A Combined SAXS/SANS Study for the in Situ Characterization of Ligand Shells on Small Nanoparticles: The Case of ZnO
A Combined SAXS/SANS Study for the in Situ Characterization of Ligand Shells on Small Nanoparticles: The Case of ZnO
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DOI：
10.1021/acs.langmuir.5b02198
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发表时间：
2015-09-22
期刊：
影响因子：
3.9
通讯作者：
Unruh, T.
中科院分区：
文献类型：
--
作者：
Schindler, T.;Schmiele, M.;Unruh, T.
ZnO纳米颗粒（NPs）具有很大的应用潜力，例如，薄膜太阳能电池由于其在纳米尺度上可调节的电光特性而被广泛应用。因此，生产定义明确的NP是主要的兴趣。对于有针对性的生产工艺，在其形成期间和之后了解NP的稳定层是特别重要的。对于在湿化学合成中由乙酸锌制备的ZnO纳米颗粒的稳定剂层的研究，迄今为止仅进行了非原位研究。发现结合到干燥NP的表面的乙酸盐层;然而，缺少解决天然分散体中NP周围的稳定层的原位研究。通过对同一样品进行中子和X射线小角散射（SANS和SAXS），我们现在能够首次在原位观察醋酸盐壳。此外，在不同的温度下，成熟过程中这种壳的变化可以跟踪。随着ZnO核（d（core））尺寸的增加，周围的壳（d（shell））变得更大，并且壳内的乙酸盐浓度降低。对于所有样品，发现壳厚度大于乙酸酯分子的最大延伸，其中壳内的乙酸酯浓度低于50体积%。因此，不存在覆盖NP的乙酸盐分子的单层，而是乙酸盐离子的溶胀壳。这种壳被认为是阻碍生长的纳米粒子更大的宏观结构。此外，我们发现，在纳米颗粒周围的壳中的乙酸盐和溶液中乙酸盐的总量之间的分配系数μ为约10%，这与通过热重分析测定的非原位数据非常一致。
ZnO nanoparticles (NPs) have great potential for their use in, e.g., thin film solar cells due to their electro-optical properties adjustable on the nanoscale. Therefore, the production of well-defined NPs is of major interest. For a targeted production process, the knowledge of the stabilization layer of the NPs during and after their formation is of particular importance. For the study of the stabilizer layer of ZnO NPs prepared in a wet chemical synthesis from zinc acetate, only ex situ studies have been performed so far. An acetate layer bound to the surface of the dried NPs was found; however, an in situ study which addresses the stabilizing layer surrounding the NPs in a native dispersion was missing. By the combination of small angle scattering with neutrons and X-rays (SANS and SAXS) for the same sample, we are now able to observe the acetate shell in situ for the first time. In addition, the changes of this shell could be followed during the ripening process for different temperatures. With increasing size of the ZnO core (d(core)) the surrounding shell (d(shell)) becomes larger, and the acetate concentration within the shell is reduced. For all samples, the shell thickness was found to be larger than the maximum extension of an acetate molecule with acetate concentrations within the shell below 50 vol %. Thus, there is not a monolayer of acetate molecules that covers the NPs but rather a swollen shell of acetate ions. This shell is assumed to hinder the growth of the NPs to larger macrostructures. In addition, we found that the partition coefficient mu between acetate in the shell surrounding the NPs and the total amount of acetate in the solution is about 10% which is in good agreement with ex situ data determined by thermogravimetric analysis.