Bi4Ti3O12 Particles Research Articles

D-π-A array structure of Bi4Ti3O12-triazine-aldehyde group benzene skeleton for enhanced photocatalytic uranium (VI) reduction

Photocatalytic reduction of UVI to UIV can help remove U from the environment and thus reduce the harmful impacts of radiation emitted by uranium isotopes. Herein, we first synthesized Bi4Ti3O12 (B1) particles, then B1 was crosslinked with 6-chloro-1,3,5-triazine-diamine (DCT) to afford B2. Finally, B3 was formed using B2 and 4-formylbenzaldehyde (BA-CHO) to investigate the utility of the D-π-A array structure for photocatalytic UVI removal from rare earth tailings wastewater. B1 lacked adsorption sites and displayed a wide band gap. The grafted triazine moiety in B2 introduced active sites and narrowed the band gap. Notably, B3, a Bi4Ti3O12 (donor)-triazine unit (π-electron bridge)-aldehyde benzene (acceptor) molecule, effectively formed the D-π-A array structure, which formed multiple polarization fields and further narrowed the band gap. Therefore, UVI was more likely to capture electrons at the adsorption site of B3 and be reduced to UIV due to energy level matching effects. UVI removal capacity of B3 under simulated sunlight was 684.9 mg g−1, 2.5 times greater than B1 and 1.8 times greater than B2. B3 was still active after multiple reaction cycles, and UVI removal from tailings wastewater reached 90.8%. Overall, B3 provides an alternative design scheme for enhancing photocatalytic performance.

Morphology-dependent photocatalytic performance of Bi4Ti3O12

Photo-catalysts with three dimensional (3D) morphologies exhibit high photo-catalytic activities and received more attention because of their large surface area and more active sites. In this work, 3D-microspheres, flower-ball and weaving-like Bi4Ti3O12 particles were prepared through a facile hydrothermal route with the assistance of different surfactants, in which all of 3D structures were assembled by Bi4Ti3O12 nano-rods. The as-prepared 3D Bi4Ti3O12 samples were characterized through power X-ray diffraction (XRD), Fourier-transform infrared (FTIR), scanning electron microscope (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption techniques and UV–vis diffuse reflectance spectra (DRS) to identify their crystal structures, morphologies, surface structure and light absorption abilities. Furthermore, the photo-catalytic abilities of samples were evaluated through the degradation Rhodamine B (RhB) under the drive of visible light. Results indicated that flower-liked Bi4Ti3O12 not only displayed the best catalytic efficiency but also possessed the good reusability and stability.

Realizing nitrogen doping in Bi4Ti3O12 via low temperature synthesis and its enhanced photocatalytic performance

Nitrogen doping in Bi-based oxides is highly desired due to the band gap tuning and chemisorption ability engineering. While it is rather difficult to incoporate nitrogen into Bi-based oxides because bismuth could be reduced easily during the high temperature synthesis process. In this work, we design a low temperature synthesis route to dope nitrogen into Bi-based Aurivillius phase compound Bi4Ti3O12 (BIT), which is a process of in-situ reaction, and the nitrogen doped Bi4Ti3O12 (N-BIT) particles have a similar morphology and structure to BIT. The positions of the substitutive nitrogen atoms in the N-BIT crystals are predicted to be at the oxygen atoms between the medial [TiO6] octahedron and the [TiO6] octahedron near the [Bi2O2]2+ layers and a smaller band gap of the N-BIT crystals is resulted by the first-principles calculations. The reduced band gap from BIT of 3.04 eV to N-BIT of 2.80 eV is confirmed by the absorption spectra measurements, which is benefical for charge separation under photoexcitaton. Furthermore, oxygen vacancies formed in the N-BIT sample due to the substitution of oxygen atoms with nitrogen atoms, gernerate more chemisorbed oxygens, which could be excited to the superoxide radicals. Therefore, the photocatalytic activity of N-BIT is enhanced after nitrogen doping.

Study of a reversible resistive switching mechanism in bismuth titanate deposited by electron cyclotron resonance sputtering

We studied the temperature dependence of the reversible resistance switching in the bismuth titanate (BiTiO) film deposited by electron cyclotron resonance sputtering. The reversible resistance switching was observed at 5 K in both the low resistance state (LRS) and high resistance state (HRS) in the film. The resistance in the LRS decreased with increasing temperature, and remained unchanged regardless of an electrode-pad area. On the other hand, the resistance in the HRS increased with temperature, exhibiting the electrode-pad area dependence. From the cross-sectional transmission electron microscope image, nanocrystalline Bi4Ti3O12 particles were uniformly distributed in the BiTiO film. We proposed the mechanism of reversible resistance switching in BiTiO, that is, (1) the filament of conduction path was generated along the grain boundaries of the nanocrystalline particles by electroforming, (2) the LRS was switched-on, and (3) the filament was cut off by applying reverse bias voltages, switching back to the HRS. We verified the conduction of three-dimensional variable range hopping in the HRS.

Plate-Like Bi4Ti3O12 Particles and their Topochemical Conversion to SrTiO3 Under HydrothermalConditions

Plate-like Bi 4 Ti 3 O 12 particles were synthesized using a one-step, molten-salt method from Bi 2 O 3 and TiO 2 nanopowders at 800 °C. The reaction parameters that affect the crystal structure and morphology were identified and systematically investigated. The differences between various Bi 4 Ti 3 O 12 plate-like particles were examined in terms of the ferroelectric-to-paraelectric phase transition and the photocatalytic activity for the degradation of Rhodamine B under UV-A light irradiation. The results encouraged us to conduct further testing of the as-prepared Bi 4 Ti 3 O 12 plate-like particles as templates for the preparation of plate-like SrTiO 3 perovskite particles using a topochemical conversion under hydrothermal conditions. The characteristics of the Bi 4 Ti 3 O 12 plates and the reaction parameters for which the SrTiO 3 preserved the shape of the initial Bi 4 Ti 3 O 12 template particles were determined.

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.

Enhanced piezoelectric properties and strain response in 〈001〉 textured BNT-BKT-BT ceramics

Highly 〈001〉 textured (~81%) ternary BNT-BKT-BT ceramics are prepared by reactive templated grain growth (RTGG) method with plate-like Bi4Ti3O12 particles as templates. Outstanding electric properties, which are both higher than state of art BNT-based ceramics, emerge in the aforementioned sample due to the grain orientation. For the textured ceramics, a high piezoelectric constant d33 of 314pC/N could be obtained, which is ~1.4-fold larger than that of a random one (221pC/N). A high electro-strain response (~0.41%) is obtained at a low applied electric field (4kV/mm) in textured ceramics, with the normalized strain d33⁎ (Smax/Emax)=1030pm/V near the TF-R (the temperature of ferroelectric to ergodic relaxor state transition). Moreover, the evolution process of relaxor phases is studied. The texture technique also could improve the TF-R from 70°C to 100°C, enhancing the temperature stability. In addition, the polarization switching process in ferroelectric phase and ergodic relaxor state are analyzed in this work, respectively.

Preparation of bismuth titanate/calcium alginate composite bead and its photocatalytic degradation of dye pollutants

In this study, the bismuth titanate/calcium alginate composite bead was synthesized by immobilizing bismuth titanate Bi4Ti3O12 particles into 1.5% sodium alginate (SA) matrix. The Bi4Ti3O12 particles were characterized by X-ray diffraction (XRD). The photocatalytic activity for the degradation of dye Rhodamine B in solution by as-prepared bismuth titanate/calcium alginate composite bead was investigated. The as-prepared composite beads CA/BTO-700 exhibited best photocatalytic efficiency for the degradation of RhB compared with CA/BTO-800 and CA/BTO-900 under simulated solar light. After 4 cycles in photocatalytic degradation of RhB, the degradation rate of the CA/BTO-700 nearly remained unchanged.

Formation Mechanism of Plate-like Bi4Ti3O12 Particles in Molten Salt Fluxes

The plate-like Bi4Ti3O12 particles were prepared by molten salt synthesis method. The influence of sintering temperature and cooling process on the microstructure of Bi4Ti3O12 powders was studied. Much larger particles were formed at higher temperatures. The particles could grow larger in slow cooling process. The formation mechanism of plate-like Bi4Ti3O12 particles in Na2SO4-K2SO4 system could be viewed as four processes: (1) solid reaction and nucleation, (2) plate-like structure formation, (3) diffusion and edge nucleation, (4) diffusion and epitaxial growth.

Crystallographic textured evolution in 0.85Na0.5Bi0.5TiO3–0.04BaTiO3–0.11K0.5Bi0.5TiO3 ceramics prepared by reactive-templated grain growth method

0.85Na0.5Bi0.5TiO3–0.04BaTiO3–0.11K0.5Bi0.5TiO3 (BNBK) lead-free piezoelectric ceramics with extensive [001]pc (pc: pseudo cubic) texture were fabricated by the reactive-templated grain growth method using anisotropic Bi4Ti3O12 (BIT) particles as templates. The degree of grain orientation increased with increasing heat treatment temperature (600–1,200 °C). The obtained textured ceramics showed dense and brick-wall like microstructure, giving a Lotgering factor of 0.6. A physical understanding of interaction between BIT templates and matrix powders and the mechanism of texture evolution were proposed and confirmed by experimental evidences of X-ray diffraction patterns, scanning electron microscope images and density measurements. The piezoelectric response was enhanced by the grain orientation, and the piezoelectric constant (d33) of the textured ceramics sintered at 1,170 °C attained a value of 254 pC/N, which was 41 % higher than random ceramics (180 pC/N).

Electrical Properties of Textured Niobium‐Doped Bismuth Titanate Ceramics

Crystallographically textured Nb‐doped bismuth titanate ceramics Bi4Ti(3−x)NbxO12, were fabricated by tape casting using plate‐like Bi4Ti3O12 particles prepared by a molten‐salt method as the templates. The templates were aligned in the fine‐grained matrix by aqueous tape casting with their major surface parallel to the casting plane. Effect of niobium on the grain orientation in the material was investigated. It was found that the use of a fine precursor powder led to enhanced densification of the ceramic, while Nb doping reduced electrical conduction and dielectric loss, which enabled poling at high temperatures and high electric fields. The textured Bi4Ti3O12 ceramic showed a high anisotropy in its dielectric properties in the directions parallel and perpendicular to the casting plane. Highly textured BiT was obtained with the use of only 5 wt% of template particles by sintering at 800°C for 1 h.

Molten Salt Synthesis of Anisotropic Bi<sub>4</sub>Ti<sub>3</sub>O<sub>12</sub> Particles

Plated-like Bi4Ti3O12 particles with anisotropic properties were prepared by the NaCl-KCl molten salt method. The effect on microstructure and patterns of Bi4Ti3O12 particles was investigated by adjusting salt quantities, calcined temperature and excessive Bi2O3 content. The results show that the size of Bi4Ti3O12 particle and the degree of anisotropy of pure perovskite structure of Bi4Ti3O12 particles prepared at 750°C simultaneously increased with the quantities of molten salt and the temperature of the calciner. Excessive Bi2O3 content also shows a positive effect to obtain the anisotropic Bi4Ti3O12 particles whose preparation process was optimized.

Electrical Properties of Textured (Bi1/2K1/2)TiO3–BaTiO3 Lead-Free Piezoelectric Ceramics

The electrical properties of (1-x)(Bi1/2K1/2)TiO3–xBaTiO3 (BKT–BT100x) ceramics prepared by an ordinary solid-state reaction and a reactive templated grain growth (RTGG) method using platelike Bi4Ti3O12 particles as a template were investigated. The degree of orientation, F, which was determined by the Lotgering method using an X-ray diffraction pattern, achieved ≈83% in the textured BKT–BT10 ceramic. A textured BKT–BT10 ceramic with a homogeneous microstructure was obtained after a long sintering time. The field-induced strains and piezoelectric properties of the BKT–BT10 ceramic were improved by improving grain orientation. In particular, the piezoelectric strain constant, d33, and the normalized strain, d33*, of the textured BKT–BT10 ceramic in the direction parallel (∥) to the tape stacking direction were 121 pC/N and 211 pm/V (at 80 kV/cm), respectively.

Control of Microstructures of Textured (Bi1/2K1/2)TiO3-BaTiO3 Ceramics

Control of the microstructures of (1–x)(Bi1/2K1/2)TiO3-xBaTiO3 (x = 0.1) [abbreviated as BKT–BT10] ceramics prepared by a reactive templated grain growth (RTGG) using platelike Bi4Ti3O12 particles as a template were investigated. All samples showed a single-phase perovskite structure. The degree of orientation F, which was determined by the Lotgering method using X-ray diffraction pattern, achieved only ∼ 60% in textured BKT-BT10 ceramics. Textured BKT-BT10 ceramics with a homogeneous microstructure were obtained by the the longer sintering time. It is very important to perform long sintering in order to promote the grain growth and improve the orientation factor for this composition.

粒子複合分散技術を用いた高磁場配向機能性セラミックスの開発

We have applied a high magnetic field to fabricate functional ceramics with textured structure. Bismuth titanate ceramics families, which are candidate for piezoelectric materials, were prepared through well-dispersed slurry preparation, orientation in a high magnetic field, and subsequent reaction sintering. a- and b- axis oriented bismuth titanate ceramics Bi4Ti3O12 had been prepared by a high magnetic field. In this study, the crystal oriented bismuth titanate families MBi4Ti4O15 (M=Ca, Sr, Ba) ceramics was fabricated by using oriented Bi4Ti3O12 particle and reaction sintering. The MBi4Ti4O15 (M=Ca, Sr, Ba), which has high coercive electric field and high piezoelectric properties, has been expected for application use. Bismuth titanate particles with about 1μm were used as host material. Reacted additives were perovskite titanate materials MTiO3 (M=Ca, Sr, Ba). Well-dispersed slurry was prepared by mixing bismuth titanate powders and other titanate powders. The slurry was poured into a mold and set in a magnetic field 10Tesla until drying. Bismuth titanate particles in the slurry were highly oriented in a magnetic field, that is, the dried powder compact was consist of highly oriented bismuth titanate particle Bi4Ti3O12 and random MTiO3 (M=Ca, Sr, Ba) particles. The crystal oriented MBi4Ti4O15 (M=Ca, Sr, Ba) ceramics with a,b-axis orientation were successfully produced after sintering. We examined the reaction sintering process between oriented bismuth titanate particle Bi4Ti3O12 and random MTiO3 (M=Ca, Sr, Ba) particle. Influence of particle size ratio of Bi4Ti3O12 and MTiO3 was discussed on the reaction and microstructure of MBi4Ti4O15 (M=Ca, Sr, Ba) ceramics.

Hydrothermal synthesis and characterization of Bi4Ti3O12 powders

The Bi4Ti3O12 powders were synthesized by a hydrothermal route. The influence of hydrothermal conditions on crystal structures and morphologies of Bi4Ti3O12 particles was studied. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared (FT-IR) spectroscopy and ultraviolet visible (UV-vis) spectroscopy. These results revealed that the Bi4Ti3O12 powders prepared thus possessed a plate-like shape, a typical bismuth layered perovskite structure, and a wide UV-vis absorption peak. Additionally, the formation mechanism of the Bi4Ti3O12 nanoplates was also discussed.

Effect of Template Particle Formation on Texture Development in Bi<sub>0.5</sub>Na<sub>0.5</sub>TiO<sub>3</sub> Ceramics

The factor determining texture development was examined for Bi0.5Na0.5TiO3 ceramics made by the reactive-templated grain growth process using platelike Bi4Ti3O12 particles as reactive template. Platelike, skeleton Bi0.5Na0.5TiO3 particles were formed by the reaction between Bi4Ti3O12 and Na2CO3 in calcined compacts. Coalescence of small grains in the skeleton particles to form single template particles was important to obtain highly textured ceramics.

Fabrication and Piezoelectric Properties of Grain-Oriented (Bi1/2K1/2)TiO3–BaTiO3 Ceramics

The piezoelectric properties of (1 - x)(Bi1/2K1/2)TiO3–xBaTiO3 (x = 0.1) [abbreviated as BKT–BT10] ceramics prepared by ordinary solid-state reaction and reactive templated grain growth (RTGG) using platelike Bi4Ti3O12 particles as a template were investigated. All samples showed a single-phase perovskite structure, and relative densities compared with theoretical densities were all higher than 95%. The degree of orientation F was determined by the Lotgering method using an X-ray diffraction (XRD) pattern. The F values of textured BKT–BT10 ceramics were relatively low at ∼35%. However, field-induced strains and piezoelectric properties of BKT–BT10 ceramics were improved by grain orientation. In particular, the piezoelectric strain constant d33 and the strain of textured BKT–BT10 ceramics in a direction parallel (∥) to the tape stacking direction were 84.5 pC/N and 168 pm/V (at 80 kV/cm), respectively.

Preparation and characterization of textured Bi0.5(Na0.8 K0.2)0.5TiO3 ceramics by reactive templated grain growth

Bi0.5(Na0.8 K0.2)0.5TiO3 (abbreviated as BNKT) piezoelectric ceramics with extensive <001> texture were prepared by the reactive templated grain growth (RTGG), using plate-like Bi4Ti3O12 (BiT) particles as the templates. Through the analysis of X-ray diffraction pattern of the obtained materials, extensive crystallographic texture was evaluated with a relatively high Lotgering factor (f≥0.9), and the incorporated (Bi0.5 K0.5)TiO3 diffused into the (Bi0.5Na0.5)TiO3 lattice to form a single solid solution. The scanning electron microscopy showed that the in-situ reaction started at the vicinity of BiT surface and proceeded with heat treatment time toward the inner part of the BiT. The high textured BNKT piezoelectric ceramics demonstrated good piezoelectric performance without decreasing the depolarization temperature when they were sintered at 1200 °C for 10 h.

Preparation of Textured Bi0.5(Na,K)0.5TiO3-BiFeO3Solid Solutions by Reactive-Templated Grain Growth Process

Textured Bi 0.5 (Na,K) 0.5 TiO₃-BiFeO₃ ceramics were prepared by the reactive-templated grain growth process, using platelike Bi4Ti₃O₁₂ particles. The effects of chemical composition in Bi 0.5 (Na,K) 0.5 TiO₃ on texture development and densification were examined. Textured ceramics were obtained by using Bi 0.5 K 0.5 TiO₃ as an end member of the solid solution but densification was limited. Dense ceramics were obtained by using Bi 0.5 Na 0.5 TiO₃ but texture did not develop. Dense, textured ceramics were obtained by using Bi 0.5 (Na 0.5 K 0.5 ) 0.5 TiO₃.