Synthesis of vertical WO3 nanoarrays with different morphologies using the same protocol for enhanced photocatalytic and photoelectrocatalytic performances

Facile Fabrication of Lilac-Like Multiple Self-Supporting WO3 Nanoneedle Arrays with Cubic/Hexagonal Phase Junctions for Highly Sensitive Ethylene Glycol Gas Sensors

Metal oxides with nanoarray structures have been demonstrated to be prospective materials for the design of gas sensors with high sensitivity. In this work, the WO3 nanoneedle array structures were synthesized by a one-step hydrothermal method and subsequent calcination. It was demonstrated that the calcination of the sample at 400 °C facilitated the construction of lilac-like multiple self-supporting WO3 arrays, with appropriate c/h-WO3 heterophase junction and highly oriented nanoneedles. Sensors with this structure exhibited the highest sensitivity (2305) to 100 ppm ethylene glycol at 160 °C and outstanding selectivity. The enhanced ethylene glycol gas sensing can be attributed to the abundant transport channels and active sites provided by this unique structure. In addition, the more oxygen adsorption caused by the heterophase junction and the aggregation of reaction medium induced by tip effect are both in favor of the improvement on the gas sensing performance.

Characterization of WO3/Silicone Rubber Composites for Hydrogen-Sensitive Gasochromic Application

WO3 and silicone rubber (SR)-based gasochromic composites were fabricated to detect hydrogen leaks at room temperature. WO3 rod-like nanostructures were uniformly distributed in the SR matrix, with a particle size of 60-100 nm. The hydrogen permeability of these composites reached 1.77 cm3·cm/cm2·s·cmHg. At a 10% hydrogen concentration, the visible light reflectance of the composite decreased 49% during about 40 s, with a color change rate of 6.4% s-1. Moreover, the composite detected hydrogen concentrations as low as 0.1%. And a color scale was obtained for easily assessing hydrogen concentrations in the environment based on the color of composites. Finally, the composite materials as disposable sensors underwent testing at several Sinopec hydrogen refueling stations.

Controlled crystal facet of tungsten trioxide photoanode to improve on-demand hydrogen peroxide production for in-situ tetracycline degradation

Advanced oxidation processes utilizing hydrogen peroxide (H2O2) are widely employed for the treatment of organic pollutions. However, the conventional anthraquinone method for H2O2 synthesis is unsuitable for this application owing to its hazardous and costly nature. Alternative approaches involve a photoelectrochemical method. Herein, tungsten trioxide (WO3) photoanode has been used for the conversion of H2O into H2O2 through oxidation reaction from a PEC system, simultaneously utilizing in-situ generated hydroxyl (OH•) radicals for tetracycline degradation. By manipulating the ratio of crystal facets between (020) and (200) of the WO3 photoanode, a significant improvement in H2O2 production has been achieved by increasing the proportion of (020) facet. The production rate of WO3 photoanode enriched with the (020) facet is approximately 1.9 times higher than that enriched with (200) facet. This enhanced H2O2 production performance can be attributed to the improved formation of OH• radicals and the accelerated desorption of H2O2 on the (020) facet. Simultaneously, the in-situ generated OH• radicals are applied for tetracycline degradation. Under illumination of sunlight stimulator for 180 min, the optimal photoanode achieves a degradation rate of 86.7% for tetracycline. Furthermore, the resulting chemicals have been analyzed, revealing that C8H10O and C7H8O were formed as the primary products. Notably, these products exhibit significantly lower toxicity compared to tetracycline. This study presents a promising approach for the rational design of WO3 based photoanodes for oxidation reaction, including not only H2O2 production but also the efficient degradation of organic pollutants.

Magnetic, Electronic, and Optical Studies of Gd-Doped WO3: A First Principle Study

Tungsten trioxide (WO₃) is mainly studied as an electrochromic material and received attention due to N-type oxide-based semiconductors. The magnetic, structural, and optical behavior of pristine WO₃ and gadolinium (Gd)-doped WO₃ are being investigated using density functional theory. For exchange-correlation potential energy, generalized gradient approximation (GGA+U) is used in our calculations, where U is the Hubbard potential. The estimated bandgap of pure WO₃ is 2.5 eV. After the doping of Gd, some states cross the Fermi level, and WO₃ acts as a degenerate semiconductor with a 2 eV bandgap. Spin-polarized calculations show that the system is antiferromagnetic in its ground state. The WO₃ material is a semiconductor, as there is a bandgap of 2.5 eV between the valence and conduction bands. The Gd-doped WO₃’s band structure shows few states across the Fermi level, which means that the material is metal or semimetal. After the doping of Gd, WO₃ becomes the degenerate semiconductor with a bandgap of 2 eV. The energy difference between ferromagnetic (FM) and antiferromagnetic (AFM) configurations is negative, so the Gd-doped WO₃ system is AFM. The pure WO₃ is nonmagnetic, where the magnetic moment in the system after doping Gd is 9.5599575 μB.

Hydrothermal Synthesis of Co-Exposed-Faceted WO3 Nanocrystals with Enhanced Photocatalytic Performance

In this paper, rod-shaped, cuboid-shaped, and irregular WO₃ nanocrystals with different co-exposed crystal facets were prepared for the first time by a simple hydrothermal treatment of tungstic acid colloidal suspension with desired pH values. The crystal structure, morphology, specific surface area, pore size distribution, chemical composition, electronic states of the elements, optical properties, and charge migration behavior of as-obtained WO₃ products were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), fully automatic specific surface area and porosity analyzer, UV-vis absorption spectra, photoluminescence (PL) spectra, and electrochemical impedance spectroscopy (EIS). The photocatalytic performances of the synthesized pHx-WO₃ nanocrystals (x = 0.0, 1.5, 3.0, 5.0, and 7.0) were evaluated and compared with the commercial WO₃ (CM-WO₃) nanocrystals. The pH7.0-WO₃ nanocrystals with co-exposed {202} and {020} facets exhibited highest photocatalytic activity for the degradation of methylene blue solution, which can be attributed to the synergistic effects of the largest specific surface area, the weakest luminescence peak intensity and the smallest arc radius diameter.