Binary-Ternary BiS-AgBiS 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, BiS-AgBiS, to detail the binary-ternary chemical transformation via partial cation exchange and its reaction thermodynamics and kinetics. The preformed BiS nanorods (NRs) act as both the reactant and the parent template, within which the partial exchange of Bi with Ag cations proceeds under a silver-rich, diffusion-controlled regime, leading to the formation of energetically favorable AgBiS. The NR shape preservation involving sulfur sublattice rearrangement is due to the proper diameter thickness (∼12 nm) of parent BiS NRs and the rapid establishment of equilibrium-phase AgBiS, as supported by X-ray diffraction measurements and the pseudobinary AgS-BiS phase diagram. Interestingly, the finding of a AgBiS-BiS-AgBiS 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 BiS NRs. Additionally, the resultant AgBiS 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.