Wen Xin, Lerch Sarah, Wang Zhihang, Aboudiab Bassem, Tehrani-Bagha Ali Reza, Olsson Eva, Moth-Poulsen Kasper
Department of Chemistry and Chemical Engineering , Chalmers University of Technology , SE-412-96 Gothenburg , Sweden.
Baha and Walid Bassatne Department of Chemical Engineering and Advanced Energy , American University of Beirut , Beirut 1107-2020 , Lebanon.
Langmuir. 2020 Feb 25;36(7):1745-1753. doi: 10.1021/acs.langmuir.9b03804. Epub 2020 Feb 16.
Surfactants are used widely to control the synthesis of shaped noble-metal nanoparticles. In this work, a mixture of hexadecyltrimethylammonium bromide (CTAB), a cationic surfactant; sodium oleate (NaOL), an anionic surfactant; palladium chloride; and a reducing agent were used in the seed-mediated synthesis of palladium nanoparticles. By controlling the surfactant mixture ratio, we initially discovered that palladium nanodendrites with narrow size distribution were formed instead of the traditional nanocubes, synthesized with only CTAB. In order to investigate the optimal ratio to produce Pd nanodendrites with a high yield and narrow size distribution, samples synthesized with multiple molar ratios of the two surfactants were prepared and studied by transmission electron microscopy, dynamic light scattering, conductance, and ultraviolet-visible spectroscopy. We propose that the addition of NaOL alters the arrangement of surfactants on the Pd seed surface, leading to a new pattern of growth and aggregation. By studying the nanodendrite growth over time, we identified the reduction period of Pd ions and the formation period of the nanodendrites. Our further experiments, including the replacement of CTAB with hexadecyltrimethylammonium chloride (CTAC) and the replacement of NaOL with sodium stearate, showed that CTA ions in CTAB and OL ions in NaOL play the main roles in the formation of nanodendrites. The formation of palladium nanodendrites was robust and achieved with a range of temperatures, pH and mixing speeds.
表面活性剂被广泛用于控制形状规整的贵金属纳米颗粒的合成。在这项工作中，十六烷基三甲基溴化铵（CTAB，一种阳离子表面活性剂）、油酸钠（NaOL，一种阴离子表面活性剂）、氯化钯和一种还原剂的混合物被用于钯纳米颗粒的种子介导合成。通过控制表面活性剂混合物的比例，我们最初发现形成了尺寸分布窄的钯纳米枝晶，而不是仅用CTAB合成的传统纳米立方体。为了研究以高产率和窄尺寸分布制备钯纳米枝晶的最佳比例，制备了用两种表面活性剂的多种摩尔比合成的样品，并通过透射电子显微镜、动态光散射、电导率和紫外可见光谱进行了研究。我们提出，添加NaOL会改变表面活性剂在钯种子表面的排列，从而导致新的生长和聚集模式。通过研究纳米枝晶随时间的生长，我们确定了钯离子的还原期和纳米枝晶的形成期。我们的进一步实验，包括用十六烷基三甲基氯化铵（CTAC）替代CTAB以及用硬脂酸钠替代NaOL，结果表明CTAB中的CTA离子和NaOL中的OL离子在纳米枝晶的形成中起主要作用。钯纳米枝晶的形成很稳定，在一系列温度、pH值和混合速度下都能实现。
