Expanded Tunability of Intraparticle Frameworks in Spherical Heterostructured Nanoparticles through Substoichiometric Partial Cation Exchange.

Partial cation exchange reactions provide a synthetic pathway for rationally constructing heterostructured nanoparticles that incorporate different materials at precise locations. Multiple sequential partial cation exchange reactions can produce libraries of exceptionally complex heterostructured nanoparticles, but the first partial exchange reaction is responsible for defining the intraparticle frameworks that persist throughout and help to direct subsequent exchanges. Here, we studied the partial cation exchange behavior of spherical nanoparticles of roxbyite copper sulfide, CuS, with substoichiometric amounts of Zn. We observed the formation of ZnS-CuS-ZnS sandwich spheres, which are already well known in this system, as well as ZnS-CuS Janus spheres and CuS-ZnS-CuS central band spheres, which have not been observed previously as significant subpopulations of samples. Aliquots taken during the formation of the heterostructured nanoparticles suggest that substoichiometric amounts of Zn limit the number of sites per particle where exchange initiates and/or propagates, thereby helping to define intraparticle frameworks that are different from those observed using excess amounts of exchanging cations. We applied these insights from mixed-population samples to the higher-yield synthesis of ZnS-CuS Janus spheres, as well as the higher-order derivatives ZnS-(CdS-CuS), ZnS-(CdS-ZnS), and ZnS-(CdS-CoS), which have unique features relative to previously reported analogues. These results demonstrate how the diversity of intraparticle frameworks in spherical nanoparticles can be expanded to produce a broader range of downstream heterostructured products.