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Aims: We investigate the structural and morphological features as well as the optical, photo- and sonophotocatalytic properties of strontium-modified CaWO4, labeled as (Ca1-xSrx)WO4 with (x = 0.25; 0.50; 0.75 and 1 mol%), synthesized by the sonochemical method (SC). The as-synthesized samples were structurally characterized by X-ray diffraction (XRD), Rietveld refinement, micro-Raman, and Fourier-transform infrared (FT–IR) spectroscopies. Field-emission scanning electron microscopy (FE–SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to analyze the morphological aspects (particle shape and size, average particle size distribution) and elemental chemical composition, respectively. Background: Currently, problems related to environmental issues have been one of the main concerns in the world, especially the contamination of freshwater supplies. Faced with this challenge, there is an enormous interest of environmental scientists in the progress of wastewater treatment technologies with superior performance to remove harmful substances in contaminated water resources. Particularly, synthetic organic dyes and pigments, widely employed as coloring agents in leather or textile industries, have a severe impact on the environment because of their toxic and carcinogenic nature. When are discharged into water sources, such chemical pollutants have an irreversible and devastating impact on flora and fauna of local ecosystems. As an alternative route to minimize these negative impacts, the heterogeneous photocatalysis has emerged as a low-cost, safe and versatile wastewater treatment approach. Objective: To analyze the effect of different strontium (Sr) contents (x = 0, 0.25, 0.50, 0.75, and 1 mol%) on the structural, morphological , optical, photo- and sonophotocatalytic (SPC) properties of (Ca1-xSrx)WO4 samples. Methods: (Ca1-xSrx)WO4 (x = 0, 0.25, 0.50, 0.75, and 1 mol%) samples were synthesized by the sonochemical method at 40 ºC for 3 h. Results: XRD patterns, Rietveld refinement data, and micro-Raman and FT–IR spectra proved that all samples are structurally organized in a scheelite-type tetragonal structure without deleterious phases. FE–SEM images showed the growth of flower-like and spindle-like crystals. UV–Vis spectra indicated that the increase of Egap (from 4.68 to 4.94 eV) in (Ca1-xSrx)WO4 samples was proportional to the amount of Sr (x concentration) inserted in the lattice. Conclusion: Among all samples, the CaWO4 exhibited the highest SPC performance for the degradation of RhB solution under UV irradiation. When irradiated for 200 min, a degradation rate at around 96% was achieved for this sample. The ultrasound-assisted photocatalysis proved to be a promising approach for the degradation of organic dyes.

In this paper, the effect of different synthesis methods, such as controlled precipitation (CP), sonochemical (SC), hot solution ion injection with fast cooling, and conventional hydrothermal (CH) in obtaining beta-disilver molybdate (β-Ag 2 MoO 4 ) are explained in details. X-ray diffraction patterns, Rietveld refinement data, cluster modeling, micro-Raman, and Fourier transform infrared spectroscopies confirmed that all β-Ag 2 MoO 4 crystals have a spinel-like cubic structure, space group (Fd 3 m), and symmetry point group (O 7 h ). Field emission scanning electron microscopy (FE-SEM) images showed that through different synthetic routes, it is possible to obtain monophasic crystals, such as regular/irregular polyhedrons (cubes, cuboctahedron, trapezohedron, rhombic dodecahedron), potatoes, and non-uniform. The crystal shape observed experimentally was modeled based on Rietveld refinement data and FE-SEM images obtained by KrystalShaper. First-principles quantum mechanical calculations based on density functional theory were employed to modulate the surfaces of the material and to obtain their surface energy (E surf ) values. From these E surf values in association with the Wulff construction, the evolution of the crystals shape was achieved correlating with the experimental results when different synthesis methods are used. Ultraviolet-Visible (UV-Vis) spectroscopy measurements in absorbance mode showed three main absorptions (280, 310, and 340 nm), while the UV-Vis analyses in diffuse reflectance mode showed a tail of energy absorption in the UV spectrum range (3.25 eV and 3.3 eV). The quantitative data from the colorimetric analysis indicated that the β-Ag 2 MoO 4 crystals are desirable for developing inorganic pigments with a beige to brown shade. Photocatalytic assays were performed using four lamps: UV-C, UV-B, UV-A, and visible light. The β-Ag 2 MoO 4 crystals prepared by the CP method showed a higher degradation rate at 85.12% for the rhodamine B dye solution under 240 min exposure to UV-C light.

In this paper, the solid solutions of strontium molybdate-tungstate [Sr(Mo 1-x-W x )O 4 ] crystals with (x = 0, 0.25, 0.50, 0.75, and 1) were synthesized by the sonochemical method. Their structure, morphology, optical, and sonophotocatalytic properties were performed in function of the replacement of Mo 6? by W 6? cations into the lattice. Their structure and elemental composition were characterized using X-ray diffraction, Rietveld refinement, micro-Raman, energy-dispersive X-ray, and Fourier-transform infrared spectroscopies proving that all samples are monophasic, crystalline, and exhibit a scheelite-type tetragonal structure. Field-emission scanning electron microscopy images revealed the octahedral and dumbbell-like morphologies for SrMoO 4 and SrWO 4 crystals. Moreover, it is noted to pass through spindle-like morphology for the microcrystals containing both Mo 6? and W 6? cations (x = 0.25, 0.50, and 0.75). Ultraviolet-visible diffuse reflectance spectroscopy showed a directly proportional increase in the optical band gap (E gap ) values from 4.27 to 5.01 eV. These data indicate an increase in the intermediary electronic levels between valance and conduction bands with the increase in the concentration of W 6? cations in the lattice. Finally, we have obtained good sonophotocatalytic performances for SrMoO 4 crystals (90%), and mainly to Sr(Mo 0.25 W 0.75 )O 4 crystals (98%) in the degradation of Rhodamine B dye until 240 min under UV-C light.

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