Institute of Physical Chemistry, University of Hamburg , Grindelallee 117, 20146 Hamburg, Germany.
Langmuir. 2017 May 30;33(21):5253-5260. doi: 10.1021/acs.langmuir.7b00615. Epub 2017 May 17.
Microemulsion (water-in-oil) methods enable the encapsulation of individual nanoparticles into SiO spheres. The major drawbacks of this method, when applied for silica encapsulation of anisotropic nanorods (NRs), are spatially unequal silica growth and long reaction times (24 h at least). In this work, various tetraalkoxysilanes [tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), and tetrapropyl orthosilicate (TPOS)] with different alkyl-chain lengths were used as silica precursors in attempt to tune the silanization behavior of CdSe/CdS NRs in a microemulsion system. We find enhanced spatial homogeneity of silica growth with decreasing alkyl-chain length of the tetraalkoxysilanes. In particular, by use of TMOS as the precursor, NRs can be fully encapsulated in a continuous thin (≤5 nm) silica shell within only 1 h reaction time. Surprisingly, the thin silica shell showed a superior shielding ability to acidic environment, even compared to the 30 nm thick shell prepared by use of TEOS. Our investigations suggest that the lower steric hindrance of TMOS compared to TEOS or TPOS strongly promotes homogeneous growth of the silica shells, while its increased hydrolysis rate decreases the porosity of these shells.
微乳液（油包水）方法可将单个纳米粒子封装到 SiO 球中。当将该方法应用于各向异性纳米棒（NRs）的二氧化硅封装时，其主要缺点是二氧化硅的生长空间不均匀且反应时间长（至少 24 小时）。在这项工作中，我们使用了不同链长的各种四烷氧基硅烷[正硅酸甲酯（TMOS）、正硅酸乙酯（TEOS）和正硅酸丙酯（TPOS）]作为硅烷化试剂，以尝试在微乳液体系中调整 CdSe/CdS NRs 的硅烷化行为。我们发现，随着四烷氧基硅烷烷基链长度的降低，二氧化硅生长的空间均匀性得到增强。特别是，使用 TMOS 作为前体，仅在 1 小时的反应时间内，NRs 就可以完全被连续的薄（≤5nm）二氧化硅壳包裹。令人惊讶的是，与使用 TEOS 制备的 30nm 厚壳相比，这种薄的二氧化硅壳具有更好的耐酸性环境能力。我们的研究表明，与 TEOS 或 TPOS 相比，TMOS 的空间位阻较小，可强烈促进二氧化硅壳的均匀生长，而其较高的水解速率则降低了这些壳的多孔性。
