Abstract
Plasmon-mediated shape conversion of spherical silver nanoparticles (NPs) to nanostructures with other shapes under the irradiation of green LEDs (520 ± 20 nm, 35 mw/cm2) at various temperatures (60, 40, 20, 10, 5, and 0 °C) was performed in this study. It was found that the bath temperature used in the reaction can influence the reaction rates, i.e., the times needed for the shape transformation process were 5, 11.5, 25, 45, 72, and 100 h at 60, 40, 20, 10, 5, and 0 °C, respectively. In addition, the bath temperature can also alter the morphologies of the final products. The major products are silver nanoplates at 60, 40 and 20 °C. However, they became decahedral silver NPs at 5 and 0 °C. The percentages of decahedral silver NPs synthesized at 60, 40, 20, 10, 5, and 0 °C are 0%, 1%, 5%, 45%, 73%, and 89%, respectively. Measuring the surface-enhanced Raman spectroscopy (SERS) spectra of the probe molecule R6G in the presence of KBr showed that both silver nanoplate colloids synthesized at 60 °C and decahedral silver NP colloids synthesized at 0 °C in the absence of PVP had good SERS activities.
Highlights
After systematically varying the reaction temperature from 0 °C to 60 °C, we found that the major products in the reaction were decahedral NPs or nanoplates if the temperature was set lower than 10 °C or higher than 20 °C, respectively
A solution of R6G (10−8 M, 0.9 mL) was added to 1 mL of silver colloids
We found that temperature is a very important factor in controlling the morphology of NPs, i.e., the major products are silver nanoplates at 60 °C but became decahedral silver NPs at 0 °C
Summary
Silver nanoparticles (NPs) have been widely applied to chemical and biological sensors [1,2,3,4], optical devices [5], optical labeling [6] and surface-enhanced Raman spectroscopy (SERS) [7,8,9,10,11,12,13,14,15,16,17,18]. Numerous methods have been developed successfully to synthesize silver nanoparticles with particular shapes, such as tetrahedral [24], bipyramids [25], cubes [26], disks [27,28,29,30,31], decahedra [32,33,34,35,36,37], hexagons [38], triangular plates [39,40,41,42,43,44,45], octahedrons [46], rods [47,48] and wires [49,50] These methods to synthesize silver NP colloids can be mainly classified into two major categories: direct chemical reduction (thermal) and photochemical approaches. Our as-prepared silver NPs had a relatively approachable surface and less limitation in applications of SERS measurements
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