Experimental and Mathematical Modeling Studies of the Separation of Zinc Blende and Wurtzite Phases of CdS Nanorods by Density Gradient Ultracentrifugation

Abstract

Identifying the phase purity of CdS nanorods (NRs) is complicated by the serious overlap between the X-ray diffraction peaks of zinc blende and wurtzite phases as well as anisotropic growth, which might hide a mixed phase. Here we show that the density gradient ultracentrifugation rate separation method can be used to sort CdS NRs synthesized under nitrogen according to differences in particle size and morphology. Furthermore, it was found that the different sized NRs formed in a single batch synthesis had different phases: the thinner ones (<3.5 nm in diameter) were predominantly wurtzite phase, while the thicker ones (>5 nm in diameter) were mainly zinc blende phase. Dark-field transmission electron microscopy (TEM) and high-resolution TEM images indicated the presence of numerous stacking faults in the thick zinc blende rods, while the wurtzite thin rods were exclusively single crystals. As a result of the differences in phase and stacking faults, the NRs showed different photoluminescent properties. The development of an effective way of separating such NRs thus leads to further insight into the differences in phase, structure, and optical properties between individual colloidal particles synthesized in a single batch. A preliminary mathematical model of the separation process has been proposed.

Assembly and Electronic Applications of Colloidal Nanomaterials

“…These sacrificial bonds can be selectively cleaved with acid treatments, leading to the flocculation of relatively pristine SWCNTs. [178] Nanocrystals dispersed in organic solvents, such as Ag, [179] Au, [179] CdSe, [179] CdS, [180] and Si, [181,182] have also been sorted in Review (6 of 32) 1603895 non-aqueous density gradients, which are typically formed by layering organic solvents of different densities. Continuous linear density gradients can be prepared prior to ultracentrifugation, or can be induced to form during ultracentrifugation, depending on the diffusion coefficients of the density-gradient media.…”

Controllable Assembly and Separation of Colloidal Nanoparticles through a One‐Tube Synthesis Based on Density Gradient Centrifugation

“…19 Moreover, in our preliminary studies, this method also provided the opportunity to isolate/capture intermediate product for the observation and understanding of chemical reaction, growth process, or phase transition 17. 20–22…”

“…[18,19] Moreover,i no ur preliminarys tudies,t his method also provided the opportunity to isolate/capture intermediate product fort he observation and understanding of chemical reaction, growth process, or phase transition. [17,[20][21][22] Herein, such am ethodw as further developed to capture the "aggregation intermediate", which means only the initial state of aggregation when severalc olloidsc ollide with each other in salt solution. Since the aggregation degree can be well-controlled and terminated in certain degree, it is also called as-sembly.S uch af acile "one-tube synthesis" approach can realize the self-assembly of Au NPs into 1D nanostructures through density gradientu ltracentrifugation rate separation.…”

Neue Strategien zur Totalsynthese von anorganischen Nanostrukturen

“…Dichtegradientenzentrifugation hat sich zur Trennung von Partikeln in unterschiedlichen Grçßen, Formen, Materialien und Polymorphen als effizient erwiesen. [193][194][195][196] Bei Hybridpartikeln, die mehrere anorganische Domänen enthalten, hat die Dichtegradientenzentrifugation auch die Trennung von Anordnungen mit unterschiedlicher Zahl von konstituierenden Partikeln ermçglicht, zum Beispiel Monomere -Dimere -Trimere -Tetramere -Oligomere hçherer Ordnung (Abbildung 20). [83,197] Differentielles magnetisches Fangen und Freisetzen ("differential magnetic catch and release", DMCR), eine Flüssigphasen-Kapillarchromatographietechnik, mit der magnetische Partikel basierend auf Unterschieden ihrer magnetischen Momente getrennt werden, [80,81] wurde erfolgreich zur Trennung von Mischungen kolloidaler Hybridnanopartikel in Fraktionen eingesetzt.…”