- Silver molybdate is a family of inorganic compounds composed of silver ions (Ag⁺) and molybdate anions derived from molybdenum in its +6 oxidation state. The most common stoichiometric forms are Ag₂MoO₄, Ag₂Mo₂O₇, and Ag₂Mo₄O₁₃, each possessing different structural motifs and physical properties. Of these, silver orthomolybdate (Ag₂MoO₄) is the most widely studied, typically appearing as a white to light-yellow crystalline powder. These compounds are often prepared by precipitation—mixing soluble silver salts with alkali molybdates—or by hydrothermal and solvothermal routes to produce nanoscale materials. Their color and morphology vary with synthesis conditions due to changes in defect concentration and silver coordination environments.
- Structurally, silver molybdates are built from MoO₄²⁻ tetrahedra, in which molybdenum is tetrahedrally coordinated by oxygen. These tetrahedra may exist as isolated units (as in Ag₂MoO₄) or can be linked into more complex polyoxo-molybdate clusters in higher molybdates. The silver cations surrounding these units display highly flexible and often distorted coordination geometries, a consequence of the soft, polarizable nature of Ag⁺. This structural flexibility leads to a variety of Ag–O bond distances and enables the formation of defect-rich lattice environments. These defects, including oxygen vacancies and coordinational irregularities, are key contributors to the optical and catalytic properties of silver molybdates.
- Chemically, silver molybdates are semiconducting metal oxides, generally with band gaps in the range of approximately 2.5–3.2 eV depending on composition, crystallinity, and nanostructure. They are stable under ambient conditions and largely insoluble in water. However, like silver tungstate, silver molybdate can undergo photoinduced reduction of Ag⁺ to metallic silver nanoparticles (Ag⁰) on its surface when exposed to light or electron beams. This phenomenon creates in situ Ag/Ag₂MoO₄ heterostructures, which significantly improve photocatalytic performance by facilitating charge separation and enhancing reactive oxygen species formation. When heated strongly, silver molybdate decomposes to Ag₂O or metallic silver and various molybdenum oxides (e.g., MoO₃).
- In terms of applications, silver molybdates—especially nanostructured Ag₂MoO₄—are valued for their photocatalytic, antibacterial, and electrochemical properties. Their photocatalytic activity is harnessed for the degradation of organic dyes, pollutants, and pharmaceutical residues under visible or UV light. Antimicrobial behavior arises from the combined effects of Ag⁺ ion release, oxidative stress, and surface plasmon resonance from in situ-formed silver nanoparticles. Consequently, silver molybdate nanostructures have been explored for antimicrobial coatings, water-purification photocatalysts, and composite materials with enhanced surface reactivity. Although less explored than silver tungstate, silver molybdate is increasingly studied in areas such as sensor materials, radiation-responsive materials, and hybrid catalysts.
- Overall, silver molybdate represents a versatile class of silver–molybdenum oxides whose properties arise from the interplay of molybdate coordination chemistry, silver’s polarizable bonding behavior, and intrinsic lattice defects. Its tunable optical, catalytic, and antimicrobial characteristics make it an active subject of research in environmental materials science, nanotechnology, and photochemistry.
