Ag⁺-Induced Shape and Composition Evolution of Covellite CuS Nanoplatelets to Produce Plate-Satellite and Biconcave-Particle Heterostructures

The creation of novel metal sulfide nanostructures and heterostructures by incorporating heterocations into template copper sulfide nanocrystals (NCs) is an important and intriguing area of colloidal synthesis. In contrast with typical incorporation using divalent, trivalent, and tetravalent cations, the mechanism for incorporation of monovalent Ag⁺ into copper sulfide NCs is less clear. In this work, we prepared new types of heterostructures by incorporating Ag⁺ into covellite CuS nanoplatelets (NPls). The incorporation process depended strongly on the initial Ag⁺ concentration. When a relatively small amount of Ag⁺ was provided (0.1 mmol, roughly 20% of the Cu present in the template NPls), CuS-Ag₂S plate-satellite heterostructures were produced by cation exchange (CE) reactions occurring at the corners of the template hexagonal NPls. In contrast, biconcave-particle Ag₂S-Ag heterostructures were obtained via the nanoscale Kirkendall effect when starting with 0.5 mmol of Ag⁺. Our observations indicate that the Ag⁺ incorporation process is also template-dependent. A redox process involving disulfide bonds in CuS is essential for producing Ag₂S domains, rather than forming a ternary Ag-Cu-S phase, which was the result when djurleite Cu_1.94S NPls were treated with Ag⁺. These results and mechanistic discussions not only provide a better understanding of a complex cation incorporation and crystal phase transition process but also provide a means to design new copper sulfide-based heterostructures.