Theoretical Investigation on the Solubilization in Water of Functionalized Single-Wall Carbon Nanotubes

An important technique to increase the solubility and reactivity of carbon nanotubes is through functionalization. In this study, the effects of functionalization of some single-walled carbon nanotubes (SWCNTs) were investigated using density functional theory. The SWCNT model utilized in the research consisted of a finite (5, 0) zigzag nanotube segment containing 60 carbon atoms, with hydrogen atoms added to the dangling bonds of the perimeter carbons. Three water-dispersible SWCNTs, functionalized with formic acid, isophthalic acid, and benzenesulfonic acid, were studied. Calculations were performed to determine the binding energies of the organic radicals to the nanotubes, as well as the HOMO-LUMO gaps and dipole moments of both the nanotubes and the functionalized nanotubes. The results indicated that binding was thermodynamically favorable, and functionalization increased electrical dipole moments, leading to enhanced solubility of the nanotubes in water as evidenced by favorable changes in the free energies of solvation. This enhancement is significant as it may lower the toxicity of nanotubes and improve their biocompatibility.