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result(s) for
"tungsten"
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Promotional Effect of Tungsten on the NH.sub.3-SCR Performance of a MnO.sub.x-TiO.sub.2 Catalyst: Balance of Surface Reducibility and Acidity
In this paper, MnO.sub.x/TiO.sub.2 catalysts with different manganese contents were prepared by using vacuum over-impregnation method to support manganese on TiO.sub.2 support. However, the activity temperature window was narrow and the denitrification efficiency was only 265-365 °C in the temperature zone above 80%. Therefore, doping W was used to improve the high temperature activity and broaden the activity temperature window. The experimental results show that the active temperature window of the catalyst is expanded to 260-550 °C when doping 20%WO.sub.3. The effects of tungsten doping on the structure and surface properties of the catalysts were investigated by XRD, TEM, Raman, XPS, H.sub.2-TPR and NH.sub.3-TPD. It is found that the increase of manganese content would increase the ratio of Mn.sup.4+ and O.sub.[alpha], and then improve the NH.sub.3-SCR activity at low temperature. Tungsten doping can provide more strong acid sites and improve the high temperature activity of the catalyst by inhibiting the oxidation of ammonia.
Journal Article
Niobium tungsten oxides for high-rate lithium-ion energy storage
The maximum power output and minimum charging time of a lithium-ion battery depend on both ionic and electronic transport. Ionic diffusion within the electrochemically active particles generally represents a fundamental limitation to the rate at which a battery can be charged and discharged. To compensate for the relatively slow solid-state ionic diffusion and to enable high power and rapid charging, the active particles are frequently reduced to nanometre dimensions, to the detriment of volumetric packing density, cost, stability and sustainability. As an alternative to nanoscaling, here we show that two complex niobium tungsten oxides—Nb
16
W
5
O
55
and Nb
18
W
16
O
93
, which adopt crystallographic shear and bronze-like structures, respectively—can intercalate large quantities of lithium at high rates, even when the sizes of the niobium tungsten oxide particles are of the order of micrometres. Measurements of lithium-ion diffusion coefficients in both structures reveal room-temperature values that are several orders of magnitude higher than those in typical electrode materials such as Li
4
Ti
5
O
12
and LiMn
2
O
4
. Multielectron redox, buffered volume expansion, topologically frustrated niobium/tungsten polyhedral arrangements and rapid solid-state lithium transport lead to extremely high volumetric capacities and rate performance. Unconventional materials and mechanisms that enable lithiation of micrometre-sized particles in minutes have implications for high-power applications, fast-charging devices, all-solid-state energy storage systems, electrode design and material discovery.
Micrometre-sized particles of two niobium tungsten oxides have high volumetric capacities and rate performances, enabled by very high lithium-ion diffusion coefficients.
Journal Article
Compositional Optimization of Sputtered WOsub.3/MoOsub.3 Films for High Coloration Efficiency
Thin films of mixed MoO[sub.3] and WO[sub.3] were obtained using reactive magnetron sputtering onto ITO-covered glass, and the optimal composition was determined for the best electrochromic (EC) properties. A combinatorial material synthesis approach was applied throughout the deposition experiments, and the samples represented the full composition range of the binary MoO[sub.3]/WO[sub.3] system. The electrochromic characteristics of the mixed oxide films were determined with simultaneous measurement of layer transmittance and applied electric current through the using organic propylene carbonate electrolyte cells in a conventional three-electrode configuration. Coloration efficiency data evaluated from the primary data plotted against the composition displayed a characteristic maximum at around 60% MoO[sub.3]. Our combinatorial approach allows the localization of the maximum at 5% accuracy.
Journal Article
Tungsten Molecular Species in Deuterium Plasmas in Contact with Sputtered W Surfaces
We show that in plasmas generated in deuterium in the presence of sputtered W surfaces, various molecular tungsten species are formed, whose chemical composition depends on the presence of gaseous impurities, namely, nitrogen, oxygen, and hydrogen. A magnetron discharge was used for plasma sustaining, and the species were investigated by mass spectrometry and optical emission spectroscopy. The identified tungsten-containing molecules are described by the chemical formula WOxNyDzHt, where x = 0–4, y = 0–3, z = 0–3, t = 0–5. Presumptively, even higher mass tungsten molecular species are present in plasma, which were not detected because of the limitation of the spectrometer measurement range to 300 amu. The presence of these molecules will likely impact the W particle balance and dust formation mechanisms in fusion plasmas.
Journal Article
Tungsten Material Behavior under Hsub.2, Dsub.2, and He Plasma Interaction Conditions in the Framework of Fusion-Relevant Studies
In the current study, bulk tungsten material surfaces are exposed to hydrogen, deuterium, and helium plasmas in the radiofrequency domain (13.56 MHz) at an input power of 250 W using the hollow-cathode configuration. The ejected material is collected on titanium substrates at various distances (from 6 mm up to 40 mm). Therefore, the exposed tungsten materials are investigated for surface changes (blister occurrence, dust formation, or nano-structuration), along with the crystallinity, depending on the plasma’s exposure times (from 30 min up to 120 min for each plasma type). Also, the collected materials are analyzed (morphological, structural, and statistical investigations) for dust and dust film-like appearance. Plasma discharges are analyzed using two methods: optical emission spectroscopy, and single Langmuir probes, to emphasize the nature of the used plasmas (cold discharges, ~2 eV), along with the presence of tungsten emission (e.g., WI 406.31 nm, WI 421.31 nm) during the plasma lifetime. By using a dedicated protocol, a method was established for obtaining fusion-relevant tungsten surfaces in the hydrogen and deuterium plasma discharges. By using the implemented method, the current paper introduces the possibility of obtaining a new tungsten morphology, i.e., the dandelion-like shape, by using helium plasma, in which the W[sub.18]O[sub.49] compound can be found.
Journal Article
Observation of moiré excitons in WSe2/WS2 heterostructure superlattices
Moiré superlattices enable the generation of new quantum phenomena in two-dimensional heterostructures, in which the interactions between the atomically thin layers qualitatively change the electronic band structure of the superlattice. For example, mini-Dirac points, tunable Mott insulator states and the Hofstadter butterfly pattern can emerge in different types of graphene/boron nitride moiré superlattices, whereas correlated insulating states and superconductivity have been reported in twisted bilayer graphene moiré superlattices
1
–
12
. In addition to their pronounced effects on single-particle states, moiré superlattices have recently been predicted to host excited states such as moiré exciton bands
13
–
15
. Here we report the observation of moiré superlattice exciton states in tungsten diselenide/tungsten disulfide (WSe
2
/WS
2
) heterostructures in which the layers are closely aligned. These moiré exciton states manifest as multiple emergent peaks around the original WSe
2
A exciton resonance in the absorption spectra, and they exhibit gate dependences that are distinct from that of the A exciton in WSe
2
monolayers and in WSe
2
/WS
2
heterostructures with large twist angles. These phenomena can be described by a theoretical model in which the periodic moiré potential is much stronger than the exciton kinetic energy and generates multiple flat exciton minibands. The moiré exciton bands provide an attractive platform from which to explore and control excited states of matter, such as topological excitons and a correlated exciton Hubbard model, in transition-metal dichalcogenides.
Moiré superlattice exciton states are observed in WSe
2
/WS
2
heterostructures with closely aligned layers.
Journal Article
Point-of-care diagnostics for rapid determination of prostate cancer biomarker sarcosine: application of disposable potentiometric sensor based on oxide-conductive polymer nanocomposite
One of the most important reasons for an increased mortality rate of cancer is late diagnosis. Point-of-care (POC) diagnostic sensors can provide rapid and cost-effective diagnosis and monitoring of cancer biomarkers. Portable, disposable, and sensitive sarcosine solid-contact ion-selective potentiometric sensors (SC-ISEs) were fabricated as POC analyzers for the rapid determination of the prostate cancer biomarker sarcosine. Tungsten trioxide nanoparticles (WO
3
NPs), polyaniline nanoparticles (PANI NPs), and PANI-WO
3
nanocomposite were used as ion-to-electron transducers on screen-printed sensors. WO
3
NPs and PANI-WO
3
nanocomposite have not been investigated before as ion-to-electron transducer layers in potentiometric SC sensors. The designated sensors were characterized using SEM, XRD, FTIR, UV-VIS spectroscopy, and EIS. The inclusion of WO
3
and PANI in SC sensors enhanced the transduction at the interface between the screen-printed SC and the ion-selective membrane, offering lower potential drift, a longer lifetime, shorter response time, and better sensitivity. The proposed sarcosine sensors exhibited Nernstian slopes over linear response ranges 10
−3
–10
−7
M, 10
−3
–10
−8
M, 10
−5
–10
−9
M, and 10
−7
–10
−12
M for control, WO
3
NPs, PANI NPs, and PANI-WO
3
nanocomposite-based sensors, respectively. From a comparative point of view between the four sensors, PANI-WO
3
nanocomposite inclusion offered the lowest potential drift (0.5 mV h
−1
), the longest lifetime (4 months), and the best LOD (9.95 × 10
−13
M). The proposed sensors were successfully applied to determine sarcosine as a potential prostate cancer biomarker in urine without prior sample treatment steps. The WHO ASSURED criteria for point-of-care diagnostics are met by the proposed sensors.
Graphical abstract
Journal Article
Imaging of pure spin-valley diffusion current in WS2-WSe2 heterostructures
Tracking the spin-valley currentTaking advantage of the electron's spin and valley degrees of freedom requires a method for generating currents of carriers that have a particular spin or come from a particular valley in the electronic structure. Jin et al. used a heterostructure made out of adjacent layers of WSe2 and WS2 to create a spin-valley diffusion current without applying an external electric field. Instead, they used circularly polarized laser light to initiate the diffusion and a second laser pulse to image the propagation of the carriers. With long lifetimes and diffusion lengths, the method may be of practical use in future valleytronic devices.Science, this issue p. 893Transition metal dichalcogenide (TMDC) materials are promising for spintronic and valleytronic applications because valley-polarized excitations can be generated and manipulated with circularly polarized photons and the valley and spin degrees of freedom are locked by strong spin-orbital interactions. In this study we demonstrate efficient generation of a pure and locked spin-valley diffusion current in tungsten disulfide (WS2)–tungsten diselenide (WSe2) heterostructures without any driving electric field. We imaged the propagation of valley current in real time and space by pump-probe spectroscopy. The valley current in the heterostructures can live for more than 20 microseconds and propagate over 20 micrometers; both the lifetime and the diffusion length can be controlled through electrostatic gating. The high-efficiency and electric-field–free generation of a locked spin-valley current in TMDC heterostructures holds promise for applications in spin and valley devices.
Journal Article