Mechanochemical Synthesis of Silver Molybdate: Influence of Precursors and Milling Conditions

This study investigates the mechanochemical synthesis of silver molybdate (Ag2MoO4). Three silver precursors (AgCl, AgNO3, Ag2SO4) in combination with sodium molybdate dihydrate as the molybdenum precursor were used. Three corresponding sodium salts, which are also formed as byproducts, were employed as process control agents (PCAs) to investigate the possibility of obtaining fine-grained silver molybdate. Milling was performed in a planetary mill at 600 and 100 rpm, and for 2 h, 15 min, and 5 min. X-ray diffraction analysis (XRD) revealed that AgCl is completely unreactive in this type of reaction, whereas AgNO3 and Ag2SO4 form crystalline Ag2MoO4. Additional sample characterization included Fourier transform infrared spectroscopy (FTIR), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and simultaneous differential thermal and thermogravimetric analysis (DTA-TGA). The results indicate that the silver molybdate formation reaction is favorable and rapid. Even under the mildest conditions, including the presence of PCA, micron-sized silver molybdate particles were obtained. A greater rotation rate and longer milling time resulted in a decrease in particle size, but also an increase in sodium content. However, unlike the few existing reports on the mechanochemical synthesis of Ag2MoO4, which, despite harsh milling conditions, did not yield a phase-pure product, our approach produced well-crystallized and pure silver molybdate even under the mildest synthesis conditions.