Separation of Nanoparticles in a Density Gradient: FeCo@C and Gold Nanocrystals

Abstract

Size and geometric control of nanomaterials are important to the discovery of intrinsic size/ shape dependent properties and bottom up approaches for the fabrication of functional nanodevices.[1-10] Two general strategies have been employed to create size-uniform nanocrystals. One method is direct particle size control during synthesis by adjusting growth parameters; [1][2][3]5,[7][8][9]] the other is post-synthesis separation. [11][12][13][14][15][16][17][18][19] Much capacity exists to improve size separation efficacy in the latter case. Differential centrifugation can remove large and unstable particles from colloidal systems, but lacks precise control over particle size. [ [11,18] that can produce particle fractions with narrow shape and size distributions.To maintain or improve the quality of nanoparticle (NP) separation, whilst addressing the issues of adhesion and clogging in liquid-solid phase separation processes, a completely liquid phase separation method is highly appealing. Isopycnic centrifugation, which is often used for biomacro-molecule separation, [20] relies upon a density gradient and ultracentrifugation to separate components according to subtle density differences, and has been applied for diameter and electronic-dependent separation of single-walled carbon nanotubes (SWNT). [13,21] However, the isopycnic density-gradient centrifugation method reaches a limitation when it is extended to the separation of metal nanoparticles. Such a method requires that the components for separation have densities within a gradient range. Aqueous density gradient media usually have densities less than 1.4 gcm −3 , which is much less than the density of metal nanoparticles. Size or shape separation of such heavy nanocrystals remains an issue, both in their preparation and utility for various applications.In contrast to isopycnic separation, ultracentrifugal rate separation can utilize density gradients to separate nanocrystals with higher densities than the gradient media itself. We have previously applied such a method to achieve length separation of suspended SWNTs[22]

Analysis of engineered nanomaterials in complex matrices (environment and biota): General considerations and conceptual case studies

“…Using this technique, Au nanoparticles of several sizes were separated from each other and from particles of differing composition [91]. Another centrifugation technique termed cloud point separation was used to separate and concentrate trace amounts of engineered AgNPs [92].…”

Size-Selective Separation Techniques for Nanoparticles in Liquid

“…One successful technique, reported by Sun et al (Sun X. et al, 2009), is the density gradient centrifugation (DGC) method. They used aqueous solutions with different concentrations of OptiPrep TM (60 % (w/v) iodixanol, 1.32 g·cm -3 , Sigma-Aldrich, Inc.).…”

“…3 shows the particle size of each fraction, which increased with fraction number (from top to bottom), measured by transmission electron microscopy. The size-selective separation from a gold NP mixture was also successfully performed in the same manner (Qiu P. and Mao C., 2011;Sun X. et al, 2009).…”

Size-Separation of Silver Nanoparticles Using Sucrose Gradient Centrifugation

“…Even though tremendous efforts are directed towards optimizing synthesis strategies, typical, as-synthesized suspensions still tend to include polydispersed sizes and shapes [5,13]. With an aim towards achieving monodispersed nanoparticles, significant efforts are focused on the post-synthesis separation of nanoparticles [5,13,14]. Various separation techniques including chromatography, magnetic separation, electrophoresis, selective precipitation, membrane filtration, solvent or solution-based extractions and density gradient centrifugation have been used for isolating nanoparticles [5,[13][14][15][16].…”

“…With an aim towards achieving monodispersed nanoparticles, significant efforts are focused on the post-synthesis separation of nanoparticles [5,13,14]. Various separation techniques including chromatography, magnetic separation, electrophoresis, selective precipitation, membrane filtration, solvent or solution-based extractions and density gradient centrifugation have been used for isolating nanoparticles [5,[13][14][15][16]. Density-based centrifugation is considered as a particularly convenient method as it is economic, non-laborious, and does not involve the use of liquidsolid phase interactions and/or hazardous chemical reactions.…”