Study On The Separation Technique Of Metallic And Semiconducting Single-Walled Carbon Nanotubes

The single-walled carbon nanotubes (SWCNTs) have excellent electrical properties, offering the possibilities of wide promising applications in various fields, such as nanodevices, sensors, transparent conducting films and so on. However, SWCNTs are tapically grown as the bundles of metallic SWCNTs and semiconducting SWCNTs (MS), thus hindering the advanced applications of SWCNTs. Therefore, it is an critical research topic to separate MS effectively. There are lots of studies on it and basically have the following kinds of methods:selective growth, selective chemistry, selective destruction, chromatography and ultracentrifugation. Some of the methods can highly purified m- or s-SWCNTs. But all of the techniques remain unsuitable for industrial application because of the high cost and low yields. A new idea, called (AGE) is put forward in this paper, which may remedy those foregoing shortages.1. In this paper, AGE technique has been used to investigate the influence of the properties of MB, Agarose, Agarose B and LRU on the separating efficiency of SWCNTs. The results indicated that different agarose have little effect on the separating efficiency of s-SWCNTs, but have a great effect on the separating efficiency of m-SWCNTs. The smaller mesh size of the gel is favorable to the enrichment of m-SWCNTs, while the higher gel strength is unfavorable. We found that the highest content of m-SWCNTs was in the fastest-running fraction of gel because of the high packing density of SDS molecules on the surface of m-SWCNTs. Furthermore, we studied the effect of the agarose gel concentration on the separation of SWCNTs by AGE. We found the purity of m-SWCNTs was increased with the increase of agarose gel concentration.2. We used the agarose gel centrifugation (AGC) method to separate the SWCNTs, and investigated the probable factors which could affect the separating efficiency of SWCNTs. It is found that higher concentration of agarose gel is favorable to the enrichment of m-SWCNTs rather than the enrichment of s-SWCNTs. A secondary separation is useless to improve the purity of m-SWCNTs. That means the separation is over after the first interaction between agarose gel and SWCNTs. And we found that a long centrifugal time is unfavorable to both enrichment of MS. The degree of gelling of agarose was very important for the separation of SWCNTs. As suggested above, we can realize the efficient separation of SWCNTs by controlling the agarose gel concentration, gelling time and centrifugal time.3. On the basis of experiments mentioned above, we have had further research on the mechanism of the separation of SWCNTs by agarose gel method. Influence of dispersant on the separation of SWCNTs was studied using 7 dispersants, and found only SDS-dispersed SWCNTs can separated by agarose gel method. This shows that SDS surfactant played an important role in the separation. By the analysis of UV-visible-Near Infrared (UV-vis-NIR) absorption spectroscopy and fluorescences (PL) spectra proved that the specific interaction between the s-SWCNTs and the agarose and the different adsorption behavior of SDS on the surface of MS leads to the separation of MS. And then we employed thionine (TN), a positively charged dye molecule which may show unique interaction with SDS molecules, can roughly evaluate the changes of SDS aggregates during the agarose gel electrophoresis. Based on the results of the electrophoretic and spectroscopic characterizations, we propose that the unique interaction of s-SWCNTs with agarose and the exfoliation of some SDS molecules from SDS-s-SWCNTs entities lead to the separation of MS. The adsorption of agarose gel film towards SDS-s-SWCNTs was the direct evidence. By understanding the role of SDS in the separation, we are able to further optimize the purification of SWCNTs and develop a more effective and low-cost, large scale separation strategy.