Valence Selectivity of Cation Incorporation into Covellite CuS Nanoplatelets

Abstract

Synthesis of copper sulfide-based nanomaterials by cation incorporation into copper deficient copper sulfide (Cu_2–<i>x</i>S) is of interest as a powerful means to obtain nanostructures with otherwise inaccessible combinations of size, shape, composition, and crystal phase. Incorporation of a heterocation (M) may produce heterogeneous Cu_2–<i>x</i>S-MS nanocrystals (NCs) or homogeneous Cu-M-S alloys. However, the factors determining whether heterogeneous NCs or homogeneous alloy NCs are produced have not been fully elucidated. In this report, we incorporate diverse cations into covellite CuS nanoplatelet (NPl) templates in the presence of dodecanethiol (DDT). These cations are categorized by their valencies. We demonstrate that trivalent and tetravalent cations can be incorporated into reduced CuS NPls to produce homogeneous ternary alloy NPls, while the divalent cations cannot coexist with Cu⁺ ions in the Cu_2–<i>x</i>S phase. In turn, the incorporation of divalent cations leads to formation of heterogeneous NPls and finally produces copper-free metal sulfide NPls. The cation valence selectivity arises from conflicts between charge balance and coordination between Cu⁺ and divalent cations. This study not only provides better understanding of the relationship among the composition, morphology, and crystal structure of copper sulfide-based nanomaterials but also provides a pathway to controllable synthesis of complex nanostructures