Structural Refinement, Morphological Features, and Optical, Photo- and Sonophotocatalytic Properties of (Ca 1-x Sr x )WO 4 Synthesized by the Sonochemical Method

摘要

Aims: We investigate the structural and morphological features as well as the sonophotocatalytic properties of (Ca 1-x Sr x )WO 4 (x = 0.25; 0.50; 0.75 and 1) 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 and elemental chemical composition, respectively. Background: Currently, environmental issues have been one of the main concerns in the world, especially the contamination of freshwater supplies. Hence, environmental scientists have an enormous interest in developing efficient wastewater treatment technologies to remove harmful substances from contaminated water resources. In general, synthetic organic dyes and pigments, widely employed as coloring agents in leather or textile industries, severely impact the environment because of their toxic and carcinogenic nature. When discharged into water sources, such chemical pollutants have an irreversible and devastating impact on flora and fauna. As an alternative route to minimize these negative impacts, 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) on the structural, morphological, optical, and sonophotocatalytic (SPC) properties of (Ca 1-x Sr x )WO 4 samples. Methods: (Ca 1-x Sr x )WO 4 (x = 0, 0.25, 0.50, 0.75, and 1) 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- and spindle-like crystals. UV–Vis spectra indicated that the increase of Egap (from 4.68 to 4.94 eV) in (Ca 1-x Sr x )WO 4 samples was proportional to Sr concentration inserted into the lattice. Conclusion: Among all samples, CaWO 4 exhibited the highest SPC performance for the degradation of RhB solution under UV irradiation. When irradiated for 200 min, a degradation rate of around 96 was achieved for this sample. The ultrasound-assisted photocatalysis proved to be a promising approach for the degradation of organic dyes.