Microwave-Assisted Bromination of Double-Walled Carbon Nanotubes

Abstract

The ability to functionalize carbon nanotubes (CNTs) through controlled structural modifications is an essential prerequisite for application purposes, as it may lead to increased solubility and processability(1-3) as well as opportunities for fine-tuning the physical and chemical properties,(4, 5) thereby enabling the exploitation of the mechanical, thermal, and optical properties of CNTs(6) in a wide range of applications in both material(7) and biomedical sciences.(5, 8, 9) A major challenge in this field, therefore, is to develop a range of reliable and effective functionalization methodologies that allow the construction of CNTs-based macromolecular species of highly versatility and usefulness, to be further modified by coupling them to a variety of organic functionalities and in the mean time do not extensively disrupt the graphitic π-conjugated surface (consequently altering their electronic(10) and thus optical properties(11-13)). In this respect, halogenated CNTs-based materials can represent a useful class of intermediates as they could act as precursors to a number of organometallic species and suitable substrates for metal-catalyzed cross coupling reactions. Halogenation of CNTs has mainly been performed with highly oxidizing F2 gas,(14-16) with electrochemically generated Cl2 and Br2(17) and with I2 through a modified Hunsdiecker-type reaction.(18) The low-susceptibility of CNTs to weak oxidizing species, such as Br2, was instead utilized as a means of purification for MWCNTs containing carbon nanoparticles(19) and to the best of our knowledge, no definitive reports about the C−Br bond formation on single- or double-walled CNTs have been reported at time. We thus report the synthesis and characterization of double-walled carbon nanotubes (DWCNTs) functionalized with Br2 (Br-DWCNTs) under microwave-assisted (MiW) conditions,(20-22) to link covalently the Br atoms to DWCNTs with a percentage of functionalization of ca. 5−8 % in weight.