A Simple Hydrothermal Method for the Large-Scale Synthesis of Single-Crystal Potassium Tungsten Bronze Nanowires

Enhancing NIR Shielding Properties of Au/CsWO3 Composite via Physical Mixing and Solvothermal Processes

This research aims to enhance the near-infrared (NIR) shielding ability of cesium tungsten bronze (CsWO3) by increasing the spectral absorption in this region through the incorporation of gold nanorods (AuNR). Two approaches were used to prepare the composite materials: physical mixing and solvothermal process. The effects of gold nanorods content on the crystalline size, particle size, shape, and optical properties of the composite were investigated systematically using DLS, TEM, XRD, and UV-Vis spectroscopy techniques, respectively. The physical mixing process synergizes AuNR and CsWO3 into a composite which has better NIR absorption than that of neat AuNR and CsWO3 nanorods. A composite with 10 mol% of AuNR shows the highest NIR absorption ability due to the surface plasmon resonance and energy coupling between Au and CsWO3. With the solvothermal process, the CsWO3 nanorods grow up to 4-7 microns when the AuNR content increases to 0.8 mol% due to the incorporation of the Au atoms. The microsized CsWO3 rods have superior NIR shielding property compared to other conditions, including the AuNR+CsWO3 nanocomposite with 10 mol% of AuNR from the physical mixing process.

Tungsten-niobium oxide bronzes: a bulk and surface structural study

Materials from the WO3-Nb2O5 system, presenting bronze-type crystal structures, display outstanding functional properties for several applications as thermoelectric materials, lithium-ion battery electrodes, or catalysts. In this work, a series of W-Nb-O oxide bronzes have been synthesized by the hydrothermal method (with Nb/(W + Nb) ratios in the range of 0-1). A combination of bulk and surface characterisation techniques has been applied to get further insights into: (i) the effect of thermal treatments on as-prepared materials and (ii) the surface chemical nature of W-Nb-O oxide bronzes. Thermal treatments promote the following structural changes: (i) loss of emerging long-range order and (ii) the elimination of NH4+ and H2O species from the structural channels of the as-synthesized materials. It has been observed that W-Nb-O bronzes with Nb at% of ca. 50% are able to retain a long-range order after heat-treatments, which is attributed to the presence of a Cs0.5[W2.5Nb2.5O14]-type structure. Increasing amounts of Nb5+ in the materials (i) promote a phase transition to pseudocrystalline phases ordered along the c-axis; (ii) stabilize surface W5+ species (elucidated by XPS); and (iii) increase the proportion of surface Lewis acid sites (as determined by the FTIR of adsorbed CO). Results suggest that pseudocrystalline oxides (with a Nb at% ≥ 50%) are closely related to NbO7 pentagonal bipyramid-containing structures. The stabilisation of Lewis acid sites on these pseudocrystalline materials leads to a higher yield of heavy compounds, at the expense of acrolein formation, in the gas-phase dehydration of glycerol.

Photothermal Polymer Nanocomposites of Tungsten Bronze Nanorods with Enhanced Tensile Elongation at Low Filler Contents

We present polymer nanocomposites of tungsten bronze nanorods (TBNRs) and ethylene propylene diene monomers (EPDM). The combination of these components allows the simultaneous enhancement in the mechanical and photothermal properties of the composites at low filler contents. The as-synthesized TBNRs had lengths and diameters of 14.0 ± 2.4 nm and 2.5 ± 0.5 nm, respectively, and were capped with oleylamine, which has a chemical structure similar to EPDM, making the TBNRs compatible with the bulk EPDM matrix. The TBNRs absorb a wide range of near-infrared light because of the sub-band transitions induced by alkali metal doping. Thus, the nanocomposites of TBNRs in EPDM showed enhanced photothermal properties owing to the light absorption and subsequent heat emission by the TBNRs. Noticeably, the nanocomposite with only 3 wt% TBNRs presented significantly enhanced tensile strain at break, in comparison with those of pristine EPDM, nanocomposites with 1 and 2 wt % TBNRs, and those with tungsten bronze nanoparticles, because of the alignment of the nanorods during tensile elongation. The photothermal and mechanical properties of these nanocomposites make them promising materials for various applications such as in fibers, foams, clothes with cold weather resistance, patches or mask-like films for efficient transdermal delivery upon heat generation, and photoresponsive surfaces for droplet transport by the thermocapillary effect in microfluidic devices and microengines.

Facile synthesis of urchin-like CsxWO3 particles with improved transparent thermal insulation using bacterial cellulose as a template

Urchin-like Cs_xWO₃ particles were synthesized using bacterial cellulose (BC) as a template by the hydrothermal method. The effects of the BC addition amount on the morphology, W⁵⁺ content and transparent thermal insulation of Cs_xWO₃ were studied. It has been confirmed that abnormal growth of Cs_xWO₃ rods was greatly reduced after introduction of BC into the precursor solution. Moreover, introduction of BC into the precursor solution could significantly improve the transparent thermal insulation properties of the Cs_xWO₃ film. In particular, when the BC amount was appropriate, the prepared Cs_xWO₃ film exhibited better visible transparency, with the visible light transmittance (T_Vis) more than 60%. In addition, the urchin-like particles could be transformed into small size nanorods after H₂ heat-treatment, exhibiting excellent visible light transparency and thermal insulation performance. In particular, it has been proved that the 20BC-HT-Cs_xWO₃ film exhibits excellent thermal insulation performance, and shows broad application prospects in the field of solar heat filters and energy-saving window glass.

Urchin-like Cs_xWO₃ particles were synthesized using bacterial cellulose (BC) as a template by the hydrothermal method. The BC could greatly reduce the abnormal growth of Cs_xWO₃ rods and improve the transparent heat-insulation properties of Cs_xWO₃ film.

Controllable synthesis of small size CsxWO3 nanorods as transparent heat insulation film additives

Small size Cs_xWO₃ nanorods synthesized using pure ethanol as the solvent exhibited the best visible transparency and NIR shielding performance.

Fast-switching electrochromic properties of mesoporous WO3 films with oxygen vacancy defects

In this study, mesoporous WO₃ films with oxygen vacancy defects have been fabricated using the camphene-assisted sol-gel method. By controlling the optimized weight ratio of camphene on the WO₃ films, we developed a unique film structure of the WO₃ phase with both mesoporous morphology and oxygen vacancy defects due to the distinctive effect of camphene. The mesoporous WO₃ films with oxygen vacancy defects fabricated using 10 wt% camphene showed superb multifunctional electrochromic (EC) properties with both fast switching speeds (5.8 s for coloration speed and 1.0 s for bleaching speed) and high coloration efficiency (CE, 51.4 cm² C^-1), which include the most prominent properties, particularly for switching speeds among WO₃-based films reported so far. The attractive EC properties are due to the synergistic effects of the mesoporous morphology and oxygen vacancy defects on the WO₃. The fast switching speeds are mainly caused by the reduced Li⁺ diffusion pathway due to the mesoporous morphology and increased electrical conductivity due to the oxygen vacancy defects. In addition, the increased CE value is due to the large transmittance modulation as a result of a more effective electrostatic contact of the mesoporous morphology and an increased optical bandgap of the oxygen vacancy defects on the WO₃. Therefore, this unique film structure of the mesoporous WO₃ films with oxygen vacancy defects can be potentially regarded as a novel EC material for high-performance EC devices.

Atomic-Scale Study of Cation Ordering in Potassium Tungsten Bronze Nanosheets

It has long been accepted that the formation of superlattices in hexagonal-based potassium tungsten bronzes is attributed to K vacancies only, together with small displacements of W cations. Here, the superlattices within potassium tungsten bronze nanosheets both structurally and spectroscopically at atomic resolution using comprehensive transmission electron microscopy techniques are studied. The multidimensional chemical analyses are realized by energy-dispersive X-ray spectroscopy, electron energy-loss spectroscopy, and X-ray photoelectron spectroscopy, the atomic-scale structures are characterized using aberration-corrected scanning transmission electron microscopy with high-angle annular-dark-field detector. The observed superstructures are mainly attributed to small amount of W vacancies within single atomic layer, which would recover to more uniform distributions of W vacancies with lower concentrations at higher temperature. The band regions of different orientation from the matrix tend to regulate the superstructures to be pinned along the same direction, forming domains of highly ordered structures. The characterization of cation ordering and recovery processes of nanostructures from chemical and structural point of view at atomic resolution enables rational design of optoelectronic devices with controlled physical properties.

Oxygen Vacancy Enables Markedly Enhanced Magnetic Resonance Imaging-Guided Photothermal Therapy of a Gd3+-Doped Contrast Agent

Gd³⁺-based contrast agents (CAs) are the most prevailing and widely used for enhanced magnetic resonance imaging (MRI). Numbers of approaches have been developed to regulate the key parameters in order to obtain high-relaxivity CAs, according to the classic Solomon-Bloembergen-Morgen theory. Herein, a method of controlling oxygen vacancies in inorganic nanosized CAs has been developed for largely accelerated proton relaxation to obtain a high r₁ value. Such a strategy is verified on oxygen-deficient PEG-Na_xGdWO₃ nanorods, which exhibit a remarkable r₁ value up to 80 mM^-1 s^-1 (at 0.7 T) and a high r₁ value of 32.1 mM^-1 s^-1 on a clinical 3.0 T scanner, offering an excellent blood pool MRI performance at a low dose. Meanwhile, free electrons and/or oxygen-vacancy-induced small polarons can endow PEG-Na_xGdWO₃ nanorods with significant photothermal conversion for MRI-guided photothermal therapy.

Two-step fabrication of NaxWO3 thin film via oxygen-vacancy-induced effect for energy efficient applications

Developing solar modulation materials such as alkali tungsten bronzes with high-performance and low-cost fabrication is extremely important for energy-saving project applications in our modern lives.

Effect of tri- and tetravalent metal doping on the electrochemical properties of lanthanum tungstate proton conductors

Rare-earth tungstates (La(28-y)W(4+y)O(54+δ)□(2-δ)) have attracted attention recently because of their relatively high proton-electron conductivity and high stability in a CO2 environment. Since doping on the tungsten-site may increase the conductivity, a new series of compounds with composition La(5.5)W(1-x)M(x)O(11.25-δ) (M = Al, Ti and Zr; x = 0, 0.05 and 0.10) have been investigated. The crystal structure of these materials has been studied using X-ray and time-of-flight neutron powder diffraction by Rietveld analysis. The concentration of oxygen vacancies for hydration in the structure has been indirectly determined by thermogravimetric analysis, and the total conductivity in several pO2, pH2O and pD2O atmospheres has been studied by impedance spectroscopy. An increase in the conductivity is observed, ranging from 4.1 mS cm(-1) for the undoped sample to 9.2 mS cm(-1) for La(5.5)W(0.9)Ti(0.1)O(11.25-δ), in wet N2 at 800 °C.

A Cs(x)WO3/ZnO nanocomposite as a smart coating for photocatalytic environmental cleanup and heat insulation

A novel CsxWO3/ZnO smart coating was proposed to achieve multiple functions, such as heat insulation, photodecomposition of toxic NO gas, blocking of harmful UV light, etc. In this composite coating, CsxWO3 nanorods were used as a NIR and UV light shielding material while ZnO nanoparticles were utilized as a photocatalyst and a material to enhance visible light transmittance and block UV light. When the mass ratio of CsxWO3/ZnO was 1, the composite coating possessed a very good visible light transmittance of over 80% and an excellent UV-shielding ability. This novel coating showed heat insulation that is superior to the ITO coating and photocatalytic decontamination of NO gas that is superior to the standard TiO2 (P25). The proposed CsxWO3/ZnO smart coating is a promising material not only for energy saving but also for environmental cleanup.

Fabrication and properties of a branched (NH₄)xWO₃ nanowire array film and a porous WO3 nanorod array film

We describe the successful fabrication of a three-dimensional branched (NH4)xWO3 nanowire array film on fluorine-doped tin oxide coated glass by a facile one-step hydrothermal method. The porous WO3 nanorod array film formed after heat treatment and recrystallization. Specifically, the branched (NH4)xWO3 nanowire array film has very thin nanowires that were about 10 nm in diameter. The results of an optical and photoelectrochemical test show that the branched (NH4)xWO3 nanowire array film could be used as a near-infrared shielder, while the porous WO3 nanorod array film can be used as a photoanode for water splitting. Moreover, the morphology, structure, and composition of the as-prepared films are revealed, and the related changes caused by heat treatment are discussed in detail.

Tuning of the crystal engineering and photoelectrochemical properties of crystalline tungsten oxide for optoelectronic device applications

WO₃crystals with {002} or {111} facets primarily exposed, WO₃films with dominant orientations, doping and heterostructuring are highlighted.

Na0.3WO3 nanorods: a multifunctional agent for in vivo dual-model imaging and photothermal therapy of cancer cells

The hydrophilic Na_0.3WO₃ nanorods showed intense NIR absorption and large HU value, and thus can be used as a promising multifunctional agent for CT imaging and photothermal treatment of cancer.

Multifunctional Rbx WO3 nanorods for simultaneous combined chemo-photothermal therapy and photoacoustic/CT imaging

Light-triggered drug delivery based on near-infrared (NIR)-mediated photothermal nanocarriers has received tremendous attention for the construction of cooperative therapeutic systems in nanomedicine. Herein, a new paradigm of light-responsive drug carrier that doubles as a photothermal agent is reported based on the NIR light-absorber, Rb(x) WO3 (rubidium tungsten bronze, Rb-TB) nanorods. With doxorubicin (DOX) payload, the DOX-loaded Rb-TB composite (Rb-TB-DOX) simultaneously provides a burst-like drug release and intense heating effect upon 808-nm NIR light exposure. MTT assays show the photothermally enhanced antitumor activity of Rb-TB-DOX to the MCF-7 cancer cells. Most remarkably, Rb-TB-DOX combined with NIR irradiation also shows dramatically enhanced chemotherapeutic effect to DOX-resistant MCF-7 cells compared with free DOX, demonstrating the enhanced efficacy of combinational chemo-photothermal therapy for potentially overcoming drug resistance in cancer chemotherapy. Furthermore, in vivo study of combined chemo-photothermal therapy is also conducted and realized on pancreatic (Pance-1) tumor-bearing nude mice. Apart from its promise for cancer therapy, the as-prepared Rb-TB can also be employed as a new dual-modal contrast agent for photoacoustic tomography and (PAT) X-ray computed tomography (CT) imaging because of its high NIR optical absorption capability and strong X-ray attenuation ability, respectively. The results presented in the current study suggest promise of the multifunctional Rb(x)WO3 nanorods for applications in cancer theranostics.

Ordered and twinned structure in hexagonal-based potassium tungsten bronze nanosheets

Non-stoichiometric hexagonal-based potassium tungsten bronze (KxWO3) nanosheets were synthesized by oxidizing tungsten foil in potassium hydroxide. The tungsten bronze nanosheets exhibited an ordered monoclinic superstructure as revealed by X-ray diffraction patterns. Further detailed structural investigation by employing electron microscopy techniques showed the coexistence of 120° rotation twinning variants in the superstructure phase, which may result from the rotation symmetry reduction induced by the ordered arrangements of K vacancies during crystal growth.

Simple route to (NH4)(x)WO3 nanorods for near infrared absorption

Described here is how to synthesize one-dimensional ammonium tungsten bronze ((NH(4))(x)WO(3)) by a facile solvothermal approach in which ethylene glycol and acetic acid were employed as solvents and ammonium paratungstate was used as a starting material, as well as how to develop the near infrared absorption properties of (NH(4))(x)WO(3) nanorods for application as a solar light control filter. The as-obtained product was characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG), atomic force microscope (AFM) and UV-Vis-NIR spectra. The SEM and TEM images clearly revealed that the obtained sample possessed rod/fiber-like morphologies with diameters around 120 nm. As determined by UV-Vis-NIR optical measurement, the thin film consisted of (NH(4))(x)WO(3) nanoparticles, which can selectively transmit most visible lights, but strongly absorb the near-infrared (NIR) lights and ultraviolet rays. These interesting optical properties make the (NH(4))(x)WO(3) nanorods suitable for the solar control windows.

Hydrothermal Synthesis of Cesium Tungsten Bronze and its Heat Insulation Properties

Using sodium tungstate and cesium carbonate as raw materials, cesium tungsten bronze (CsxWO3) powders were synthesized by low temperature hydrothermal reaction with citric acid as the reducing agent. The CsxWO3 films were prepared on glass using polyvinyl alcohol solution as dispersing agent. The microstructure and morphology of CsxWO3 powders were characterized by XRD and SEM, and the optical spectra and heat insulation properties of CsxWO3 powder and films were investigated. The results indicate that the synthesized cesium tungsten bronze powders have hexagonal Cs0.32WO3 crystal structure. The as-prepared CsxWO3 powder and films show strong near-infrared absorption and near-infrared shielding properties. Furthermore, the near-infrared shielding performance of glass coated with CsxWO3 film has been further improved after UV irradiation. Especially, the glasses coated with CsxWO3 films which was synthesized from the non-ethanol precursor solution exhibit most outstanding near-infrared shielding performance and best heat insulation effect. In comparison with the blank glass without CsxWO3 film, the heat insulation temperature difference can achieve 24.8°C.

Synthesis of W18O49 nanorod via ammonium tungsten oxide and its interesting optical properties

W(18)O(49) nanorods were synthesized by pyrolyzing (NH(4))(x)WO(3+x/2) nanorods precursors, which were prepared by a hydrothermal reaction using sulfate as a structure-directing agent, in a reductive atmosphere of H(2)(5 vol %)/N(2) at 500 °C for 1 h. W(18)O(49) nanorods showed high transmittance in the visible region as well as excellent shielding properties of NIR lights. A simulated experiment revealed that excellent heat insulating performance can be realized by applying a 70% visible light transparent W(18)O(49) coating on a quartz glass. Meanwhile, the W(18)O(49) nanorods also showed strong absorption of NIR light and instantaneous conversion of photoenergy to heat. In a word, W(18)O(49) nanorods hold interesting optical properties and are a promising material in a wide range of applications.

Synthesis of one-dimensional potassium tungsten bronze with excellent near-infrared absorption property

Potassium tungsten oxide nanofibers were successfully synthesized via a facile hydrothermal reaction route in the presence of sulfate. After reduction under a reductive atmosphere of H(2)(5 vol %)/N(2), the potassium tungsten oxide transformed to potassium tungsten bronze. Because of the lack of free electrons, the potassium tungsten oxide (K(x)WO(3+x/2)) showed no NIR shielding performance; however, the potassium tungsten bronze (K(x)WO(3)) showed promising optical characteristics such as high transmittance for visible light, as well as high shielding performance for near-infrared lights, indicating its potential application as a solar filter. Meanwhile, the potassium tungsten bronze (K(x)WO(3)) showed strong absorption of near-infrared light and instantaneous conversion of photoenergy to heat.

A novel additive-free oxides–hydrothermal approach for monazite-type LaPO4nanomaterials with controllable morphologies

A facile oxides–hydrothermal (O–HT) method is demonstrated to prepare high-purity monazite-type LaPO4nanomaterials. In this approach, La2O3and P2O5powder are first directly used as precursors under additive-free hydrothermal conditions. The as-prepared samples are characterized with X-ray diffraction, Fourier transform IR spectroscopy, thermogravimetry, scanning electron microscopy, transmission electron microscopy (high-resolution TEM, energy dispersive spectroscopy) and selected-area electron diffraction. The typical sample obtained at 433 K in 24 h comprises uniform single-crystal nanofibres with a diameter of ∼15–28 nm and an aspect ratio of 30–50. The influences of treatment time, synthesis temperature and P/La molar ratio are investigated. The phase transition from hexagonal hydrate to monoclinic anhydrous lanthanum phosphate and the growth process of nanofibres are revealed by the experimental results. The formation mechanism of the monoclinic LaPO4is discussed. The result indicates that the P/La ratio does not influence the composition and crystal phase but changes the morphology of the product in the O–HT system.

One-dimensional CdS nanostructures: synthesis, properties, and applications

One-dimensional (1D) semiconductor nanostructures are of prime interest due to their potential in investigating the size and dimensionality dependence of the materials' physical properties and constructing nanoscale electronic and optoelectronic devices. Cadmium sulfide (CdS) is an important semiconductor compound of the II-VI group, and its synthesis and properties have been of growing interest owing to prominent applications in several fields. This article provides a comprehensive review of the state-of-the-art research activities that focus on the rational synthesis, novel properties and unique applications of 1D CdS nanostructures in nanotechnology. It begins with the rational design and synthesis of 1D CdS nanostructures, and then highlights a range of unique properties and applications (e.g. photoluminescence, cathodoluminescence, electrochemiluminescence, photocatalysis, lasers, waveguides, modulators, solar cells, field-effect transistors, photodetectors, field-emitters, and nanogenerators) associated with them. Finally, the review is concluded with the author outlook of the perspectives with respect to future research on 1D CdS nanostructures.