Rebuildable Silver Nanoparticles Employed as Seeds for Synthesis of Pure Silver Nanopillars with Hexagonal Cross-Sections under Room Temperature

Abstract

Silver nanopillars with strong plasmonic effects are used for localized electromagnetic field enhancement and regulation and have wide potential applications in sensing, bioimaging, and surface-enhanced spectroscopy. Normally, the controlled synthesis of silver nanopillars is mainly achieved using heterometallic nanoparticles, including Au nanobipyramids and Pd decahedra, as seeds for inducing nanostructure growth. However, the seed materials are usually doped in silver nanopillar products. Herein, the synthesis of pure silver nanopillars with hexagonal cross-sections is achieved by employing rebuildable silver nanoparticles as seeds. An environmentally friendly, stable, and reproducible synthetic route for obtaining silver nanopillars is proposed using sodium dodecyl sulfate as the surface stabilizer. Furthermore, the seed particles induce the formation of regular structures at different temperatures, and, specifically, room temperature is beneficial for the growth of nanopillars. The availability of silver nanoparticle seeds using sodium alginate as a carrier at different temperatures was verified. A reproducible method was developed to synthesize pure silver nanopillars from silver nanoparticles at room temperature, which can provide a strategy for designing plasmonic nanostructures for chemical and biological applications.

Keywords: high repeatability; room temperature; silver nanoparticle seed; silver nanopillar synthesis.

Figure 1

(a) The scanning electron microscopy (SEM) image of silver nanopillars (SNPs) synthesized from silver nanoparticles in 1 h, with candle-like structures and other by-products; inset shows the hexagonal cross-section of a nanopillar. (b) (i) The high-resolution transmission electron microscopy (HRTEM) image showing the lattice fringes of the SNP in the inset; (ii) The HRTEM image of the amorphous epitaxial layer on the side of SNP in the inset. (c) The HRTEM image of the nanopillar in the inset, revealing the lattice fringes and dislocations between layers at the one nanopillar’s side. (d) The energy-dispersive spectrum (EDS) spectrum of SNPs. (e) The X-ray diffraction (XRD) pattern of SNPs containing four peaks consistent with face-centered cubic (fcc) silver crystal structures.

Figure 2

(a) Schematic depicting SNPs’ growth from silver nanoparticle seeds. (b) The transmission electron microscopy (TEM) image of silver nanoparticles; inset shows silver nanoparticle suspension. (c) SEM images and corresponding histograms (as shown in insets) showing the SNPs’ size distributions obtained during synthesis for (i) 1 h; (ii) 2 h; and (iii) 3.5 h. The scale bar is 500 nm. (d) The samples of the blank experiments using SA without nanoparticles and reacting for 2 h at (i) 0 °C; (ii) 27 °C; and (iii) 80 °C. The scale bar is 500 nm.

Figure 3

Images of the silver nanostructures prepared at 27 °C using different amounts of silver nanoparticles: (a) 0 μL; (b) 40 μL; (c) 200 μL; and (d) 400 μL, where the inset shows the irregular top, similar to nanopillars with nodes (the scale bar in inset corresponds to 200 nm).

Figure 4

Images of the silver nanostructures prepared from 4 μL of silver nanoparticle suspension after 1 h at (a) 0 °C; (b) 27 °C; and (c) 80 °C. The scale bar is 500 nm.