Monoclinic WO3 Research Articles

Bi-functional hydrogen tungsten bronze/carbon composite catalysts towards biomass conversion and solar water purification

We presented a novel bi-functional catalyst composed of HxWO3 and carbon composites, which exhibits excellent catalytic activity in biomass conversion and has the ability to effectively purify water via a wide range of wavelengths in the light spectrum. The HxWO3/carbon composites were effectively produced from commercially available monoclinic tungsten trioxide (WO3) and polypropylene (PP) powders to a single-step mechanochemical reaction employing high-energy ball milling. We systemically investigated how different synthesis parameters, such as rotation speed, processing duration, and ball diameter, affect the mechanochemically-induced phase transformation to either tetragonal or cubic HxWO3 during planetary ball milling. The crystal phase of HxWO3 was controllable by altering the total impact energy in the ball milling. In addition, real-time monitoring of the pressure increment inside the pot and evaluation of the evolved gas revealed the degassing behavior through the oxidative degradation of PP assisted by WO3. The CV and Rietveld analysis proved that HxWO3 exhibited significant enhancement by two orders of magnitude in the rate of H+ diffusion compared to monoclinic WO3. This enhancement would be attributed to the expansion of a mechanically-formed tunnel along the a-axis, which facilitates the migration of H+ ions. The HxWO3/carbon composites performed approximately 12-fold higher efficiency in generating soluble solids (glucose and furfural derivatives) compared to untreated WO3 through the catalytic hydrolysis of cellulose, owing to the enhanced Brønsted acidity. Moreover, the composite particles showed broad light absorption in the UV–Vis–NIR range and demonstrated a considerable enhancement of over three orders of magnitude in the photocatalytic degradation of methyl orange pollutants when exposed to NIR and visible light.

Thermomechanical and Structural Analysis of WO3 Array for Optimized Photoelectrochemical Chloride Oxidation Performance.

Understanding the crystal structure of WO3 is essential for optimizing its photoelectrochemical performance. This study comprehensively analyzes the structural characteristics of WO3 during synthesis and investigates their correlation with photoelectrochemical activity. Structural analysis, incorporating annealing procedure and WO3 thickness, identifies a blend of hexagonal, monoclinic, and orthorhombic phases within WO3 array. Specifically, detailed analysis reveals a predominance of monoclinic WO3 phase alongside the orthorhombic WO3 phase, both of which are commonly characterized by their monoclinic structure. Three-dimensional thermomechanical simulations using the finite element method reveal that thermal displacement in WO3 layers increases with thickness during the thermally induced synthesis process. These results highlight a direct correlation between WO3 thickness, thermal displacement, and phase transition, with thicker layers favoring the transformation from orthorhombic to monoclinic structures due to increased thermally induced deformation. The heightened monoclinic structure, which possesses lower symmetry than the orthorhombic structure, induces more defect sites, suggesting increased donor density. Notably, the monoclinic-dominated WO3 exhibits superior performance under UV-visible irradiation in 0.5 M NaCl. Furthermore, the WO3 array demonstrates over 85% Faradaic efficiency for chloride oxidation, indicating preferential selectivity over oxygen evolution reaction in 0.5 M NaCl. This study emphasizes the pivotal role of the crystal structure of WO3 in achieving efficient photoelectrochemical seawater splitting.

(Digital Presentation) The Effects of Heat Treatment on Electroreduction of Tungsten (VI) Oxide

According to the classic scheme of the FFC Cambridge process, oxides of refractory metals are reduced in the solid state. Before electrolysis, oxides are shaped into cylindrical preforms and annealed at high-temperatures (~1000 °С). Therefore, the purpose of this study is to establish the effect of heat treatment of the initial sample of tungsten trioxide on its electrochemical reduction on a solid cathode in a CaCl2–NaCl melt.There are two types of tablets (preforms) were used for research: non-sintered (only compressed) WO3 and annealed at a temperature of 1000 °C. The surface of a pelletized tungsten trioxide sample without sintering is characterized by a uniform distribution of particles, shown in the SEM image (Fig. a). The particles agglomeration is characteristic for the sample WO3 after heat treatment (1000 °С) (Fig. b), which leads to a decrease in the area and an increase in the size of the voids. The unsintered sample has a larger surface area between the particles due to their dispersed state, which facilitates the penetration of the melt compared to the annealed sample.Electrochemical reduction of pressed WO3 samples (d=0.8 cm, h=0.15±0.20 cm, m=0.45–0.50 g) was carried out under galvanostatic conditions (800 °С) with using steel as the cathode and graphite as the anode. It was established that preliminary heat treatment of WO3 does not contribute to its electrochemical reduction. After applying 1.20 A·h of electricity, the porous granules of unsintered WO3 were completely transformed into metallic tungsten (W), which is shown in Fig. c, line 1. However, sintered samples after electrolysis (quantity of electricity is 1.42 A·h) reduced only partially: W – 74.1%; CaWO4 – 25.9% (Fig. c, line. 2).The results show that the reduction occurs more intensively in samples with more micropores, through which mass transfer occurs at the phase interface: tungsten compound to be reduced molten electrolyte mixture. That is why in the unsintered WO3 sample, the electrochemical reduction is faster. It can be assumed that the degree of reduction of WO3 on a solid electrode in CaCl2–NaCl also depends on its crystal structure. The annealed sample (tetragonal structure) is less susceptible to electrochemical reduction compared to the unannealed sample of tungsten trioxide (monoclinic structure). This is due to the fact that tetragonal WO3 (above 740 °C) is resistant to chemical attack, a poor conductor of electricity and has a low surface area. Monoclinic WO3 (from 17 to 330 °C) is more reactive, a better conductor of electricity and has a higher surface area. Figure 1

Itaconic acid modified carboxylic-acid functionalized (002) faceted monoclinic WO3 nanorods for electrochemical hydrogen evolution reaction

Itaconic acid modified carboxylic-acid functionalized (002) faceted monoclinic WO3 nanorods for electrochemical hydrogen evolution reaction

The interaction of light with oxygen-vacancy-rich W18O49 nanoparticles synthesized using different acid molarities for acidic and neutral water treatments

Toxic industrial compounds as a global difficulty can adversely impact people's health and the environment which motivates studies on the interaction of light and metal oxide nanoparticles to treat the water through adsorption or photocatalysis mechanism by nanoparticles. In the paper, oxygen-vacancy-rich W18O49 nanorods are successfully synthesized by a facile one-pot hydrothermal method using different molarities of hydrochloric acid (HCl) (2–12 M) as proposed candidates to treat the wastewater and solve the global difficulty related to treating the acidic water. The results declare that the change in acid molarity leads to noteworthy changes in the characteristic properties of the produced W18O49 nanorods, and the lowest acid molarity (2 M) causes the formation of uniform and pure monoclinic W18O49 nanorods with the high specific surface area (SSA) of 51.33 m2/g. Furthermore, the nanorods exhibit indirect and direct band gap energies in the range of 2.52–2.68 eV and 2.54–3.08 eV, respectively, as influenced by varying acid molarities (2–12 M). Furthermore, the impressive effects of acid molarity on the methylene blue removal efficiency of the nanorods under ultraviolet (UV) light are observed. The highest efficiency is obtained for W18O49 nanorods synthesized using the acid molarity of 2 M which can be explained by its high SSA, small band gap energy, generation of a large number of electron-hole pairs, and its efficient charge separation. The efficiencies of water treatment reach up to 99 % and 99.5 % at pH of 7 and 5, respectively, which is an excellent achievement and leads to proposing the mentioned W18O49 nanorods as an excellent candidate for treating wastewater and acid factory effluent which represents an appreciable breakthrough in addressing the issue.

Raman Study of Novel Nanostructured WO3 Thin Films Grown by Spray Deposition.

The present communication reports on the effect of the sprayed solution volume variation (as a thickness variation element) on the detailed Raman spectroscopy for WO3 thin films with different thicknesses grown from precursor solutions with two different concentrations. Walls-like structured monoclinic WO3 thin films were obtained by the spray deposition method for further integration in gas sensors. A detailed analysis of the two series of samples shows that the increase in thickness strongly affects the films' morphology, while their crystalline structure is only slightly affected. The Raman analysis contributes to refining the structural feature clarifications. It was observed that, for 0.05 M precursor concentration series, thinner films (lower volume) show less intense peaks, indicating more defects and lower crystallinity, while thicker films (higher volume) exhibit sharper and more intense peaks, suggesting improved crystallinity and structural order. For higher precursor concentration 0.1 M series, films at higher precursor concentrations show overall more intense and sharper peaks across all thicknesses, indicating higher crystallinity and fewer defects. Differences in peak intensity and presence reflect variations in film morphology and structural properties due to increased precursor concentration. Further studies are ongoing.

Steering Photooxidation of Methane to Formic Acid over A Priori Screened Supported Catalysts.

Efficient methane photooxidation to formic acid (HCOOH) has emerged as a sustainable approach to simultaneously generate value-added chemicals and harness renewable energy. However, the persistent challenge lies in achieving a high yield and selectivity for HCOOH formation, primarily due to the complexities associated with modulating intermediate conversion and desorption after methane activation. In this study, we employ first-principles calculations as a comprehensive guiding tool and discover that by precisely controlling the O2 activation process on noble metal cocatalysts and the adsorption strength of carbon-containing intermediates on metal oxide supports, one can finely tune the selectivity of methane photooxidation products. Specifically, a bifunctional catalyst comprising Pd nanoparticles and monoclinic WO3 (Pd/WO3) would possess optimal O2 activation kinetics and an intermediate oxidation/desorption barrier, thereby promoting HCOOH formation. As evidenced by experiments, the Pd/WO3 catalyst achieves an exceptional HCOOH yield of 4.67 mmol gcat-1 h-1 with a high selectivity of 62% under full-spectrum light irradiation at room temperature using molecular O2. Notably, these results significantly outperform the state-of-the-art photocatalytic systems operated under identical condition.

Ultraefficient Ammonia Gas Sensors Based on Pt‐Loaded WO3 Nanobars

Herein, unloaded WO3 (WO3) and Pt‐loaded WO3 (Pt‐WO3) nanobars are successfully synthesized through simple hydrothermal and impregnation methods. X‐ray diffractometer analysis confirms the formation of a monoclinic WO3 structure. Surface analysis reveals that the Pt impregnation results in a significant increase in the specific surface area of WO3 nanobars. The gas‐sensing performance of sensors based on nanobars is measured toward ammonia (NH3) with varying NH3 concentrations at different operating temperatures. Compared with the pristine WO3 sensor, the Pt‐WO3‐based sensor with an optimal Pt content of 1 wt% exhibits a relatively low optimum operating temperature of 250 °C and a superior response of 960–50 ppm NH3. Furthermore, the Pt‐WO3‐based sensor also displays fast response, excellent NH3 selectivity to ammonia, moderate humidity dependence, and good stability. Therefore, the developed hydrothermal and impregnation methods could be a suitable alternative procedure for the synthesis of Pt‐WO3 nanobars useful for advanced NH3‐sensing applications.

Inhibiting the phase transition of WO3 for highly stable aqueous electrochromic battery

Aqueous electrochromic battery (ECB) has shown intense potential for achieving energy storage and saving simultaneously. While tungsten oxide (WO3) is the most promising EC material for commercialization, the cycling stability of WO3-based aqueous ECBs is currently unsatisfactory due to the repeated phase transition during the redox process and the corrosion by acidic electrolytes. Herein, we present a titanium-tungsten oxide alloy (Ti-WO3) with controllable morphology and crystal phase synthesized by a facile hot injection method to overcome the challenges. In contrast to conventional monoclinic WO3, the Ti-WO3 nanorods can stably maintain their cubic crystal phase during the redox reaction in an acidic electrolyte, thus leading to dramatically enhanced response speed and cycling stability. Specifically, when working in a well-matched hybrid Al3+/Zn2+ aqueous electrolyte, our phase-transition-free cubic Ti-WO3 exhibits an ultra-high cycling stability (>20000 cycles), fast response speed (3.95 s/4.65 s for bleaching/coloring), as well as excellent discharge areal capacity of 214.5 mA h m−2. We further fabricate a fully complementary aqueous electrochromic device, for the first time, using a Ti-WO3/Prussian blue device architecture. Remarkably, the complementary ECB shows >10000 stable operation cycles, attesting to the feasibility of our Ti-WO3 for practical applications. Our work validates the significance of inhibiting the phase transitions of WO3 during the electrochromic process for realizing highly cyclable aqueous ECB, which can possibly provide a generalized design guidance for other high-quality metallic oxides for electrochemical applications.

Tungsten oxide encapsulated phosphate-rich porous alginate composites for efficient U(VI) capture: Insights into synthesis, adsorption kinetics and thermodynamics

In this work, novel monoclinic tungsten oxide (WO3)-encapsulated phosphate-rich porous sodium alginate (PASA) microspherical hydrogel beads were prepared for efficient U(VI) capture. These macroporous and hollow beads were systematically characterized through XRD, FTIR, EDX-mapping, and SEM-EDS techniques. The O and P atoms in the PO and monoclinic WO3 offered inner-spherical complexation with U(VI). The in situ growth of WO3 played a significant role inside the phosphate-rich biopolymeric network to improve its chemical stability, specific surface area, adsorption capacity, and sorption rate. The phytic acid (PA) served for heteroatom doping and crosslinking. The encapsulated WO3 mass ratio was optimized in different composites, and WO3/PASA3 (the microspherical beads with a mass ratio of 30.0 % w/w) exhibited remarkable maximum sorption capacity qm (336.42 mg/g) computed through the best-fit Langmuir model (R2 ≈ 0.99) and rapid sorption equilibrium, teq (150 min). The isothermal sorption studies were conducted at different temperatures (298, 303, and 308 K) and thermodynamic parameters concluded that the process of U(VI) sorption using WO3/PASA3 is endothermic and feasible having ΔHo (8.19 kJ/mol), ΔGo (−20.75, −21.38, and − 21.86 kJ/mol) and proceeds with a minute increase in randomness ΔSo (0.09 kJ/mol.K). Tungsten oxide (WO3)-encapsulated phosphate-rich porous microspherical beads could be promising material for uranium removal.

The Influence of 2-Methoxyethanol as Capping Agent on WO3-Based Carbon Monoxide Gas Sensor Characteristics

Carbon monoxide (CO) gas detection using a modified WO3-based sensor is being developed. The solvent for solvothermal use, a combination of 2-Propanol and 2-Methoxyethanol, was employed as a capping agent before graphene was used as a component of nanocomposites. Following the creation of the powder, it is combined with ethyl glycol and applied to an alumina substrate using the Doctor Blade process.By X-ray diffraction research, it was discovered that the solvent combinations of 2-Propanol and 2-Methoxyethanol formed monoclinic WO3 in the amounts of 40-0 and 30-10, respectively, while the solvent combinations of 20-20 are thought to have produced W18O49 and 10-30, WO2.9, respectively. According to the SEM examination, the WO3 generated was first present as nanowires and nanorods before being calcined at 500 degrees Celsius, and it then appeared as nanoparticles. The sensor may work at a low temperature of 150°C, and the best sensitivity is found when the sensor is used at a temperature of 250°C, according to the CO gas test findings.

Selective Photoelectrochemical Oxidation of Glycerol to Glyceric Acid on (002) Facets Exposed WO3 Nanosheets

AbstractGlycerol is a byproduct of biodiesel production. Selective photoelectrochemical oxidation of glycerol to high value‐added chemicals offers an economical and sustainable approach to transform renewable feedstock as well as store green energy at the same time. In this work, we synthesized monoclinic WO3 nanosheets with exposed (002) facets, which could selectively oxidize glycerol to glyceric acid (GLYA) with a photocurrent density of 1.7 mA cm−2, a 73 % GLYA selectivity and a 39 % GLYA Faradaic efficiency at 0.9 V vs. reversible hydrogen electrode (RHE) under AM 1.5G illumination (100 mW cm−2). Compared to (200) facets exposed WO3, a combination of experiments and theoretical calculations indicates that the superior performance of selective glycerol oxidation mainly originates from the better charge separation and prolonged carrier lifetime resulted from the plenty of surface trapping states, lower energy barrier of the glycerol‐to‐GLYA reaction pathway, more abundant active sites and stronger oxidative ability of photogenerated holes on the (002) facets exposed WO3. Our findings show great potential to significantly contribute to the sustainable and environmentally friendly chemical processes via designing high performance photoelectrochemical cell via facet engineering for renewable feedstock transformation.

Selective Photoelectrochemical Oxidation of Glycerol to Glyceric Acid on (002) Facets Exposed WO3 Nanosheets.

Glycerol is a byproduct of biodiesel production. Selective photoelectrochemical oxidation of glycerol to high value-added chemicals offers an economical and sustainable approach to transform renewable feedstock as well as store green energy at the same time. In this work, we synthesized monoclinic WO3 nanosheets with exposed (002) facets, which could selectively oxidize glycerol to glyceric acid (GLYA) with a photocurrent density of 1.7 mA cm-2 , a 73 % GLYA selectivity and a 39 % GLYA Faradaic efficiency at 0.9 V vs. reversible hydrogen electrode (RHE) under AM 1.5G illumination (100 mW cm-2 ). Compared to (200) facets exposed WO3 , a combination of experiments and theoretical calculations indicates that the superior performance of selective glycerol oxidation mainly originates from the better charge separation and prolonged carrier lifetime resulted from the plenty of surface trapping states, lower energy barrier of the glycerol-to-GLYA reaction pathway, more abundant active sites and stronger oxidative ability of photogenerated holes on the (002) facets exposed WO3 . Our findings show great potential to significantly contribute to the sustainable and environmentally friendly chemical processes via designing high performance photoelectrochemical cell via facet engineering for renewable feedstock transformation.

Asymmetric supercapacitor performance of hydrothermally-synthesized MWCNT-WO3 composite electrode

Supercapacitors are energy storage devices that have the potential to significantly contribute to meeting energy demands in the modern era. However, the charge storage capacity and stability of pseudocapacitive materials should be improved. To improve the electrode storage capacity, tungsten trioxide (WO3) has been synthesized and deposited on multi-walled carbon nanotubes (MWCNT-WO3) on stainless-steel substrates via hydrothermal technique. The structural, morphological, elemental, and compositional studies on WO3 and MWCNT-WO3 samples were done with X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform Infrared Spectroscopy (FTIR), contact angle, and Brunauer-Emmett-Teller (BET). The electrochemical features of the WO3 and MWCNT-WO3 materials were studied for supercapacitor application using a three-electrode set-up. The results obtained show highly crystalline films with porous nanoplates at the surface and monoclinic WO3 phase. The basic elemental constituents and chemical bonds present in the synthesized samples were confirmed using EDX and FTIR spectra. The MWCNT-WO3 exhibited an optimized capacitive behavior when compared to WO3. A specific capacitance of 818.31 Fg−1 was obtained at a scan rate of 5 mVs−1 in 0.5 M H2SO4 electrolyte. The composite MWCNT-WO3 was further used as an electrode in a solid-state asymmetric supercapacitor, PANI||MWCNT-WO3 fabricated with polyaniline (PANI) and MWCNT-WO3 as positive and negative electrodes in polyvinyl alcohol/sulphuric acid (PVA/H2SO4) gel electrolyte. The fabricated materials exhibited excellent electrochemical performance which makes them useful for supercapacitor applications.

Plasma assisted pulsed laser deposition of WO3 films for thermochromism

Tungsten trioxide (WO3) is one of the extensively investigated transition metal oxides. Its excellent chromogenic properties make WO3 promising for a variety of scientific and technological applications. We report a new method for reactively depositing WO3 films by plasma assisted pulsed laser deposition that combines electron cyclotron resonance microwave discharge and pulsed laser ablation. The plasma formed during film deposition was spectroscopically characterized by optical emission measurement, revealing that the plasma contains high density of reactive gaseous oxygen and tungsten species which are essential for efficiently synthesizing WOx precursors and depositing WO3 films. The structure of the deposited films and the effect of post-deposition thermal annealing on the film structure were characterized by X-ray diffraction and Raman spectroscopy. The as-deposited WO3 film appears amorphous in nature. Annealing resulted in the growth of crystalline grains and the improvement in the crystallinity of monoclinic WO3. Optical properties of the prepared WO3 films were studied by measuring ultraviolet–visible–near infrared transmission spectra. With the increase of annealing temperature, the WO3 films show a continuous change in color, decline in transmittance, red shift in absorption edge, and narrowing in band gap, clearly manifesting the thermochromic features of the deposited WO3 films.

Decoupled Electrolysis: A Novel Method for Water Splitting Using WO3 Auxiliary Electrode

More emphasis must be placed on the use of clean and renewable energy sources. Production of electricity using solar, wind geothermal etc is becoming more widespread however these types of energy production suffer from intermittence in production and a mismatch of production and consumption cycles. These problems result in a need for an energy storage medium. A hydrogen is a viable option because of its high gravimetric heat capacity (143 MJ/kg) and low flashpoint (-231°C) [1]. For now, most of the produced hydrogen is from hydrocarbons and only 4% is being produced using electrolysis. Hydrogen production via electrolysis is an efficient way how to store surplus energy from renewable energy sources but electrolysis must be made more achievable. Commonly used water electrolysis is limited by the need for complicated gas distribution systems to avoid mixing of H2 and O2 which can lead to a serious safety hazard. Membranes and diaphragms can solve gas mixing problems but they significantly reduce efficiency and increase hydrogen production costs.Here we demonstrate the principle of decoupled electrolysis where oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is separated in space with the use of a WO3 redox mediator. WO3 was produced by the solvothermal method. In accordance with SEM (Fei, NanoSEM 650), XRD (Rigaku, Ultima+) and XPS (Thermo Scientific, Escalab Xi+) data, monoclinic WO3 nanosheet assemblies with a cluster size of 10-20 μm and plate thickness of 50-100 nm were produced without lower oxidation states. Electrodes were produced using carbon felt which was saturated with ink suspension containing active material (WO3), carbon black and polyvinyl difluoride (PVDF) in a mass ratio of 60-30-10. DMF was used as a solvent. Electrolysis was achieved in a two-step process. In the first step, an OER reaction occurs and the H ion is intercalated into WO3 forming tungsten bronze HxWO3. OER reaction occurs on platinum and O2 is released with gas purity above 99.9 %. In the second step, H ion deintercalation occurs and H2 is released at the Pt electrode with a purity greater than 99.9%. Gas purity was determined using a gas mass spectrometer. Electrochemical measurements were performed using Metohm AutoLAB potentiostat with Nova software. The electrode was analysed using cyclic voltammetry (CVP), impedance spectroscopy (EIS) and chronopotentiometry. 0.5 M H2SO4 was used as an electrolyte solution.In accordance with the CVP capacity of the WO3 electrode reaches 325 F/g at a scan rate of 2 mV/s and decreases with an increase in scan speed. A decrease in capacity due to an increase in scanning speed can be associated with limited charge diffusion [2]. The shift of the maximum in the anodic direction associated with the transition from W5+ to W6+ with an increase in scan speed is polynomial and can be associated with the pseudocapacitive behaviour of electrode material. The Nyquist plot from EIS measurements shows the formation of an incomplete arc in the high-frequency interval and linear correlation in lower frequencies. In chronopotentiometry with a current density of 100 mA/g faradaic efficiency reached 90.2% and increased to 100% when 1000 mA/g were used, however taking into account both OER and HER reactions, cycle efficiency decreased from 65 to 43 % with the same current densities. If only HER reaction is analysed when hydrogen is being released and deintercalation happens, cycle efficiency reaches 341 %. High efficiency can be explained by extra energy obtained from the building potential of the WO3 electrode that lowers the standard potential for water electrolysis. Long-term tests showed good stability and no degradation was observed in accordance with SEM and XPS studies. At high intercalation-deintercalation cycle times, a non-Faradaic process can be observed which reduced HER cycle time. A spontaneous deintercalation can be observed. One of the future goals is to prevent this process by the use of different auxiliary electrode materials.[1]-Tashie-Lewis BC, Nnabuife SG. Hydrogen production, distribution, storage and power conversion in a hydrogen economy - a technology review. Chemical Engineering Journal Advances 2021;8:100172.[2]- Das AK, Karan SK, Khatua BB. High energy density ternary composite electrode material based on polyaniline (PANI), molybdenum trioxide (MoO3) and graphene nanoplatelets (GNP) prepared by sonochemical method and their synergistic contributions in superior supercapacitive performance. Electrochim Acta 2015;180:1e15. Figure 1

In-situ construction of g-C3N4/WO3 heterojunction composite with significantly enhanced photocatalytic degradation performance

g-C3N4/WO3 heterojunction composites were synthesized via an in-situ method by thermal polymerizing the mixture of dual precursors (urea and thiourea with molar ratio of 3:1) and different amount of tungstic acid. The as-synthesized g-C3N4/WO3 composites, with lamellar and rod-like nano-porous structure, were mainly composed of g-C3N4 and monoclinic WO3, in which the crystal size of WO3 was about 5–10 nm. The specific surface area of the composite increased gradually with the tungstic acid dosage and reached 79.41 m2/g when the addition amount of tungstic acid was 1 wt%. The in-situ construction of g-C3N4/WO3 heterojunction contributed to the reduction of band gap, improvement of the visible response range as well as the acceleration of the separation and migration of the photogenerated carriers. As the dosage of tungstic acid increased, the photocatalytic degradation performance of g-C3N4/WO3 composite towards tetracycline improved gradually and achieved the optimum when the addition amount of tungstic acid was 0.1 wt% (CN/WO3-10). CN/WO3-10 (0.05g) degraded 83 % of tetracycline molecules (100 mL, 20 mg/L) after photocatalysis for 100 min, whose degradation rate constant was 10.1 and 1.48 times that of pure WO3 and g-C3N4, respectively. Moreover, g-C3N4/WO3 composite exhibited excellent stability and reusability for the photocatalytic degrading tetracycline. This work provides a facile and practicable approach for the preparation of g-C3N4/WO3 composite.

Hydrothermal synthesis of hierarchical microstructure tungsten oxide/carbon nanocomposite for supercapacitor application

A hierarchical nanocomposite of carbon microspheres decorated with tungsten oxide (WO3) nanocrystals resulted from the hydrothermal treatment of a precursor solution containing glucose and tungstic acid. The dehydration of glucose molecules formed oligosaccharides, which consequently carbonized, turning into carbon microspheres. The carbon microspheres then acted as a spherical nucleus onto which WO3 nanocrystals grew via heterogeneous nucleation. The reaction product showed a phase junction of orthorhombic and monoclinic WO3, which transitioned to mix-phase of tetragonal and monoclinic WO3 after a subsequent heat treatment at 600 °C in an inert condition. The electrochemical tests showed that incorporating WO3 onto the carbon (WO3/C) resulted in a three-fold increase in the specific capacitance compared to WO3 alone and a high coulombic and energy efficiencies of 98.2% and 92.8%, respectively. The nanocomposite exhibited supercapacitance with both Faradaic and non-Faradaic charge storage mechanisms. Electrochemical impedance spectroscopy showed a lower charge transfer resistance for the composite at Rct = 11.7Ω.

Fabrication of WO3 photocatalyst by plasma assisted ball milling under different discharge atmospheres

A convenient method for producing single oxide WO3-x at room temperature through plasma milling was reported, resulting in a highly efficient visible-light photocatalyst. By altering the discharge atmosphere during plasma milling from ammonia and nitrogen to argon, the color of the milled monoclinic WO3 powders deepens from blue to dark blue, indicating an increased concentration of oxygen vacancies. The morphological and structural properties of the monoclinic WO3 powders, prepared using different ball milling techniques, are characterized using XRD, SEM, TEM, Raman, XPS, EPR, and UV–vis. These results reveal that plasma milling leads to a higher surface area, increased presence of oxygen vacancies, and more defects compared with conventional milling, resulting in a greater number of more reactive sites and a larger contact area between monoclinic WO3 nanoparticles and RhB solution. Consequently, monoclinic WO3 samples fabricated through Ar-P-milling exhibit the highest photocatalytic activity. This is attributed to the reduction of the WO3−x band gap to 2.28 eV by Ar-P-milling with high oxygen vacancies. This lower bandgap markedly improves the light utilization rate, thereby enhancing the overall photocatalytic efficiency. The Ar-P-milled WO3 shows the highest degradation rate constant of 0.037 min−1, which is 4 times higher than that of pure monoclinic WO3.

Fabrication of Pd-decorated tungsten oxide nanoflakes for hydrogen sensors via facile anodizing oxidation method

Accurate and reliable hydrogen sensing is crucial for safety and efficiency in industries like energy, transportation, and environmental monitoring. This study presents the synthesis and characterization of Pd-decorated WO3 nanoflakes with palladium (Pd) nanoparticles from anodizing derived WO3.2(H2O) nanoflakes for gas sensing applications. We investigate the crystal structure and phase composition of the synthesized nanoflakes using X-ray diffraction (XRD) and Raman spectroscopy, which confirm the presence of well-crystallized monoclinic WO3.2(H2O) phase without any impurities or secondary phases. Field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) reveal the unique morphology of the nanoflakes with irregular edges and varying sizes, as well as the successful decoration of Pd nanoparticles on the nanoflake surface. X-ray photoelectron spectroscopy (XPS) analysis indicates partial oxidation of tungsten species upon interaction with PdCl2 solution. We evaluate the gas sensing characteristics of the decorated nanoflakes towards hydrogen gas, demonstrating an enhanced response at elevated temperatures (>300 °C). The introduction of Pd nanoparticles improves the gas sensing response up to 6000 due to increased hydrogen dissociation and catalytic activity, as well as enhanced electrical conductivity. The response and recovery times of the sensors are rapid, indicating efficient response-recovery behavior. These findings suggest the potential of anodizing method for fabrication of WO3.2(H2O) nanoflakes as promising candidates for gas sensing applications.