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.

In this study, nanostructured ferberites (FeWO₄) were synthesized via hydrothermal routes in an acidic medium. It was then investigated as an efficient photocatalyst for degrading organic dye molecules, with methylene blue (MB) as a model pollutant. The formation mechanism of ferberite revealed that the physical form of the precursor, FeSO₄·7H₂O, acts as a decisive factor in morphological evolution. Depending on whether it is in a solid or dilute solution form, two distinct nanostructures are produced: nanoplatelets and self-organized microspheres. Both structures are composed of stoichiometric FeWO₄ (Fe: 49%, W: 51%) in a single monoclinic phase (space group P2/c:1) with high purity and crystallinity. The p-type semiconductor behavior was confirmed using Mott–Schottky model and the optical analysis, resulting in small band gap energies (≈1.7 eV) favoring visible absorption light. Photocatalytic tests under simulated solar irradiation revealed rapid and efficient degradation in less than 10 min under near-industrial conditions (pH 5). This was achieved using only a ferberite catalyst and a low concentration of H₂O₂ (4 mM) without additives, dopants, or artificial light sources. Advanced studies based on photocurrent measurements, trapping and stability tests were carried out to identify the main reactive species involved in the photocatalytic process and better understanding of photodegradation mechanisms. These results demonstrate the potential of nanostructured FeWO₄ as a sustainable and effective photocatalyst for water purification applications.

A cobalt vanadate (CoV₂O₆) photocatalyst was successfully synthesized and characterized for the degradation of organic dyes under visible light. Structural analysis revealed a monoclinic crystalline phase with a band gap energy of 2.13 eV, indicating strong visible light absorption. X-ray photoelectron spectroscopy (XPS) confirmed the presence of cobalt (Co), vanadium (V), and oxygen (O) in the material composition. Morphological investigations using SEM and TEM showed highly irregular particles with no defined geometric shape. Photocatalytic activity was evaluated using Rhodamine B (RhB) and Methyl Orange (MO) as model pollutants. Degradation efficiencies of 80% and 50% were achieved for RhB and MO, respectively, highlighting a selective performance towards the cationic dye. Radical scavenging experiments indicated that hydroxyl radicals and photogenerated holes were the dominant reactive species in RhB decomposition. The photocatalytic process was further optimized using response surface methodology (RSM), and the ANOVA analysis confirmed the significance of the quadratic model (p < 0.05). These findings demonstrate the potential of CoV₂O₆ as an efficient and selective photocatalyst for treating dye-contaminated wastewater.

This study aims to discuss the combined theoretical and experimental results of elastic properties of tungsten trioxide films supported on Quartz (YX)/45°/10° resonator to form surface acoustic wave (SAW) devices. The SAW systems with different thicknesses of WO₃ thin films were imaged and structurally characterized by X-ray diffraction, atomic force, and transmission electron microscopy. The deposited WO₃ films (100, 200, and 300 nm of thickness) crystallized in a single monoclinic phase. The acoustoelectric properties of the SAW system were obtained by combining theoretical simulations with experimental measurements. The modeling of the SAW devices has been performed by the finite element and boundary element methods (FEM/BEM). The elastic constants of the films at room temperature were assessed via electrical admittances experiments in light of theoretical calculations. The gravimetric effect of the deposited layers is observed by a shift of the resonance frequency to lower values as the thickness of the films increases. Moreover, the acoustic losses are affected by the dielectric losses of the WO₃ films while the resonant frequency decreases almost linearly. SAW devices revealed strong displacement fields with low acoustic losses as a function of WO₃ thicknesses. For all the deposited layers, the measured Young’s moduli and Poisson’s ratios are 8 GPa and 0.5, respectively.

In this study, the influence of nanostructure and morphology was used as a comparative strategy to investigate the material’s performance. For this purpose, two distinct morphologies, one of which is novel for iron tungstate (nanoplatelets) and obtained by the hydrothermal method, were tested to verify their influence on the catalytic activity, reaction kinetics, and operational stability of the oxygen evolution reaction. Although the self-organized rosette and nanoplatelet morphologies maintain a monoclinic ferberite-type structure, the 2D nanoplatelet architecture shows an almost 30% reduction in catalytic activity and a 16% increase in reaction rate in basic medium (1 M KOH), in addition to four times higher turnover frequencies (TOF). Furthermore, the new morphology (nanoplatelets) provides higher charge density, lower charge transfer resistance, and favorable band edge positions, resulting in greater oxidation capacity (10 times more). Regarding the stability factor, both morphologies show a slight degradation over 1000 cycles, but the nanoplatelet morphology maintains almost constant activity, while the self-organized rosette morphology shows a performance drop of approximately 25%. These results demonstrate that morphological engineering is an effective means of improving electrocatalytic performance.