Density functional theory investigation on the electronic and solubility properties of functionalized single-walled carbon nanotubes

• Main Author: Mananghaya, Michael Rivera
• Format: text
• Language: English
• Published: Animo Repository 2012
• Subjects: Carbon nanotubes; Physics
• Online Access: https://animorepository.dlsu.edu.ph/etd_doctoral/341
• Institution: De La Salle University

In order to overcome the difficulties in the synthesis of SWCNTs with uniform electronic and magnetic properties, dopants and topological defects as well as the intercalation of metals into single wall carbon nanotubes (SWCNTs) were introduced to significantly widen their application areas. To achieve this, the following models were systematically investigated: (i) (10,0) and (5,5) SWCNT doped with nitrogen (CNxNT) (ii) (10,0) and (5,5) SWCNT with pyridine-like defects (3NV-CNxNT) and (iii) chemical functionalization of (10,0) and (5,5) 3NV-CNxNT with 12 different transition metals (TMs - Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd and Pt). Stable configurations, formation energies, the effects of the doping concentration of nitrogen and pyridine-like defects on the electronic properties of the nanotubes were all examined based on spin-unrestricted density functional theory (DFT). Furthermore, calculations on the corresponding binding energies and effects of chemical functionalization of TMs on the electronic and magnetic properties of the nanotubes were implemented. Results showed that the electronic properties of SWCNTs were modified and they were strongly dependent not only on the concentration of the adsorbed nitrogen but also on the configuration of the adsorbed nitrogen impurities, the pyridine-like nitrogenated defects, and the TMs adsorbed. Due to the strong interaction between the d orbitals of TMs and the p orbitals of N atoms, the binding strengths of TMs with the 3NV-CNxNT were significantly enhanced as compared to the pure SWCNTs. v De La Salle University SWCNTs also have enormous potential in nanomedicine. For successful applications in the field of nanomedicine, these carbon-based nanostructures demand an improved solubility to diminish their toxicity. Covalent-binding of acid groups at the CNT surface is an important technique that could result to increased solubility and lower the toxicity of SWCNTs. In this study, the effects of surface modification to the solubility of some SWCNTs were also investigated with the aid of DFT. The SWCNT model used in the study consist of a finite, (5, 0) zigzag nanotube segment containing 60 C atoms with hydrogen atoms added to the dangling bonds of the perimeter carbons. Three waterdispersible SWCNTs used in this study were bonded with: (a) formic acid, as a model for carboxylic acid; (b) isophthalic acid, as a model for aromatic dicarboxylic acid; and (c) benzenesulfonic acid, as a model for aromatic sulfonic acid. The binding energies of the organic radicals to the nanotubes and dipole moments of both pristine nanotubes and modified nanotubes were calculated. The results were thermodynamically favorable. The electrical dipole moments were increased and resulted in an enhancement in the solubility of the nanotubes in water manifested through favorable changes in the free energies of solvation. This should lower the toxicity of nanotubes and improve their biocompatibility.