Experimental and Theoretical Correlation of Modulated Architectures of β-Ag2MoO4 Microcrystals: Effect of Different Synthesis Routes on the Morphology, Optical, Colorimetric, and Photocatalytic Properties

Abstract

In this paper, the effect of different synthesis methods, such as controlled precipitation (CP), sonochemical, hot solution ion injection with fast cooling, and conventional hydrothermal in obtaining beta-disilver molybdate (β-Ag2MoO4) are explained in details. X-ray diffraction patterns, Rietveld refinement data, cluster modeling, micro-Raman, and Fourier transform infrared spectroscopies confirmed that all β-Ag2MoO4 crystals have a spinel-like cubic structure, space group (Fd 3¯¯¯ m), and symmetry point group (O7h ). 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 program. First-principles quantum mechanical calculations based on density functional theory were employed to modulate the crystals’ surfaces and to obtain their surface energy (Esurf) values. From these Esurf 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-Ag2MoO4 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-Ag2MoO4 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.