Study On The Selective Dispersion Of Single-walled Carbon Nanotubes By Polysilane

The individually dispersed metallic or semiconducting single-walled carbon nanotubes are applicable in the assembly of nano electronics,and the dispersion of bundled single-walledcarbon nanotubes in aqueous and/or non-aqueous solution is a must to achieve single-walledcarbon nanotubes with single electrical conductivity.In this study,four water-soluble polysilane derivatives were synthesized and applied to the selective dispersion of metallic single-walled carbon nanotubes in aqueous solution.The water-soluble polysilane derivatives were synthesized by two-step method.Firstly,poly(methyl)silane was synthesized by traditional Wurtz synthesis with dichloromethylsilane as monomer,toluene as solvent,and sodium metal as catalyst.Secondly,branched chains with varying lengths were bonded to the main chain of polysilane via hydrosilation reaction between poly(methyl)silane and crilic acid,4-dioxane acid,7-octynoic acid,and 10-11 olefinic acid,respectively,initiated by azodiisobutyronitrile in THF solution.After washing with hexane to get rid of unreacted poly(methyl)silane,olefine acid and impurities like initiator,water-soluble polysilane derivatives were obtained as yellow sticky and transparent liquids.The success in the synthesis of polymethyl(3-propionic acid)silane,polymethyl(5-pentanoic acid)silane,polymethyl(8-octylic acid)polysilane,and polymethyl(11-acid)polysilane was confirmed by IR and ~1H-NMR.Raw single-walled carbon nanotubes were prepared by arc dischargemethod.The as-prepared single-walled carbon nanotubes were subjected to heat treatment in the air and then two step acidtreatment,leading to samples dispersible in water.The water dispersion of single-walled carbon nanotubes was centrifuged at a speed of 3000 rmp,and the upper 80%supernatant was collected as purified single-walled carbonanotubes.Thealkalinesolutionsofpolymethyl(3-propionicacid)silane,polymethyl(5-pentanoic acid)silane,polymethyl(8-octylic acid)polysilane,and polymethyl(11-acid)polysilane were prepared,respectively.After the purified single-walled carbon nanotubes were ultrasonically dispersed in,four stable dispersions of single-walled carbon nanotube were prepared.These dispersions were transferred to centrifugal tubes and then subjected to ultracentrifugation at a speed of 15000 rmp.UV-vis-NIR and resonant Raman spectra evidence that the upper supernatants were enriched in metallic single-walled carbon nanotubes with chiral indices of(13,1),(12,3),(15,3),(13,4),(14,2),(19,1),(14,8),and(15,6).In comparison with those reported previously,these metallic single-walled carbon nanotubes have features of larger diameter and smaller chiral angle.Therefore,it is concluded that water-soluble polysilane derivatives with varying side chain lengths hadselective dispersing ability towards metallic single-walled carbon nanotubes withlarge diameters and small chiral angles to some extent.Moreover,it was found that the side chain length of the polysilane derivatives had great effect on the selective dispersion of metallic single-walled carbon nanotubes,and that the longer the side chain is the better the selective dispersing dispersing ability towards metallic single-walled carbon nanotubes.The characterizationresults of FT-IR,UV and resonance Raman spectroscopy confirmed the noncovalent bonding interaction between the polysilane derivatives and single-walled carbon nanotubes(especially the metallic single-walled carbon nanotubes),engendering the water soluble polysilane derivatives a dispersing ability towards single-walled carbon nanotubes.Because the Fermi level of metallic single-walled carbon nanotubes is higher than that of semiconducting single-walled carbon nanotubes,and the former have stronger ability to donating electrons to and then form greaternoncovalent bonding interaction with water-soluble polysilane than the latter,engendering water-soluble polysilane derivatives with specially selective dispersing ability towards metallic single-walled carbon nanotube.On the other hand,because of the flexibility of alkyl side chain of polysilane,the longer the side chain of polysilane derivatives is,the more efficient wrapping ofsingle-walled carbon nanotubes by polysilane derivatives.Thus,the selective dispersing ability of polysilane derivatives towards metallic single-walled carbon nanotube elevates with the increase of the side chain lengths of polysilane derivatives.Electrochemical characterization was carried out on the selectively dispersed metallic single-walled carbon nanotubes.The results of cyclic voltammograms and electrochemical impedance the showed that themetallic single-walled carbon nanotubes modified glassy carbon electrode has much improved ability to deliver electrons.