Time-resolved SAXS characterization of the shell growth of silica-coated magnetite nanocomposites
Time-resolved SAXS characterization of the shell growth of silica-coated magnetite nanocomposites
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DOI：
10.1007/s11051-014-2475-2
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发表时间：
2014-06
影响因子：
2.5
通讯作者：
A. Gutsche;Alexander Daikeler;Xiaoai Guo;N. Dingenouts;H. Nirschl
中科院分区：
文献类型：
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作者：
A. Gutsche;Alexander Daikeler;Xiaoai Guo;N. Dingenouts;H. Nirschl
利用自行研制的小角X射线散射（SAXS）仪器对二氧化硅包覆的磁铁矿纳米粒子的合成过程进行了时间分辨表征。壳生长（5-20 nm）使用核-壳球模型定量测定。尽管合成的纳米复合材料的几何形状复杂，但SAXS分析提供了关于壳厚度的可靠信息。它们与透射电子显微镜（TEM）观察结果吻合得很好。首先，时间分辨小角X射线散射分析被用来研究前体浓度（正硅酸乙酯）对生长动力学的影响。壳厚度的时间演变可以通过扩散限制壳生长来描述，服从前体浓度中的一阶动力学。此外，SAXS测量提供了关于作为涂覆时间的函数的壳厚度的标准偏差的信息。其减少观察到的涂层时间的增加是由一个自锐机制和/或形态演变为更多的等距形状解释。此外，还研究了氨的影响。通过增加其浓度，生长速率受到影响。然而，最终壳体厚度和标准偏差没有显著变化。对于低氨浓度，相比之下，SAXS和TEM观察显示叠加的二氧化硅凝胶化。此外，在高温（40 °C）下进行涂覆反应。SAXS图案测量作为涂布时间的函数和TEM显微照片显示在这些条件下同时生产经典Stöber颗粒。因此，小角X射线散射被认为具有很大的潜力，在线监测的外壳属性。
Time-resolved characterization of silica-coated magnetite nanoparticles during synthesis is performed using our self-developed small-angle X-ray scattering (SAXS) instrument. The shell growth (5–20 nm) is determined quantitatively using a core–shell sphere model. SAXS analyses provide reliable information on the shell thickness despite the complex geometry of the synthesized nanocomposites. They are in good agreement with transmission electron microscope (TEM) observations. Firstly, time-resolved SAXS analyses are used to study the influence of the precursor concentration (tetraethyl orthosilicate) on growth kinetics. Time evolution of the shell thickness can be described by diffusion-limited shell growth, obeying kinetics of first order in the precursor concentration. Furthermore, SAXS measurements provide information on the standard deviation of the shell thickness as a function of the coating time. Its decrease observed with increasing coating time is explained by a self-sharpening mechanism and/or a morphology evolution to more isometric shapes. Additionally, the influence of ammonia is studied. By increasing its concentration, the growth rate is affected. However, the final shell thickness and the standard deviation do not change significantly. For low ammonia concentration, by contrast, the SAXS and TEM observations reveal superimposed silica gelation. In addition, coating reaction was conducted at elevated temperature (40 °C). SAXS patterns measured as a function of the coating time and TEM micrographs reveal simultaneous production of classic Stöber particles under these conditions. Hence, SAXS is found to have a big potential for on-line monitoring of the shell properties.