Structural refinement, morphology and photocatalytic properties of β-(Ag2−2xZnx)MoO4 microcrystals synthesized by the sonochemical method

Abstract

In this paper, we report on structure, morphology, and photocatalytic (PC) properties of silver zinc molybdate [β-(Ag2−2xZnx)MoO4] microcrystals (x = 0; 0.01; 0.02 and 0.04) synthesized by the sonochemical method at 30 °C for 3 h. These microcrystals were structurally characterized by X-ray diffraction (XRD) patterns, Rietveld refinement data, micro-Raman and Fourier transform-infrared (FT-IR) spectroscopies. The morphological aspects (shape and average crystal size) and the chemical composition of β-Ag2MoO4 microcrystals were performed by field emission-scanning electron microscope (FE-SEM) and energy dispersive X-ray spectrometry (EDX), respectively. The optical behavior was monitored by ultraviolet–visible (UV–Vis) spectroscopy at room temperature. We investigate the PC properties for degradation of Remazol Brilliant Violet 5R (RBV5R) anionic dye by using four UV-C lamps (18 W each). XRD patterns, Rietveld refinement data, micro-Raman and FT-IR spectra indicate that all β-(Ag2−2xZnx)MoO4 microcrystals (x = 0; 0.01; 0.02 and 0.04) have a spinel-type cubic structure and space group $$\left( {Fd\bar {3}m} \right)$$ . Rietveld refinement results indicated that the Ag atoms were replaced by Zn atoms at A-site in Wyckoff positions. The micro-Raman spectra exhibited the presence of four Raman-active vibrational modes, while FT-IR spectra revealed only one infrared-active vibrational mode. FE-SEM images showed that the replacement of Ag atoms by those of Zn changed the growth process. Particularly, the increase of Zn content into the lattice changed the crystal shape from irregular sphere, cube, and octahedrons to irregular octahedrons and rhombic dodecahedron microcrystals, resulting in the appearance of pores on the crystal surfaces. Moreover, FE-SEM images indicated that the growth of these crystals is governed by aggregation and Ostwald ripening. Finally, we demonstrate for the first time that PC activity can be enhanced up to 80 min by approximately 97.28% for the degradation of RBV5R dye by using β-(Ag1.96Zn0.02)MoO4 microcrystals as photocatalyst and ammonium oxalate as hole scavenger.