Monoclinic WO3 Research Articles

Rapid elimination of thiamethoxam insecticide under visible light using novel Au nanoparticles/CdSe/WO3 ternary nanocomposite

In this study, we have created a unique ternary photocatalyst using WO3 nanostructures in conjunction with CdSe and gold nanoparticles (Au NPs), which exhibits remarkable efficacy in purifying contaminated water under visible light. The Au, CdSe, and WO3 assembled ternary photocatalyst was synthesized through ultrasonication followed by a photoreduction process. The X-ray diffraction (XRD) analysis confirmed the presence of monoclinic WO3, hexagonal CdSe, and Au NPs in the ternary photocatalyst. Structural analysis and elemental composition were further substantiated through X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) studies. Transmission electron microscopy (TEM) examinations revealed irregularly shaped Au NPs (5–15 nm), CdSe, and WO3 particles. Diffuse reflectance studies demonstrated a reduction in the band gap energy of the Au@CdSe/WO3 nanostructures. The Au@CdSe/WO3 ternary photocatalyst exhibited remarkable efficiency in the photocatalytic degradation of thiamethoxam (TXM) insecticide and methylene blue (MB) dye under visible light. It achieved an impressive 94.13 % removal efficiency for TXM in just 40 min, which was ∼2.04 more efficient than undoped WO3. Additionally, the Au@CdSe/WO3 nanostructures successfully decolorized MB dye under visible light within 14 min. This exceptional photocatalytic performance can be attributed to the increased surface area, enhanced light absorption capacity, and improved photo-induced carrier transfer with efficient separation behavior, as evidenced by photoluminescence and photocurrent transient analyses.

Role of Deep Eutectic Solvent in the surface modification of Yttria based WO3 nanocomposite for application in Nanoarchitectonics

This work is emphasized on the synthesis of WO3:Y2O3 nanocomposite involving cetyl trimethylammonium bromide based Deep Eutectic Solvent (DES), for the rapid surface modification of the composite. DESs, being a new class of green solvents, are proved to bring about changes in size, morphologies and porous nature of the nanomaterials. The X-ray diffraction patterns showed the diffraction peaks for both monoclinic WO3 and cubic Y2O3 in the composite material. The morphologies of the composite material were scanned using SEM and the EDS confirmed the elemental composition of the material. The BET adsorption isotherms proved that DES has played a crucial role in increasing the surface area and pore volume of the composite material. The optical properties were studied using the UV-DRS exhibiting a band gap value of 3.13 eV. The frequency and temperature dependent ac and dc conductivities and dielectric properties of WO3:Y2O3 were analyzed. Finally the electrochemical studies of the composite material show a specific capacitance value of 460 Fg-1 at a current density of 2 Ag-1 and also having the percentage capacitance retention of 79.29% for 3050 cycles.

Electron and Hole Polaron Formation and Transport in Monoclinic WO3 Studied by Hybrid Functional Approach

Electron and Hole Polaron Formation and Transport in Monoclinic WO₃ Studied by Hybrid Functional Approach

Hexagonal/monoclinic phase junction modulated WO3 heterostructures for the detection of ammonia

Engineering the formation of phase junctions in the metal oxide is a powerful way to improve their gas-sensing performance. Here, we report a successful synthesis of different WO3 nanostructures. A simple and cost-effective hydrothermal technique was employed for the synthesis of monoclinic (m-WO3) and mixed hexagonal-monoclinic WO3 nanostructures (h-/m-WO3). The h-/m-WO3 exhibits a higher response than m-WO3 at 200℃. Among the various reducing gases, h-/m-WO3 is more sensitive toward ammonia whereas m-WO3 is sensitive toward H2S. The h-/m-WO3 device could detect a low ammonia concentration of 10 ppm and show spontaneous recovery, good repeatability, and long-term stability.

Cu-doped monoclinic WO3 nanoplates with superior photocatalytic activity for CO2 photoreduction

Cu-doped monoclinic WO3 nanoplates with superior photocatalytic activity for CO2 photoreduction

Defect-Mediated Growth of Crystallographic Shear Plane.

As representative extended planar defects, crystallographic shear (CS) planes, namely Wadsley defects, play an important role in modifying the physical and chemical properties of metal oxides. Although these special structures have been intensively investigated for high-rate anode materials and catalysts, it is still experimentally unclear how the CS planes form and propagate at the atomic scale. Here, the CS plane evolution in monoclinic WO3 is directly imaged via in situ scanning transmission electron microscope. It is found that the CS planes nucleate preferentially at the edge step defects and proceed by the cooperative migration of WO6 octahedrons along particular crystallographic orientations, passing through a series of intermediate states. The local reconstruction of atomic columns tends to form (102) CS planes featured with four edge-sharing octahedrons in preference to the (103) planes, which matches well with the theoretical calculations. Associated with the structure evolution, the sample undergoes a semiconductor-to-metal transition. In addition, the controlled growth of CS planes and V-shaped CS structures can be achieved by artificial defects for the first time. These findings enable an atomic-scale understanding of CS structure evolution dynamics.

Synthesis of WO3 nanopowder using a green surfactant for efficient gas sensing applications

WO3 has attracted great attention for chemical gas sensing applications. However, the synthesis of WO3 is mainly performed by using hazardous organic solvents and corrosive acidic solutions, which can result in environmental and health issues. The development of safe synthesis procedures using green compounds and solvents is in great demand to overcome the aforementioned drawbacks. Therefore, the effect of different eco-friendly chemical compounds on the growth of WO3 materials has yet to be thoroughly studied. Meanwhile, the fabrication of material at the nanoscale with specific crystalline properties may improve its sensitivity to the target gas. In this work, we report an efficient method for the synthesis of WO3 nanopowder by using water and a green surfactant such as vitamin C. The growth mechanism of the structure is analyzed considering the nature of solutions and surfactants. The studies indicate that the surfactant has a crucial effect on the formation of nanoparticles. Furthermore, the experimental findings show that the fabricated monoclinic WO3 material is highly sensitive and selective to low concentrations of acetone. Moreover, the structure exhibits quite stable functionalities at different levels of environmental humidity. Hence, this work may have a considerable impact on the existing techniques for the preparation of WO3 nanomaterials providing new insights into their green synthesis procedures. In addition, it can significantly affect the development of high-performance gas sensors and other catalytic devices based on WO3 nanostructures.

Rapid synthesis and characterizations of defect-enhanced WO3-δ thin film electrode for effective energy storage application in asymmetric supercapacitor devices

Oxygen vacancy-doped WO3-δ thin film electrode with improved conductivity and high areal capacitance was synthesized via mild electrochemical oxygen de-intercalation of electrodeposited WO3 thin film. The X-ray diffraction (XRD) analysis revealed the presence of monoclinic phase W18O49 of the doped thin film electrode. Raman spectroscopy analysis confirmed the presence of lower valence W5+ in the WO3-δ film. Electrical characterizations of doped WO3-δ and undoped WO3 films show that the doped electrode exhibits far lower sheet resistance and resistivity than the undoped WO3 sample. Mott-Schottky analysis of the samples shows that the vacancy-doped WO3-x possesses a higher donor concentration than the stoichiometric WO3. Electrochemical characterizations by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD,) and electrochemical impedance spectroscopy (EIS) confirmed the superior pseudocapacitive charge storage metrics via its improved volumetric capacitance of 366.12 F·cm−3 (16.0 mF·cm−2) and reduced equivalent series as well as charge transfer resistance over WO3 thin film. This study demonstrated the synthesis of oxygen vacancy-doped WO3-δ thin film using a homemade two-electrode cell facility instead of the popular energy-consuming vacuum-assisted film deposition under controlled-atmosphere conditions. Besides, the vacancy-doped WO3-δ electrode shows a strong charge storage capability in the far negative operating potential range, indicating its suitability as an anode electrode for fabricating high-energy asymmetric supercapacitors.

Band engineering in monoclinic WO3 with C+H co-doping for optoelectronic applications: A hybrid functional study

Using the hybrid functional method, we systematically investigate the band engineering induced by C + H co-doping in monoclinic WO3, and the associated effect on the optoelectronic functionality as well. First, we find that C substitution for O in WO3 improves the optical absorption through narrowing the band gap by 11% and introducing a curved intermediate level within the band gap (which functions as a stepping stone to relay the excited valence electrons to the conduction band). Further H incorporation into C-doped WO3 stabilizes the C substitution via clustering with C in the form of C-H and H-C-H chains, which reduces the band gap to less than 2 eV and simultaneously drives the deep C-induced intermediate level to be shallow. Such dopant clustering and the induced band engineering remarkably promote the optical absorption and optoelectronic functionality of WO3. The positive influence of dopant clustering has been fully analysed and discussed, and the favorability for forming C-H and H-C-H clusters in WO3 has been well presented through the detailed thermodynamic and kinetic analyses. The outcome of this work is expected to offer insightful guidance to tuning the properties of WO3 materials towards optoelectronic applications.

Full-temperature all-solid-state dendrite-free Zn-ion electrochromic energy storage devices for intelligent applications

Zn-ion electrochromic energy storage devices (ZEESDs) incorporate electrochromism and energy storage into one platform that can visually indicate the working status through a real-time color change, attracting considerable attention in energy-saving buildings and intelligent electronics. However, typical ZEESDs generally consist of Zn metal electrodes and normal liquid electrolytes, resulting in the dendrite issues and restricted operating temperatures as well as inferior cycle stability. Herein, an all-solid-state dendrite-free ZEESD was constructed based on polyaniline (PANI) positive electrode, monoclinic WO3 (m-WO3) negative electrode and Zn2+-based gel electrolyte. Benefiting from the complementary synergistic effect of electrodes and electrolytes, the resultant ZEESD avoids heavy Zn metals, addresses the dendrite formation problem, and exhibits remarkable electrochromic and electrochemical performances. The prototype ZEESD possesses high energy/power density (97 Wh kg−1/976.2 W kg−1 and 28.6 μWh cm−2/0.27 mW cm−2), large optical modulation (∼52.4%@630 nm), high coloration efficiency (96.8 cm2 C−1 at 630 nm), along with outstanding cycling stability (∼94.4% capacity retention even after 6000 cycles). Impressively, the quasi-solid-state electrolyte maintained outstanding electrochemical activity enabling the ZEESD to cycle efficiently even under hash temperatures, presenting enormous potential for intelligent electronics in all-climate (−30 °C to 60 °C) conditions. This work provides a novel strategy to construct next-generation dendrite-free Zn-ion electrochromic energy storage devices for innovative consumer electronics even in harsh environments.

Temperature-Controlled Transformation of WO3 Nanowires into Active Facets-Exposed Hexagonal Prisms toward Efficient Visible-Light-Driven Water Oxidation.

A unique transformation of WO3 nanowires (NW-WO3) into hexagonal prisms (HP-WO3) was demonstrated by tuning the temperature of the (N2H4)WO3 precursor suspension prepared from tungstic acid and hydrazine as a structure-directing agent. The precursor preparation at 20 °C followed by calcination at 550 °C produced NW-WO3 nanocrystals (ca. <100 nm width, 3-5 μm length) with anisotropic growth of monoclinic WO3 crystals to (002) and (200) planes and a polycrystalline character with randomly oriented crystallites in the lateral face of nanowires. The precursor preparation at 45 °C followed by calcination at 550 °C produced HP-WO3 nanocrystals (ca. 500-1000 nm diameter) with preferentially exposed (002) and (020) facets on the top-flat and side-rectangle surfaces, respectively, of hexagonal prismatic WO3 nanocrystals with a single-crystalline character. The HP-WO3 electrode exhibited the superior photoelectrochemical (PEC) performance for visible-light-driven water oxidation to that for the NW-WO3 electrode; the incident photon-to-current conversion efficiency (IPCE) of 47% at 420 nm and 1.23 V vs RHE for HP-WO3 was 3.1-fold higher than 15% for the NW-WO3 electrode. PEC impedance data revealed that the bulk electron transport through the NW-WO3 layer with the unidirectional nanowire structure is more efficient than that through the HP-WO3 layer with the hexagonal prismatic structure. However, the water oxidation reaction at the surface for the HP-WO3 electrode is more efficient than the NW-WO3 electrode, contributing significantly to the superior PEC water oxidation performance observed for the HP-WO3 electrode. The efficient water oxidation reaction at the surface for the HP-WO3 electrode was explained by the high surface fraction of the active (002) facet with fewer grain boundaries and defects on the surface of HP-WO3 to suppress the electron-hole recombination at the surface.

Sources of n-Type Conductivity in Single Crystal β-Ga2O3 and Monoclinic WO3 Nanoparticles

The source of the commonly observed unintentional n-type conductivity in wide-band-gap oxides is controversial. For high-quality β-Ga2O3 single crystals, the physical characteristics of H-containing defects are studied by solid-state nuclear magnetic resonance (ssNMR) and Fourier transform infrared (FT-IR) spectroscopy. NMR observation demonstrated that the hydrogen atoms occur exclusively in the positive charge state, and three trapped protons are housed in two “half vacancies” left by the Ga vacancy to form a VGa–H2+1 complex. Protons trapped in the vacancies are hardly ever able to diffuse out due to the strong hydrogen bonds they establish, even at relatively high temperatures. The hydrogen atoms in one of the two “half vacancies” are the bridged protons in Ga–O(H2)–Ga bonds, the hydrogen atoms can readily donate electrons to the conduction band, and these hydrogen atoms become the shallow donors. The VGa–H2+1 complex provides high-quality β-Ga2O3 single crystals with the extra-stability and the n-type conductivity. For monoclinic WO3 nanoparticles, NMR, FT-IR, and EPR results show that the bridged proton in W–O(H2)–W groups was assumed to be responsible for the so-called “hidden” hydrogen, which can be converted into a shallow donor in the course of sample processing. Our results provide a guide to more refined experimental studies of point defects and impurities in wide-band-gap oxides and their influence on the control of n-type conductivity.

Chemical reduction of porous WO3 and TiO2 photoelectrocatalysts by atomic hydrogen

The donor properties of atomic hydrogen were exploited to chemically reduce nanoparticle-based WO3 and TiO2 electrodes giving rise to a n-type doping of the semiconductors. For this purpose, a reactor system allowing for meticulous materials processing under high vacuum conditions and for the controlled electrode transfer into an aqueous electrolyte was designed and hydrogen doping-induced activity-changes in water photooxidation were studied. The chemical reduction of monoclinic WO3 electrodes leads to increased charge carrier separation at the semiconductor/electrolyte interface. Importantly, the beneficial doping effect is quite stable. However, bronze formation has a negative impact on the photoelectrocatalytic activity of WO3 electrodes upon strong sample reduction. For anatase TiO2 nanoparticle films de-doping of the reduced film is fast due to the small particle size. Correspondingly, the beneficial doping effect is transient. The small particle size allows, however, to estimate the number and energetic distribution of trapped electrons in hydrogen doped films.

Comparison study of WO3 thin film and nanorods for smart window applications

The WO3 thin films were deposited at oxygen partial pressure of 8x10-4 mbar. A template-free straightforward hydrothermal method is employed to produce vertical alignment hierarchical WO3 nano-architectures on clear conducting substrates (3x2.5 cm2 in size and slides resistance 4 O). After being deposited at ambient temperature, the samples were air annealed at 400 °C for 4 h. The optical, electrochromic, surface and structural morphology behavior of the deposited material after annealing were studied using XRD, Raman, FTIR, SEM, electrochemical analyzer and UV–Visible spectrometer characterization methods. After annealing at 400 °C for 4 h in air, every characteristic peak are matched to a monoclinic (crystalline) WO3 phase. The Nano flower array achieved a considerable coloration efficiency (24.09 cm2/s) and low cathodic peak current (−2.03 mA) compare to the Tungsten trioxide thin film produced by the DC magnetron sputtering method. The vertically oriented geometry and the porosity space between the Nano flower, which improve H+ diffusion and provide a considerable contact area for charge-transfer processes, are primarily responsible for the improved electrochromic properties.

A sight of view on electrical impacts, structural properties and surface roughness of tungsten trioxide thin film: effect of substrate temperatures in WO3/Si device fabrication

Monoclinic WO3 thin films have been effectively deposited by a simple spray pyrolysis technique at a molar concentration of 0.01 M on a glass substrate in the temperature range of 473 to 673 K. These WO3 films were used as an interlayer between the metal and the semiconductor, which formed the basic structure of the photodetector. Effect of substrate temperature on WO3 films during the process of the deposition was systematically interpreted with respect to the structural, morphological, optical and electrical properties of the WO3 films. The x-ray diffraction pattern revealed the polycrystalline nature of the prepared films with monoclinic phases. At the substrate temperature of 623 K, the nano-thin films were strongly bonded to each other as observed from the FE-SEM images. Visible and ultraviolet spectroscopies indicated the band gap (Eg) of the WO3 thin film is 3.30 eV. The dc electrical study recorded a sharp increase in the electrical conductivity of the prepared film at substrate temperature of 623 K for tungsten trioxide. It is worth noting that all diodes showed a positive photoresponse under illumination. In particular, the photodetector with the thickness of 300 nm showed higher responsivity 0.02 A/W and detection specificity 8.29 × 1010 Jones.

Evaluation of photocatalytic activity, water contact angle, and annealing for TiO2 thin films deposited with mixed WOX–SiO2 thin films using radiofrequency sputtering

A mixture of hydrophilic silicon dioxide (SiO2) and visible-light-reactive tungsten oxide (WOX) has the potential to improve the photocatalytic activity of conventional titanium dioxide (TiO2). This study deposits mixed WOX–SiO2 thin films on TiO2 surfaces by controlling the composition of WOX:SiO2 using radiofrequency sputtering to improve photocatalytic activity and hydrophilicity. The photocatalytic activity is evaluated via the degradation of a methylene blue solution, and hydrophilicity is measured using the water contact angle. In addition, the effect of annealing is determined at 400 °C after deposition. The optical bandgap decreases as the composition of WOX increases and subsequently anneals. The XRD measurements show that polycrystalline monoclinic WO3 peaks appear after annealing when the composition of the mixed WOX–SiO2 thin films only consists of WOX. In contrast, monoclinic WO3 (200) appears after adding SiO2. Atomic force microscopy images show that the grain size decreases as the SiO2 content increases. Moreover, the photocatalytic activity of the mixed WOX–SiO2 thin films improves after annealing. In particular, the mixed WOX–SiO2 thin films that are deposited at a sputter power of WOX:SiO2 = 100:50 W demonstrate a remarkable improvement in photocatalytic activity. Furthermore, the water contact angle of the mixed WOX–SiO2 thin films decreases as the SiO2 content increases and after annealing. This proposed approach can be used for high-performance photocatalytic materials and be widely applied for the fabrication of various semiconducting devices.

Controllable synthesis of W18O49 nanoneedles for high-performance NO2 gas sensors

Controlling the morphology of W18O49 nanostructures is an effective way to achieve high NO2-sensing performance. Herein, we describe the synthesis of W18O49 nanostructures via a facile solvothermal process by reacting a WCl6 precursor with a reducing agent. Several well-designed experiments were performed to realize the morphology-controlled synthesis of W18O49 nanostructures by adjusting solvent types, WCl6 dosages, solvothermal temperatures and times. One-dimensional (1D) nanoneedles composed of monoclinic W18O49 with preferential growth along the (010) direction, which expose more surface oxygen vacancies and demonstrate a significant benefit for improved gas sensing performance, were obtained under optimized synthetic conditions. Subsequently, the W18O49 nanoneedles displayed a high response to NO2 with excellent dynamic response-recovery characteristics at the optimal operating temperature of 160 °C. Moreover, the W18O49 sensor detected NO2 in a wide range of concentrations (0.2–500 ppm) and showed good selectivity and long-term stability. The gas sensing ability of W18O49 nanoneedles toward NO2 is discussed, and rich oxygen vacancies, 1D needle-shaped nanostructures, and high BET surface area contributed to their outstanding gas sensing performance.

Formation Pathways of Lath-Shaped WO3 Nanosheets and Elemental W Nanoparticles from Heating of WO3 Nanocrystals Studied via In Situ TEM.

WO3 is a versatile material occurring in many polymorphs, and is used in nanostructured form in many applications, including photocatalysis, gas sensing, and energy storage. We investigated the thermal evolution of cubic-phase nanocrystals with a size range of 5-25 nm by means of in situ heating in the transmission electron microscope (TEM), and found distinct pathways for the formation of either 2D WO3 nanosheets or elemental W nanoparticles, depending on the initial concentration of deposited WO3 nanoparticles. These pristine particles were stable up to 600 °C, after which coalescence and fusion of the nanocrystals were observed. Typically, the nanocrystals transformed into faceted nanocrystals of elemental body-centered-cubic W after annealing to 900 °C. However, in areas where the concentration of dropcast WO3 nanoparticles was high, at a temperature of 900 °C, considerably larger lath-shaped nanosheets (extending for hundreds of nanometers in length and up to 100 nm in width) were formed that are concluded to be in monoclinic WO3 or WO2.7 phases. These lath-shaped 2D particles, which often curled up from their sides into folded 2D nanosheets, are most likely formed from the smaller nanoparticles through a solid-vapor-solid growth mechanism. The findings of the in situ experiments were confirmed by ex situ experiments performed in a high-vacuum chamber.

Facile fabrication of nanoflower-like WO3/WS2 heterojunction for highly sensitive NO2 detection at room temperature.

Realizing efficient detection of ultra-low concentrations of hazardous gases contributes to air pollution monitoring, ecosystem and human health protection. Herein, we firstly fabricated the nanoflower-like WO3/WS2 composites by a facile process to highly sensitively detect NO2 at room temperature. The WO3 content in the WO3/WS2 composites can be adjusted by altering the calcination temperature, and the WO3 nanoparticles disperse uniformly on the WS2 surface, forming the WO3/WS2 heterojunction. The room-temperature responses of WO3/WS2 composites gradually climb with the NO2 concentration increasing from 0.005 to 5ppm, and the WW-280 and WW-300 composites possess the optimal gas sensitivity when the NO2 concentrations are lower and higher than 100 ppb, respectively. In particular, the two WO3/WS2 composites present the limitation of detection (LOD) of ≤5 ppb, and they exhibit the excellent selectivity, good reproducibility and long-term stability towards NO2. A possible gas sensing mechanism was also proposed from the point of views of gas adsorption, redox reactions and electron transfer. The appropriate WO3 content and molar ratio of hexagonal to monoclinic WO3, and the formation of WO3/WS2 p-n heterojunction can contribute to the high sensitivity of WO3/WS2 composite to various concentrations of NO2. This work offers a promising gas sensing material for room-temperature detection to low concentrations of NO2.

Flame-Spray-Synthesized La2O3-Loaded WO3 Nanoparticle Films for NO2 Sensing

In this investigation, flame-made La2O3-loaded WO3 nanoparticle films prepared with varying La contents (0–2 wt %) and spin-coating cycle numbers (1–6) were comprehensively explored for nitrogen dioxide (NO2) detection. Detailed material analysis revealed the creation of secondary La2O3 nanoparticles on primary monoclinic WO3 nanoparticles. Gas-sensing measurements were conducted toward 50–5000 ppb NO2 at 100–350 °C in dry and humid air (0–80 %RH). The obtained data dictated that the La content of 0.2 wt % and three spin-coating cycles provided optimal NO2 response and response time. Consequently, the 0.2 wt % La2O3-loaded WO3 three-cycle spin-coated film offered an ultrahigh response of ∼7213.6 and a response time of ∼31.8 s to 5000 ppb NO2 at a low best sensing temperature of 150 °C in dry air. Moreover, high NO2 selectivity was attained relative to CH2O, HCOOH, CH3OH, C2H5OH, CH3COOH, C6H6, C8H10, C3H6O, C3H7COOH, CH3CHOHCOOH, CH4, C2H4, C2H2, CO2, H2, H2S, and CH3SH. Therefore, the loading of La2O3 nanoparticles on flame-made WO3 sensors was attractive for highly responsive and specific NO2 detections at low working temperatures.