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

Ag nanoparticles are successfully assembledon the surfaceof Co(OH)(2) nanoflower arrays by a spontaneous redox reaction.The Co(OH)(2) nanoflowers assembled with Ag nanoparticleshave rich nanogaps and a large specific surface area, which contributeto the formation of 3D SERS "hot spots". The Ag-nanoparticledecorated Co(OH)(2) nanoflowers exhibit a highly active andhomogeneous SERS effect, showing promising potential as reliable SERSsubstrates. A simple and reliable method is developed to fabricateAg-nanoparticle-decoratedCo(OH)(2) nanoflowers grafted on polyacrylonitrile (PAN)nanopillar arrays as uniform and sensitive surface-enhanced Ramanscattering (SERS) substrates. First, Co(OH)(2)-nanosheet-assemblednanoflowers are achieved on the highly uniform PAN nanopillar arraysvia electrochemical deposition. Then, Ag nanoparticles (Ag-NPs) aredecorated onto the Au-nanoparticle-precoated Co(OH)(2) nanoflowersbased on a spontaneous redox reaction (SRR) between the silver ionsand Co(OH)(2) nanosheets at room temperature. Ag-NPs canbe 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 structuredoes not collapse. Because of the highly uniform PAN nanopillar arraysand the high-density sub-10 nm gaps between the neighboring Ag-NPson the surface of the Co(OH)(2) nanoflowers, the hierarchicalthree-dimensional Ag@Co(OH)( x ) grown onPAN nanopillar arrays can produce a reproducible and sensitive SERSeffect. 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 theSERS substrate. As a result, 4-ATP concentrations as low as 10(-10) M can still be identified, exhibiting high SERSactivity. Additionally, the relative standard deviation value of themain characteristic peak of 10(-5) M 4-ATP is 9.43%,indicating good uniformity of the SERS signal of the substrate. TheSRR between silver ions and Co(OH)(2) can provide a simpleroute to prepare heterostructures as SERS substrates, which has greatpotential for application in the field of analysis.