Growth mechanism of Ag2S nanocrystals in a nonpolar organic solvent

Understanding the growth process of nanomaterials enables the control of their sizes/morphologies to enhance their performance for a given application. Herein we report the investigation into the synthesis of Ag2S nanocrystals by reacting Ag+ ions and/or Ag nanoparticles with S powder in a nonpolar organic solvent. The results show that the growth of Ag2S nanocrystals follows a coalescence-fracture-ripening mechanism, which is different from the commonly accepted LaMer nucleation growth model. At the initial stage of the reaction, Ag2S nanoclusters are formed on the surface of massive S powders and then coalesce to form extensive network of nanowires, which later are hollowed and fragmented into quasispherical particles due to the inside-out diffusion of S in nanowires. The quasi-spherical particles finally grow into uniform Ag2S nanocrystals through a ripening process. It has been found that the Ag2S growth process can be greatly accelerated by increasing the temperature of the reaction system and the sizes/morphologies of the final Ag2S nanocrystals can be easily tuned by varying the molar ratio of the starting precursors.