Kinetically controlled morphology and composition of colloidal nanoparticles: cation exchange reactions from copper sulfide to transition metal (Mn, Zn, Fe, and Co) sulfides.

The cation exchange reaction is a powerful method for generating nanomaterials with unique structures because of the easy control of the size, morphology, composition, and crystal structure of the nanoparticles. This study investigated the kinetically controlled morphology and composition of colloidal nanoparticles (NPs) through cation exchange reactions, specifically focusing on variations from copper sulfide to transition metal sulfides, including Co, Fe, Zn, and Mn sulfides. In the cation exchange reaction, Co exhibited the fastest exchange rate, followed by Fe, Mn, and Zn. The difference in kinetics rates affected the change in morphology; Co, with the fastest rate, was immediately and uniformly distributed in the NPs. For Fe, a sandwich structure was initially formed and this gradually transformed into a solid-solution phase. After exchanging Cu with Mn and Zn, a heterostructure was formed, which became increasingly clear as the reaction progressed. The transformation of the morphology and crystal structure were confirmed using XRD, TEM, and SEM analyses. The findings of this study suggest that the morphology and distinct structures of the exchanged particles can be controlled by manipulating the kinetics rates of cations through cation exchange reactions. This process offers a powerful tool for the tailored synthesis of colloidal nanoparticles and provides a design principle for enabling predictable outcomes through cation exchange reactions.