WO3 Microspheres Research Articles

Selective trimethylamine sensors based on Co3O4 modified WO3 spheres

Co3O4 modified WO3 microspheres with excellent trimethylamine (TMA) gas sensitive performance were prepared by a simple hydrothermal method using ZIF-67 as a template. The morphology, elemental composition, structure of the compounds, and gas-sensitive properties of the sensors based on them were researched by SEM, XRD, XPS as well as the gas-sensing analysis system. The prepared Co3O4 modified WO3 spheres exhibit significantly enhanced TMA gas sensitive properties, such as high response (198) to 100 ppm TMA, excellent selectivity, rapid response/recovery rate (11.7/2.1 s), good repeatability, long-term stability, and low detection limit (0.17 ppm) at 285 ℃. The sensing properties of the WO3/Co3O4 sensor may be due to the large surface area, significant resistance modulation effect of the p-n heterostructure, and catalytic effect of Co3O4. This work suggests that Co3O4 modified WO3 spheres may play an important role in the field of high-performance TMA sensors.

3D-engineered WO3 microspheres assembled by 2D nanosheets with superior sodium storage capacity.

Because of the inadequate sodium storage capacity of graphite, the exploration of high-performance SIB anodes is a crucial step forward. Herein, we report the hydrothermally synthesized self-assembled interconnected nanosheets of WO3 microspheres possessing admirable sodium storage in terms of cycling stability and acceptable rate capability. Benefitting from the interconnected nature of the nanosheets with a hollow interior, the WO3 microspheres exhibited a high sodiation capacity of 431 mA h g-1 at 100 mA g-1 and an excellent rate performance of 60 mA h g-1 at 500 mA g-1 with an impressive coulombic efficiency of around 99%. Importantly, even after continuous cycling with increasing current densities, a specific capacity as high as 220 mA h g-1 could be recovered at a current density of 50 mA g-1, suggesting excellent sodium storage reversibility.

Synthesis of hierarchical wo3 microspheres for photoelectrochemical water splitting application

Synthesis of hierarchical wo3 microspheres for photoelectrochemical water splitting application

A three-dimensional fibrous tungsten-oxide/carbon composite derived from natural cellulose substance as an anodic material for lithium-ion batteries

To meet the ever-growing demands over electrochemical energy storage, tungsten trioxide (WO3) has aroused substantial attention as a promising anodic material for lithium-ion batteries due to its high theoretical capacity, abundant earth storage, and eco-friendliness. However, developing high-performance WO3-based electrodes is hampered by its restrictive conductivity and tremendous structural as well as the volumetric changes during the charge/discharge processes. Herein, a novel bio-inspired nanofibrous WO3/carbon composite was synthesized via a facile hydrothermal method employing pre-carbonized cellulose substrate (e.g., ordinary filter paper) as both the structural scaffold and the carbon source. The urchin-like WO3 microspheres with diameters of 3–6 μm assembled by nanorods were uniformly anchored on the surfaces of the cellulose-derived carbon fibers. The three-dimensional network structure of the composite was beneficial in alleviating the volume expansion of WO3 nanorods and enhanced the charge-transport kinetics of the electroactive materials. The composite with an optimized content of WO3 (26.36 wt%) exhibited superior lithium storage properties with an initial discharge capacity of 1470 mAh g−1 and an extraordinary long-term cycling performance of 682 mAh g−1 capacity retention after 300 cycles at 100 mA g−1. Furthermore, cyclic voltammetry, ex-situ XRD, and SEM measurements for mechanism studies were carried out to yield deeper insights into the synergism in the WO3/carbon electrodes, revealing the predominance of reversible pseudocapacitive intercalation of lithium-ions during the electrochemical reaction inside the WO3/carbon anode.

Enhanced Performance of WO3/SnO2 Nanocomposite Electrodes with Redox-Active Electrolytes for Supercapacitors.

For effective supercapacitors, we developed a process involving chemical bath deposition, followed by electrochemical deposition and calcination, to produce WO3/SnO2 nanocomposite electrodes. In aqueous solutions, the hexagonal WO3 microspheres were first chemically deposited on a carbon cloth, and then tin oxides were uniformly electrodeposited. The synthesized WO3/SnO2 nanocomposite was characterized by XRD, XPS, SEM, and EDX techniques. Electrochemical properties of the WO3/SnO2 nanocomposite were analyzed by cyclic voltammetry, galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy in an aqueous solution of Na2SO4 with/without the redox-active electrolyte K3Fe(CN)6. K3Fe(CN)6 exhibited a synergetic effect on the electrochemical performance of the WO3/SnO2 nanocomposite electrode, with a specific capacitance of 640 F/g at a scan rate of 5 mV/s, while that without K3Fe(CN)6 was 530 F/g. The WO3/SnO2 nanocomposite catalyzed the redox reactions of [Fe(CN)6]3/[Fe(CN)6]4- ions, and the [Fe(CN)6]3-/[Fe(CN)6]4- ions also promoted redox reactions of the WO3/SnO2 nanocomposite. A symmetrical configuration of the nanocomposite electrodes provided good cycling stability (coulombic efficiency of 99.6% over 2000 cycles) and satisfied both energy density (60 Whkg-1) and power density (540 Wkg-1) requirements. Thus, the WO3/SnO2 nanocomposite prepared by this simple process is a promising component for a hybrid pseudocapacitor system with a redox-flow battery mechanism.

Polymerization-Induced Aggregation Approach toward Uniform Pd Nanoparticle-Decorated Mesoporous SiO2/WO3 Microspheres for Hydrogen Sensing

Hydrogen as an important clean energy source with a high energy density has attracted extensive attention in fuel cell vehicles and industrial production. However, considering its flammable and explosive property, gas sensors are desperately desired to efficiently monitor H2 concentration in practical applications. Herein, a facile polymerization-induced aggregation strategy was proposed to synthesize uniform Si-doped mesoporous WO3 (Si-mWO3) microspheres with tunable sizes. The polymerization of the melamine-formaldehyde resin prepolymer (MF prepolymer) in the presence of silicotungstic acid hydrate (abbreviated as H4SiW) leads to uniform MF/H4SiW hybrid microspheres, which can be converted into Si-mWO3 microspheres through a simple thermal decomposition treatment process. In addition, benefiting from the pore confinement effect, monodispersed Pd-decorated Si-mWO3 microspheres (Pd/Si-mWO3) were subsequently synthesized and applied as sensitive materials for the sensing and detection of hydrogen. Owing to the oxygen spillover effect of Pd nanoparticles, Pd/Si-mWO3 enables adsorption of more oxygen anions than pure mWO3. These Pd nanoparticles dispersed on the surface of Si-mWO3 accelerated the dissociation of hydrogen and promoted charge transfer between Pd nanoparticles and WO3 crystal particles, which enhanced the sensing sensitivity toward H2. As a result, the gas sensor based on Pd/Si-mWO3 microspheres exhibited excellent selectivity and sensitivity (Rair/Rgas = 33.5) to 50 ppm H2 at a relatively low operating temperature (210 °C), which was 30 times higher than that of the pure Si-mWO3 sensor. To develop intelligent sensors, a portable sensor module based on Pd/Si-mWO3 in combination with wireless Bluetooth connection was designed, which achieved real-time monitoring of H2 concentration, opening up the possibility for use as intelligent H2 sensors.

Novel ultrasensitive Raman assay method based on enzyme mimetics for ultra trace of H2O2

Enzyme mimetics have been widely applied on H2O2 assay, but it is still challenging and interesting to realize the sensitive detection for ultra-trace H2O2. Here, an ultrasensitive Raman assay method based on novel WO3@IP6-Fe3+ enzyme mimetics with peroxidase-like activity was established. WO3 microspheres (MSs) were found to have weak peroxidase-like activity, and the combination of IP6-Fe3+ and WO3 can produce stronger activity. WO3@IP6-Fe3+ MSs showed polyhedron-like structure, uniform size, and smooth surface. Although WO3@IP6-Fe3+ enzyme mimetics have low catalytic efficiency and high absorbance background, the proposed Raman method can bypass the above problems. In Raman method, high concentration of WO3@IP6-Fe3+ can be used to overcome low catalytic efficiency without high absorbance background. Moreover, 3,3′,5,5′-tetramethylbenzidine oxide has prominent characteristic Raman peak at 1608 cm−1, greatly improving the sensitivity and eliminating interference of impurities. Due to the high sensitivity and low background, Raman assay showed the ultra-low limit of detection (5.49 × 10−15 M), which was 4–7 orders of magnitude lower than other detection methods. The ultrasensitive Raman assay not only provided the possibility for the enzyme mimetics-based detection of ultra-trace H2O2, but also enable the enzyme mimetics with low activity to be applied.

FeOOH quantum dot decorated flower-like WO3 microspheres for visible light driven photo-Fenton degradation of methylene blue and acid red-18

In this study, nano-flower WO3 hollow microspheres were synthesized by calcining SrWO4 precursors at 300 °C. The WO3-FeOOH-X series photocatalysts were synthesized by successfully anchoring the amorphous FeOOH quantum dots uniformly on the WO3 nanoflower petals. Azo dyes in single system (MB, AR-18) and mixed system (MB+AR-18) were treated synergistically by light and Fenton. The reusability of WO3-FeOOH-3 samples at ambient temperature was investigated. Active species removal experiments were conducted to reveal their photo-Fenton degradation mechanism of organic pollutants. The results showed that the degradation rate of WO3-FeOOH-3 was 98.69% for MB within 5 min. The degradation rate of AR-18 was 92.55%. The mixed dye system (MB+AR-18) became clarified within 5 min. The efficient degradation rate was attributed to the homogeneous dispersion centers and the multiple active sites provided by the WO3 petals for FeOOH anchoring. In conclusion, WO3-FeOOH-X provides a new pathway and applicability for the efficient degradation of MB and AR-18 azo dyes.

Highly Selective and Sensitive Detection of Breath Isoprene by Tailored Gas Reforming: A Synergistic Combination of Macroporous WO3 Spheres and Au Catalysts.

Precise detection of breath isoprene can provide valuable information for monitoring the physical and physiological status of human beings or for the early diagnosis of cardiovascular diseases. However, the extremely low concentration and low chemical reactivity of breath isoprene hamper the selective and sensitive detection of isoprene using oxide semiconductor chemiresistors. Herein, we report that macroporous WO3 microspheres whose inner macropores are surrounded by Au nanoparticles exhibit a high response (resistance ratio = 11.3) to 0.1 ppm isoprene under highly humid conditions at 275 °C and an extremely low detection limit (0.2 ppb). Furthermore, the sensor showed excellent selectivity to isoprene over five interferants that could be exhaled by humans. Notably, the selectivity to isoprene is critically dependent on the location of Au nanocatalysts and macroporosity. The mechanism underlying the selective isoprene detection is investigated in relation to the reforming of less reactive isoprene into more reactive intermediate species promoted by macroporous catalytic reactors, which is confirmed by the analysis using a proton transfer reaction quadrupole mass spectrometer. The sensor for breath analysis has high potential for simple physical and physiological monitoring as well as disease diagnosis.

Facile route for fabricating Co(OH)2@WO3 microspheres from scheelite and its environmental application for high-performance peroxymonosulfate activation

The production integration from mineral resources to materials is favorable for reducing the environmental impacts, shortening the production cycle and improving resource utilization. In this work, we developed a facile and eco-friendly method to prepare Co-doped WO3 microspheres from low-grade scheelite, by which the use of chemicals and discharge of wastewater were significantly decreased compared with traditional preparation methods. The as-prepared Co(OH)2@WO3 composite was employed as a peroxymonosulfate (PMS) activator for rhodamine B (RhB) degradation. Density functional theory (DFT) calculation illustrated its adsorption capacity for PMS, and the adsorption effect of Co(OH)2 was more obvious than WO3. Compared with the Co(OH)2, the composites displayed excellent catalytic performance, by which RhB was completely removed within 7 min and a high rate constant of 0.57 min−1 was achieved. This was attributed the lower electrical transfer resistance and better electrical conductivity of the composites confirmed by different electrochemical tests. Quenching experiments revealed that both SO4•− radicals and 1O2 were involved in the reaction system, and 1O2 served as the dominant reactive oxygen species. Furthermore, catalyst stability was assessed by reuse experiments and no significant decrease of degradation efficiency was noticed after five cycles, suggesting good stability of the catalyst. This work might shed new light on preparing efficient catalyst from natural minerals, and the findings would be helpful for the development of the tungsten industry and the improvement of organic wastewater treatment.

Novel S-scheme WO3/CeO2 heterojunction with enhanced photocatalytic degradation of sulfamerazine under visible light irradiation

In this work, hierarchical WO3-CeO2 hollow sphere heterojunctions were fabricated via a two-step hydrothermal method and applied for degradation of sulfamerazine antibiotic under visible light irradiation. The incorporation of CeO2 into the WO3 microspheres was confirmed by XRD, BET, HRTEM, and XPS analysis. The results revealed that the photocatalytic activity of WO3-CeO2 heterojunction was greatly enhanced compared to pure CeO2 and WO3 samples, and the highest degradation percentage of sulfamerazine was achieved on the WO3-CeO2 heterojunction with 30 mol. % CeO2 content. This could be ascribed to the efficient separation of charge carriers which was facilitated by oxygen vacancies formed at the interfaces of two coupled semiconductors. EIS analysis verified that the charge transfer resistance of WO3-30CeO2 heterojunction was decreased, which is due to the heterojunction effect. Moreover, based on the Mott-Schottky calculations, radical trapping experiments and ESR analysis, hydroxide radicals were identified as the main active species, and an S-scheme charge transfer mechanism was suggested to explain the enhanced photocatalytic activity. The possible degradation pathway of sulfamerazine was suggested through the detection of degradation intermediates by mass spectroscopy.

Synthesis of nanorods assembled V‐doped WO3 microspheres and the catalytic performance in thermal decomposition of ammonium perchlorate

AbstractV‐doped WO3 microspheres composed of nanorods radially grown from the center were fabricated via a simple hydrothermal method. The as‐obtained products were characterized by several techniques such as X‐ray powder diffraction (XRD), energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectrum, and Brunauer–Emmett–Teller (BET). It was found that V atoms were incorporated inside the hexagonal WO3 lattice. On the basis of time‐dependent experiments, the formation mechanism for the as‐prepared V‐doped WO3 micro‐nanostructures was discussed. In addition, the catalytic properties of the synthesized material on the thermal decomposition of ammonium perchlorate (AP) were evaluated by thermal gravimetric and differential thermal analysis (TG/DTA), which showed the thermal decomposition temperatures of AP in the presence of 1, 2, and 4 wt% of V‐doped WO3 micro‐nanostructures were reduced to 399, 393, and 380°C, respectively.

Hierarchical hollow WO3 microspheres with tailored surface oxygen vacancies for boosting photocatalytic selective conversion of biomass-derived alcohols

Selective conversion of biomass-derived alcohols into carbonyl compounds via visible-light photocatalysis is realized over hierarchical hollow WO3 microspheres with tailored surface oxygen vacancies, which presents the remarkably boosted photoactivity in terms of selectivity and activity, intrinsically attributing to the strong synergetic effect of hierarchical spherical cavity and surface oxygen vacancies simultaneously. The hierarchical spherical cavity, substantially constructed by the self-interconnected nanosheets, enhances the light-harvesting ability via multiple light reflections not only in spherical cavity but also among the self-interconnected nanosheets. Surface oxygen vacancies favor the energy band gap narrowing via forming a miniband just below the conduction band and then extend the photoresponse region, further boosting the light-harvesting ability. Importantly, surface oxygen vacancies function as the electron sinks to capture photoelectrons and thus restrict their recombination probability with holes, finally improving the photoelectron-hole separation efficiency. Meanwhile, this photocatalyst presents excellent reusability, showing its promising potential in practical applications. This work sheds light on a new application of hierarchical WO3 microspheres with tailored surface oxygen vacancies and its strong synergetic effect of hierarchical structures and surface oxygen vacancies on photocatalytic performance, delivering new insights for rationally designing highly active photocatalysts applied in future green and sustainable organic transformation reactions.

Z-scheme heterojunction based on NiWO4/WO3 microspheres with enhanced photocatalytic performance under visible light.

The green treatment of dye wastewater has always been a research hotspot in the environmental field. The photocatalytic technology is considered to be a simple and effective strategy to remove dyes in wastewater. A new type of NiWO4/WO3 Z-scheme heterojunction microspheres were synthesized by a simple hydrothermal method and impregnation-calcination process. The crystal structure, microscopic morphology, optical and electrochemical properties of the samples were systematically characterized. The photocatalytic activity of methylene blue (MB) was studied by visible light irradiation. The results show that the direct Z-scheme heterojunction formed by NiWO4/WO3 effectively reduces the transfer resistance of photogenerated carriers and improves the separation efficiency of photogenerated carriers. The degradation rates of NiWO4/WO3-4 Z-scheme heterojunction microspheres to MB dye are 1.8 and 3.2 times higher than that of pure WO3·2H2O and WO3 microspheres, respectively. Combined with the Mott-Schottky curve and the active species capture experiments, a possible Z-scheme photogenerated carrier transfer mechanism is proposed. This study provides a method for the development and design of Z-scheme heterojunction photocatalysts in the field of wastewater purification.

Hydrothermal synthesis of V-doped hexagonal WO3 microspheres comprising of nanoblocks for catalytic ammoxidation of dichlorotoluene

V-doped hexagonal WO3 microspheres comprising of nanoblocks were successfully prepared via a facile hydrothermal approach. Several techniques such as XRD, SEM, TEM, FTIR, EDS, TPR, BET and Raman have been performed and the characterization results reveal that V replaced W atoms into the hexagonal lattice-structure. The microspheres possess diameter of about 4.4 μm and the nanoblocks have thicknesses of 40–100 nm and widths of about 150 nm. In addition, the catalytic performance of the obtained V-doped WO3 nanomaterial was investigated in the ammoxidation of dichlorotoluene. The catalytic results indicate that the as-prepared nanostructures show significantly improved selective performance with the selectivities of 3,4-DCBN and 2,6-DCBN reaching up to 89.8% and 86.2%, respectively.

Low-Temperature and Highly Enhanced NO2 Sensing Performance of Au-Functionalized WO3 Microspheres with a Hierarchical Nanostructure

Hierarchically nanostructured WO3 microspheres that had two types of Au functionalization modes (Au-loaded mode and Au-doped mode) were characterized in terms of their microstructure and NO2 sensing performance. Pure, Au-loaded, and Au-doped WO3 microspheres were synthesized using a hydrothermal method, followed by a dipping method for Au-loaded WO3 microspheres. Microstructure characterization indicated that uniform microspheres with 3–6 μm in diameter were assembled from numerous well-defined individual WO3 nanorods with a single crystal hexagonal structure. The morphology and size of the WO3 microspheres were not affected by the functionalization of the Au nanoparticles, and the W, O, and Au elements were well-distributed in the WO3 microspheres. The NO2 sensing properties indicated that the Au nanoparticles not only improved the sensor response and reproducibility but also decreased the operating temperature at which the sensor response reached a maximum. Gas sensors based on pure, Au-loaded, and Au-doped WO3 microspheres exhibited a linear relationship between the sensor response and NO2 concentration. The sensing performance was significantly enhanced in the following order: pure, Au-loaded, and Au-doped WO3 microspheres. This result is due to the modulation of the depletion layer via oxygen adsorption as well as chemical and electronic sensitization of Au nanoparticles.

Preparation of Monodispersed Cs0.33WO3 Nanocrystals by Mist Chemical Vapor Deposition for Near-Infrared Shielding Application.

In this study, single-phase Cs0.33WO3 nanocrystals were synthesized by a novel mist chemical vapor deposition method. As prepared, Cs0.33WO3 nanocrystals exhibited a microsphere-like appearance constructed with angular crystal grains with an average size of about 30–40 nm. Characterization by X-ray photoelectron spectroscopy indicated that Cs0.33WO3 nanocrystals consisted of mixed chemical valence states of tungsten ions W6+ and W5+, inducing many free electrons, which could scatter and absorb near-infrared (NIR) photons by plasmon resonance. These Cs0.33WO3 microspheres consisted of a loose structure that could be crushed to nanoscale particles and was easily applied for producing long-term stable ink after milling. Herein, a Cs0.33WO3/polymer composite was successfully fabricated via the ultrasonic spray coating method using mixed Cs0.33WO3 ink and polyurethane acrylate solution. The composite coatings exhibited excellent IR shielding properties. Remarkably, only 0.9 mg cm−2 Cs0.33WO3 could shield more than 70% of NIR, while still maintaining the visible light transmittance higher than 75%. Actual measurement results indicate that it has really good heat insulation properties and shows good prospect in heat insulation window applications.

Porous and visible-light-driven p–n heterojunction constructed by Bi2O3 nanosheets and WO3 microspheres with enhanced photocatalytic performance

Bi2O3/WO3 porous microspheres were constructed by the p-type Bi2O3 nanosheets firmly embedded in the n-type WO3 microspheres. These composites were systematically characterized by various analytical tools such as XRD, SEM, TEM, UV-DRS, PEC, PL and EIS. Comparing with bare Bi2O3 and WO3 samples, the modified Bi2O3/WO3 composites demonstrate superior photocatalytic efficiency for the photo-degradation of MG dye under visible-light illustration with excellent stability and repeatability, which can be ascribed to the coupling of p-n junction between the p-type Bi2O3 nanosheets and n-type WO3 microspheres, as well as the porous three-dimensional hierarchical structure. Based on the radical capturing experiments and theoretical analysis, the mechanism for the improved visible-light photocatalytic performance was proposed, which is significant for the theoretical study and application o in environmental remediation.

Synergistic Effects of PdOx-CuOx Loadings on Methyl Mercaptan Sensing of Porous WO3 Microspheres Prepared by Ultrasonic Spray Pyrolysis.

In this work, PdOx-CuOx co-loaded porous WO3 microspheres were synthesized with varying loading levels by ultrasonic spray pyrolysis (USP) using polymethyl methacrylate (PMMA) microspheres as a vehicle template. The as-prepared sensing materials and their fabricated sensor properties were characterized by X-ray analysis, nitrogen adsorption, and electron microscopy. The gas-sensing properties were studied toward methyl mercaptan (CH3SH), hydrogen sulfide (H2S), dimethyl sulfide (CH3SCH3), nitric oxide (NO), nitrogen dioxide (NO2), methane (CH4), ethanol (C2H5OH), and acetone (C3H6O) at 0.5 ppm under atmospheric conditions with different operating temperatures ranging from 100 to 400 °C. The results showed that the CH3SH response of USP-made WO3 microspheres was collaboratively enhanced by the creation of pores in the microsphere and co-loading of CuOx and PdOx at low operating temperatures (≤200 °C). More importantly, the CH3SH selectivity against H2S was significantly improved and high selectivity against CH3SCH3, NO, NO2, CH4, C2H5OH, and CH3COCH3 were upheld by the incorporation of PdOx to CuOx-loaded WO3 sensors. Therefore, the co-loading of PdOx-CuOx on porous WO3 structures could be promising strategies to achieve highly selective and sensitive CH3SH sensors, which would be practically useful for specific applications including biomedical and periodontal diagnoses.

Highly stable 3D/2D WO3/g-C3N4 Z-scheme heterojunction for stimulating photocatalytic CO2 reduction by H2O/H2 to CO and CH4 under visible light

Well-designed 3D/2D WO3/g-C3N4 microspheres with an effective interfacial contact, synthesized through facile single step hydrothermal method, for stimulating photocatalytic CO2 reduction under visible light has been investigated. The direct growth of WO3 microspheres with g-C3N4 enables good interaction among the both semiconductors, enabling proficient charge carrier separation. Highest CO and CH4 production over WO3/g-C3N4 of 145 and 133 μmole g−1 h−1 was achieved, 1.91 and 4.03-fold higher than using pristine g-C3N4, respectively. This enhanced photoactivity was noticeable due to the synergistic effect with the larger interfacial contact area and proficient charge carrier separation. More importantly, CH4 and CO production was increased by 2.51 and 1.64-fold with optimized H2O/CO2 feed ratio due to efficient adsorption of both the reactants. Similarly, by replacing water with H2, CO2 reduction efficiency was increased by 1.5 and 2.6-fold higher for CO and CH4 production. The photon flux also has a significant contribution in CO2 reduction, whereas, 1.6 and 1.7-fold higher CO and CH4 production observed by increasing light intensity. The stability analysis reveals continuous production of CO and CH4 in cycles without any obvious deactivation under both the lower and higher light intensity. This work demonstrates a new approach to construct composite heterojunction and would be beneficial for further investigation in selective CO2 conversion to solar fuels.