Strong tribocatalytic dye degradation by tungsten bronze Ba4Nd2Fe2Nb8O30

The triboelectric effect has recently demonstrated its great potential in environmental remediation and even new energy applications for triggering a number of catalytic reactions by utilizing trivial mechanical energy. In this study, Ba₄Nd₂Fe₂Nb₈O₃₀ (BNFN) submicron powders were used to degrade organic dyes via the tribocatalytic effect. Under the frictional excitation of three PTFE stirring rods in a 5 mg/L RhB dye solution, BNFN demonstrates a high tribocatalytic degradation efficiency of 97% in 2 h. Hydroxyl radicals (?OH) and superoxide radicals (?O₂－) were also detected during the catalysis process, which proves that triboelectric energy stimulates BNFN to generate electron-hole pairs. The tribocatalysis of tungsten bronze BNFN submicron powders provides a novel and efficient method for the degradation of wastewater dye by utilizing trivial mechanical energy.     

Influence of size and shape on optical properties of cesium tungsten bronze: An experimental and theoretical approach

Although the optical properties of nanocrystalline cesium tungsten bronze have been widely studied, there is a lack of research on the effect of particle size on its optical properties. In order to further investigate size and shape effect on the NIR shielding performance, cesium tungsten bronze nanoparticles with different sizes and morphologies were prepared by two methods. The size of irregular shaped samples prepared by solvothermal method is tens of nanometers, while the size of hexagonal prism shaped samples prepared by solid state reaction method is hundreds of nanometers. The element spectrums shows that there are more oxygen vacancies in large particles than in small particles. The NIR shielding performance of large particles far lower than that of small particles, indicating that the influence of shape and size on optical properties is more obvious than that of oxygen vacancy. Theoretical calculation on hexagonal prism shaped particles exhibits that the NIR extinction of large aspect ratio is better at longer wavelength and small aspect ratio is better at shorter wavelength.     

The effect of co-substitution on the microwave dielectric properties of Ba6-3xNd8+2xTi18O54(x=2/3) ceramics

In this work, the microwave dielectric properties of Ba₄(Nd_1-yBi_y)_28/3Ti_18-x(Al_1/2Ta_1/2)_xO₅₄(0≤x≤2, 0.05≤y≤0.2) ceramics co-substituted by A/B-site were studied. Firstly, (Al_1/2Ta_1/2)⁴⁺ was used for substitution at B-site. At 0≤x≤1.5, the above mentioned ceramic was found to exist in single-phase tungsten bronze structure, but at x = 2.0, the secondary phase appeared. Although the dielectric constant decreased by doping the (Al_1/2Ta_1/2)⁴⁺, but the quality factor was observed to improve by 40% and the temperature coefficient of resonant frequency decreased by 75%. Based on the above results, Bi³⁺ was introduced to Ba₄Nd_28/3Ti₁₇(Al_1/2Ta_1/2)O₅₄. The introduction of Bi³⁺ reduced the sintering temperature, greatly improved the dielectric constant, and ultimately decreased the temperature coefficient of resonant frequency, but it led to deterioration of quality factor. At last, with appropriate site-substitution content control (x = 1.0,y = 0.15), excellent comprehensive properties (ε_r = 89.0, Q × f = 5844 GHz @ 5.89 GHz，TCF = +8.7 ppm/°C) were obtained for the samples sintered at 1325 °C for 4 h.     

Tungsten(VI) oxide supported rhodium nanoparticles: Highly active catalysts in hydrogen generation from ammonia borane

Herein, we report the use of tungsten(VI) oxide (WO₃) as support for Rh⁰ nanoparticles. The resulting Rh⁰/WO₃ nanoparticles are highly active and stable catalysts in H₂ generation from the hydrolysis of ammonia borane (AB). We present the results of our investigation on the particle size distribution, catalytic activity and stability of Rh⁰/WO₃ catalysts with 0.5%, 1.0%, 2.0% wt. Rh loadings in the hydrolysis reaction. The results reveal that Rh⁰/WO₃ (0.5% wt. Rh) is very promising catalyst providing a turnover frequency of 749 min^?1 in releasing 3.0 equivalent H₂ per mole of AB from the hydrolysis at 25.0 °C. The high catalytic activity of Rh⁰/WO₃ catalyst is attributed to the reducible nature of support. The report covers the results of kinetics study as well as comparative investigation of activity, recyclability, and reusability of colloidal(0) nanoparticles and Rh⁰/WO₃ (0.5 % wt. Rh) catalyst in the hydrolysis reaction.     

Contributions of oxygen vacancies to the hydrogen evolution catalytic activity of tungsten oxides

The tungsten trioxide attracts less attention due to the low electron transfer kinetics that hinders the interaction of electrons and ions during the hydrogen evolution reaction (HER). But the oxygen vacancy strategy can inspire its electrocatalytic activity for HER because it has a positive effect on improving the charge transfer and compensating for the weak hydrogen adsorption of the tungsten trioxide. By synthesizing a series of substoichiometric tungsten oxides, we reveal the linear relationship between the catalytic activity and the content of oxygen vacancies, which indicates that the oxygen vacancy strategy is an achievable route to enhance the HER for metal oxides.     

Fabrication of tungsten oxide photoanode by doctor blade technique and investigation on its photocatalytic operation mechanism

WO₃ is a potential material candidate for construction of photoanode for solar driven water splitting. In this work, μm-thick porous WO₃ photoanode is prepared by depositing a stable ink made of WO₃ nanoparticles and Aristoflex velvet polymer in water using the doctor blade technique, followed by a sintering in air. The nature of WO₃ nanoparticles, its loading mass on F-doped tin oxide electrode as well as sintering temperature are examined in order to optimize the photocatalytic activity of the resultant WO₃ photoanode. The operation of WO₃ photoanode is investigated by varying the light illumination direction and light incident intensity as well as changing the nature of the electrolyte. Dissolved tungsten in electrolyte is quantified by ICP-MS providing insights into the influences of electrolyte nature and operating conditions to the corrosion of WO₃. It is proposed that the H₂O₂ and OH^. radical generated as by-products of the photo-driven water oxidation on the photoanode surface are harmful species that accelerate the dissolution of WO₃.     

Constraint effect caused by graphene on in situ grown Gr@WO3 -nanobrick hybrid material

This work reported the abnormal constraint effect of graphene on the structural and optical properties of in situ grown Gr@WO₃ nanobrick (NB) hybrid nanomaterials. Stable hybrid Gr@WO₃ nanomaterials were synthesized through a one-step hydrothermal method, in which different graphene contents (0.1, 0.3 and 0.5 wt%) were directly introduced into the precursor solution of tungsten oxide. The existence of graphene in the nucleation phase of tungsten oxide NB decreased the crystallite size from 49.5 nm to 45.3 nm, increased the microstrain from 1.10% to 1.44% and the optical bandgap of the hybrid samples from 2.68 eV to 2.78 eV, and reduced the radiative recombination efficiency of tungsten oxide NB. The hybridization between graphene and tungsten oxide NBs was confirmed by X-ray diffraction and Raman scattering analysis. The optical properties of materials were studied based on the absorbance and diffuse reflectance spectra. In this work, we also proposed a reliable method to estimate the optical bandgap of the sample from the diffuse reflectance spectrum. These findings would introduce an alternative method of fabrication and enhance the understanding of in situ hybrid materials.     

First demonstration of photoelectrochemical water splitting by commercial W–Cu powder metallurgy parts converted to highly porous 3D WO3/W skeletons

Hydrogen evolution through photoelectrochemical (PEC) water splitting by tungsten oxide-based photoanodes, as a stable and environmental-friendly material with moderate band gap, has attracted significant interest in recent years. The performance of WO₃ photoanode could be hindered by its poor oxygen evolution reaction kinetics and high charge carrier recombination rate. Additionally, scalable and cost-effective commercial procedure to prepare nanostructured electrodes is still challenging. We present, for the first time, a novel and scalable method to fabricate highly efficient self-supported WO₃/W nanostructured photoanodes from commercial W–Cu powder metallurgy (P/M) parts for water splitting. The electrodes were prepared by electrochemical etching of Cu networks followed by hydrothermal growth of WO₃ nanoflakes. Interconnected channels of W skeleton provided high active surface area for the growth of WO₃ nanoflakes with a thickness of ~40 nm and lateral dimension of ~250 nm. The optimized photoelectrode having 35% interconnected porosity exhibited an impressive current density of 4.36 mA cm⁻² comprising a remarkable photocurrent of 1.71 mA cm⁻² at 1.23 V vs. RHE under 100 mW cm⁻² simulated sunlight. This achievement is amongst the highest reported photocurrents for WO₃ photoelectrodes with tungsten substrate reported so far. Impedance and Mott-Schottky analyses evidenced fast charge transfer, low recombination rate, and accelerated O₂ detachment provided by optimum 3D porous WO₃/W electrode. Due to the nature of the commercial P/M parts and low-temperature hydrothermal processing, the procedure is cost-effective and scalable which can pave a new route for the fabrication of highly porous and efficient water splitting electrodes.     

The relationship between enhanced dielectric property and structural distortion in Ca doped Ba2NaNb5O15 tungsten bronze ceramics

The relationship between enhanced dielectric property and structural distortion in tungsten bronze structure ceramics was discussed in this work. The ceramics with the composition of (Ba_1-xCa_x)₂NaNb₅O₁₅ (x = 0, 0.1, 0.2, 0.3, 0.4) were fabricated via conventional solid-state method. All ceramics were pure without secondary phase and the distinct lattice distortion in structure was testified by Rietveld XRD refinement. Compared with the un-doped composition, the maximum polarization and energy storage density were strongly enhanced according to the ferroelectric property measurements, which were contributed to the distortion of NbO₆ octahedron induced by the variation of ionic radius. The actually pulsed charge-discharge property of x = 0.3 ceramic was tested, whist excellent power density (P_D = 35.106 MV/cm³) and discharge energy density (W_d = 0.29 J/cm³) were obtained at 100 °C under 120 kV/cm, revealing the potential for application of Ba₂NaNb₅O₁₅ system-based ceramics in harsh environment.     

Effect of strontium substitution on the structure and dielectric properties of unfilled tungsten bronze Ba4-xSrxSmFe0.5Nb9.5O30 ceramics

The effects of Sr²⁺ substitution for Ba²⁺ on phase structure, microstructure, dielectric and electric properties for Ba_4-xSr_xSmFe_0.5Nb_9.5O₃₀ (x = 0, 1, 2, 3 and 4) ceramics were systematically researched. X-ray diffraction patterns show that Ba_4-xSr_xSmFe_0.5Nb_9.5O₃₀ (x = 0, 1, 2 and 3) ceramics are tetragonal tungsten bronze compound with a space group of P4bm, while the sample for x = 4 is an orthorhombic structure compound. The result can be corroborated by the analysis of Raman spectroscopy. As the Sr²⁺ contents increase from 0 to 3, the full width at half maximum of Raman lines of all samples increase gradually, indicating that the degree of lattice distortion increase. All tetragonal tungsten bronze ceramics exhibited a broad permittivity peaks, accompanied by frequency dispersion, indicating all samples are relaxor. The electrical properties of BSSFN ceramics were further studied by complex impedance spectroscopy. XPS spectrum shows that Fe²⁺ and Fe³⁺ coexist in Ba_4-xSr_xSmFe_0.5Nb_9.5O₃₀ ceramics, and their proportion varies with the concentration of Sr²⁺.