Kembuan Cynthia, Saleh Maysoon, Rühle Bastian, Resch-Genger Ute, Graf Christina
Institut für Chemie und Biochemie, Physikalische und Theoretische Chemie, Freie Universität Berlin, Takustraße 3, D-14195 Berlin, Germany.
Bundesanstalt für Materialforschung und -prüfung (BAM), Richard-Willstätter-Str. 11, D-12489 Berlin, Germany.
Beilstein J Nanotechnol. 2019 Dec 9;10:2410-2421. doi: 10.3762/bjnano.10.231. eCollection 2019.
A concept for the growth of silica shells with a thickness of 5-250 nm onto oleate-coated NaYF:Yb/Er upconversion nanoparticles (UCNP) is presented. The concept enables the precise adjustment of shell thicknesses for the preparation of thick-shelled nanoparticles for applications in plasmonics and sensing. First, an initial 5-11 nm thick shell is grown onto the UCNPs in a reverse microemulsion. This is followed by a stepwise growth of these particles without a purification step, where in each step equal volumes of tetraethyl orthosilicate and ammonia water are added, while the volumes of cyclohexane and the surfactant Igepal CO-520 are increased so that the ammonia water and surfactant concentrations remain constant. Hence, the number of micelles stays constant, and their size is increased to accommodate the growing core-shell particles. Consequently, the formation of core-free silica particles is suppressed. When the negative zeta potential of the particles, which continuously decreased during the stepwise growth, falls below -40 mV, the particles can be dispersed in an ammoniacal ethanol solution and grown further by the continuous addition of tetraethyl orthosilicate to a diameter larger than 500 nm. Due to the high colloidal stability, a coalescence of the particles can be suppressed, and single-core particles are obtained. This strategy can be easily transferred to other nanomaterials for the design of plasmonic nanoconstructs and sensor systems.
提出了一种在油酸包覆的NaYF:Yb/Er上转换纳米颗粒（UCNP）上生长厚度为5 - 250 nm的二氧化硅壳层的概念。该概念能够精确调整壳层厚度，以制备用于等离子体和传感应用的厚壳纳米颗粒。首先，在反相微乳液中在UCNP上生长初始厚度为5 - 11 nm的壳层。随后，在不进行纯化步骤的情况下逐步生长这些颗粒，在每个步骤中加入等体积的正硅酸四乙酯和氨水，同时增加环己烷和表面活性剂Igepal CO - 520的体积，以使氨水和表面活性剂浓度保持恒定。因此，胶束数量保持恒定，其尺寸增大以容纳不断生长的核壳颗粒。从而抑制了无核二氧化硅颗粒的形成。当在逐步生长过程中持续下降的颗粒负ζ电位降至-40 mV以下时，颗粒可分散在氨乙醇溶液中，并通过持续添加正硅酸四乙酯进一步生长至直径大于500 nm。由于高胶体稳定性，可抑制颗粒的聚结，从而获得单核颗粒。该策略可轻松转移到其他纳米材料上，用于设计等离子体纳米结构和传感器系统。
