Spontaneous Redox-Reaction-Driven Growth of Ag Nanoparticles on Co(OH) 2 Nanoflower Arrays for Surface-Enhanced Raman Scattering.

A simple and reliable method is developed to fabricate Ag-nanoparticle-decorated Co(OH) 2 nanoflowers grafted on polyacrylonitrile (PAN) nanopillar arrays as uniform and sensitive surface-enhanced Raman scattering (SERS) substrates. First, Co(OH) 2 -nanosheet-assembled nanoflowers are achieved on the highly uniform PAN nanopillar arrays via electrochemical deposition. Then, Ag nanoparticles (Ag-NPs) are decorated onto the Au-nanoparticle-precoated Co(OH) 2 nanoflowers based on a spontaneous redox reaction (SRR) between the silver ions and Co(OH) 2 nanosheets at room temperature. Ag-NPs can be successfully in situ synthesized on the Co(OH) 2 nanoflowers, and Au nanoparticles precoated on the surface of the Co(OH) 2 nanosheets can ensure that the Co(OH) 2 nanoflower structure does not collapse. Because of the highly uniform PAN nanopillar arrays and the high-density sub-10 nm gaps between the neighboring Ag-NPs on the surface of the Co(OH) 2 nanoflowers, the hierarchical three-dimensional Ag@Co(OH) x grown on PAN nanopillar arrays can produce a reproducible and sensitive SERS effect. To verify the SERS performance of the substrate, 4-aminothiophenol (4-ATP) is used as the probe molecule, and the Ag@Co(OH) x grown on PAN nanopillar arrays is employed as the SERS substrate. As a result, 4-ATP concentrations as low as 10 -10 M can still be identified, exhibiting high SERS activity. Additionally, the relative standard deviation value of the main characteristic peak of 10 -5 M 4-ATP is 9.43%, indicating good uniformity of the SERS signal of the substrate. The SRR between silver ions and Co(OH) 2 can provide a simple route to prepare heterostructures as SERS substrates, which has great potential for application in the field of analysis.