High purity separation of left and right spiral images of carbon nanotubes

At present, the selective growth of the left and right spiral mirror bodies of carbon nanotubes cannot be achieved by the current carbon nanotube growth technology, so the structural separation of carbon nanotubes after growth is the only way to obtain carbon nanotube mirror bodies. The structural separation of carbon nanotubes can be divided into metal/semiconductor separation, single chiral separation, and mirror body separation. In contrast to the widely studied metal/semiconductor separation and single chiral separation, mirror body separation is the ultimate goal of structural separation of carbon nanotubes, requiring more sophisticated separation techniques that can identify both chirality and helicity of carbon nanotubes. As a result, the maximum separation purity (less than 90%) of carbon nanotube images is much lower than that of metal/semiconductor and single chiral separation purity, which limits the exploration of physical properties and functional applications of carbon nanotube images. Therefore, how to effectively separate and prepare high-purity carbon nanotube mirror materials has always been a hot issue in the field of carbon materials research, and it is also a challenging research topic.

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Wei Xiaojun, Associate Researcher and Liu Huaping, Researcher of A05 Group, Key Laboratory of Advanced Materials and Structure Analysis, Institute of Physics, Chinese Academy of Sciences/Beijing Condensed Matter Physics Research Center, have long been committed to the structural isolation, characterization and application of carbon nanotubes [Adv.Sci. 2022, 9, 2200054]. In recent years, the team has developed high-precision gel chromatography separation technology to achieve high-purity macro separation of different types of single chiral carbon nanotubes [Sci.Adv. 2021, 7, eabe0084; Nat. Commun. 2023, 14, 2491; Carbon 2023, 207, 129], which laid an important technical foundation for the industrial separation and preparation of carbon nanotubes.

Figure 1 Length separation and characterization of (6,5) and (5,6) carbon nanotube mirror bodies. (a) Schematic diagram of length separation of carbon nanotubes based on long gel columns. (b) Chromatogram of effluent (6,5) and (5,6) carbon nanotube solutions at 570 nm. AFM diagram and corresponding length distribution of F1 and F6 solutions after length separation of (c,d) (6,5) and (5,6) carbon nanotubes. (e) Length The average length of (6,5) and (5,6) carbon nanotubes after separation.

Recently, on the basis of the length separation of carbon nanotubes, the team systematically studied the interaction force between the mirror body and gel of carbon nanotubes of different lengths, and found that gel chromatography has higher mirror body selectivity for long carbon nanotubes. Based on these findings, a strategy is proposed to achieve high purity image separation by controlling the length of carbon nanotubes. In addition, in order to reduce the clipping effect of carbon nanotube raw materials during the dispersion process, a milder pulsed ultrasonic mode was used to prepare low-defect long carbon nanotube dispersion solution. Finally, a single chiral (6,5) carbon nanotube left and right spiral image was successfully isolated from the dispersion solution, and its image purity was as high as 98%. The purity of the current separation is significantly higher than all previous reports, reaching the highest level to date. The isolated carbon nanotube images show perfect symmetry in the circular dichroism spectrum, which lays an important foundation for the standardized characterization and evaluation of carbon nanotube images in the future. At the same time, the successful separation and preparation of high-purity carbon nanotube images will open up a series of new opportunities for their properties and functional applications.

Figure 2: (6,5) and (5,6) image body length separation absorption spectrum and circular dichroism spectrum characterization. Absorption spectra of F1-F6 solution after length separation of (a,b) (6,5) and (5,6) carbon nanotubes. Illustration: Absorbance of solution F1-F6 at 572 nm. Circular dichroism spectra of F1-F6 solution after separation of (c,d) (6,5) and (5,6) carbon nanotube lengths. Illustration: Circular dichroism of solution F1-F6 at 572 nm.

Figure 3: Characterization of the relationship between intensity and length of circular dichroism spectra of image bodies after length separation (6,5) and (5,6). Circular dichroism spectra normalized for E22 absorbance of (6,5) and (5,6) carbon nanotube length separation of F1-F6 solution. The relationship between circular dichroic spectral intensity (CDnorm) and carbon nanotube length after normalized E22 absorbance of (c,d) (6,5) and (5,6) carbon nanotube length separation of F1-F6 solution.

Figure 4: Spectral characterization and image purity evaluation of high purity (6,5) and (5,6) obtained from low defect long carbon nanotubes dispersions. (a)-(c) Absorption, fluorescence, and circular dichroism spectra of (6,5) and (5,6) carbon nanotubes isolated from long carbon nanotube dispersions. (d) Comparison of image body purity of (6,5) and (5,6) carbon nanotubes separated by different methods.

The above results were published online in the title of "Length-Dependent Enantioselectivity of Carbon Nanotubes by Gel Chromatography" on April 24. This work was supported and guided by Academician Xie Sicen and researcher Zhou Weiya of Institute of Physics, Chinese Academy of Sciences. Wei Xiaojun is the first/corresponding author of the paper, and Liu Huaping is the co-corresponding author. The above research work has been supported by the National Key Research and Development Program (grant nos.2020YFA0714700 and 2018YFA0208402) and the National Natural Science Foundation (grant nos.51820105002, 11634014, 51872320, and 52172060), the Chinese Academy of Sciences (grant no. XDB33030100, QYZDBSSW-SYS028), and the Chinese Academy of Sciences Youth Promotion Association (grant no. 2020005).