Facile Ultrasound-Assisted Synthesis of Cs₂AgBiBr₆ Nanocrystals for Enhanced Visible-Light Photocatalysis

We report a novel, simple, and environmentally friendly ultrasound-assisted method for the synthesis of Cs2AgBiBr6 nanocrystals. The synthesis is performed entirely at room temperature and under ambient air, without the need for inert atmospheres. Transmission electron microscopy (TEM) confirms an average particle size of approximately 6 nm, while X-ray diffraction (XRD) and Raman spectroscopy verify the high phase purity and structural stability of the nanocrystals. These nanocrystals exhibit enhanced photocatalytic activity under visible light, achieving complete degradation of rhodamine B in 60 minutes. This improved performance, compared to bulk Cs2AgBiBr6, is attributed to the increased surface area and more efficient charge carrier separation at the nanoscale. The nanocrystals also show good stability over multiple cycles and can degrade methyl orange, highlighting their versatility. Electron paramagnetic resonance (EPR) measurements confirm the formation of superoxide radicals (˙O2-) as the primary active species, supporting a surface-driven photocatalytic mechanism. Unlike conventional hot-injection methods, this approach is low-cost, scalable, and sustainable. It offers a practical route for the development of lead-free halide perovskite materials for environmental and energy-related applications.