Magnetically Controllable Flowerlike, Polyhedral Ag–Cu–Co₃O₄ for Surface-Enhanced Raman Scattering

Syntheses of Cu-, Ag-, and Ag–Cu–Co3O4 nanomaterials are of interest for a wide range of applications including electrochemistry, thermal catalysis, energy storage, and electronics. However, Co3O4-based nanomaterials have not been explored for surface-enhanced Raman scattering (SERS). Here, we present Cu-, Ag-, and Ag–Cu–Co3O4 nanomaterials of a hierarchical flower shape comprising two separate phases: a pure Cu or Ag core and multiple Co3O4 branches, in which the optical properties of the core and the magnetic properties of the branches are integrated. In addition, a series of nonmagnetic Cu-dominant Cu–Co–O polyhedra without Co3O4 branches were derived from Cu–Co3O4. The polyhedron morphology can be controlled and transformed among cubes, cuboctahedra, and truncated octahedra by tuning the amounts of ligands and additives to vary the potential energy and growth rate of specific crystal facets. The flowerlike Cu-, Ag-, and Ag–Cu–Co3O4 were characterized for SERS enhancement, showing that Ag–Cu–Co3O4 does not enhance SERS from 4-mercaptobenzoic acid (4-MBA) but dramatically and selectively does so for adsorbed rhodamine 6G. Obviously, the synergy of Ag and Cu within the Co3O4 flower constraint promotes the SERS activity. This type of spinel with not only excellent SERS activity but also ferromagnetism could be of great potential in tandem SERS detection/magnetic separation and related applications.