WO3 Nanostructures Research Articles

WO3 Nanostructures Modified with Carbon and Sulfur Used as Anode for Li-Ion Batteries

Nowadays, energy problems have become one of the biggest challenges in our society and they have drawn worldwide attention. Rechargeable lithium-ion batteries (LiBs) are a good option thanks to their potential applications as power sources for electric vehicles and mobile devices due to their high energy density and good cycle stability. Much effort has recently been devoted to find alternative anode materials and replace graphite in LiBs, like transition metal oxides that are currently being investigated (1).Specifically, tungsten oxide (WO3) has attracted much interest as an anode due to its excellent properties: high electronic conductivity (10–10−6 s cm−1), high intrinsic density (>7 g cm−3), small radius, and correct crystalline phase for rapid ion insertion and superior electrochemical performance (2).In this research, the effects of the morphology and composition of WO3 nanostructures on the charge/discharge behavior for Li-ion batteries are methodically examined.On the one hand, a simple method is used to synthesize crystalline WO3 nanostructures, with a well-defined morphology by means of an electrochemical procedure known as electrochemical adodization. Then, an annealing treatment at 600◦C in air environment for 4 h was carried out. In the second electrode synthesized, a carbon layer was uniformly deposited on WO3 nanostructures to obtain a WO3/C electrode. Finally, WO3/WS2 electrodes were prepared by means of in situ sulfurization of WO3 one-step solid-state synthesis using tungsten trioxide (WO3) and thiourea as precursor material.The different electrodes synthesized have been morphologically characterized by using X-ray photoelectron spectroscopy, X-ray diffraction analysis, transmission electron microscopy, Raman spectra, and field-emission scanning electron microscopy.The performance of the nanostructures applied as anodes for energy storage in Li-ion batteries and their specific capacity was evaluated by Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and Charge-Discharge curves. Among all the synthesized samples, WO3/C nanostructures reveal the best performance as they exhibit the greatest discharge capacity and cycle performance (820 mA h g−1). Acknowledgments Authors would like to express their gratitude to AEI (PID2019-105844RB-I00/ AEI/10.13039/501100011033) for the financial support. M. Cifre-Herrando thank Ministerio de Universidades for the concession of the pre-doctoral grant (FPU19/02466). G. Roselló-Márquez also thanks the UPV for the concession of a post-doctoral grant (PAID-10-21) and for the grant to promote postdoctoral research at the UPV (PAID.-PD-22). Finally, project co-funded by FEDER operational programme 2014-2020 of Comunitat Valenciana (IDIFEDER/18/044) is acknowledged. References Li P, Li X, Zhao Z, Wang M, Fox T, Zhang Q, et al. Correlations among structure, composition and electrochemical performances of WO3 anode materials for lithium ion batteries. Electrochim Acta. 2016;192:148–57. 2. Lian C, Xiao X, Chen Z, Liu Y, Zhao E, Wang D, et al. Preparation of hexagonal ultrathin WO3 nano-ribbons and their electrochemical performance as an anode material in lithium ion batteries. Nano Res. 2016;9(2):435–41.

Developing a Highly Stable Quaternary Sn-Sb-Mo-W Scaffold to Protect Active Metals for Corrosion during the Oxygen Evolution in Acidic Media

Proton exchange membrane (PEM) water electrolysis powered by renewable energies is seen as one of the most powerful techniques for the high production of ultra-pure hydrogen. However, PEM requires of noble metals as catalysts while operating under harsh acidic conditions, creating a detrimental environment which conducts to fast corrosion of the catalyst. Reducing and extending the lifetime of noble metals under acidic conditions will benefit the hydrogen economy. Currently, one of the major limitations relies on the high corrosion that anode electrocatalysts suffer, where the oxygen evolution reaction (OER) takes place. The best performing electrocatalysts are based on ruthenium (Ru) and iridium (Ir) either in the pure oxide form or as engineered composites, being Ru the most active but less stable even at moderate cell potentials. Here, we investigate the quaternary Sn-Sb-Mo-W mixed oxide (MO) as an effective scaffold to protect RuO2 for corrosion. The acid-stable MO was produced via plasma spraying forming an interconnected network of nanostructured WO3, Sb2O3, SnO2, and MoO3. Low quantities of Ru (2.64% w/w Ru) were stabilized into the matrix (Ru-MO) and finally supported on FTO. The Ru deactivation was described by a second-order reaction with a deactivation rate constant of k = 0.067 cm2 (mA·min)-1. Titanium fiber felt was later used as support (Ru-MO@Ti) where a mass activity of 4440 A g-1 Ru@1.8V(RHE) was obtained, and solely a reduction of 20% was seen in the OER activity after 2000 CVs (1.2 – 1.8 V vs RHE), in contrast to unprotected RuO2 (RuO2@Ti) which showed an activity loss of nearly 90%. In addition, chronopotentiometry studies on Ru-MO@Ti (2.5 A cm-2 @ 1.7V) confirmed the high satiability of the Ru experienced only a minor increase in potential of 10 mV, while RuO2@Ti exhibited a significant degradation of 500 mV after 10 h. The superior stability of Ru-MO@Ti was possible due to impeded formation of higher valence ruthenium (Ru+8), a typical dissolution path for Ru-based electrocatalysts. Our work shows that multi-metal oxides have the potential to host and extend the lifetime of active metals and Ti substrates when used for water electrolysis in acidic media. Figure 1

Controlled Growth of WO3 Photoanode under Various pH Conditions for Efficient Photoelectrochemical Performance.

Herein, the effects of the precursor solution's acidity level on the crystal structure, morphology, nucleation, and growth of WO3·nH2O and WO3 nanostructures are reported. Structural investigations on WO3·nH2O using X-ray diffraction and Fourier-transform infrared spectroscopy confirm that the quantity of hydrate groups increases due to the interaction between H+ and water molecules with increasing HCl volume. Surface analysis results support our claim that the evolution of grain size, surface roughness, and growth direction on WO3·nH2O and WO3 nanostructures rely on the precursor solution's pH value. Consequently, the photocurrent density of a WO3 photoanode using a HCl-5 mL sample achieves the best results with 0.9 mA/cm2 at 1.23 V vs. a reversible hydrogen electrode (RHE). We suggest that the improved photocurrent density of the HCl-5 mL sample is due to the efficient light absorption from the densely grown WO3 nanoplates on a substrate and that its excellent charge transport kinetics originate from the large surface area, low charge transfer resistance, and fast ion diffusion through the photoanode/electrolyte interface.

Studying the Effect of Oxidation on the Thermolysis of (NH4)2WS4 with In‐ and Ex‐Situ Electron Microscopy

AbstractThermolysis is a common technique in materials synthesis; however, oxidation of precursors used in these processes destroys the ability to generate end‐products with the desired composition and structure. Herein, the effects of oxidation on the thermolysis of (NH4)2WS4, a common precursor in the production of WS2 films, are studied utilizing electron microscopy. Specifically, in situ bright field, dark field, and secondary electron images were collected during heating of the aforementioned oxidized precursor from RT to 800 °C in 100 °C steps within a low kV scanning transmission electron microscope. These imaging results detail how the precursor transforms from its largely nondescript room temperature morphology to one having well formed 2D, 1D, and 0D nanostructures. Subsequent ex situ atomic level imaging shows that the 2D and 1D nanomaterials are composed of δ‐WO3 which has grown along its c‐axis, whereas the 0D nanoparticles are made solely of α‐W. Through the combination of both in and ex situ images, we have gained valuable insights into the structural and chemical changes that occur owing to the additional oxygen in the system, as well as the role that precursor density plays on the formation of these as formed nanomaterials.

Visible light-driven photo remediation of hazardous cationic dye via Ce-doped WO3 nanostructures

Ce-doped WO3 nanoparticles were successfully synthesized by the sol–gel method and characterized through advanced characterization techniques. The high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) results show a reduction in the agglomeration of nanoparticles upon doping. The energy dispersive X-ray (EDX) analysis validates the existence of the Ce element in all the doped samples. X-ray photoelectron spectroscopy (XPS) and Raman spectra justify the presence of structural defects (oxygen vacancies) and successful formation of the monoclinic WO3 phase, respectively. The Kubelka–Munk function indicates a decrease in band gap with doping, while photoluminescence (PL) spectra show intense visible and UV emissions. Significantly, all doped samples exhibit higher photocatalytic performance than pure WO3 nanoparticles, with the 6 wt% Ce-doped sample displaying the highest degradation rate. Doping with Ce can help to increase the surface area of WO3, thereby improving its photoactivity. Moreover, a correlation between PL and photocatalysis is established in the light of oxygen vacancies suggesting a direct dependence of high photocatalytic activity on strong PL signals of WO3 nanostructures. Trapping experiments further reveal that the degradation process is primarily driven by active species, providing insight into a plausible photocatalytic mechanism.

Introducing of WO3@NiCo2O4/rGO ternary nanocomposites as active material for high-performance supercapacitor applications

The combined materials with synergistic effects and integrate of properties of each component can be widely used for high capacity and high-power density storage devices. In this study, synthesis, energy storage ability and characterization of the novel ternary WO3@NiCo2O4/rGO nanocomposites (NWG) as active electrode materials are studied. NWG nanocomposites as high-efficiency supercapacitors material which is perfect transferring ions/electrons are constructed with multiple-step synthesis for supercapacitor application for the first time. For this purpose, at first, intertwined nanosheets of NiCo2O4 was synthesized through the hydrothermal process, afterwards, WO3 nanostructures were fabricated on the surface of NiCo2O4 via sonochemical method and finally, NWG nanocomposites were synthesized during the mild hydrothermal conditions. Towards the studying the physicochemical properties of as-fabricated NWG nanocomposites, the X-ray diffraction (XRD), Fourier transform infrared (FT-IR), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDX) analysis were used. Also, the electrochemical behavior of innovative NWG nanocomposites as energetic electrode materials was investigated in two and three electrode configurations for high-performance supercapacitor application. Additionally, the synergetic effect between NiCo2O4, WO3 and rGO substrates in final product (NWG) was investigated based on cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS) and cyclic stability test. The well-designed NWG nanostructures with layered shape can acceleration the ion electrolyte diffusion and provided more redox active sites through energy storage process. The electrochemical results of the NWG nanocomposite electrodes represented a high specific capacity of 1211.75 F g−1 at a current density of 1.5 A g−1. Furthermore, the suggested electrode exhibited the great energy density of 11.92 Whkg−1, power density of 3000.8 Wkg−1 and excellent rate capability (91.51 % of capacity retention after 1000 cycles). Moreover, the specific capacitance of bare and binary nanocomposites i.e. NiCo2O4 and WO3@NiCo2O4 were investigated and compared with NWG at a current density of 2 A g−1. The results show that the specific capacitance of NWG ~1.5 times greater than NiCo2O4 and WO3@NiCo2O4 nanostructures [NiCo2O4 (498.33 F g−1), WO3@NiCo2O4 (580.33 F g−1) and NWG (917.67 F g−1)]. Remarkably, an asymmetric supercapacitor (ASC) assembled by newly-designed NWG electrode as a positive electrode and activated carbon (AC) as a negative electrode exhibited the good specific capacitance 37.2 mF g−1 at of 1.5 mA g−1. Also, the ASC device could provide energy density of 4.75 mWh kg−1 at the power density of 799.9 mWkg−1. This research recommends that NWG nanocomposites have an extraordinary potential for evolution of active electrode materials forthcoming supercapacitors in energy storage systems.

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.

Plasmonic Photocatalysts Based on Au Nanoparticles and WO3 for Visible Light-Induced Photocatalytic Activity

In this work, we report the application of Au/WO3 composite as a photocatalyst for the degradation of dyes under solar light irradiation. Au/WO3 nanocomposites were synthesized using an acid precipitation method followed by an impregnation/reduction at room temperature. Two composites were obtained by loading gold nanoparticles on two morphologies of nanostructured WO3, nanoplatelets (NP), and pseudospheres (PS). The elaboration parameters of the nanocomposites were optimized according to the gold mass percentage, the HAuCl4 precursor concentration, and the impregnation time. The structural, microstructural, and textural characterization were conducted using advanced techniques: XRD, SEM/TEM microscopies, and XPS and DRS spectroscopies. The optimal synthesis parameters are a 48 h impregnation of a five mass percentage of gold from a HAuCl4 precursor with a concentration of 10−3 mol·L−1. The obtained composites were formed with Au nanoparticles of 7 nm in size. The XRD analyses did not reveal any modification of the oxide supports structure after gold grafting, contrary to the sorption analyses, which evidenced a change in the state of the materials surface. XPS analysis revealed the reduction of W6+ ions into W5+, favoring the presence of oxygen vacancies. Furthermore, a localized surface plasmon resonance effect was observed in the composite at 540 nm. The photocatalysis results of several dye pollutants have shown a selective degradation efficiency depending on the charge of the polluting molecules, pH medium, and mass loading of the catalysts. At the native pH, the photocatalysis process is highly efficient on a cationic molecule, with a low adsorption capacity. Au/WO3 PS composite appears to be the most efficient, degrading almost the whole RhB and MB only in 60 min and 90 min, respectively, while, for the MO anionic dye, the degradation is more efficient in acidic medium (80%) than in basic medium (0%). Trap tests of the main active species were investigated and a photodecomposition mechanism is proposed.

Enhanced photoelectrochemical water oxidation by Fe(II) modified nanostructured WO3 photoanode

Herein, we demonstrate a facile surface treatment of a nanostructured tungsten oxide (WO3) film by Fe2+ ions as a novel post-fabrication technique for enhanced photo-electrochemical water oxidation under sunlight. The structural, optical, morphological and elemental characterizations of the n-type WO3 nanoplates based electrodes have been done using X-ray diffraction, UV–visible diffuse reflectance spectroscopy, fluorescence spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray analysis and X-ray photoelectron spectroscopy, respectively. The modified WO3 photoanodes have been subsequently examined for photo-electrochemical response by linear sweep voltammetry, photo-amperometry, electrochemical impedance spectroscopy (Nyquist plot) and Mott-Schottky analysis under AM 1.5 G solar simulated light. The optimized WO3 film with Fe:W ratio of ∼1:25, (Fe2+:Fe3+ ratio of ∼3:2) at the surface exhibited up to 3 times higher and more stable photocurrent under back illumination than that for untreated WO3 indicating the success of the surface treatment. Investigations revealed that the improved performance is a consequence of an improved charge transfer process at the interface resulting in lowering of unwanted recombination.

In-situ grown hydrated tungsten oxide nanosheets for low temperature ppb-level NO2 detection with alleviated humidity interference

Gas sensors operated at low temperature or room temperature are highly desirable from the point of view of low power consumption. Unfortunately, the senor performance is significantly affected by the environmental moisture due to the adsorption of water on the surface of the sensing materials at low temperature. Instead of employing a traditional oxide as the sensing material, monohydrate of tungsten oxide, WO3·H2O, is investigated for low temperature NO2 detecting. WO3·H2O thin films constructed from vertically aligned nanosheets are in-situ grown on the sensor chip. The electronic structure of WO3·H2O and the crystalline structure, morphology, thermal stability, optical properties of the thin films have been studied. The NO2 sensing performance of WO3·H2O is evaluated by operating at low temperatures (less than 150 °C) or at room temperature with intermittent UV irradiation. Effect of humidity on the sensor performance has also been elaborated. The results indicate that the nanostructured WO3·H2O thin films are highly sensitive to ppb-level NO2 and the sensor performance of WO3·H2O is less affected by humidity when compared with that of WO3. The crystalline hydrate WO3·H2O is found to reduce the adsorption of water and the interference of ambient moisture on sensor performance.

Gas Sensing Properties of CuWO4@WO3 n-n Heterojunction Prepared by Direct Hydrolysis of Mesitylcopper (I) on WO3·2H2O Nanoleaves

The nanometer size Cu2O@WO3·H2O composite material has been prepared by the direct hydrolysis of mesitylcopper (I) on WO3·2H2O nanoleaves. The synthesis has been performed in toluene without the addition of any ancillary ligands. The prepared nanocomposite has been deposited as a gas-sensitive layer on miniaturized silicon devices and heated up gradually to 500 °C in the ambient air. During the heating, the CuWO4 phase is formed upon the reaction of Cu2O with the WO3 support as revealed by the XRD analyses. The as-prepared CuWO4@WO3 sensors have been exposed to 10 ppm of CO or 0.4 ppm of NO2 (RH = 50%). At the operating temperature of 445 °C, a normalized response of 620% towards NO2 is obtained whereas the response to CO is significantly lower (S = 30%). Under these conditions, the sensors prepared either with pristine CuO or WO3 nanostructures are sensitive to only one of the two investigated gases, i.e., CO and NO2, respectively. Interestingly, when the CuWO4@WO3 sensitive layer is exposed to UV light emitted from a 365 nm Schottky diode, its sensitivity towards CO vanishes whereas the response towards NO2 remains high. Thus, the application of UV illumination allowed us to modify the selectivity of the device. This new nanocomposite sensor is a versatile sensitive layer that will be integrated into a gas sensor array dedicated to electronic nose platforms.

Enhancement of visible light photocatalytic removal of residual tetracycline by Ni doped WO3 nano structures

In this study, Ni was used to dope into WO3 structure to improve its photocatalytic performance for tetracycline degradation. The obtained characterized results indicated that Ni dopants acted as nuclei during crystallization resulting in crystal size increase. However, Nickel dopants substituted several Tungsten elements in the WO3 leading to lattice distortion preventing agglomeration of these newly formed Ni-WO3 crystals resulting in particle size decrease. Thus, Ni-WO3 crystals were larger than WO3 crystals while Ni-WO3 particles were much smaller than WO3 particles. Ni dopants also induced formation of mesopore on WO3 surface resulting in surface areas increase of the Ni-WO3. On other hand, as compared to pristine WO3, the synthesized Ni-WO3 exhibited significant enhancement in visible light absorption as well as effectively prevented electron-hole recombination. Thus, the Ni-WO3 exhibited novel photocatalytic performance even under visible light. Among synthesized Ni-WO3, the 3Ni-WO3, which mole ratio of Ni/WO3 was 3 %, presented the highest photocatalytic performance for tetracycline degradation.

(Invited) Hybrid Mixed-Metal-Oxide-Based Catalytic Systems for Efficient Electroreduction of Carbon Dioxide

Of particular interest to the preparation of advanced catalytic materials is efficient utilization of nanosized materials with well-defined composition, structure and thickness that exhibit desirable electrocatalytic properties. There has been growing interest in the electrochemical conversion of carbon dioxide (a potent greenhouse gas and a contributor to global climate change) to useful carbon-based fuels or chemicals. Given the fact that the CO2 molecule is very stable, its electroreduction processes are characterized by large over-potentials. It is often postulated that, during electroreduction, the rate limiting step is the protonation of the adsorbed CO product to form the CHO adsorbate. In this respect, the proton availability and its mobility at the electrochemical interface has to be addressed. On the other hand, competition between such parallel processes as hydrogen evolution and carbon dioxide reduction has also to be considered.We explore here the ability of polynuclear transition metal oxide based systems to function as cocatalysts and to stabilize and activate metal nanocenters. Here certain nanostructured metal oxides of zirconium, titanium, molybdenum or tungsten have been demonstrated to influence supported catalytic metal sites in ways other than simple dispersion over electrode area. Evidence is presented that the support can modify activity (presumably electronic nature) of catalytic metal nanoparticles (e.g. Cu, Ru), thus affecting their chemisorptive and catalytic properties during CO2-reduction. Metal oxide (WO3, MoO3, TiO2) nanostructures can generate highly reactive –OH groups at electrocatalytic interface.Evidence is presented that the support can modify activity (presumably electronic nature) of catalytic metal nanoparticles (e.g. Cu, Pd), thus affecting their chemisorptive properties. Metal oxide (ZrO2, WO3) nanospecies can generate –OH groups at electrocatalytic interface. Our electrocatalytic results with copper nanostructures over-coated with ZrO2 or WO3 nanostructures imply the systems’ improved selectivity toward CO2-reduction relative to the competitive hydrogen evolution as well as the lower tendency of copper sites to undergo poisoning.

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.

Acid substitutions for WO3 nanostructures synthesis by the hydrothermal route and its effect on physio-chemical and electrochemical properties for supercapacitors

In this study, we have developed a feasible and eco-friendly electrode material for supercapacitor (SCs) application by effectively synthesizing different morphological structures of tungsten oxide nanostructures (WO3-NSs). The concentrated acids play a crucial role in the synthesis of WO3-NSs and are employed to evaluate the electrochemical activity. The stable phase formation and the crystal structures of WO3-NSs were confirmed by thermogravimetric and X-ray analysis. From the field emission scanning electron microscope (FE-SEM), the hexagonal-shaped nanosheets, one-dimensional nanorods (1D NRs), and heterogeneous non-uniform agglomerated nanosheets were observed for the WO3-NSs. The presence of functional groups and the stretching-bending vibrations of WO bonds were detected by Fourier transform infrared, and Raman spectroscopy respectively. The transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) offers a more in-depth morphological, structural, and elemental composition and electronic states investigation of the optimized WO3-NRs. Additionally, the electrochemical properties of the WO3-NSs have been examined in 1 M KOH electrolyte using Nickel Foam (NF) as a current collector. Furthermore, the M-WO3-NF electrode reveals higher specific capacity (Csp) and gravimetric capacitance (Cg) of 72 mAh/g and 600 F/g with high energy density (Ed) of 17 Wh/kg, and power density (Pd) of 321 W/kg as well as the superior Columbic efficiency (96.9 %) at 5 mA/cm2. The M-WO3 electrode exhibits 91 % capacitive retention over 5000 cycles. The M-WO3-NF is used as the cathode and activated carbon (AC) as the anode in the design of an aqueous hybrid supercapacitor (AHSC) device. Notably, the M-WO3-NF//AC-NF device offers a Pd of 1060 W/kg at an Ed of 9 Wh/kg and remarkable electrochemical stability of 80 % over 3000 charge-discharge cycles. These results highlight the excellent electrochemical functionality and advantages of the M-WO3-NRs as a promising cathode for practical energy-storage systems.

Integration of Ag Plasmonic Metal and WO3/InGaN Heterostructure for Photoelectrochemical Water Splitting.

In this study, a Ag/WO3/InGaN hybrid heterostructure was successfully developed by sputtering and molecular beam epitaxy techniques, to obtain unique Ag nanospheres adorned with cauliflower-like WO3 nanostructure over the InGaN nanorods (NRs). Exploiting the localized surface plasmon resonance of Ag, the Ag/WO3/InGaN heterostructure exhibited superior photoabsorption ability in the visible region (400-700 nm) of the solar spectrum, with a surface plasmon resonance band centered around 440 nm. Comprehensive analysis through photoluminescence spectroscopy, photocurrent measurements, and electrochemical impedance spectroscopy revealed that the Ag/WO3/InGaN hybrid heterostructure significantly enhances the charge carrier separation and transfer kinetics leading to improved overall photoelectrochemical (PEC) performance. The photocurrent density of the Ag/WO3/InGaN photoanode is 1.17 mA/cm2, which is about 2.72 times higher than that of pure InGaN NRs under visible light irradiation. The photoanode exhibited excellent stability for about 12 h. From the study, it has been found that the maximum applied bias photon-to-current efficiency (ABPE) is ∼1.67% at the applied bias of 0.6 V. The improved PEC water splitting efficiency of the Ag/WO3/InGaN photoanode is attributed to the synergistic effects of localized surface plasmon resonance (LSPR), efficient charge carrier separation and transport, and the presence of a Schottky junction. Consequently, the plasmonic metal-assisted heterojunction-based semiconductor Ag/WO3/InGaN demonstrates immense potential for practical applications in photoelectrochemical water splitting.

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.

Visible-light-driven photocatalytic activity of WO3/ZIF-67 S-scheme heterojunction for upgrading degradation of oxytetracycline

The S-scheme heterojunction engineering has been regarded as a promising strategy for sufficiently using photogenerated charge carriers. Therefore, how to design a suitable nanostructure for efficient photogenerated carrier transfer/separation can be the key to upgrading the photocatalytic activity. The present study was planned for the design and fabrication new type of S-scheme WO3/ZIF-67 heterojunction for the degradation of oxytetracycline (OTC) under visible light irradiation. First, the WO3 nanostructure was fabricated with the hydrothermal method. Subsequently, microcrystals ZIF-67 were grown onto WO3 nanoplate with the sol-gel method for designing a new type of WO3/ZIF-67 nanocomposite. HA–XRD pattern revealed epitaxial growth of ZIF-67 on the monoclinic α-WO3 surface. According to FESEM and TEM images, WO3 had a plate-like nanostructure with a thickness of about 90 nm that was spread heterogeneously on the surface and core of ZIF-67. The results revealed that 91.5% of OTC is degraded in 60 min of 20 W LED light following pseudo-first-order kinetics. Investigating the reaction mechanism and quenching tests indicated hydroxyl and superoxide anion radicals play a vital role in OTC degradation. The reusable ability of the prepared WO3/ZIF-67 nanocomposite was tested up to six runs with 82% removal efficiency, confirming the suitable recyclability and stability of the proposed photocatalyst. The smart strategy of designing metal organic framework-based photocatalysts provides an innovative perspective for the development of S-scheme heterojunctions for organic contamination degradation.

Tungsten oxide nanostructures peculiarity and photocatalytic activity for the efficient elimination of the organic pollutant.

The WO3 nanostructures were synthesized by a simple hydrothermal route in the presence of C14TAB and gemini-based twin-tail surfactant. The impact of using these special shape and size directing agents for the synthesis of nanostructures was observed in the form of different shapes and sizes. The WO3 web of chains type nanostructure was obtained using C14TAB in comparison to the cube-shaped nanoparticles through twin-tail surfactant. On contrary, the twin-tail surfactant provides sustainable and controlled growth of cube shape nanoparticles of size ~ 15nm nearly half of the size ~ 35nm obtained using conventional surfactant C14TAB, respectively. For the detailed structural features, the Williamson-Hall analysis method was implemented to find out the crystalline size and lattice strain of the prepared nanostructures. Owing to the strong quantum confinement effect, the WO3 cube-shaped nanoparticles with an optical band gap of 2.69eV of the prepared nanoparticles showed excellent photocatalytic efficacy toward organic pollutant (fast green FCF) compared to the web of chain nanostructures with an optical band gap of 2.66eV. The ability of the prepared systems to decompose the organic pollutant (fast green FCF) in water was tested under visible light irradiations. The percentage degradation was found to be 94% and 86% for WO3 cube-shaped nanoparticles and WO3 web of chains, respectively. The simplicity of the fabrication method and the high photocatalytic performance of the systems can be promising in environmental applications to treat water pollution.

Photoelectrochemical Selective Oxidation of Glycerol to Glyceraldehyde with Bi-Based Metal-Organic-Framework-Decorated WO3 Photoanode.

The conversion of glycerol to high-value-added products via photoelectrochemical (PEC) oxidation has emerged as a promising approach for utilizing a sustainable and clean energy source with environmental and economic benefits. Moreover, the energy requirement for glycerol to produce hydrogen is lower than that for pure water splitting. In this study, we propose the use of WO3 nanostructures decorated with Bi-based metal-organic frameworks (Bi-MOFs) as the photoanode for glycerol oxidation with simultaneous hydrogen production. The WO3-based electrodes selectively converted glycerol to glyceraldehyde, a high-value-added product, with remarkable selectivity. The Bi-MOF-decorated WO3 nanorods enhanced the surface charge transfer and adsorption properties, thereby improving the photocurrent density and production rate (1.53 mA/cm2 and 257 mmol/m2·h at 0.8 VRHE). The photocurrent was maintained for 10 h, ensuring stable glycerol conversion. Furthermore, at 1.2 VRHE, the average production rate of glyceraldehyde reached 420 mmol/m2·h, with a selectivity of 93.6% between beneficial oxidized products over the photoelectrode. This study provides a practical approach for the conversion of glycerol to glyceraldehyde via the selective oxidation of WO3 nanostructures and demonstrates the potential of Bi-MOFs as a promising cocatalyst for PEC biomass valorization.