Showing papers on "Bismuth published in 2017"

Rational design on 3D hierarchical bismuth oxyiodides via in situ self-template phase transformation and phase-junction construction for optimizing photocatalysis against diverse contaminants

Abstract: Design of three-dimensional (3D) hierarchical architectures and nano-phase-junctions are of huge significance for semiconductor photocatalysis. Herein, we report the fabrication of a series of 3D hierarchical bismuth oxyiodides via in situ phase transformation and phase-junction construction utilizing BiOI microspheres as self-sacrificed template through a facile calcination strategy. The multiform bismuth oxyiodides obtained at different temperatures include hierarchical BiOI, Bi4O5I2, Bi4O5I2-Bi5O7I phase-junction and Bi5O7I. These bismuth oxyiodides exhibit very distinct microstructure and band structure, and their photoabsorption was orderly tuned from 700 to 400 nm, rendering the adjustable oxidation and reduction ability of band energy levels. The photocatalytic activity of the bismuth oxyiodide series is systematically assessed by degradation of diverse antibiotic and contaminants, such as tetracycline hydrochloride, bisphenol A (BPA) and azo dye Rhodamine B (RhB). It disclosed that they present discrepant photocatalytic performance with activity order of Bi4O5I2-Bi5O7I > Bi4O5I2 > Bi5O7I > BiOI, which is closely associated with the charge separation efficiency, band structure and surface area. Additionally, the photocatalytic mechanism and degradation pathway are also surveyed. The study may furnish new insights into development of novel 3D hierarchical architectures and nano-phase-junctions for heterogeneous photocatalysis.

Bismuth Oxychalcogenides: A New Class of Ferroelectric/Ferroelastic Materials with Ultra High Mobility

Abstract: Atomically thin Bi2O2Se has been recently synthesized, and it possesses ultrahigh mobility (Nat. Nanotechnol. 2017, 12, 530; Nano Lett. 2017, 17, 3021). Herein, we show first-principles evidence that Bi2O2Se and a related class of bismuth oxychalcogenides, such as Bi2O2S and Bi2O2Te, not only are novel semiconductors with ultrahigh mobility but also possess previously unreported ferroelectricity/ferroelasticity. Such a unique combination of semiconducting with ferroelectric/ferroelastic properties enables bismuth oxychalcogenides to potentially meet a great challenge, that is, integration of room-temperature functional nonvolatile memories into future nanocircuits. Specifically, we predict that bulk Bi2O2S is both ferroelastic and antiferroelectric and that a thin film with odd number of layers can even be multiferroic with nonzero in-plane polarization, and this polarization can be switchable via ferroelasticity. Moreover, Bi2O2Te possesses intrinsic out-of-plane ferroelectricity, while Bi2O2Se possesses...

Synthesis of hierarchical bismuth-rich Bi4O5BrxI2-x solid solutions for enhanced photocatalytic activities of CO2 conversion and Cr(VI) reduction under visible light

Abstract: Bismuth oxyhalides (BiOX, X = Br, I) photocatalysts are rarely applied for photocatalytic reduction reaction withthe photo-induced electron, as this is impeded by their low conduction band. As a widely used approach for enhancing the photocatalytic reduction activity, bismuth-rich strategy results the bismuth content of BiOX photocatalysts increasing. In this paper, a solid solutions of bismuth-rich Bi4O5BrxI2-x were prepared applying the molecular precursor method. Bi4O5BrxI2-x were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), element mapping, Brunauer–Emmett–Teller surface analysis (BET), UV–vis diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). The obtained photocatalytic data showed that Bi4O5BrxI2-x solid solutions had higher photocatalytic activities than Bi4O5Br2 and Bi4O5I2. At an optimal ratio of x = 1, the Bi4O5BrI photocatalyst showed the highest photocatalytic reduction activity for CO2 conversion (22.85 μmol h−1 g−1 CO generation, AQE was 0.372 at 400 nm) and Cr(VI) removal (88%). CO2 adsorption data and CO2 temperature programmed desorption (CO2-TPD) revealed that Bi4O5BrI exhibited the highest chemical adsorption ability of CO2 molecules Photocurrent and electrochemical impedance (EIS) spectroscopy demonstrated the enhanced photo-induced carrier separation efficiency of Bi4O5BrI. These mechanistic studies suggest that Bi4O5BrxI2-x solid solutions are excellent photocatalysts for solar fuel generation and environmental remediation.

Construction of Compact Methylammonium Bismuth Iodide Film Promoting Lead-Free Inverted Planar Heterojunction Organohalide Solar Cells with Open-Circuit Voltage over 0.8 V

Abstract: A bismuth-based organohalide material, methylammonium bismuth iodide (MA3Bi2I9), has been recently explored as an efficient lead-free light absorber in photovoltaic applications. However, the poor surface morphology of the MA3Bi2I9 film fabricated via conventional one-step spin-coating methods has limited the performance of the device. In this work, a smooth, uniform, and compact MA3Bi2I9 thin film was realized by a novel two-step evaporation–spin-coating film fabrication strategy for the first time. Taking advantage of the superior MA3Bi2I9 thin film, the best-performing inverted planar heterojuncion photovoltaic device exhibited a power conversion efficiency of 0.39% with open-circuit voltage as high as 0.83 V, which demonstrated the lowest loss-in-potential to date in MA3Bi2I9-based solar cells. Moreover, the facile film fabrication strategy utilized in this work paves the way for high reproducibility of lead-free organohalide films and devices.

Evidence for bulk superconductivity in pure bismuth single crystals at ambient pressure

Abstract: At ambient pressure, bulk rhombohedral bismuth is a semimetal that remains in the normal state down to at least 10 millikelvin. Superconductivity in bulk bismuth is thought to be unlikely because of the extremely low carrier density. We observed bulk superconductivity in pure bismuth single crystals below 0.53 millikelvin at ambient pressure, with an estimated critical magnetic field of 5.2 microteslas at 0 kelvin. Superconductivity in bismuth cannot be explained by the conventional Bardeen-Cooper-Schrieffer theory because its adiabatic approximation does not hold true for bismuth. Future theoretical work will be needed to understand superconductivity in the nonadiabatic limit in systems with low carrier densities and unusual band structures, such as bismuth.

Valence Band Engineering of Layered Bismuth Oxyhalides toward Stable Visible-Light Water Splitting: Madelung Site Potential Analysis

Abstract: A layered oxychloride Bi4NbO8Cl is a visible-light responsive catalyst for water splitting, with its remarkable stability ascribed to the highly dispersive O-2p orbitals in the valence band, the origin of which, however, remains unclear. Here, we systematically investigate four series of layered bismuth oxyhalides, BiOX (X = Cl, Br, I), Bi4NbO8X (X = Cl, Br), Bi2GdO4X (X = Cl, Br), and SrBiO2X (X = Cl, Br, I), and found that Madelung site potentials of anions capture essential features of the valence band structures of these materials. The oxide anion in fluorite-like blocks (e.g., [Bi2O2] slab in Bi4NbO8Cl) is responsible for the upward shift of the valence band, and the degree of electrostatic destabilization changes depending on building layers and their stacking sequence. This study suggests that the Madelung analysis enables a prediction and design of the valence band structures of bismuth and other layered oxyhalides and is applicable even to a compound where DFT calculation is difficult to perform.

Recent Advances in Bismuth-Based Nanomaterials for Photoelectrochemical Water Splitting

Abstract: In recent years, bismuth-based nanomaterials have drawn considerable interest as potential candidates for photoelectrochemical (PEC) water splitting owing to their narrow band gaps, nontoxicity, and low costs. The unique electronic structure of bismuth-based materials with a well-dispersed valence band comprising Bi 6s and O 2p orbitals offers a suitable band gap to harvest visible light. This Review presents significant advancements in exploiting bismuth-based nanomaterials for solar water splitting. An overview of the different strategies employed and the new ideas adopted to improve the PEC performance of bismuth-based nanomaterials are discussed. Morphology control, the construction of heterojunctions, doping, and co-catalyst loading are several approaches that are implemented to improve the efficiency of solar water splitting. Key issues are identified and guidelines are suggested to rationalize the design of efficient bismuth-based materials for sunlight-driven water splitting.

Poor Photovoltaic Performance of Cs3Bi2I9: An Insight through First-Principles Calculations

Abstract: Bismuth-based halide perovskite derivatives have now attracted huge attention for photovoltaic (PV) applications after the unparalleled success of lead-based halide perovskites. However, the performances of PV devices based on these compounds are poor, despite theoretical predictions. In this Article, we have investigated the electronic structure and defect formation energies of Cs3Bi2I9 using density functional theory (DFT) calculations. The calculated electronic bandstructure indicates an indirect bandgap and high carrier effective masses. Our calculations reveal a large stability region for this compound; however, deep level defects are quite prominent. Even the varying chemical potentials from the stoichiometric region do not eliminate the presence of deep defects, ultimately limiting photovoltaic efficiencies.

A binder-free wet chemical synthesis approach to decorate nanoflowers of bismuth oxide on Ni-foam for fabricating laboratory scale potential pencil-type asymmetric supercapacitor device.

Abstract: The present study involves the synthesis of a bismuth oxide (Bi2O3) electrode consisting of an arranged nano-platelets for evolving a flower-type surface appearance on nickel-foam (Bi2O3-Ni-F) by a simple, inexpensive, binder-free and one-step chemical bath deposition (CBD) method, popularly known as a wet chemical method. The as-prepared Bi2O3 on Ni-foam, as an electrode material, demonstrates 557 F g-1 specific capacitance (SC, at 1 mA cm-2), of which 85% is retained even after 2000 cycles. With specific power density of 500 kW kg-1, the Bi2O3-Ni-F electrode documents a specific energy density of 80 Wh kg-1. Furthermore, a portable asymmetric supercapacitor device, i.e. a pencil-type cell consisting of Bi2O3-Ni-F as an anode and graphite as a cathode in 6 M KOH aqueous electrolyte solution, confirms 11 Wh kg-1 and 720 kW kg-1 specific energy and specific power densities, respectively. An easy and a simple synthesis approach for manufacturing a portable laboratory scale pencil-type supercapacitor device is a major outcome of this study, which can also be applied for ternary and quaternary metal oxides for recording an enhanced performance. In addition, we presented a demonstration of lighting a light emitting diode (LED) using a home-made pencil-type supercapacitor device which, finally, has confirmed the scaling and technical potentiality of Bi2O3-Ni-F in energy storage devices.

Electrodeposition of Isolated Platinum Atoms and Clusters on Bismuth—Characterization and Electrocatalysis

Abstract: We describe a method for the electrodeposition of an isolated single Pt atom or small cluster, up to 9 atoms, on a bismuth ultramicroelectrode (UME). This deposition was immediately followed by electrochemical characterization via the hydrogen evolution reaction (HER) that occurs readily on the electrodeposited Pt but not on Bi. The observed voltammetric current plateau, even for a single atom, which behaves as an electrode, allows the estimation of deposit size. Pt was plated from solutions of femtomolar PtCl62–, which allowed precise control of the arrival of ions and thus the plating rate on the Bi UME, to one ion every few seconds. This allowed the atom-by-atom fabrication of isolated platinum deposits, ranging from single atoms to 9-atom clusters. The limiting currents in voltammetry gave the size and number of atoms of the clusters. Given the stochasticity of the plating process, we show that the number of atoms plated over a given time (10 and 20 s) follows a Poisson distribution. Taking the potent...

High precision hyperfine measurements in Bismuth challenge bound-state strong-field QED.

Abstract: Electrons bound in highly charged heavy ions such as hydrogen-like bismuth 209Bi82+ experience electromagnetic fields that are a million times stronger than in light atoms Measuring the wavelength of light emitted and absorbed by these ions is therefore a sensitive testing ground for quantum electrodynamical (QED) effects and especially the electron–nucleus interaction under such extreme conditions However, insufficient knowledge of the nuclear structure has prevented a rigorous test of strong-field QED Here we present a measurement of the so-called specific difference between the hyperfine splittings in hydrogen-like and lithium-like bismuth 209Bi82+,80+ with a precision that is improved by more than an order of magnitude Even though this quantity is believed to be largely insensitive to nuclear structure and therefore the most decisive test of QED in the strong magnetic field regime, we find a 7-σ discrepancy compared with the theoretical prediction Precision measurements provide a sensitive test of fundamental constants and their uncertainties Here the authors precisely measure the hyperfine structure splitting in bismuth ions, and report significant discrepancy with the theoretical prediction of quantum electrodynamics

AgBiI4 as a Lead-Free Solar Absorber with Potential Application in Photovoltaics

Abstract: AgBiI4 powder, crystals, and polycrystalline films were synthesized by sealed tube solid state reactions, chemical vapor transport (CVT), and solution processing, respectively, and their structural, optical and electronic properties are reported. The structure of AgBiI4 is based unambiguously upon a cubic close packed iodide sublattice, but it presents an unusual crystallographic problem: we show that the reported structure, a cubic defect-spinel, cannot be distinguished from a metrically cubic layered structure analogous to CdCl2 using either powder or single crystal X-ray crystallography. In addition, we demonstrate the existence a noncubic CdCl2-type polymorph by isolation of nontwinned single crystals. The indirect optical band gap of AgBiI4 is measured to be 1.63(1) eV, comparable to the indirect band gap of 1.69(1) eV measured for BiI3 and smaller than that reported for other bismuth halides, suggesting that structures with a close-packed iodide sublattice may give narrower band gaps than those with...

Ultrathin Cs3Bi2I9 Nanosheets as an Electronic Memory Material for Flexible Memristors

Abstract: Methylammonium lead halide (MAPbX3) perovskites have attracted tremendous attention due to their remarkable performances in solar cells, light-emitting diodes, photodetectors, lasers, and electronic memories. However, the issue of toxicity still greatly restricts their further large-scale applications. Here, this study presents a series of nontoxic and stable methylammonium (or cesium) bismuth halides A3Bi2I9 (A = Cs+ and MA+) nanosheets for using in flexible memories. The ultrathin A3Bi2I9 nanosheets can be easily prepared by a dissolution–recrystallization process. This is the first attempt that reports the ultrathin bismuth halides and explores their potential applications in flexible electronic devices. The flexible memristors based on such ultrathin Cs3Bi2I9 nanosheets exhibit typical bipolar resistive switching behavior and remarkable characteristics such as high Ron/Roff ratio (≈103), very low working voltage (≈0.3 V), and long data retention (>104 s), as well as excellent endurability, reproducibility, environmental stability, and flexibility. With such appealing characteristics, the cesium bismuth halide memristors have great potential for practical applications. The results of this work demonstrate that cesium bismuth halide ultrathin nanosheets will be promising candidates for more emerging applications in electronics and optoelectronics such as memories, photodetectors, photovoltaics, and light-emitting diodes.

Photovoltaic enhancement of bismuth halide hybrid perovskite by N-methyl pyrrolidone-assisted morphology conversion

Abstract: Low toxicity and highly stable methylammonium bismuth iodide (MBI) ((CH3NH3)3Bi2I9) as a solution-processable photovoltaic absorber produces hexagonal non-uniform morphology leading to poor interfacial contacts with the electron and hole transporting layers. Herein, we tuned the morphology of MBI perovskite by bringing in a small amount of N-methyl-2-pyrrolidone (NMP) as a morphology controller into the MBI–DMF solution. The incorporation of various concentrations of NMP into the precursor solution was found to control the rate of crystallization. An optimal low concentration of 2.5% NMP added to the MBI–DMF precursor solution showed a 50% enhancement in short-circuit current (Jsc). The device showed power conversion efficiencies up to 0.31% with high reproducibility. Moreover, the devices were quite stable when exposed to an ambient atmosphere (relative humidity of 50–60%) for 30 days.

Double Perovskite Cs2BBiX6 (B = Ag, Cu; X = Br, Cl)/TiO2 Heterojunction: An Efficient Pb-Free Perovskite Interface for Charge Extraction

Abstract: Motivated from the recent success in synthesizing bismuth-based double perovskites (J. Am. Chem. Soc. 2016, 138, 2138–2141), we perform a comprehensive study of interfacial properties of bismuth-based double perovskites Cs2AgBiX6 (X = Br, Cl) and TiO2 interfaces. The bismuth-based double perovskites possess desirable electronic and optical properties as excellent light absorber and thus may serve as lead-free alternatives to the organic–inorganic perovskites. On the basis of density functional theory computation, we systematically study the Cs2BBiX6 (B = Ag, Cu; X = Br, Cl)/TiO2 interfaces and analyze the trend of charge transfer across the interfaces. We find that the Cs4X4 (X = Br and Cl)/TiO2-mediated interfaces are prospective interfaces for charge extraction and separation due largely to the withdrawn trap states for the TiO2 part when in contact with the Cs4X4 termination. Moreover, the ionic interaction and charge redistribution across the specific interfaces can lead to the appropriate band alignm...