Nanoseparation-lnspired Manipulation of the Synthesis of CdS Nanorods

CdS nanorods have been sorted by length using a density gradient ultracentrifuge rate separation method. The fractions containing longer rods showed relatively stronger oxygen-related surface trap emission, while the shorter ones had dominant band-edge emission. These results suggest that the final length distribution of CdS nanorods is not a result of random nucleation and growth, but is related to the local synthesis conditions. Inspired by these findings, different synthesis environments （N2, air, and 02） have been employed in order to tailor the length distribution. In addition to the rod length, the photoluminescence properties of CdS nanorods can also be manipulated. Increasing the oxygen partial pressure significantly changed the growth behavior of CdS nanorods by improving the anisotropic growth.

Development of hydrophilicity gradient ultracentrifuga- tion method for photoluminescence investigation of separated non-sedimental carbon dots

Carbon nanodots （CDs） formed by hydrothermal dehydration occur as mixtures of differently sized nanoparticles with different degrees of carbonization. Common ultracentrifugation has failed in sorting them, owing to their extremely high colloidal stability. Here, we introduce an ultracentrifugation method using a hydrophilicity gradient to sort such non-sedimental CDs. CDs, synthesized from citric acid and ethylenediamine, were pre-treated by acetone to form clusters. Such clusters ＂de-clustered＂ as media comprising gradients of ethanol they were forced to sediment through and water with varied volume ratios. Primary CDs with varied sizes and degrees of carbonization detached from the clusters to become well dispersed in the corresponding gradient layers. Their settling level was highly dependent on the varied hydrophilicity and solubility of the environmental media. Thus, the proposed hydrophilicity-triggered sorting strategy could be used for other nanoparticles with extremely high colloidal stability, which further widens the range of sortable nanoparticles. Furthermore, according to careful analysis of the changes in size, composition, quantum yield, and transient fluorescence of typical CDs in the post-separation fractions, it was concluded that the photoluminescence of the as-prepared hydrothermal carbonized CDs mainly arose from the particles＇ surface molecular state rather than their sizes.

Density gradient ultracentrifugation for colloidal nanostructures separation and investigation

In this article,we review the advancement in nanoseparation and concomitant purification of nanoparticles(NPs) by using density gradient ultracentrifugation technique(DGUC) and demonstrated by taking several typical examples.Study emphasizes the conceptual advances in classification,mechanism of DGUC and synthesis-structure-property relationships of NPs to provide the significant clue for the further synthesis optimization.Separation,concentration,and purification of NPs by DGUC can be achieved at the same time by introducing the water/oil interfaces into the separation chamber.We can develop an efficient method ‘‘lab in a tube" by introducing a reaction zone or an assembly zone in the gradient to find the surface reaction and assembly mechanism of NPs since the reaction time can be precisely controlled and the chemical environment change can be extremely fast.Finally,to achieve the best separation parameters for the colloidal systems,we gave the mathematical descriptions and computational optimized models as a new direction for making practicable and predictable DGUC separation method.Thus,it can be helpful for an efficient separation as well as for the synthesis optimization,assembly and surface reactions as a potential cornerstone for the future development in the nanotechnology and this review can be served as a plethora of advanced notes on the DGUC separation method.