Water-soluble Polymethylsilane-dispersed Single-walled Carbon Nanotubes And Their Density Gradient Separation

In comparison with multi-walled carbon nanotubes,single-walled carbon nanotubes have fewer structural defects,and they also have metal conductivity and semiconductor conductivity.Thus,single-walled carbon nanotubes are superior to multi-walled ones for their better electromagnetic,thermal,optical,and mechanical properties.Especially,individually dispersed metallic or semiconducting single-walled carbon nanotubes display great application potential in logic circuits,field-effect transistors,information memory,and photoelectric sensors.In recent years,although the controlled synthesis of single-walled carbon nanotubes has made great progress,the subsequent processing of crude materials prepared by the traditional synthesis method is still the main approach to obtaining a large number of individually dispersed metallic and semiconducting single-walled carbon nanotubes.Herein,we applied the traditional arc discharge method to the preparation of assynthesized single-walled carbon nanotubes,which were preliminarily purified by high-temperature oxidation under air atmosphere and soaking in concentrated hydrochloric acid.The experimental results evidenced that the vast majority of the amorphous carbon was removed via high-temperature oxidation treatment and many metal catalyst particles were removed through soaking in concentrated hydrochloric acid.Under the catalytic action of the metal,sodium polymethylsilane was synthesized from methyl dichlorosilane through Wurtz dechlorination coupling reaction.Successively,the water-soluble polymethyl(1-butyric acidyl)silane was synthesized by the hydrosilylation of 3-butenic acid and polymethylsilane under the catalytic action of2,2'-azodiisobutyronitrile.Fourier transform infrared spectroscopy(FTIR)showed that the intermediate polymethylsilane and the target polymethyl(1-butyric acidyl)silane were successfully synthesized.Under the action of ultrasonic wave,the primarily purified single-walled carbon nanotubes were dispersed into the alkaline solution of polymethyl(1-butyric acidyl)silane,and the resulting dispersions were subjected to initial centrifugation and the supernatant was collected.Transmission electron microscopy(TEM),atomic force microscopy(AFM),visible-near-infrared(vis-NIR)spectroscopy,and resonance Raman scattering spectroscopy proved that the single-walled carbon nanotubes in the supernatant were individually dispersed,among which metallic species were enriched to a certain extent.Finally,a series of density gradients were constructed with sucrose as a density gradient medium.With the assistance of co-surfactant sodium dodecyl sulfate,individual single-walled carbon nanotubes dispersed in the aqueous solution of polymethyl(1-butyric acidyl)silane were separated by density gradient ultracentrifugation,and high purity metallic single-walled carbon nanotubes and ultrahigh purity semiconducting single-walled carbon nanotubes were successfully isolated.