Facile preparation of heterostructured Bi2O3/Bi2MoO6 hollow microspheres with enhanced visible-light-driven photocatalytic and antimicrobial activity

Hierarchical β-Bi₂O₃/Bi₂MoO₆ heterostructured flower-like microspheres assembled from nanoplates with different β-Bi₂O₃ loadings (0–26.5 mol%) were synthesized through a one-step template-free solvothermal route. Under visible-light illumination (λ > 420 nm), over 99% of rhodamine B was degraded within 90 min on the 21.9 mol% of β-Bi₂O₃ loading Bi₂O₃/Bi₂MoO₆ microspheres. The remarkable enhancement of photocatalytic activity of the hierarchical Bi₂O₃/Bi₂MoO₆ micro/nanostructures can be attributed to the effective separation of the photoinduced charge carriers at the interfaces and in the semiconductors. The electrons (e⁻) are the main active species in aqueous solution under visible-light irradiation. The Bi₂O₃/Bi₂MoO₆ also displays visible-light photocatalytic activity for the destruction of E. coli. In addition, the β-Bi₂O₃ in the hierarchical Bi₂O₃/Bi₂MoO₆ microspheres is very stable and the composite can be easily recycled by a simple filtration step, thus the second pollution can be effectively avoided. A possible photocatalytic mechanism was proposed based on the experimental results.     

Variants of the Bi6TiP2O16 structure: The preparation and crystal structure of the isomorph Bi6(Mn0.6Bi0.4)P2O15

Compounds with the composition Bi₆(Bi_1−yM_y)X₂O_16−z, M = transition metal or Pb, X = P, V, As, display pseudo-tetragonal crystal systems. They are, however, monoclinic with space group I2 and the heavy atom positions mimic the δ-Bi₂O₃ structure. The title compound is monoclinic, a = 11.284(2) Å, b = 5.4259(11) Å, c = 11.112(2) Å, β = 96.25(3)°, I2, Z = 2. Least-squares refinement of single-crystal X-ray diffraction data on F² converged to R1 = 0.050, wR2 = 0.130. The crystal is twinned by two-fold rotation about [0 1 0] and each twin consists of its inverted component forming a racemate. The structure consists of chains of edge sharing (OBi₄) tetrahedra parallel to [1 0 −1]. The chains are bridged parallel to [1 0 1] by linked PO₄ tetrahedra and (Mn/Bi)O₆ octahedra parallel to [1 0 −1], into a three-dimensional structure. The lone-pair electrons of adjacent Bi atoms along the chain point in opposite directions along the b-axis. The Bi atoms are in distorted trigonal prismatic coordination that has one or two faces capped. The BiO bond lengths vary from 2.08(5) to 3.05(2) Å. The Mn/Bi atoms are disordered around the two-fold axis. Three oxygen atom sites contain vacancies.     

Heteroepitaxial growth of δ-Bi2O3 thin films on CaF2(1 1 1) by chemical vapour deposition under atmospheric pressure

We have succeeded in achieving the heteroepitaxial growth of a δ-Bi₂O₃ thin film on a CaF₂(1 1 1) substrate by means of chemical vapour deposition under atmospheric pressure. The film grew with a strong (1 1 1) orientation. From X-ray pole figures, it was observed that the δ-Bi₂O₃ film grew on the CaF₂(1 1 1) substrate with 60° rotational in-plane domains. The growth mode was of a 3D island type, and the grain size decreased with increasing oxygen pressure during the δ-Bi₂O₃ film growth, improving the overall surface smoothness.     

Preparation,characterization and photocatalytic activity of Bi2O3–MgO composites

A series of Bi₂O₃–MgO composites were synthesized by solvent-thermal method. It was found that the Bi₂O₃–MgO composites perform much better than TiO₂ (P25), Bi₂O₃ and MgO in the photocatalytic degradation of rhodamine B (RhB) in the presence of HCl and under irradiation of visible light (λ > 400 nm). The effects of Bi/Mg molar ratio, crystallization temperature of Bi₂O₃–MgO and reaction conditions on photocatalytic activity were studied. The best performance was observed over the composite with Bi:Mg molar ratio equal to 2:1 that had been subject to crystallization at 120 °C for 20 h. In addition, the photocatalytic efficiency of the composite can be significantly enhanced by the presence of hydrochloric acid. The prepared samples were characterized by XRD and UV–vis DRS techniques. The relationships between the structure and photocatalytic performance of the as-prepared Bi₂O₃–MgO samples were also investigated.     

Photoelectrochemical characterization of Bi2Se3 thin films deposited by SILAR technique

Bi₂Se₃ thin films have been deposited by simple and less investigated successive ionic layer adsorption and reaction (SILAR) technique onto fluorine-doped tin oxide (FTO) coated glass substrates at room temperature (27 °C). The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies indicate that Bi₂Se₃ thin films are nanocrystalline. These films are used for photoelectrochemical (PEC) characterization in cell with configuration as n-Bi₂Se₃/0.1 M polysulfide/C. The studies such as current–voltage characteristics in dark and light, photovoltaic power output, transient photoresponse, and capacitance–voltage have been carried out. The study reveals that fill factor and power conversion efficiency of the cell are low (0.43 and 0.032%, respectively).The flat bond potential is found to be −0.04 V (SCE).     

Time-resolved spectroscopy of Bi3+ centers in Y4Al2O9

Steady-state and time-resolved emission and excitation spectra as well as luminescence decay kinetics are studied at 4.2–400 K under excitation in the 3–6 eV energy range for Bi³⁺ ions substituting for Y³⁺ ions in four inequivalent crystal lattice sites of Y₄Al₂O₉:Bi ceramics. Luminescence characteristics of Bi³⁺ centers of all the four types are identified and are shown to arise from the radiative decay of the triplet relaxed excited state (RES) of Bi³⁺ ions. The parameters of the triplet RES, namely, probabilities of the radiative and nonradiative transitions from the metastable and emitting levels as well as the energy distance between these levels, are determined. The influence of the nearest surroundings of Bi³⁺ ions on the luminescence characteristics and the parameters of the triplet RES of Bi³⁺ centers is discussed.     

Synthesis and characteristics of nature-superlattice-structured Bi3TiNbO9–Bi4Ti3O12 ferroelectric thin films by MOD

Natural-superlattice-structured ferroelectric thin films, Bi₃TiNbO₉–Bi₄Ti₃O₁₂ (BTN–BIT), have been synthesized on Pt/Ti/SiO₂/Si by metal organic decomposition (MOD) using BTN–BIT (1 mol:1 mol) solution. BTN–BIT films show natural-superlattice peaks below 2θ = 20° in X-ray diffraction patterns, which indicate that the BTN–BIT films annealed at 700–800 °C in O₂ ambient are consisted of iteration of two unit cells of Bi₃TiNbO₉ and one unit cell of Bi₄Ti₃O₁₂. As the annealing temperature increases from 600 to 750 °C, uniform and crack-free films, better crystallinity and ferroelectric properties can be obtained, but the pyrochlore phase in BTN–BIT films annealed over 800 °C would impair the ferroelectric properties. With the increase of O₂ flow rate from 0.5 to 1.5 L/min, both remanent polarization P_r and coercive electric field E_C increase, which are mainly attributed to reduction of the vacanvies of Bi and oxide ions in the films. Natural-superlattice-structured BTN–BIT thin films having 2–1 superlattice annealed at 750 °C in O₂ ambient with a flow rate of 1.5 L/min exhibit superior ferroelectric properties of P_r = 23.5 μC/cm² and E_C = 135 kV/cm.     

Enhancement of photosensitivity by annealing in Bi2S3 thin films grown using SILAR method

Bi₂S₃ thin films were grown by successive ionic layer adsorption and reaction method (SILAR) onto the glass substrates at room temperature. The as prepared thin film were annealed at 250 °C in air for 30 min. These films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrical measurement systems. The X-ray diffraction patterns reveal that Bi₂S₃ thin film have orthorhombic crystal structure. SEM images showed uniform deposition of the material over the entire glass substrate. The optical energy band gap observed to be decreased from 1.69 to 1.62 eV for as deposited and annealed films respectively. The I–V measurement under dark and illumination condition (100 W) show annealed Bi₂S₃ thin film gives good photoresponse as compared to as deposited thin film and Bi₂S₃ thin film exhibits photoconductivity phenomena suggesting its useful in sensors device. The thermo-emf measurements of Bi₂S₃ thin films revealed n-type electrical conductivity.     

Spray pyrolysed bismuth oxide thin films and their characterization

Uniform, adherent and reproducible bismuth oxide thin films have been deposited on glass substrates from aqueous Bi(NO₃)₃ solution, using the solution spray technique. Their structural, surface morphological, optical, and electrical properties were investigated by XRD, AFM, optical absorption, electrical resistivity and thermo-emf measurements. The structural analysis from XRD pattern showed the formation of mixed phases of monoclinic Bi₂O₃ (predominant), tetragonal β-Bi₂O₃ and nonstiochiometric Bi₂O_2.33. The surface morphological studies on atomic force micrographs revealed round grain morphology of bismuth oxide crystallites. The optical studies showed a direct band gap of 2.90 eV for as-prepared bismuth oxide films. The electrical resistivity measurements of bismuth oxide films indicated a semiconducting behavior with the room temperature electrical resistivity of the order of 10⁷ Ω cm. From thermo-emf measurements, the electrical conductivity was found to be of n-type.     

Controlled growth,characterization and thermodynamic behavior of bismuth–tin nanostructures sheathed in carbon nanotubes

We report the controlled synthesis of bismuth–tin (Bi–Sn) nanostructures sheathed in graphitic shells that resemble carbon nanotubes (CNTs). Our approach is based on a simple catalytic chemical vapor deposition over a mixture of Bi₂O₃ and SnO₂ supplied as starting materials. Shape control of the nanostructures strongly relies on the weight ratio of Bi₂O₃ and SnO₂. Sheathed nanoparticles and nanorods are formed at SnO₂ to Bi₂O₃ weight ratios of less than 4:1. They are composed of two separate crystals: rhombohedral Bi and tetragonal Sn₁₉Bi crystals. On the other hand, the sheathed nanowires are formed at SnO₂ to Bi₂O₃ weight ratios above 4:1. The nanowires have only tetragonal Sn₁₉Bi structure with a diameter of approximately 100 nm. Elementary analyses support the core/shell heterostructure of the resulting products. A favorable temperature for the Sn-rich Sn₁₉Bi nanowires is in the range of 700–800 °C, more specifically around 750 °C. Thermodynamic analysis reveals that the CNTs play a significant role in the protection of the Bi–Sn nanostructures during phase transition by temperature change. This simple and reproducible method may be extended to the fabrication of similar binary or ternary nanostructures.     

The super-hydrophilicities of Bi–TiO2, V–TiO2, and Bi–V–TiO2 nano-sized particles and their benzene photodecompositions with H2O addition

This study focused on the super-hydrophilicities of metal-TiO₂ photocatalysts, including metals with three-oxidation and five-oxidation states, and their benzene photodecompositions with or without H₂O addition. The nanometer-sized metal-TiO₂s, including Bi³⁺, V⁵⁺, and Bi³⁺–V⁵⁺ ions, were prepared using a solvothermal method. The XRD result identified these to have pure anatase structures after solvothermal treatment at 200 °C for 10 h, without any treatment. The spherical particle sizes were distributed within the range of 10–50 nm after 500 °C calcinations, and the particle sizes decreased with an increase of the Bi component, while it increased with the V component compared with that of pure TiO₂. The XPS result showed that the peaks for O1s (Ti–O) shifted to the larger binding energy in Bi–TiO₂; on the other hand, it shifted to the smaller binding energy in V–TiO₂. In particular, the Ti–OH peak, which means to hydrophilicity, decreased with an increase of the Bi component; it increased, however, with the V component. The contact angle expressed about 3° on the Bi–TiO₂ nano-sized film (200-nm thickness) after irradiation for 2 h; otherwise, it approached 0° on the V–TiO₂ nano-sized film after 30 min. In particular, the decreased angle was continued under dark condition on the Bi–V–TiO₂ nano-sized film. The benzene photodecomposition in the batch system increased in the order of Bi (3.3)–V (6.7)–TiO₂ > V–TiO₂ > pure TiO₂ > Bi–TiO₂, and the maximum benzene conversion was 35% after 60 min. The conversion remarkably increased, however, in almost all catalysts with H₂O addition during the benzene photo-decomposed reaction, and in particular, the conversion reached up to 80% after 180 min in Bi–V–TiO₂. In the continuous system for Bi–V–TiO₂ with H₂O addition, the photodecomposition rate of 50% was maintained for 168 h, without catalytic deactivation. After photoreaction, there were minimal deposited cokes in the photocatalyst in both reaction conditions, with and without H₂O addition. The deposited amounts were smaller, however, in the reaction with H₂O addition. This result is a proof that photocatalytic deactivation can be retarded by an H₂O supplement during VOC decomposition.     

Photoluminescence properties of novel KBaBP2O8:M (M = Pb2+ and Bi3+) phosphors

A series of novel inorganic phosphors KBa_1−xPb_xBP₂O₈ and K_1+xBa_1−2xBi_xBP₂O₈ (0.01 ⩽ x ⩽ 0.08) were synthesized by using a solid-state reaction technique at high-temperature and their photoluminescence properties were investigated. The dependence of the emission intensity on the Pb²⁺ and Bi³⁺ concentration for the KBa_1−xPb_xBP₂O₈ and K_1+xBa_1−2xBi_xBP₂O₈ was studied, in which the optimal concentration as well as the critical transfer distance R_c for Pb²⁺ and Bi³⁺ was obtained and determined. The as-prepared phosphors can be effectively excited with ultraviolet (UV), and exhibit UV − blue emission with large Stokes shift. The above work indicates these phosphors could be potential candidates for application in UV lamps industry.     

Fabrication and electrical properties of Si-based La10−xBix(SiO4)6O3 apatite ionic conductor

In this paper we report an investigation about the relationship between Bi content and conductivity for the La_10?xBi_x(SiO₄)₆O₃ (x = 0.5–2) specimens. Increasing Bi content in apatite-type La_10?xBi_x(SiO₄)₆O₃ specimen leads to increasing the average grain size and sinterability because some Bi ion deposited at grain boundaries which promotes grain growth. The relative sintered density of the La₈Bi₂(SiO₄)₆O₃ specimen is 98%. There is a small shift in diffraction angle of XRD peaks, complicated lattice distortion was observed in the X-ray pattern with increasing content of Bi. Electrical conductivity of La_10?xBi_x(SiO₄)₆O₃ specimen increased with increasing Bi contents and the value of the La₈Bi₂(SiO₄)₆O₃ specimen is 2.4 × 10^?4 S cm^?1 at 700 °C.     

Phase transition in (1 − x)Bi(Mg1/2Ti1/2)O3-xPbTiO3 ceramics

The phase structure and phase transition of (1 ? x)Bi(Mg_1/2Ti_1/2)O₃-xPbTiO₃ (BMT-PT) ceramics with x = 0.0–0.42 were investigated. It was found that pure perovskite phases were achieved for x ≥ 0.28, while Bi₄Ti₃O₁₂ or Bi₁₂TiO₂₀ phase existed for x ≤ 0.15. The anomaly dielectric peaks were observed around 620 °C for BMT-(0.28–0.38)PT samples, thus phase transition in (1 ? x)Bi(Mg_1/2Ti_1/2)O₃-xPbTiO₃ ceramics was studied using thermal expansion. It was found that dielectric anomalies at ~ 620 °C were resulted from the phase transition of the second phase and defects inside samples.     

Effect of Bi substitution level on dielectric characteristics of Pb[(Mg1/3Nb2/3),Ti]O3 ceramics

Bi(Mg_2/3Nb_1/3)O₃ was systematically substituted (up to 30 mol%) into Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ and resultant changes in the phase formation, crystallographic aspects as well as dielectric properties of the ceramic samples were investigated. Columbite and rutile solid solutions were mostly detected in the B-site precursor compositions, whereas only a monophasic perovskite structure was identified after the addition of PbO and Bi₂O₃. Frequency-dependent dielectric relaxation behavior was observed in all of the compositions investigated. The maximum dielectric constant values decreased substantially with increasing substituent fractions of Bi. By contrast, the dielectric maximum temperatures changed in somewhat complicated ways in that the increase became comparatively insensitive to the PbTiO₃ concentration with increasing levels of Bi substitution.     

Room temperature multiferroic properties of (Bi0.95La0.05)(Fe0.97Mn0.03)O3/NiFe2O4 double layered thin film

(Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film was prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. X-ray diffraction and Raman scattering spectroscopy studies confirmed the formation of the distorted rhombohedral perovskite and the inverse spinel cubic structures for the (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film. The (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film exhibited well saturated ferromagnetic (2 M_r of 18.1 emu/cm³ and 2H_c of 0.32 kOe at 20 kOe) and ferroelectric (2P_r of 60 μC/cm² and 2E_c of 813 kV/cm at 866 kV/cm) hysteresis loops with low order of leakage current density (4.5 × 10⁻⁶ A/cm² at an applied electric field of 100 kV/cm), which suggest the ferroelectric and ferromagnetic multi-layers applications in real devices.     

Lithium solubility limit in ZnGa2O4:Bi0.0013+,Li+ phosphor

The lithium solubility limit, photoluminescence (PL) and photoluminescence excitation (PLE) properties of lithium ion co-activated ZnGa₂O₄:Bi³⁺,Li⁺ phosphor have been investigated. A LiGaO₂ second phase began to appear from 3 mol% Li⁺ ion co-activated ZnGa₂O₄:Bi³⁺,Li⁺ phosphor. The enhanced brightness of blue (λ_ex = 254 nm) and white (λ_ex = 315 nm) colors of bismuth ions doped ZnGa₂O₄:Bi³⁺,Li⁺ phosphor was assigned to the formation of LiGaO₂. Bi³⁺ activated lithium zinc gallate phosphor showed a more enhanced PLE peak around 315 nm than that of lithium zinc gallate phosphor when λ_em = 520 nm. Thus, we observed that the PL intensity of ZnGa₂O₄:Bi³⁺,Li⁺ phosphor with λ_em = 520 nm was much greater than that of ZnGa₂O₄:Li⁺ phosphor. Also, ZnGa₂O₄:Bi³⁺,Li⁺ phosphor exhibited a shorter decay time than that of ZnGa₂O₄:Li⁺ phosphor by about a factor of about 2.     

Second-order optical nonlinearities of metastable BiBO3 phases in crystallized glasses

Metastable BiBO₃ and rare-earth (RE)-doped RE_xBi_1−xBO₃ crystals were prepared through the crystallization of 50Bi₂O₃ · 50B₂O₃ and xRE₂O₃ · (50−x)Bi₂O₃ · 50B₂O₃ glasses (RE = Y, La, Gd, Yb), and their second harmonic (SH) intensities were examined using the Kurtz powder method. It was confirmed that BiBO₃ has two different crystalline forms, i.e., BiBO₃(I) and BiBO₃(II), and that BiBO₃(I) transforms into BiBO₃(II) at temperatures around 500 °C. Both phases were found to be nonlinear optical crystals with a phase matchable character, and the SH intensity of BiBO₃(II) powders was approximately 110 times as large as α-quartz powders. The incorporation of RE³⁺ into BiBO₃(II) was confirmed from X-ray diffraction analysis, and in particular, Gd_xBi_1−xBO₃(II) showed an enhanced SH intensity of approximately 145 times as large as α-quartz.     

Structural and thermoelectric characterizations of high pressure sintered nanocrystalline Bi2Te3 bulks

Using Bi₂Te₃ nanopowders prepared from ball milling of elemental Bi and Te, nanocrystalline Bi₂Te₃ bulks were fabricated with high pressure sintering technique under variable pressures. The structural and thermoelectric properties were characterized, revealing a strong correlation with the sintering pressure. The nanocrystalline Bi₂Te₃ bulk fabricated under 2 GPa exhibits good thermoelectric properties with ZT over 0.8 from 300 to 460 K and a peak ZT of 1.03 occurring at 403 K, which can be attributed to the small thermal conductivity from enhanced phonon scattering by grain boundaries and defects, as well as to the good electrical property comparable to that of the zone melting material.     

Thermoelectric properties of Bi2O2Se

Bi₂O₂Se was synthesized from Bi₂Se₃ and Bi₂O₃ by solid state reaction in an evacuated quartz ampoule. The product crystallizes in the tetragonal type lattice and X-ray pattern displays lines of the Bi₂O₂Se only. Samples for thermoelectric property measurements were prepared using hot pressing in rectangular graphite dies. The samples were characterized by the measurements of Seebeck coefficient, electrical conductivity and thermal conductivity as a function of temperature. From the experimental data we calculate the dimensionless figure of merit ZT that for a non-optimized material approaches the value 0.2 at 800 K.