Solvation Enhances the Distinction between Carboxylated Armchair and Zigzag Single-Wall Carbon Nanotubes (SWNT-COOH)

Abstract

The effect of various solvents on the structures and properties of carboxylated SWNTs has been explored using the same level different basis set approach (SLDB), where B3LYP functional of density functional theory (DFT) was applied. Armchair (4,4) and zigzag (8,0) and (9,0) tubes were considered as the testbed. In order to simulate varying concentration of −COOH groups, one to five acids groups were placed at one end of these tubes. These samples were placed in different solvents (namely, CS2, THF, and water) with varying polarity and results were compared with gas-phase properties. Similar to the gas-phase, zigzag tubes also exhibit both regular (r-COOH, ν­(CO) above 1700 cm–1) and low-frequency (lf-COOH, ν­(CO) below 1700 cm–1) acid groups. Characteristics of the r-COOH group are not affected much in solvents, but lf-COOH of the zigzag tube is the one that makes these tubes distinguishable from its armchair cousin. Stability and charge distribution of SWNT-COOH strongly depend on the number of acid groups in different solvents which may help controlling further functionalization. Vibrational analyses reveal certain features in the 1400–1600 cm–1 range that are characteristic of lf-COOH and in different solvents, which may help in the assignment of experimental spectra of oxidized SWNT in solvents.

Intramolecular Hydrogen Bonds in Tip-Functionalized Single-Walled Carbon Nanotubes as pH-Sensitive Gates

“…The energetic differences between closed and open conformations of the functionalized nanotubes were compared by full geometry optimizations with three different DFT functionals (PBE0, B3LYP, and M06-2X), , and five same level different basis (SLDB) ,, approaches based on the 3-21G/6-31G level in which diffuse and polarization functions are successively added in the high layer. In the SLDB approach, the functional groups and the adjacent terminal C and H atoms are treated with the larger basis set, while the remaining layer of atoms is treated with the 3-21G basis set.…”

“…The hydrogen bond analysis was performed with the quantum theory of atoms in molecules (QTAIM), , the noncovalent interactions index (NCI), , the electron localization function (ELF) , and the atomic dipole moment corrected Hirshfeld charge fitting (ADCH) . The continuum solvation model based on electron density SMD ,, was employed to simulate the solvation effects on the nanotube structure. Acid dissociation constant values were calculated according to the direct thermodynamic cycle (eqs , , and ), where G aq *­(H + ) = −270.30 kcal·mol –1 as reported in the literature …”