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.

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.

While gold has long been regarded as a poorly active catalyst, it is now widely investigated in the field of catalysis and gas sensing. Indeed, it exhibits surprisingly high catalytic activity when deposited as nanoparticles (NPs) on base metal oxides, carbon materials or organic polymers. Especially, gold nanoparticles catalysts with 2 to 10 nm diameters are active for many reactions, such as CO oxidation at a temperature as low as - 70°C. The catalytic performance of supported gold NPs depends on the kind of support materials, the size of gold NPs, and the gold/metal oxide interface structure[1]. A variety of preparation methods (more than 10) have been developed to obtain gold NPs with homogeneous dispersions on supports. Classical chemical methods need a calcination step in order to (i) reduce Au³⁺ ions deposited from a precursor (HAuCl₄ is the most popular one) by means of impregnation or deposition–precipitation techniques; (ii) remove organic ligands such as polyvinyl pyrrolidone or polyvinyl alcohol, which prevent the aggregation of gold NPs in the sol-immobilisation method;(iii) crystallize the metal oxide support in coprecipitation method. During the calcination step, the deposited gold particles generally grow to larger ones, so a precise control of the NPs size is difficult with these methods. On the other side, physical methods (PVD, Cathodic Arc Plasma Deposition) are cleaner and allow precise size distribution of the gold NPs on supporting materials, but they needs specific and expansive devices. In this work, an original chemical method to prepare gold NPs deposited on a metal oxide is presented. No calcination is required. The gold precursor is HAuCl₄. The oxide used as supporting material must have a lamellar structure. In this work, we choose an Aurivillius phase (Bi_3.25La_0.75Ti₃O₁₂).The preparation consists in two steps. First, lithium is intercalated in the oxide structure, using n-butyl-lithium. After washing and drying at room temperature, a stable lithiated compound is obtained, in which some metallic cations have been reduced at a lower oxidation state [2]. Then, the lithiated powder is mixed with a gold precursor in aqueous solution. Gold ions are directly reduced near the support surfaces, without any other reducing agent. and the nanoparticles are formed only atthe oxide surface and they are well dispersed (figure 1). In addition, the NPs formation is accompanied by a partial delamination of the oxide grains which are separated in nanoplatelets (figures 2 and 3). The materials have been characterized by electronic microscopies (HRSEM, TEM) at each step of the preparation process. The effect of the gold concentration has been investigated and the kinetics of the NPs deposition has been studied by UV-VIS spectroscopy (figure 4), using the gold NPs localized plasmon surface resonance property.

Aluminum powders are used as a component in propellant formulations, explosives and pyrotechnics [1]. Their reactive and propulsive properties are linked to the exothermic reaction of aluminum with an oxidant. Powders with a high specific surface area (higher than 10 m²/g) i.e. aluminum nanopowders (Al-NPs) have a higher reactivity than micronic powders. Moreover, we have shown that shape and nanostructuration of the grains influence the reactivity [2]. The reactivity of the powders is characterized by thermogravimetric (TG) analyses. In this work, the powders which are obtained by high energy ball milling, show a flake like morphology (fig. 1). The influence of the milling parameters and additives on the morphology, structure and reactivity of the powder was investigated. Among the milling parameters, we have changed the size of the balls, the atmosphere of the process and the post-treatment of the powder. The nanoflakes are highly dispersed in lateral size and thickness; the biggest ones have micronic lateral sizes (1-4 mm) and thickness less than 200 nm, and the smallest ones 100 nm in lateral size and 30 nm in thickness (fig. 2). The nanoflakes contain several crystallites with an orientation relationship; a [110] texture was observed (fig. 3). They are surrounded by an amorphous layer of aluminum oxide, whose thickness depends on the size of the crystallite. Small crystallites exhibit thicker amorphous layer at the edges than on basal planes (fig. 4), this could induce different oxidation rates of the powder. To remove the passivation agent used in the milling process, the powder is rinsed several times. This is a rather tedious process, so a simple annealing of the powder was tested as an alternative to remove paraffin. Heating the powder at 420°C led to an early crystallization of the Al₂O₃ amorphous layer, which is an unwanted effect. In-situ heating in a transmission electron microscope, under inert atmosphere, are in progress, in order to follow the crystallisation of the amorphous alumina layer and the different phase transitions, which are predicated to play an important role in the oxidation mechanism [3].