Gram-scale fractionation of nanodiamonds by density gradient ultracentrifugation

Abstract

Size is a defining characteristic of nanoparticles; it influences their optical and electronic properties as well as their interactions with molecules and macromolecules. Producing nanoparticles with narrow size distributions remains one of the main challenges to their utilization. At this time, the number of practical approaches to optimize the size distribution of nanoparticles in many interesting materials systems, including diamond nanocrystals, remains limited. Diamond nanocrystals synthesized by detonation protocols - so-called detonation nanodiamonds (DNDs) - are promising systems for drug delivery, photonics, and composites. DNDs are composed of primary particles with diameters mainly <10 nm and their aggregates (ca. 10-500 nm). Here, we introduce a large-scale approach to rate-zonal density gradient ultracentrifugation to obtain monodispersed fractions of nanoparticles in high yields. We use this method to fractionate a highly concentrated and stable aqueous solution of DNDs and to investigate the size distribution of various fractions by dynamic light scattering, analytical ultracentrifugation, transmission electron microscopy and powder X-ray diffraction. This fractionation method enabled us to separate gram-scale amounts of DNDs into several size ranges within a relatively short period of time. In addition, the high product yields obtained for each fraction allowed us to apply the fractionation method iteratively to a particular size range of particles and to collect various fractions of highly monodispersed primary particles. Our method paves the way for in-depth studies of the physical and optical properties, growth, and aggregation mechanism of DNDs. Applications requiring DNDs with specific particle or aggregate sizes are now within reach.

On the relation between chemical composition and optical properties of detonation nanodiamonds

“…Chemical composition and sample cleanliness of as-prepared DNDs, prepared by the established procedure, [26] was studied with XPS ( Fig. S1) and showed that the DNDs mainly comprise of C, with small amounts of O, N, and traces of Cl.…”

“…The DNDs, purchased from Sigma Aldrich, were prepared by rate-zonal density gradient ultracentrifugation, described elsewhere [26].…”

Assembly and Electronic Applications of Colloidal Nanomaterials

“…[167] Another strategy incorporates sacrificial bonds, such as coordination bonds, [156] hydrogen bonds, [168] or imine bonds, [157] in polyfluorene-based supramolecular copolymers. [174] Other examples that employ aqueous density-gradient media include MoS 2 nanosheets, [175] nanodiamonds, [176] zeolite nanosheets, [177] and Fe/Co graphitic-shell nanocrystals. [156,157,168] Density-gradient ultracentrifugation (DGU), developed initially for biochemistry, [149,169] is another separation strategy based on centrifugation, which utilizes density-gradient media to influence the motion of nanomaterials in centrifugal fields.…”

Nanodiamonds: From Synthesis and Purification to Deposition Techniques, Hybrids Fabrication and Applications

“…Another protocol was developed by Mahfouz et al [27] including cycles of grinding, chemical purification and fractioning by ultracentrifugation [28]. HPHT diamond microparticles (size 210-250 μm) with a nitrogen concentration of 200 ppm were used as raw material.…”