Modeling of Chemical Reactivity of Carbon Nanotubes: A Review

Abstract

In this review, we summarize recent progress on quantum mechanical (QM) computational studies of single wall carbon nanotubes (SWCNs) functionalized covalently. In particular, we focus on the additions of carbene into SWCNs and the associated changes in the carbon-carbon (CC) bonds. A variety of functionalizations are discussed: inner (endo-) and outer (exo-) additions, and additions into bonds that are at various orientations with respect to the tube axis across a wide range of research groups active in the field. Substituents studied ranged from alkyl radicals, amidogen, and a wide range of carbenes to bifunctional organic molecules.

The methods used in the reviewed literature are dominated by density functional theory (DFT). Other methods included QM/MM modeling (ONIOM) and some widely used wave function methods such as MP2 and the occasional semi-empirical quantum chemical method. Both periodic boundary condition (PBC) and cluster models were employed. Some of the results from different laboratories are compared in tabular form. Methodological and computational convergency issues are also discussed.

Two types of modification patterns on the tube surface near the addition site were obtained in a number of studies due to carbene addition, depending on whether the original CC bond in the honeycomb network is retained or broken. There are also subtle surface modifications in the neighborhood of the addition, which in turn modulates the electronic properties as well as has the power to direct a functional group into a specific preferred site. Patterns of the surface modification correlate with whether the CC bond at the carbene attachment remains connected or is cleaved. The correlation can be understood by counting the π electrons of the carbon nanotube and by using Clar’s simple valence bond concept. Strategies to control structural and electronic properties of functionalized SWCNs are also reviewed.