Binary–Ternary Bi₂S₃–AgBiS₂ Rod-to-Rod Transformation via Anisotropic Partial Cation Exchange Reaction

Nanoscale chemical transformations based on partial cation exchange reactions are known as a component-increased, shape-maintaining means for the design and tunable preparation of ternary or multinary metal chalcogenide compounds. Herein, we present a new material couple, Bi₂S₃–AgBiS₂, to detail the binary–ternary chemical transformation via partial cation exchange and its reaction thermodynamics and kinetics. The preformed Bi₂S₃ nanorods (NRs) act as both the reactant and the parent template, within which the partial exchange of Bi³⁺ with Ag⁺ cations proceeds under a silver-rich, diffusion-controlled regime, leading to the formation of energetically favorable AgBiS₂. The NR shape preservation involving sulfur sublattice rearrangement is due to the proper diameter thickness (∼12 nm) of parent Bi₂S₃ NRs and the rapid establishment of equilibrium-phase AgBiS₂, as supported by X-ray diffraction measurements and the pseudobinary Ag₂S–Bi₂S₃ phase diagram. Interestingly, the finding of a AgBiS₂–Bi₂S₃–AgBiS₂ intermediate with axially segmented heterostructures reveals the real NR-to-NR conversion trajectory and the shape-induced exchange reaction anisotropy at the ends and middle of Bi₂S₃ NRs. Additionally, the resultant AgBiS₂ NRs with a measured band gap of ∼0.86 eV exhibit potential for photoelectronic applications because of their impressive visible–near-infrared absorption and photoconductivity.