – TiO2, Na2O – TiO2, and Na2O – Bi2O3 – TiO2

The lead-free piezoelectric material sodium bismuth titanate (NBT, Na_0.5Bi_0.5TiO₃) has attracted considerable attention owing to its promising dielectric, piezoelectric, and electrical properties. However, the literature on the binary subsystems is contradictory and there are only limited data for the ternary system. The present work surveys all of the reports of the binary subsystems Bi₂O₃ – TiO₂ and Na₂O – TiO₂ and synthesizes these data into inclusive revised versions. The compatibilities for the ternary system Na₂O – Bi₂O₃ – TiO₂ were determined experimentally, thus enabling the construction of a complete isothermal section at 800 °C. The compatibilities associated with the problematic binary subsystem Na₂O – Bi₂O₃, which experiences extreme volatilisation, were determined through the generation of the absent standard-state thermodynamic functions for the relevant binary and ternary phases, thus providing a full suite of thermodynamic data for this system. The thermodynamic stability diagrams for Na₂O, Bi₂O₃, and TiO₂ thus were calculated. The isothermal section also addresses the contradictions in the literature concerning the formation of solid solutions of Bi₁₂TiO_20-x / Bi_12-xTi_1+xO_20+0.5x, pyrochlore (Bi₂Ti₂O₇ / Na_wBi_2-xTi_2-yO_7-z), BTO (Bi₄Ti₃O₁₂ / Na_xBi₄Ti₃O_12+0.5x), and NBT (Na_0.5Bi_0.5TiO₃ / Bi_1±xNa_xTiO_3.5±x). Further, it was observed that the congruent melting point of NBT, which was determined to be 1225 °C, was preceded by the onset of gradual structural destabilization at 940 °C. Also, the NBT rhombohedral → tetragonal phase transformation was observed at an onset temperature of ∼250 °C. The present work thus provides platform data for the fabrication and reactivities of materials in the ternary system Na₂O – Bi₂O₃· TiO₂ and its binary subsystems.     

The effect of Bi2O3 compensation during thermal treatment on the crystalline and electrical characteristics of bismuth titanate thin films

Bismuth titanate thin films are deposited on ITO/glass substrates by rf magnetron sputtering at room temperature using a Bi₄Ti₃O₁₂ ceramic target. The deposited Bi₄Ti₃O₁₂ films are annealed in a conventional furnace in ambient air for 10 min at temperatures ranging from 550 to 640 °C. One specimen is annealed in a crucible containing additional Bi₂O₃ compensation powder, while the other specimen is annealed in ambient air. XRD analysis shows that the crystal phases of films annealed with Bi₂O₃ powder are better than those of films annealed without Bi₂O₃ powder. Furthermore, the EDS results reveal that the bismuth weight percentage of the former is higher than that of the latter. SIMS analysis shows that the bismuth decreases near the surface of Bi₄Ti₃O₁₂ film annealed without Bi₂O₃ powder, but reveals a stable distribution throughout the film annealed with Bi₂O₃ powder. These results imply that bismuth is readily evaporated during the thermal treatment process, particularly from the region near the film surface. Finally, the dielectric and polarization properties of the thin films annealed with Bi₂O₃ powder are found to be superior to those of the films annealed in ambient air.     

BiOCl nanosheet/Bi4Ti3O12 nanofiber heterostructures with enhanced photocatalytic activity

Aurivillius oxide semiconductors are important photocatalyst because of their unique electronic structure and layered crystal. In this paper, two kinds of Aurivillius oxide semiconductors heterostructures based on Bi₄Ti₃O₁₂ nanofibers frameworks and BiOCl nanosheets are successfully synthesized by combining the electrospinning technique and solvothermal method. The high-resolution transmission electron microscopy results reveal that an intimate interface between Bi₄Ti₃O₁₂ nanofibers and BiOCl nanosheets forms in the heterojunctions. Photocatalytic tests show that the BiOCl/Bi₄Ti₃O₁₂ heterostructures exhibit enhanced photocatalytic activity than bare Bi₄Ti₃O₁₂ and BiOCl, mainly owing to the photoinduced interfacial charge transfer based on the photosynergistic effect of the BiOCl/Bi₄Ti₃O₁₂ heterojunction. At the end, the photocatalytic mechanism with O₂⁻ production was studied.     

Mechanism of Bi0.5Na0.5TiO3 and Bi4.5Na0.5Ti4O15 template synthesis during topochemical microcrystal conversion and texturing of Bi0.5(Na0.8K0.2)0.5TiO3 piezoelectric ceramics

The mechanism by which Bi_0.5Na_0.5TiO₃ and Bi_4.5Na_0.5Ti₄O₁₅ templates are synthesized via a topochemical microcrystal conversion method using Bi₄Ti₃O₁₂ precursor and TiO₂ particles was investigated based on their crystal structures. The Bi_0.5Na_0.5TiO₃ template consisted of a mixture of plate-like and equiaxed particles, whereas the Bi_4.5Na_0.5Ti₄O₁₅ template consisted only of plate-like particles. The size of the plate-like and equiaxed particles was dependent on the size of the Bi₄Ti₃O₁₂ precursor and TiO₂ particles, respectively. The Lotgering factor and piezoelectric constant of textured Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ ceramics prepared using the Bi_0.5Na_0.5TiO₃ template were lower than those of the textured Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ ceramics prepared from the Bi_4.5Na_0.5Ti₄O₁₅ template. This can be attributed to the small amount of plate-like particles in the Bi_0.5Na_0.5TiO₃ template caused by the inevitable co-existence of equiaxed particles.     

Bi4Ti3O12 nanoparticles prepared by hydrothermal synthesis

The influence of hydrothermal conditions (including starting materials, reaction temperature and time) on the crystal structure and the morphology of Bi₄Ti₃O₁₂ particles are discussed in this paper. Bi₄Ti₃O₁₂ nanocrystalline particles were hydrothermally synthesized at temperatures in the range of 180–230 °C for 4–12 h, from Bi(NO₃)₃·5H₂O, TiCl₄ and NaOH solution. The XRD results revealed that a typical bismuth layered perovskite structure Bi₄Ti₃O₁₂ was obtained. The TEM showed that the Bi₄Ti₃O₁₂ nanoparticles are tabular, and the sizes are about 200 nm.     

Wetting behavior and bonding characteristics of bismuth-based glass brazes used to join Li-Ti ferrite systems

A series of bismuth-based glass brazes were used to join Li-Ti ferrite. The wetting behavior and bonding characteristics of glass brazes utilized to join Li-Ti ferrite were systematically investigated. The glass brazes feature a good CTEs match, and a favorable wetting ability over Li-Ti ferrite mating surfaces. Upon brazing, the Bi-rich phases (Bi₄₆Fe₂O₇₂, Bi₁₂SiO₂ and Bi₂₄B₂O₃₉) and Zn-rich phase (ZnO) were observed in the Li-Ti ferrite/Bi40 and Li-Ti ferrite/Bi35 joints. The Zn₂SiO₄, ZnFe₂O₄ and Bi₅Ti₃FeO₁₅ whiskers were detected in the Li-Ti ferrite/Bi25, Li-Ti ferrite/Bi20 and Li-Ti ferrite/Bi25-BC joints, respectively. No crystalline phase was detected in the Li-Ti ferrite/Bi30-BF joint. Multiple factors impact the joint strength, such as the three-point bending strength of glass brazes, the CTE match of the glass braze and the Li-Ti ferrite, as well as the crystal phases within the seam. The joint strength has the maximum value of 86 MPa for a Li-Ti ferrite/Bi25-Ba couples. The main impact is attributed to the strengthening effect of Bi₅Ti₃FeO₁₅ whiskers. The dielectric properties of Li-Ti ferrite/glass braze joints show a stronger frequency dependence than that of Li-Ti ferrite at low frequency. This is attributed to the formation of new interfaces. The glass matrix or a crystal phase with a higher dielectric constant could counteract the decrease in the dielectric constant of heat-treated Li-Ti ferrite. Therefore, the dielectric constant of joint, especially that of Li-Ti ferrite/Bi25-BC joint, would be near that of the original Li-Ti ferrite at a high frequency. Meanwhile, no increase in the dielectric loss tangent of a joint takes place.     

Preparation and gaseous photocatalytic activity of smooth potassium dititanate film

A new smooth potassium dititanate film was prepared by sol-gel method and characterized by thermogravimetry (TG) and differential scanning calorimetry (DSC), X-ray diffraction (XRD), atomic force microscopy (AFM), UV-Visible diffuse reflectance and Raman spectroscopy. The gaseous photocatalytic activity of smooth K₂Ti₂O₅ films was studied using contact angle analysis from the photocatalytic decomposition of octadecyltrichlorosilane (OTS) based self-assembled monolayers (SAMs) formed on K₂Ti₂O₅ films. The photocurrent response of the film was determined by an electrochemical method. It was shown that the films were smooth, compact, and transparent when formed on glass. Compared with TiO₂ film, the K₂Ti₂O₅ film showed wide absorption in the ultraviolet and visible region. It was found that the monolayers on K₂Ti₂O₅ decomposed much faster than those on TiO₂ under UV irradiation of 254 nm in air. The film also exhibited a stronger photoresponse and a more stable anodic photocurrent. The K₂Ti₂O₅ film efficiently decomposes the alkylsiloxane monolayers under UVirradiation in air and it was found to be a good photocatalyst for gaseous organic pollutant treatment. __________ Translated from Journal of functional materials, 2007, 38(7): 1067–1070, 1073 [译自: 功能材料]     

Preparation of Bi4Ti3O12 particles by crystallization from glass

Glass from the Bi₂O₃–TiO₂–B₂O₃ system was formed by rapid quenching of the melt. After annealing at 500 °C, the glass crystallized in the form of plate-like particles. The particles thus formed were separated through an acid treatment. Field emission scanning electron microscopy showed a layered structure for the particles. XRD observations revealed that the crystalline form was Bi₄Ti₃O₁₂, a useful material in the electronics industry.     

Mg3Y2Ge3O12:Bi3+ UV fluorescent phosphor as the TiO2 “sensitizer” for enhancing the heavy oil viscosity reduction

Nowadays, visible fluorescent materials based on rare earth (RE) and non-RE ions doping have been extensively explored for white LEDs. As for the UV fluorescent materials, it is well known that they are not suitable for the lighting applications. As a result, when compared to the visible fluorescent materials, previous works paid little attention to the UV fluorescent materials. In this work, we report a type of Mg₃Y₂Ge₃O₁₂:Bi³⁺ UV fluorescent phosphor. To understand the crystal structural information and photoluminescence (PL) properties of samples, we have used the X-ray diffraction (XRD), scanning electronic microscope (SEM), UV–visible diffuse reflectance and PL spectra to characterize them. The structural results reveal that the Bi³⁺ doped sample show their particle size at about 30 μm. The PL results show that the Bi³⁺ doped sample upon excitation at 230 nm can show a broad emission band that can almost cover the whole UV spectral region from 290 nm to 410 nm. Since this UV fluorescent band is exactly in agreement with the UV absorption region of TiO₂ semiconductor, we have fabricated several Mg₃Y₂Ge₃O₁₂:Bi³⁺/TiO₂-based ceramic plates and proposed used them to serve as an efficient UV irradiation source for photocatalytic application. As a result, we find that the TiO₂ can exhibit the significantly enhanced photocatalytic property for the heavy oil viscosity reduction after adding the Mg₃Y₂Ge₃O₁₂:Bi³⁺ UV fluorescent phosphor.     

Thermally-stable large strain in Bi(Mn0.5Ti0.5)O3 modified 0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3 ceramics

(1-x)[0.8Bi_0.5Na_0.5TiO₃-0.2Bi_0.5K_0.5TiO₃]-xBi(Mn_0.5Ti_0.5)O₃ (x = 0–0.06, BNKMT100x) lead-free ferroelectric ceramics were prepared via solid state reaction method. Bi(Mn_0.5Ti_0.5)O₃ induces a structure transition from rhombohedral-tetragonal morphotropic phases to pseudo-cubic phase. Moreover, the wide range of compositions within x = 0.03–0.055 exhibit large strain of 0.31%–0.41% and electrostrictive coefficient of 0.027–0.041 m⁴/C². Especially, at x = 0.04, the large strain and electrostrictive coefficient are nearly temperature-independent in the range of 25–100 °C. The impedance analysis shows the large strain and electrostrictive coefficient originate from polar nanoregions response due to the addition of Bi(Mn_0.5Ti_0.5)O₃.     

A novel high reflective glass-ceramic ink with Bi2Ti2O7 nanocrystals used for the photovoltaic glass backplane

Photovoltaic glass ink is a kind of ink used for the photovoltaic glass backplane to enhance the photoelectric conversion efficiency of solar cells. In this work, a novel kind of photovoltaic glass-ceramic ink, with Bi₂Ti₂O₇ nanocrystals precipitated from the low-melting glass for the first time in the short sintering process, was successfully designed and prepared to further improve the reflectance of near-infrared light. Bi₂Ti₂O₇ nanocrystals fill the gap between TiO₂ color pigments to a certain extent, which reduce the diffraction of light and greatly improve the reflectivity of the photovoltaic glass backplane to near-infrared light. In the near-infrared wavelength range (780–2500 nm), the average reflectance of photovoltaic glass ink with Bi₂Ti₂O₇ nanocrystals is 20.6% higher than that without Bi₂Ti₂O₇ nanocrystals. The maximum reflectance of photovoltaic glass-ceramic ink is 86.18%. Our research and findings have provided an important reference point for future development of photovoltaic glass inks.