Meena Santosh Kumar, Lerouge Frederic, Baldeck Patrice, Andraud Chantal, Garavelli Marco, Parola Stephane, Sulpizi Marialore, Rivalta Ivan
Chemical Engineering and Process Development Division, CSIR-National Chemical Laboratory (NCL), Dr. HomiBhabha Road, Pune-411008, India.
Univ Lyon, Ens de Lyon, CNRS UMR 5182, Université Claude Bernard Lyon 1, Laboratoire de Chimie, F69342, Lyon, France.
Nanoscale. 2021 Sep 23;13(36):15292-15300. doi: 10.1039/d1nr01768c.
We elucidate the crucial role of the cetyl trimethylammonium bromide (CTAB) surfactant in the anisotropic growth mechanism of gold nano-bipyramids, nano-objects with remarkable optical properties and high tunability. Atomistic molecular dynamics simulations predict different surface coverages of the CTAB (positively charged) heads and their (bromide) counterions as function of the gold exposed surfaces. High concentration of CTAB surfactant promotes formation of gold nanograins in solution that work as precursors for the smooth anisotropic growth of more elongated nano-bipyramidal objects. Nanobipyramids feature higher index facets with respect to nanorods, allowing higher CTAB coverages that stabilize their formation and leading to narrower inter-micelles channels that smooth down their anisotropic growth. Absorption spectroscopy and scanning electron microscopy confirmed the formation of nanograins and demonstrated the importance of surfactant concentration on driving the growth towards nano-bipyramids rather than nanorods. The outcome explains the formation of the monodisperse bipyramidal nano-objects, the origin of their controlled shapes and sizes along with their remarkable stability.
我们阐明了十六烷基三甲基溴化铵（CTAB）表面活性剂在金纳米双锥体各向异性生长机制中的关键作用，金纳米双锥体是具有显著光学性质和高可调性的纳米物体。原子分子动力学模拟预测了CTAB（带正电）头部及其（溴化物）抗衡离子的不同表面覆盖率与金暴露表面的函数关系。高浓度的CTAB表面活性剂促进溶液中金纳米颗粒的形成，这些金纳米颗粒作为更细长的纳米双锥体物体平滑各向异性生长的前体。与纳米棒相比，纳米双锥体具有更高指数的晶面，允许更高的CTAB覆盖率，从而稳定其形成，并导致更窄的胶束间通道，使它们的各向异性生长更加平滑。吸收光谱和扫描电子显微镜证实了纳米颗粒的形成，并证明了表面活性剂浓度对驱动生长形成纳米双锥体而非纳米棒的重要性。这一结果解释了单分散双锥体纳米物体的形成、其可控形状和尺寸的起源以及它们显著的稳定性。
