Carbon nanotube chemistry

Carbon nanotube chemistry involves chemical reactions, which are used to modify the properties of carbon nanotubes (CNTs). CNTs can be functionalized to attain desired properties that can be used in a wide variety of applications. The two main methods of CNT functionalization are covalent and non-covalent modifications. Carbon nanotube chemistry involves chemical reactions, which are used to modify the properties of carbon nanotubes (CNTs). CNTs can be functionalized to attain desired properties that can be used in a wide variety of applications. The two main methods of CNT functionalization are covalent and non-covalent modifications. Because of their hydrophobic nature, CNTs tend to agglomerate hindering their dispersion in solvents or viscous polymer melts. The resulting nanotube bundles or aggregates reduce the mechanical performance of the final composite. The surface of CNTs can be modified to reduce the hydrophobicity and improve interfacial adhesion to a bulk polymer through chemical attachment. Covalent modification attaches a functional group onto the carbon nanotube. The functional groups can be attached onto the side wall or ends of the carbon nanotube. The end caps of the carbon nanotubes have the highest reactivitydue to its higher pyrimidization angle and the walls of the carbon nanotubes have lower pyrimidization angles which has lower reactivity. Although covalent modifications are very stable, the bonding process disrupts the sp2hybridization of the carbon atoms because a σ-bond is formed. The disruption of theextended sp2 hybridization typically decreases the conductance of the carbon nanotubes. The purification and oxidation of carbon nanotubes (CNTs) has been well represented in literature. These processes were essential for low yield production of carbon nanotubes where carbon particles, amorphous carbon particles and coatings comprised a significant percentage of the overall material and are still important for the introduction of surface functional groups. During acid oxidation, the carbon-carbon bonded network of the graphitic layers is broken allowing the introduction of oxygen units in the form of carboxyl, phenolic and lactone groups, which have been extensively exploited for further chemical functionalisation. First studies on oxidation of carbon nanotubes involved a gas-phase reactions with nitric acid vapor in air, which indiscriminately functionalized the carbon nanotubes with carboxylic, carbonyl or hydroxyl groups. In liquid-phase reactions, carbon nanotubes were treated with oxidizing solutions of nitric acid or a combination of nitric and sulfuric acid to the same effect. However, overoxidation may occur causing the carbon nanotube to break up into fragments, which are known as carbonaceous fragments. Xing et al. revealed sonication assisted oxidation, with sulfuric and nitric acid, of carbon nanotubes and produced carbonyl and carboxyl groups. After the oxidation reaction in acidic solution, treatment with hydrogen peroxide limited the damage on the carbon nanotube network. Single-walled carbon nanotubes can be shortened in a scalable manner using oleum (100% H2SO4 with 3% SO3) and nitric acid. The nitric acid cuts carbon nanotubes while the oleum creates a channel. In one type of chemical modification, aniline is oxidized to a diazonium intermediate. After expulsion of nitrogen, it forms a covalent bond as an aryl radical: Carboxylic groups are used as the precursor for most esterification and amidation reactions. The carboxylic group is converted into an acyl chloride with the use of thionyl or oxalyl chloride which is then reacted with thedesired amide, amine, or alcohol. Carbon nanotubes have been deposited on with silver nanoparticles with the aid of amination reactions. Amide functionalized carbon nanotubes have been shown to chelate silver nanoparticles. Carbon nanotubes modified with acyl chloride react readily with highly branched molecules such as poly(amidoamine), which acts as a template for silver ion and later being reduced by formaldehyde. Amino-modified carbon nanotubes can be prepared by reacting ethylenediamine with an acyl chloride functionalized carbon nanotubes. Carbon nanotubes can be treated with peroxytrifluroacetic acid to give mainly carboxylic acid and trifluroacetic functional groups. The fluorinated carbon nanotubes, through substitution, can be further functionalized with urea, guanidine, thiourea and aminosilane. Using the Hunsdieckerreaction, carbon nanotubes treated with nitric acid can react with iodosobenzenediacetate to iodate carbon nanotubes. Also known are protocols for cycloadditions such as Diels-Alder reactions, 1,3-dipolar cycloadditions of azomethine ylides and azide–alkyne cycloaddition reactions. One example is a DA reaction assisted by chromium hexacarbonyl and high pressure. The ID/IG ratio for reaction with Danishefsky’s diene is 2.6.