Oxide Bronzes Research Articles

Mixed metal oxide bronzes as catalysts for the gas-phase aerobic transformation of glycerol to acrylic acid: Single or double catalytic bed approaches

Metal-doped hexagonal tungsten oxide bronzes (h-WVOx and h-WNbOx) and metal-doped orthorhombic molybdenum oxide bronzes-M1 type (MoVOx, MoVTeOx and MoVTeNbOx) have been synthesized hydrothermally and heat-treated at 400, 550 or 600 °C in N2. The catalysts were characterized by several techniques and tested in the one-pot aerobic transformation of glycerol at 350 °C. From all of them, h-WNbOx resulted as the most selective to acrolein (80 % yield), whereas both h-WVOx and MoVTeNbOx were more effective to acrylic acid (with a yield lower than 25 %). Subsequently, a double-bed reactor comparative study was conducted, with h-WNbOx acting as the first catalytic bed. In this case, the yield to acrylic acid decreased as follows: MoVTeNbOx > MoVTeOx > MoVOx >h-WVOx. IR spectroscopy of acrolein adsorbed on these catalysts allows to explain the catalytic performance of these catalysts.

In-situ growth of Cs0·33WO3@ATO composite material with enhanced NIR shielding rate for energy-saving coating

Driven by the global goal of “carbon neutrality”, energy conservation, emission reduction and low-carbon development have become important research directions. Transparent thermal insulation materials can effectively shield near-infrared radiation while maintaining high visible light transmittance, making them widely applicable in building energy conservation. In this paper, antimony-doped tin oxide (ATO) and cesium tungsten bronze (CsxWO3, or CWO) are chosen to be composited in order to solve the problems of the poor shielding effect of ATO for short-wavelength near-infrared (NIR) light and the unsatisfactory shielding effect of CWO for long-wavelength NIR light. Therefore, in this study, we employed a one-step hydrothermal method to form a novel CWO@ATO core-shell structure to combine the advantages of both ATO and CWO. By adjusting the composite ratio of ATO and CWO, both the physical and electronic stucutres are effectively tuned to promote the optical modulation in a broad bandwidth. Enventually, the core-shell structured composite exhibit an excellent near-infrared blocking property, surpassing the pure ATO by 27.8 % in the wavelength region of 780∼1500 nm while improving by 14.9 % compared to CWO in the long wavelength between 1500 and 2500 nm. Furthermore, the prepared CWO@ATO core-shell structure repesents near-infrared shielding rate as high as 93.1 % in the full NIR spectrum, and possesses an overall thermal insulation coefficiency (THI) of 9.33 in the full range from 780 nm to 2500 nm, which is substantially larger than that of pure ATO and CWO by a factor of 2.37 and 3.05, respectively. This core-shell structure engineering realizes the utilization of complementary advantages of ATO and Cs0·33WO3 materials, providing a new method to improve the near-infrared performance of energy-saving glass coating, and having broad application prospects in the field of low-carbon buildings.

Reversible Intercalation of Protons in Tungsten Oxide Films for Multi-Transduction Sensor Applications

Tungsten oxide films under electrochemical bias, can form tungsten oxide bronzes (MxWO3 with M being small cations such as H+ or Li+) featuring high electronic conductivity and change in coloration to deep blue1. This doping process occurs through the reduction of W6+, as described by the following equation:WO3 + x H+ + xe- -> HxWO3The bronze phase can also be formed through exposure of tungsten oxide to H2 at high temperatures (> 200 oC) or in presence of catalysts2, as described by the following equation:WO3 + x/2 H2 -> HxWO3 Because of the significant changes in both optical and electrical proprieties of the films, electrochemical control of proton doping can be used as a strategy for the development of ion-gated transistors3,4, hydrogen sensors and smart windows5.In this work, we report the use of thin films prepared by sol-gel synthesis using polyperoxotungstic acid (PPTA) as a precursor. We used three different types of substrates (conductive transparent fluorine-doped tin oxide (FTO) glass, Si/SiO2 patterned with Au source-drain electrodes and Interdigitated electrodes patterned on transparent glass) to study the changes of color and conductivity following the formation of the bronze in both electrochemical and dry environments. In electrochemical environment, we show that gating by ionic liquid in transistor configuration can be used to propose an iontronic sensor to detect H2 and H2O6. In dry environment, we show that simultaneous monitoring of visible light transmittance and electrical conductivity can be used a double transducer for H2 sensors6.1 M. S. Whittingham, in Solid State Ionics, 2004, vol. 168, pp. 255–263.2 C. C. Chan, W. C. Hsu, C. C. Chang and C. S. Hsu, Sensors and Actuators, B: Chemical, 2011, 157, 504–509.3 M. Barbosa, X. Meng, F. Soavi, C. Santato and M. O. Orlandi, J Mater Chem C Mater, 2018, 6, 1980–1987.4 G. V. de Oliveira Silva, A. Subramanian, X. Meng, S. Zhang, M. S. Barbosa, B. Baloukas, D. Chartrand, J. C. Gonzáles, M. O. Orlandi, F. Soavi, F. Cicoira and C. Santato, J Phys D Appl Phys,5 G. Cai, J. Wang and P. S. Lee, Acc Chem Res, 2016, 49, 1469–1476.6 M. S. Barbosa, R. A. da Silva, C. Santato and M. O. Orlandi, Journal of Vacuum Science & Technology A, 2022, 40, 013202.

Tungsten Oxide-Based Z-Scheme for Visible Light-Driven Hydrogen Production from Water Splitting.

The stoichiometric water splitting using a solar-driven Z-scheme approach is an emerging field of interest to address the increasing renewable energy demand and environmental concerns. So far, the reported Z-scheme must comprise two populations of photocatalysts. In the present work, only tungsten oxides are used to construct a robust Z-scheme system for complete visible-driven water splitting in both neutral and alkaline solutions, where sodium tungsten oxide bronze (Na0.56WO3-x) is used as a H2 evolution photocatalyst and two-dimensional (2D) tungsten trioxide (WO3) nanosheets as an O2 evolution photocatalyst. This system efficiently produces H2 (14 μmol h-1) and O2 (6.9 μmol h-1) at an ideal molar ratio of 2:1 in an aqueous solution driven by light, resulting in a remarkably high apparent quantum yield of 6.06% at 420 nm under neutral conditions. This exceptional selective H2 and O2 production is due to the preferential adsorption of iodide (I-) on Na0.56WO3-x and iodate (IO3-) on WO3, which is evidenced by both experiments and density functional theory calculation. The present liquid Z-scheme in the presence of efficient shuttle molecules promises a separated H2 and O2 evolution by applying a dual-bed particle suspension system, thus a safe photochemical process.

Effect of synthesis conditions on morphology, crystal structure and electrochemical properties of β-NaV6O15

Current–voltage characteristics of nanostructured vanadium oxide bronze β-NaV6O15 obtained from oxalate solutions by ultrasonic spray pyrolysis (USP) under various conditions were studied. The conditions of USP synthesis significantly affected the particle morphology, specific surface area, defect structure and oxidizing ability of the compound.

Garment buttons from a Hallstatt period tumulus

Abstract A Hallstatt period burial mound (tumulus) in Schandorf, Burgenland, Austria, was opened and archaeologically investigated in 2021. Not only numerous pottery fragments, but also some garment buttons were found, one of which was provided for metallographic examinations, aiming at identifying the method of manufacture: soldering, riveting, casting? Prior to the metallographic examinations, micro-computed tomography (μm CT) was carried out at a resolution of 5 μm. The Figures show that large areas are oxidized. It was, however, found that metallic portions still existed. The overall appearance suggests investment casting as the manufacturing method. Analytical measurements revealed that the material is tin bronze. Despite severe corrosion, the metallographic sections still exhibit a clearly recognizable cast structure. There are presumably two types of corrosion: first, high temperature corrosion, which resulted in the formation of bronze oxides in the grain boundary areas during the cremation, and, second, corrosion in an aqueous environment, during which malachite formed. So far, no comparable studies can be found in the literature.

Sodium ion intercalation in vanadium oxide promotes low-temperature NH3-SCR activity: Sodium vanadium bronzes (Na0.33V2O5) for NOx removal

NH3-SCR (selective catalytic reduction) is a key technique for converting harmful NOx to harmless N2 and H2O in exhaust gases. Herein, V2O5, Na0.33V2O5 and Na1.2V3O8 are synthesized by a simple chemical process (the oxalate method) as examples of Na-intercalated vanadium oxide (sodium vanadium oxide bronze) for low-temperature NH3-SCR less than 150 °C. Among them, Na0.33V2O5 shows 92% (dry) and 86% (in the presence of 10 vol% water) NO conversions at 150 °C. The reaction rate of Na0.33V2O5 is 6.1-times higher than that of V2O5, indicating that Na intercalation accelerates NH3-SCR cycles. Mechanistic analysis suggests that the reaction mechanism of Na0.33V2O5 is different from those of other V-based catalysts. Although it has been believed that alkali ions inhibit catalytic cycles of NH3-SCR, the results of this study suggest that alkali ions affect the structural, redox and adsorption properties of bulk V2O5, leading to an increase in NH3-SCR activity.

Optical hydrogen sensing by MoO3 films deposited by a facile flame synthesis method

Nanostructured MoO3 films were deposited on glass by an atmospheric solid-fed flame vapor deposition (SF-FVD) technique at different substrate temperatures (25 (SRT), 300 (S300) and 400 °C (S400)). FESEM showed web-like morphology for SRT and S300 and plate-like for S400. TEM revealed existing spherical at lower and 2D structures at higher temperatures. Monoclinic and orthorhombic phases were observed for SRT and S300/S400, respectively. With a sputter-deposited Pd film, MoO3 films turn dark blue after hydrogen exposure, for which localized surface plasmon resonance (LSPR) absorption bands have appeared in the NIR region. The LSPR showed a linear blue shift up to 35 nm with < 4% hydrogen concentration. Using a 640 nm LED light source, the capability at very low concentrations of hydrogen and different working temperatures (up to 200 °C) was investigated. Significant sensitivity was observed with a sigmoidal behavior toward hydrogen concentration (0.05–10%). Also, the repeatability and selectivity among interfering gases were desirable. Sample S300 at a working temperature of 150 °C showed the best sensing performance in coloration, reversibility and response time. Raman, XRD and FESEM were used that reveal structural and morphological degradation, where the partial formation of molybdenum oxide bronze (H0.93MoO3) was observed.

Small Changes, Big Impact: Tungsten Bronzes with Extremely Large Second Harmonic Generation Achieved by the Transition Metal Doping on the B‐Site

AbstractTwo novel transition metal‐doped tungsten bronze oxides, Pb2.15Li0.85Nb4.85Ti0.15O15 (PLNT) and Pb2.15Li0.55Nb4.85W0.15O15 (PLNW), are synthesized by high‐temperature solid‐state reactions. The Rietveld method using the high‐resolution synchrotron radiation indicates that PLNT and PLNW crystallize in the orthorhombic polar noncentrosymmetric space group, Pmn21 (no. 31). As a class of tungsten bronze oxide, PLNT and PLNW retain a unique rigid framework composed of d0 transition metal cation (Ti4+ or W6+)‐doped highly distorted NbO6 octahedra along with the subsequently generated Pb/LiO12 and PbO15 polyhedra. Interestingly, the d0 transition metal‐doped tungsten bronzes, PLNT and PLNW, exhibit extremely large second‐harmonic generation (SHG) responses of 56 and 67 × KH2PO4, respectively. The observed immeasurably strong SHG is mainly attributed to a net polarization originating from the alignment of highly distorted NbO6 octahedra with doped transition metals in the frameworks. It is believed that doping transition metal cations at the B‐site of the tungsten bronze structures should be an innovative strategy to develop novel high‐performance nonlinear optical materials.

Realization of multiple luminescence manipulation in tungsten bronze oxides based on photochromism toward real-time, reversible, and fast processes

Multiple luminescence manipulation in tungsten bronze oxides based on photochromism.

Engineering luminescence switching and photochromic performance in tungsten bronze oxides for handwriting display based on variable valence ion strategy

Inorganic luminescence materials with intelligent response to external stimuli have drawn considerable interest owing to their alluring applications. Photochromic (PC) is a reversible process which can be adopted to construct subtle luminescence regulation. However, the PC effect is commonly weak for most inorganic materials. It is still challenging to realize strong luminescence switching and PC effect in general inorganic compounds. To fill this gap, tetragonal tungsten bronze (TTB) oxides with ingenious upconversion (UC) luminescence modulation and prominent PC phenomenon were designed by introducing variable valence ion (Mo6+). Under this decorating, the UC luminescence switching ratio and PC contrast could be increased up to 2 and 4 times, respectively. The real-time information encoding based on PC and UC modulation was realized in TTB wafer, confirming the instant handwriting dual-mode display capacity. It is believed that this work will shed new light on the designing of terminal display devices.

The role of promoters on the catalytic performance of MxV2O5 bronzes for the selective partial oxidation of H2S

Metal-containing vanadium oxide bronzes (MxV2O5; M= Cu, Ag and Ca) have been prepared, characterized (before and after reaction) by various physicochemical techniques, and tested in the partial oxidation of H2S. The catalysts were prepared hydrothermally at 175 °C (from gels containing M/V molar ratios of 0.17 or 0.33) and heat-treated at 500 °C/2 h in N2. The most effective catalysts, showing a sulfur selectivity greater than 95 % for a H2S conversion beyond 90 %, were those presenting vanadium oxide bronze (β-Cu0.261V2O5 or Ag0.333V2O5) as the main crystalline phase. Cu- and Ag-containing vanadium oxide bronzes were stable under reaction conditions. For calcium containing materials (mainly presenting the Ca0.17V2O5 bronze phase), the formation of CaSO4 has been observed during the reaction, which resulted in a negative effect on both activity and selectivity. The nature of active and selective sites in this type of catalysts, as well as the role of promoters, are also discussed.

The relationship of dispersion and properties of powder materials on the example of titanium oxide bronze

The subject of this work is oxide potassium-titanium bronzes.&#x0D; The purpose of the work: to establish the relationship between the dispersion of samples of oxide potassium-titanium bronze and its physicochemical properties.&#x0D; Synthesis methods: self-propagating high-temperature synthesis (SHS), mechanosynthesis. Research methods used in the work: X-ray phase analysis (XRF), optical method for determining particle size, four-probe method for determining electrical conductivity, thermal analysis, method for determining chemical resistance.&#x0D; Results of the study: particle sizes were determined, which are 400, 200 and 40 nm. The work is devoted to the study of the influence of fineness on the structure and physicochemical properties of compounds of variable composition on the example of titanium oxide bronzes. A nanocrystalline sample of oxide potassium-titanium bronze was obtained by mechanosynthesis, coarse powders were obtained by SHS. The obtained samples were identified by X-ray phase analysis. The optical method of analysis determined the particle sizes, which are 400, 200 and 40 nm. It has been established that nanocrystalline samples of oxide potassium-titanium bronze are less resistant to aggressive media. Reducing the particle size does not affect the thermal stability. In the transition to nanoscale, the specific electrical conductivity increases by 1.5 times and amounts to 0,076 Ohm-1cm-1. The volume density of defects in the nanocrystalline structure of oxide potassium-titanium bronze is calculated, which is 1013 cm-2.

Cation‐Vacancy Ordered Superstructure Enhanced Cycling Stability in Tungsten Bronze Anode

AbstractNiobium‐based tungsten bronze oxides have recently emerged as attractive fast‐charging anodes for lithium‐ion batteries (LIBs), owing to their structural openings and adjustability. However, electrodes with tungsten bronze structures usually suffer from structural variability induced by Li+ intercalation/de‐intercalation, leading to unsatisfactory cycling performance. To circumvent this limitation, a novel tetragonal tungsten bronze (TTB) structure, Ba3.4Nb10O28.4 (BNO), is developed as an anode material for LIBs with prominent cycling performance. An unprecedented cation‐vacancy ordered superstructure with a periodic distribution of active and inactive sites is revealed inside the BNO. Through multiple characterizations and theoretical studies, it is demonstrated that this superstructure can improve the lithium‐ion diffusion and disperse the structural strain induced by Li+‐intercalation to enable stable Li+‐storage. Benefiting from the superstructure‐induced local structural stability, both the BNO bulk and Ba3.4Nb10O28.4@C (BNO@C) microspheres can deliver &gt;90% capacity retention after 250 cycles at 2 C and close to 90% capacity retention after 2000 cycles at 10 C. These results are of significant importance for establishing the structure–property relationship between the cation‐vacancy ordered superstructure and Li+‐storage performance, facilitating the rational design of stable tungsten bronze anodes.

An alternative way to design excellent energy-storage properties in Na0.5Bi0.5TiO3-based lead-free system by constructing relaxor dielectric composites

With growing concerns over environmental protection, lead-free dielectric ceramic capacitors are attracting much attention. In this work, a series of novel (1-x) Na0.5Bi0.5TiO3-x Ba5LaTi3Ta7O30 ((1-x)NBT-xBLTT) dielectric composite ceramics were fabricated by a traditional solid‐state method. All the samples possess a compact microstructure with refined grain morphology with increasing BLTT content, and tend to exhibit a diphase dielectric composite as x reaches up to 0.05. Furthermore, the addition of BLTT enhances the dielectric relaxor behavior of NBT-based ceramics, such that the x = 0.15 composite ceramic exhibits a typical feature of relaxor ferroelectrics. As a result, a high recoverable energy-storage density of Wrec~3.67 J/cm3, an ultrahigh energy-storage efficiency of η~97.3%, and a high power density of PD~333 MW/cm3 can be simultaneously obtained in the x = 0.15 relaxor composite ceramic. This study provides an alternative way to design excellent energy-storage performances in NBT-based compositions through constructing dielectric relaxor composites via introducing non-polar tungsten bronze oxides.

Toward Effective CO2 Reduction in an Acid Medium: Electrocatalysis at Cu2O-Derived Polycrystalline Cu Sites Immobilized within the Network of WO3 Nanowires.

A hybrid catalytic system composed of copper (I)-oxide-derived copper nanocenters immobilized within the network of tungsten oxide nanowires has exhibited electrocatalytic activity toward CO2 reduction in an acid medium (0.5 mol dm-3 H2SO4). The catalytic system facilitates conversion of CO2 to methanol and is fairly selective with respect to the competing hydrogen evolution. The preparative procedure has involved voltammetric electroreduction of Cu2O toward the formation and immobilization of catalytic Cu sites within the hexagonal structures of WO3 nanowires which are simultaneously partially reduced to mixed-valence hydrogen tungsten (VI, V) oxide bronzes, H x WO3, coexisting with sub-stoichiometric tungsten (VI, IV) oxides, WO3-y . After the initial loss of Cu through its dissolution to Cu2+ during positive potential scanning up to 1 V (vs RHE), the remaining copper is not electroactive and seems to be trapped within in the network of hexagonal WO3. Using the ultramicroelectrode-based probe, evidence has also been provided that partially reduced nonstoichiometric tungsten oxides induce reduction of CO2 to the CO-type reaction intermediates. The chronocoulometric data are consistent with the view that existence of copper sites dispersed in WO3 improves electron transfers and charge propagation within the hybrid catalytic layer. The enhanced tolerance of the catalyst to the competitive hydrogen evolution during CO2R should be explained in terms of the ability of H x WO3 to consume protons and absorb hydrogen as well as to shift the proton discharge at Cu toward more negative potentials. However, the capacity of WO3 to interact with catalytic copper and to adsorb CO-type reaction intermediates is expected to facilitate removal of the poisoning CO-type adsorbates from Cu sites.

Минералогические и биологические свидетели Редикарского захоронения X–XI вв.

The study of products of copper alloys of the Lomatov culture of the X-XI centuries from the collection of the Cherdyn Museum revealed two types of patina. The first pseudomorphic might be composed of intergrowths of chlorides formed upon interaction with the sweat of the hands, or a zonal rim of cuprite-malachite-azurite composition, due to interaction with groundwater. The second type, which distorts the shape of the original product, is associated with the leaching of copper and other metals and the crystallization of oxides and salts on the surface in the form of worm-like, kidney-shaped and drusoid aggregates. Fragments of mineralized biological objects (wings, eggs and larvae of flies, mole hair) found on the surface of the patina testify to the rapid oxidation of bronze, which is associated with flooding of the soil of the burial ground immediately after burial.

Simultaneous Pre-Intercalation of Caesium and Sodium Ions into Vanadium Oxide Bronze Nanowires for High-Performance Aqueous Zinc-Ion Batteries

Simultaneous Pre-Intercalation of Caesium and Sodium Ions into Vanadium Oxide Bronze Nanowires for High-Performance Aqueous Zinc-Ion Batteries

Simultaneous pre-intercalation of caesium and sodium ions into vanadium oxide bronze nanowires for high-performance aqueous zinc-ion batteries

The simultaneous pre-intercalation of caesium and sodium ions into vanadium oxide bronze nanowires can enlarge the interplanar spacing and afford surface oxygen defects conducive to improving zinc energy storage performance.

Optimization and experimental analysis of drilling process parameters in radial drilling machine for glass fiber/nano granite particle reinforced epoxy composites

Matrix cracking, fibre damage, increased hole surface roughness, delamination, circularity, and thermal deterioration, among other things, all occur throughout the drilling process, reducing hole quality. The most concerning of the unfavorable effects is delamination. Delamination can be reduced and hole quality improved by using the optimum cutting parameters and drill bit type. When drilling glass fiber/nano granite powder reinforced epoxy composites, the influence of drill bit coating material, drill bit speed, and drill bit feed rate on surface quality is investigated. The Taguchi L9 rotationally symmetric array is used to develop the experiments. As a result, to coincide radial drilling parameters of the process and response parameters, the statistical analysis of the experimental results is done using ANOVA. The results of the tests show that, high spindle speeds and a bronze oxide coated drill bit produce better hole quality and are also the most important factors influencing the drilled hole quality.