Bismuth Tungsten Oxide Research Articles

Observation of Hidden Polar Phases and Flux Closure Domain Topology in Bi2WO6 Thin Films.

Topological textures of ferroelectric polarizations have promise as alternative devices for future information technology. A polarization rotation inevitably deviates from the stable orientation in axial ferroelectrics, but local energy losses compromise the global symmetry, resulting in a distorted shape of the topological vortex or inhibiting the vortex. Easy planar isotropy helps to promote rotating structures and, accordingly, to facilitate access to nontrivial textures. Here, we investigate the domain structure of an epitaxial thin film of bismuth tungsten oxide (Bi2WO6) grown on a (001) SrTiO3 substrate. By using angle-resolved piezoresponse force microscopy and scanning transmission electron microscopy, we find the existence of a hidden phase with ⟨100⟩-oriented ferroelectric polarizations in the middle of the four variant ⟨110⟩-oriented polarization domains, which assists in the formation of flux closure domains. The results suggest that this material is one step closer to becoming an isotropic two-dimensional polar material.

A comparative study between pure bismuth/tungsten and the bismuth tungsten oxide for flexible shielding of gamma/X rays

Thermoplastic vulcanizate based flexible W/Bi and bismuth tungsten oxide composites with different doping ratios from 20% to 100% are successfully fabricated. The ray attenuation abilities of the composites are determined at X-ray tube voltages of 80 KVp–120 KVp, and at gamma rays of 59 keV, 122 keV, 343 keV and 960 keV. The surface morphology and elements mapping of W/Bi and bismuth tungsten oxide particles within the polymer have confirmed a more uniform dispersion of bismuth tungsten oxide than W/Bi. Shielding parameters such as transmittance T, mass/linear attenuation coefficients μm and μ, as well as lead equivalent δPb are investigated experimentally and numerically by Monte Carlo code NECP-MCX as well as XCOM program. The transmittance of γ ray decreases exponentially with the areal density of the functional particles, and the best shielding of X-ray goes to 100 KVp tube voltage, followed by 80 KVp and 120 KVp. A comparison of the two series of composites are made that W/Bi always has advantages over bismuth tungsten oxide in attenuation coefficients and lead equivalent, because the extra containing oxygen atoms in bismuth tungsten oxide crystal actually provide very weak additional shielding. Test of mechanical property also reflects the advantage of using pure W/Bi over bismuth tungsten oxide in flexibility. As substitutes for Pb containing materials, these two types of composites could be of potential use in medical diagnosis, interventional surgery, or biological radiation protection, etc.

A facile green approach to the synthesis of Bi2WO6@V2O5 heterostructure and their photocatalytic activity evaluation under visible light irradiation for RhB dye removal

Bismuth tungsten oxide and vanadium pentoxide (Bi2WO6/V2O5) heterostructures are produced by a green synthesis approach using Azadirachta indica extract for photocatalytic performance. The hydrothermal method at temperatures between 120 °C and 140 °Cis used to synthesize Bi2WO6. Bi2WO6 and V2O5 phases are formed in pure orthorhombic wells according to the XRD pattern. The SEM displays V2O5 nanorods, Bi2WO6 hierarchical microspheres that resemble flowers at 120 °C, and particles with a particle-like character at 140 °C. In V2O5, the asymmetric stretching vibrations of the triplely coordinated oxygen (chain oxygen) bonds and the vibration of the doubly coordinated oxygen (bridge oxygen) bonds are responsible for a peak at 611 cm−1. In FTIR spectra between 600 and 1600 cm−1, the major absorption bands in Bi2WO6 are attributed to the W-O stretching, Bi-O stretching, and W-O-W bridging stretching modes. Bi2WO6@V2O5 at 120 °C has the lowest bandgap energy (2.32 eV) and optical electronegativity (0.62), as well as the highest refractive index (2.57), extinction coefficient (2.21), and dielectric constant (εr = 0.72 and εi = 11.4) among all samples, making it a suitable material for photocatalysis. Rhodamine blue (RhB) dye degradation is used to measure the photocatalytic activity (PCA) of certain materials. The results showed that heterostructure V2O5@Bi2WO6 synthesized at 120 °C is more attractive among all samples due to high degradation of RhB dye under sunlight irradiation in 90 min.

Effect of metal doping in Bi2WO6 micro-flowers for enhanced photoelectrochemical water splitting

Design and fabrication of artificial catalytic systems to mimic natural photosynthesis which can harvest solar energy and directly convert into useable or storable energy resources may resolve the global energy crisis. Remarkably, photocatalysis is an efficient approach to utilize solar photons in order to drive the thermodynamic uphill reaction to generate chemical fuels in presence of efficient photocatalyst. Bismuth tungsten oxide (Bi2WO6) is a typical Aurivillius double perovskite oxides and has received an increasing research interest for water splitting due to moderate bandgap, superior chemical and thermal stability. However, the solar light absorption of bare Bi2WO6 is not significant in visible region, and low charge separation efficiency limits the photocatalytic performance. In the present work, in situ doping of flower like Bi2WO6 microstructure (∼6–8 μm) by metal (Mo, Fe, Zn) may improve the absorption and charge transfer efficiency. The metal doping effectively reduces the bandgap of Bi2WO6 which in turn enhances light absorption in the visible region. Notably, photoelectrochemical water splitting highly improved after metal doping, for example, Mo doping showed highest photocurrent density which is fifty-seven times higher than bare Bi2WO6. The band structure of Bi2WO6 before and after doping has been investigated on the basis of valence band XPS and Mott-Schottky analysis to understand the effect of doping in optoelectronic properties. The enhanced activity may originate due to presence of additional electronic states via doping, lower ionization potential, work function energy and enhanced number of charge carriers at the electrode-electrolyte interface during water splitting.

Silicone rubber composite reinforced by bismuth tungsten oxide as an effective gamma ray protective materials

The workers’ continual exposure to nuclear radiation makes it indispensable to invent and form lightweight materials as flexible radiation shields. So, in this article, silicone rubber SR inlaid with varying filler ratios of bismuth tungsten oxide Bi2(WO4)3 was produced. Mechanical properties, hardness, tensile strength, tensile modulus, and elongation at break, of the SR/Bi2(WO4)3 composites were studied as a function of filler concentration and irradiation dose. The Bi2(WO4)3 filler enhanced these properties. On the other hand, with augmentation of irradiation dose, hardness of the SR/Bi2(WO4)3 composites increased and the other mechanical properties decreased. Under accurate geometry conditions, the gamma ray attenuation coefficients of the SR/Bi2(WO4)3 composites were studied at the energies 661.66, 1173.24, and 1332.5 keV. The attenuation parameters, linear attenuation coefficients mu, experimental mass attenuation coefficients {sigma }_{exp.}, and half value layer HVL results revealed that the attenuation ability of the composite was enhanced with the increase of Bi2(WO4)3 concentration. The results of {sigma }_{exp.} were confirmed through their congruence with the theoretical calculations of mass attenuation coefficients {sigma }_{theo.} Considering the merits of lightweight, high mechanical properties, superior attenuation ability, and appropriate irradiation resistance, the produced SR/Bi2(WO4)3 composite is suitable as durable and flexible gamma ray shields such as anti-radiation coats, gloves, shoes.

Electrochemical Detection of Nitrite Using an Asymmetrically Substituted Cobalt Phthalocyanine Conjugated to Metal Tungstate Nanoparticles

AbstractThis paper explores the synthesis and characterisation of an asymmetrical Co phthalocyanine (CoPc), and its covalent linking to two tungsten nanoparticles: bismuth tungsten oxide (Bi2WO6) and nickel tungsten oxide (NiWO4). The nanoparticles were also mixed with the CoPc. The CoPc, nanoparticles and their respective conjugates were used as electrocatalysts in the electrochemical detection of nitrite. The electrocatalysts studied in this work had sensitivities ranging from 3–133 μA/mM while the limits of detection (LoDs) ranged between 0.063 μM and 1.7 μM. Bi2WO6 and its conjugate exhibited better LoD than corresponding NiWO4 and conjugate.

Enhanced solar-light-driven photocatalytic and photoelectrochemical properties of zinc tungsten oxide nanorods anchored on bismuth tungsten oxide nanoflakes

At present, sustainable water supply and energy generation are the most important challenges faced by humankind globally. Thus, it is crucial to progress ecological techniques for sustainable removal of organic pollutants from wastewater and generation of hydrogen as an alternative to fossil fuels. In this study, zinc tungsten oxide (ZnWO4) nanorods, bismuth tungsten oxide (Bi2WO6) nanoflakes, and Bi2WO6/ZnWO4 (BO–ZO) nanocomposites were prepared via a simple hydrothermal approach. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, diffuse reflectance spectroscopy, and electrochemical analyses were conducted to confirm the formation of the BO–ZO heterostructure. The structural and morphological analyses revealed that the ZnWO4 nanorods were moderately dispersed on the Bi2WO6 nanoflakes. The bandgap tuning of BO–ZO nanocomposite confirmed the establishment of the heterostructure with band bending properties. The BO–ZO nanocomposite could degrade 99.52% of methylene blue (MB) within 60 min upon solar-light illumination. The photoelectrochemical (PEC) measurement results showed that the BO–ZO nanocomposite showed low charge-transfer resistance and high photocurrent response with good stability. The BO–ZO photoanode showed a low charge-transfer resistance of 35.33 Ω and high photocurrent density of 0.1779 mA/cm2 in comparison with Ag/AgCl in a 0.1 M Na2SO3 electrolyte under solar-light illumination. The MB photocatalytic degradation and PEC water oxidation mechanisms of the nanocomposite were investigated.

Direct observation of oxygen-vacancy formation and structural changes in Bi2WO6 nanoflakes induced by electron irradiation.

The prominent role of oxygen vacancies in the photocatalytic performance of bismuth tungsten oxides is well recognized, while the underlying formation mechanisms remain poorly understood. Here, we use the transmission electron microscopy to investigate the formation of oxygen vacancies and the structural evolution of Bi2WO6 under in situ electron irradiation. Our experimental results reveal that under 200 keV electron irradiation, the breaking of relatively weak Bi–O bonds leads to the formation of oxygen vacancies in Bi2WO6. With prolonged electron irradiation, the reduced Bi cations tend to form Bi clusters on the nanoflake surfaces, and the oxygen atoms are released from the nanoflakes, while the W–O networks reconstruct to form WO3. A possible mechanism that accounts for the observed processes of Bi cluster formation and oxygen release under energetic electron irradiation is also discussed.

Synthesis and electrochemical performance of bismuth tungsten oxides with different composition and morphology

A series of bismuth tungsten oxides, Bi2WO6, Bi3.84W0.16O6.24, Bi2WO6/WO3(H2O)0.33 and Bi2W2O9 have been synthesized with different morphologies. Their electrochemical performance as Li-ion battery anodes has been found to be strongly dependent on the composition and morphology. Among the obtained materials, Bi2WO6/WO3(H2O)0.33 exhibits the highest capacity and best cycling stability with a reversible discharge capacity of 391 mAh g−1 at the end of 100 cycles at 50 mA g−1. Bi2WO6 nanosheets possess more stable cycling performance than Bi3.84W0.16O6.24 nanoparticles and Bi2W2O9 block. For Bi2WO6 nanosheets, the thinner the sheets, the better the electrochemical cyclic stability.

Radiation protective characteristics of some selected tungstates

Abstract The mass attenuation coefficients (μ/ρ) of calcium tungstate, ammonium tungsten oxide, bismuth tungsten oxide, lithium tungstate, cadmium tungstate, magnesium tungstate, strontium tungsten oxide and sodium dodecatungstophosphate hydrate were measured at 14 photon energies in the energy range of 81–1333 keV using 22Na, 54Mn, 57Co, 60Co, 133Ba and 137Cs radioactive sources. The measured μ/ρ values were compared with those obtained from WinXCOM program and the differences between the experimental and theoretical values were very small. The bismuth tungsten oxide has the highest μ/ρ among the present samples in the studied energy region. From the μ/ρ values, we calculated the half value layer, tenth value layer and mean free path, and the results showed that ammonium tungsten oxide (which has the lowest density) and bismuth tungsten oxide (which has the highest density) possess the highest and lowest values of these three parameters, respectively. Additionally, from the incident and transmitted photon intensities, we calculated the radiation protection efficiency (RPE). The bismuth tungsten oxide was found to have RPE 98.53 % at 81 keV, which has the maximum value among the present samples and this suggested that bismuth tungsten oxide is the best to be chosen as the γ radiation shielding material candidate among the selected samples.

Oxygen deficiencies and metallic Bi-mediated photocatalytic activity of bismuth tungsten oxides

Herein, the metallic Bi-modified Bi3.84W0.16O6.24 hybrid with oxygen deficiencies is synthesized via a facile one-pot solvothermal reduction method. The synergistic effect of the deposited Bi metal and oxygen deficiencies results in the effective separation of the photogenerated carriers in Bi3.84W0.16O6.24 and the enhancement of the photo-response properties. As a result, Bi/Bi3.84W0.16O6.24 exhibited outstanding visible-light photocatalytic activities and sustained cycling performance. Under visible-light irradiation, nearly 96% of RhB is degraded after 15 min. Radical trapping experiments indicate that h+ and •OH are the main active species. This study provides an attractive avenue to design and fabricate highly efficient Bi-based photocatalysts, which possess a high application value in the field of environmental remediation, especially for wastewater purification.

Remarkable enhancement on photoelectrochemical water splitting derived from well-crystallized Bi2WO6 and Co(OH)x with tunable oxidation state

Bismuth tungsten oxide (Bi2WO6) has been extensively utilized as a promising photocatalyst for water splitting and contaminant degradation. However, its applications as the photoanodes for photoelectrochemical (PEC) water splitting have been greatly restricted owing to the intrinsically poor charge transport and sluggish oxygen evolution reaction (OER) kinetics. Herein, we demonstrated that the PEC performances of Bi2WO6 photoanodes could be remarkably enhanced by the well-crystallized construction, which could achieve the favorable conductivity for the bulk charge transport. More importantly, amorphous Co(OH)x nanofilms with optimized oxidation state were decorated on Bi2WO6 photoanode by a facile impregnation method, an unprecedented photocurrent density of 0.94 mA/cm2 and a high surface charge separation efficiency of 98% at 1.23 VRHE has been achieved, more than 58-fold enhanced OER activity compared with traditional Bi2WO6 sample. These results demonstrated that the appropriate crystal construction and cocatalyst decoration with tunable oxidation state could serve as an effective strategy toward developing high-efficiency PEC water splitting systems.

Facile Fabrication of Nanoporous Bi2WO6 Photoanodes for Efficient Solar Water Splitting

AbstractNanoporous bismuth tungsten oxide (Bi2WO6) photoanodes are synthesized by using a facile drop‐casting strategy for one‐step fabrication. The Bi2WO6 photoanode exhibits significantly improved solar photo‐electrochemical capability for water oxidation. The photocurrent density is nearly 10 times higher than the traditional particle photoanodes. In addition, synchronous illumination X‐ray photoelectron spectroscopy (SIXPS) was employed to directly identify the charge separation and electron transfer in the nanoporous Bi2WO6 photoanodes, which clearly reveals that the electrons transfer from the Bi and W atomic sites to the O sites. These demonstrations provide further new insights into the origin of high efficiency in nanoporous photoanodes, which may be promising for the rational construction of solar conversion and storage devices.

Creation of bismuth-tungsten oxide nanoclusters using lacunary polyoxometalates.

Three types of heterometallic bismuth-tungsten oxide nanoclusters were successfully synthesized by the reactions of lacunary silicotungstates (trivacant [A-α-SiW9O34]10- and divacant [γ-SiW10O36]8-) and Bi3+ in organic solvents. Lone pairs on Bi3+ acted as structure-directing groups in these nanoclusters.

Sol–gel synthesis and enhanced photocatalytic activity of doped bismuth tungsten oxide composite

Pristine Bi2WO6 and Bi2WO6/Bi14W2O27 photocatalysts were synthesized by sol–gel method using Co(II) cation as dopant. The influence of Co dopant to the formation of Bi2WO6/Bi14W2O27 heterostructure composite was discussed. The photocatalytic activities of as-prepared samples were evaluated sufficiently by using rhodamine B as target organic pollutants under visible light. The as-prepared Bi2WO6/Bi14W2O27 heterostructure achieved enhanced optical absorption in the visible-light region, and exhibited much higher photocatalytic activities than that of pristine Bi2WO6. The optimum Bi/Co molar ratio and calcining temperature were also explored. The enhanced activities were attributed to the formation of heterostructure in suppressing the recombination of photo-generated carriers. The Co dopant species would participate to reduce the charge carrier recombination by acting as trapping sites for photogenerated charges. A possible photocatalytic mechanism over Bi2WO6/Bi14W2O27 heterostructure was proposed.

Ultrathin {001}‐Oriented Bismuth Tungsten Oxide Nanosheets as Highly Efficient Photocatalysts

Orient express: Ultrathin nanosheets of bismuth tungsten oxide (Bi2WO6) with {001}-orientation are prepared by a pH-controlled synthesis. The sheets have aspect ratios as large as 30:1, and offer superior adsorption and hole oxidation properties as well as prolonged charge-carrier lifetimes.The ultrathin structures show enhanced photocatalytic activity towards organic contaminant degradation and water oxidation.

The preparation and characterization of composite bismuth tungsten oxide with enhanced visible light photocatalytic activity

A composite photocatalyst (Bi3.84W0.16O6.24–Bi2WO6) containing Bi, W and O elements was prepared by a facile hydrothermal method. Various characterization methods such as X-ray powder diffraction, UV-vis diffuse reflectance spectroscopy, scanning electron microscopy and transmission electron microscopy were employed to investigate the structure and optical properties. The activities of the samples were evaluated by the photocatalytic degradation of methylene blue under visible light irradiation. The results showed that when the pH of the precursor solution is 12.3, and a hydrothermal treatment at 140 °C for 20 h was used, the prepared sample shows the mixed phases of Bi3.84W0.16O6.24 and Bi2WO6. The Bi3.84W0.16O6.24–Bi2WO6 composite exhibited an enhanced photocatalytic activity compared with single Bi2WO6 or Bi3.84W0.16O6.24. The rate constant of Bi3.84W0.16O6.24–Bi2WO6 is about 5 times that of Bi2WO6. It is proposed that the increased photocatalytic activity may be attributed to the formation of a heterojunction between Bi3.84W0.16O6.24 and Bi2WO6, which suppresses the recombination of photoexcited electron–hole pairs.

MO‐F‐BRA‐01: Polymer Composite‐Based Shielding of Diagnostic X‐Rays

Purpose: To develop lead‐free polymer composites for shielding diagnostic x‐rays employed in interventional radiological (IVR) procedures. Methods: Polydimethylsiloxane (PDMS) composites of different weight percentages (wt%) were developed from the following high atomic‐number (Z) materials: (i) bismuth tungsten oxide (BTO), (ii) bismuth oxide (BO). X‐ray attenuation tests were performed using the diagnostic x‐ray machine (Ysio, Siemens) for energies from 40 kV to 150 kV. Each sample was placed at a distance of about 20 cm from the ion chamber (x‐ray detector) connected to an electrometer (Capintec). For each experiment, the distance between the ion chamber and the floor was at least 50 cm in order to avoid backscattered radiation. All measurements were normalized with reference to the readings obtained with no sample between the source and the detector. Results: Analysis of percentage attenuation versus x‐ray energy indicates that the attenuation capability of all the composites decreases with increasing energy. PDMS composite with 36.36 wt% of BTO shows an overall increase of 18.3% and 50% attenuation relative (absolute differential between the % attenuation) to that achieved by 18.18 wt% of BTO and pure PDMS (no BTO) respectively. For both BTO and BO composites, doubling of the sample thickness showed a relative increase of 16.4% and 12.3% attenuation respectively at 60 kV, the energy typically employed in IVR. Conclusions: Protective aprons made of high Z metals such as lead or composites of lead are heavy and also toxic due to the presence of lead. In this study, we have shown that light‐weight, conformable, cost effective, and non‐toxic polymer composites of high Z materials can be designed to effectively attenuate diagnostic x‐rays. A composite sample with 60.6 wt% of BO (thickness of 2.67 mm) has shown the best result, by far, with 92.5% attenuation of the beam at 60 kV.

Characterization of photocatalyst Bi3.84W0.16O6.24 and its photodegradation on bisphenol A under simulated solar light irradiation

Bismuth tungsten oxide Bi3.84W0.16O6.24 was prepared by hydrothermal process under pH 12. Both the hydrothermal reaction temperature and time affected the crystallinity and morphology of the prepared catalysts, which in turn affected their degradation efficiency. Although all the prepared catalysts showed adsorption in the visible region around 450nm, the catalyst synthesized at 140°C for 20h displayed the highest photocatalytic degradation capacity to bisphenol A (BPA) under simulated solar light irradiation due to the combination of its good crystallinity and perfect disk morphology. In the photodegradation system of BPA and Bi3.84W0.16O6.24, no OH was detected by electron spin resonance analysis, suggesting that direct hole is predominant in the degradation of BPA by Bi3.84W0.16O6.24. It displayed high photocatalytic degradation and mineralization capacities to BPA as compared with P25 TiO2 under simulated solar light irradiation. The analytical results of both LC–MS and GC–MS demonstrated that no hydroxylated intermediates were formed. A simple and direct photodegradation pathway of BPA by Bi3.84W0.16O6.24 was proposed by the analysis of intermediates.

Quasi‐One‐Dimensional Bismuth Tungsten Oxide Nanostructures Templated by Cotton Fibers

Using cotton fibers as templates, quasi‐one‐dimensional bismuth tungsten oxide (Bi2WO6) nanostructures were successfully synthesized using a combination of solution dipping and calcinating at 500°C. The Bi2WO6 nanostructures were characterized using X‐ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and N2 adsorption and desorption measurements. Their optical property was studied using a UV‐vis spectrum, and the photocatalytic activity was investigated by degrading the organic compound. It was found that the Bi2WO6 nanostructures maintained the quasi‐one‐dimensional morphology of the cotton fibers and were composed of nanoparticles about 40 nm in size. The mechanism of formation of the quasi‐one‐dimensional Bi2WO6 nanostructures was also discussed. Moreover, the quasi‐one‐dimensional Bi2WO6 nanostructures exhibited good visible light absorption and could efficiently decompose rhodamine B under visible light irradiation.