Experimental Insights into Partial Cation Exchange Reactions for Synthesizing Heterostructured Metal Sulfide Nanocrystals

Nanocrystal cation exchange is a post-synthetic process that modifies the composition of a nanoparticle while maintaining other important characteristics, including morphology and crystal structure. Partial cation exchange reactions can be used to rationally synthesize heterostructured nanoparticles that contain two or more material segments. Increasingly complex heterostructured nanoparticles are accessible using multiple sequential cation exchange reactions, but achieving targeted structures in high yield requires careful consideration of synthetic parameters and chemical reactivity. Here, we discuss in detail the synthetic protocols used in two distinct partial cation exchange pathways that are differentiated based on the relative amounts of metal salt reagents-excess vs stoichiometric-that are used during the reaction. Using a model system obtained through Zn2+ exchange on roxbyite copper sulfide nanorods, we demonstrate how targeted products can be synthesized reproducibly. We show how small deviations in reaction conditions, such as temperature, time, and particle concentration, can significantly impact the outcome of these reactions. We highlight important chemical and physical hazards, issues that can be encountered when characterizing heterostructured nanoparticles, and troubleshooting suggestions for overcoming commonly encountered pitfalls. Clear and detailed descriptions of these aspects of partial cation exchange reactions are important for enabling widespread reproducibly and further development of the field.