Gold (Au) bipyramid (BP) has consisted of two pentagonal pyramids that share a base, which pentagonal pyramid consists of five equal angularly faces sharing edges. The most interesting performance of Au BPs is their high mono-dispersity and then enhance homogeneous spectral narrowing for the plasmon peaks. In addition, Au BPs have more chemically stability than Au nanorods, possess a larger figure of merit value and higher sensitive refractive index than Au nanorods. Thus, local electric field enhancements of Au BPs are multiple times larger than Au nanorods. Therefore, Au BPs have attracted the most attention recently. However, the yield and aspect-ratio controllable of Au BPs are the two key factors in obtaining high performance. Recently, high-yield Au BPs can be obtained by using the thermal treatment Au seeds due to drastic improvement penta-twinned nanoparticles and the aspect ratios of Au BPs could be readily tuned by simply varying the thermal treatment Au seed concentration. However, it is few research focuses on precisely tuning the reducing agent ability to control Au BPs size.<br/>It is well known that the reduced ability of polyol compounds has internal relation with the pH. In this work, we started with the commonly used reducing agent in the literature, that’s ascorbic acid, by controlling pH below 7 to regulate the reaction rate and obtained Au BPs with average aspect ratios ranging from ∼1.69 ± 0.14 to ∼3.01 ± 0.19. Compared to ascorbic acid, the reduced ability of other polyol compounds, such as phenol, resorcinol or hydroquinone, are weaker. And they are not active enough to reduce Au ions to form BPs with seeds at the natural pH of the growth solution. To boost these hydroxybenzenes, higher pH is required to enhance their reactivity by adding base. Thus, we choose phenol as the reducing agent. We also demonstrated that the phenol’s reactivity can be tunability by introducing base. The average length and width of Au BPs were from 22.1 ± 2.0 to 80.3 ± 2.7 nm and from 17.0 ± 1.5 to 25.4 ± 1.9 nm, respectively. The corresponding aspect ratios were from 1.30 ± 0.08 to 3.17 ± 0.22. In conclusion, this work demonstrated the pH can regulate the Au BPs size and it may be developed for the synthesis other noble metal nanostructures.

Effect of pH on the synthesis of monodispersed gold bipyramids with finely tunable LSPR peaks

2019 Spring National Meeting

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