Downsizing Mo ₆ I ₁₂ to Nanocrystals Unveils Visible-Light Photocatalytic Antibacterial Activity

Molybdenum(II) iodide (Mo₆I₁₂) serves as a versatile precursor to phosphorescent octahedral molybdenum cluster complexes that exhibit properties relevant to energy, environmental, and biomedical applications. Despite its straightforward synthesis, stability, and extended visible-light absorption, the photophysical and photocatalytic properties of Mo₆I₁₂ have remained unexplored, because the compound has historically been available only as an insoluble bulk material. Herein, we report the top-down preparation of Mo₆I₁₂ nanocrystals via ultrasonic treatment, yielding stable colloidal suspensions in acetone and water. The nanocrystals exhibited broad visible-light absorption extending up to ∼700 nm and weak red to near-infrared photoluminescence intensifying at low temperatures. These features indicate an indirect semiconducting nature, which was confirmed by density functional calculations. Upon blue-light illumination, the nanocrystals generate reactive oxygen species, including the hydroxyl radical via a photocatalytic mechanism that operates even under anaerobic conditions. Their photocatalytic potential in the context of water disinfection was validated through bacterial photodynamic inactivation, demonstrating effective inactivation (up to >4 log reduction) of clinically relevant strains of Gram-positive bacteria under visible-light irradiation. The low toxicity of the nanocrystals on HeLa cells highlighted their favorable safety profile for water disinfection. This work reveals the unique light-induced properties of Mo₆I₁₂ nanocrystals and establishes them as promising materials for photocatalytic and photodynamic applications.