Functionalization of Shortened SWCNTs Using Esterification

Carbon nanotubes (CNTs) have been one of the inten sively-studied topics in the fields of nanoscience and nanotechnology due to their unique electronic, mechanical, and chemical properties.1,2Shortened single-walled carbon nanotubes (s-SWCNTs) with length of 100-300 nm are promising nanomaterials in the applications of nanoscale electronic devices,3 field-emission displays,4 chemical sensors,5 and nanobiosensors.6s-SWCNTs can be soluble in common organic solvents by covalent functionalization of CNTs.Several reactions have been developed for chemical modification and functionalization of CNTs including noncovalent (ionic) interaction,7 amidation,8 and esterification.9Among the reported reactions, the ester bond formed by esterification of CNT-acid chloride and alcohols can be cleaved easily through acid-or base-catalyzed hydrolysis.This method was used for the purification of carbon nanotubes, where CNTs are solubilized by esterification and the soluble CNTs are purified by the cleavage.10,11In this paper, we report a new esterification scheme for functionalizing s-SWCNTs: an ester bond formation be tween carboxylate and alkyl bromide (Scheme 1).Compared with the reported method where the formation of acid chloride is required, the new scheme needs a simple deprotonation of CNT-COOH.The chemical shortening of full-length SWCNTs was carried out by oxidation in the mixture of concentrated H2SO4 and HNO3 (3 : 1) under