Determinants of regioselectivity of heterostructures in cation exchange reactions.

A cation exchange (CE) reaction offers a remarkable opportunity to create versatile metal sulfide nanocrystals (NCs) with arbitrary complexity in composition, structure, and functionality. The concept of regioselectivity has been discovered and developed to build the target heterostructures through CE reactions, yet a general principle of regioselectivity remains unclear. In this work, we establish connections between experimental results and theoretical insights to elucidate the determinants of regioselectivity using designed aliovalent CE reactions on a two-dimensional template. Our findings demonstrate that the local density of delocalized electrons between the host lattice and guest cations determines the reaction heat on different facets, thereby dictating the resulting structure of the nanoplates after CE reactions. We unravel the mechanism of CE reactions occurring primarily at the edges of the nanoplates and manipulate the occurrence of these reactions by employing active or passivated edges. Consequently, a series of heterostructures with distinct combinations of metal sulfide phases can be synthesized by manipulating these determinants. Our work paves the way for the synthesis of copper sulfide-based heterostructures with multifunctionalities and emergent properties.