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

Direct Vapor-Phase Bromination of Multiwall Carbon Nanotubes

“…• C. This value is higher than temperature of desorption of physically absorbed Br 2 , which was most probably removed during vacuum treatment after bromination and is close to that observed elsewhere for microwave-brominated DWNTs [3] and can be associated to decomposition of C-Br bonds. The second decomposition step occurs at 400-600…”

“…%, correspondingly. Note that total oxygen content decreases after bromination in contrast to observed elsewhere [3] for the process of CNT bromination in water media by microwaves. Slight decrease of oxygen content can be attributed to the substitution of oxygen atoms in carboxylic functional groups by bromine with no parallel reactions such as Br substitution by water due to nucleophilic mechanism.…”

“…Several approaches were used for functionalization of carbon nanomaterials with halogens-for example, microwave-and plasma-assisted halogenation [3][4][5], radiationinduced chlorination and bromination [6,7], bromination with Lewis acids [8], usage of liquid bromine or vapors at room temperature [9][10][11], or electrochemically generated Br 2 and Cl 2 [12]. Almost all of these methods require usage of special techniques or experimental methods.…”

Covalent bromination of multi-walled carbon nanotubes by iodine bromide and cold plasma treatments

“…Nevertheless, bromine and its chemical derivatives are less reactive than fluorine and chlorine and their derivatives and, hence, bonding bromine covalently to carbon nanotubes is more difficult. It has been reported the bromination of carbon nanotubes and other carbon materials in several degrees [20][21][22][23][24][25][26][27][28][29][30][31][32], generally to a smaller extent than fluorination and chlorination, but the reported data show that bromine is merely adsorbed in many of these cases. For this reason the aim of this paper is to set up new methods to covalently bond bromine to MWCNTs.…”

Application of Microwave Irradiation in Carbon Nanostructures

“…Finally, MWCNT derivatives have also been synthesized using microwave irradiation as the activation source [123] and to assist the bromination of double-walled CNTs [124]. …”