Exploring Anion Exchange Phase Transformations in 1D Solid Systems

Phase transformations through ion exchange reactions represent a relatively new strategy, offering a promising route for synthesizing complex and metastable morphologies and phases in nanoscaled solid ionic materials, which are challenging or even impossible to achieve through standard bottom-up approaches. Moreover, they provide a unique opportunity to investigate the mechanisms and new, yet unexplored phenomena accompanying the chemical modifications in the solid state. These mechanisms remain largely unknown and unexplored, thereby limiting the full potential of ion exchange reactions as one of the primary synthesis or modification strategies for complex ionic nanomaterials. In this study, copper oxide (CuO) nanowires were prepared via thermal oxidation method and used as a template material to explore oxide-sulfide anion exchange transformation mechanism. Following the synthesis, CuO nanowires underwent treatment with sulfur-containing gases in both thermal and non-thermal environments under various conditions to achieve a controllable exchange of oxygen anions with sulfur. The mechanisms underlying these transformations were unraveled with the use of electron microscopy. The copper oxide–sulfide system is particularly intriguing due to the promising properties of copper oxide and sulfide in gas sensing, solar cells, energy storage systems, and photocatalysis. The full or partial transformation between the two phases can therefore represent a route to manipulate and enhance the properties desired for each application.