In situ high-energy synchrotron X-ray diffraction revealing precipitation reaction kinetics of silver ions with mixed halide ions

Precipitation of silver ions simultaneously with chloride and bromide ions in ethylene glycol at a mild temperature (e.g., 60°C) has been successfully demonstrated for the synthesis of silver chlorobromide (AgCl_xBr_1-x, 0 < x < 1) nanoparticles, which is realized by injecting a AgNO₃ solution into a solution containing both halogen ions. The injection rate of the AgNO₃ solution has been determined to be critical for controlling the uniformity of AgCl_xBr_1-x nanoparticles. Time-resolved in situ high-energy synchrotron X-ray diffraction has been applied, for the first time, to quantitatively monitor the reaction kinetics of nanocrystal formation. The real-time results shed light on the fact that the injection rate of AgNO₃ solution significantly influences the nucleation and growth processes, and thus the quality of resulting AgCl_xBr_1-x nanoparticles. Specifically, fast injection enables the complete addition of AgNO₃ solution to the reaction solution before the nucleation process starts, leading to a good separation of nucleation and growth and thus the formation of uniform AgCl_xBr_1-x nanocubes with well-defined composition and narrow size distribution. By contrast, slow injection results in a continuous addition of AgNO₃ solution to the reaction solution even after nucleation starts, leading to continuous multiple nucleation/growth processes and thus the formation of AgCl_xBr_1-x nanoparticles with broad dimensional and morphological distributions.