Adsorption of Small Gas Molecules onto Pt-Doped Single-Walled Carbon Nanotubes

Abstract

The adsorption of small gaseous molecules to the metal center in Pt-doped (5,5) single-walled carbon nanotubes has been explored within density functional theory. A model system consisting of a single Pt atom residing in the middle of a carbon nanotube with capping H atoms is used for our investigation. For all gases studied, the overall process of adsorption was found to be exothermic, where the affinity strongly depended on the orientation of the molecule. By examining the density of states and molecular orbitals of these nanotube−adsorbate complexes in comparison to the bare Pt-doped nanotube, we show that the electronic structure of these materials is strongly influenced by the presence of gases. Hence, we propose an application of Pt-doped single-walled carbon nanotubes as gas sensors and hope to motivate experimental work in this field.

Theoretical Studies of Substitutionally Doped Single-Walled Nanotubes

“…For triple adsorption, we were unable to locate a structure in which three molecules were bound strongly to the Pt atom via C-end adsorption; instead, based on our studies, it appeared that a third additional molecule of CO could interact weakly with the nanotube itself (cf. 3.13Å between the Pt atom and the C atom of CO) [113]. Structurally, this (CO) 3 -adsorbed HSWCNT was similar to the corresponding (CO) 2 -adsorbed HSWCNT.…”

“…We will denote the use of singlet ground-state Ptdoped SWCNT as a starting material as doublet-s, while the corresponding reaction of the triplet excited-state Ptdoped SWCNT will be termed doublet-t. Quartet states are also possible. In all cases examined, the quartet spin state had higher energy than the doublet states (−46.97 and −56.49 kcal/mol for doublet-s and doublet-t, respectively) [113]. The Pt center now bears a charge of 0.99, while the N atom exhibits a charge of −0.21 and the O atom, −0.18.…”

“…We considered both exo-and endo-substitutions (vide infra). We also chose Pt for further investigations [35,36,110,113,114] due to its prevalence in well-defined organometallic complexes [184][185][186][187] and heterogeneous catalysis [188][189][190][191][192]. Based on the aforementioned studies, only exo-substitution was considered.…”

“…Based on the aforementioned studies, only exo-substitution was considered. For our gas adsorption studies, two such (5,5) models were selected: (1) a C 170 fragment with D 5h symmetry and hemispheric caps [35], and (2) a C 70 H 20 fragment terminating with H atoms [113,114]. Substitution gave C 169 Pt and C 69 H 2 Pt, respectively.…”

“…In particular, defected [81,[110][111][112] and doped nanotubes [35,36,45,110,113,114] have been the focus of our attention. Since nanomaterials have such great potential for application in biological systems, sensory technology, electronics, and catalysis, their fundamental chemistry warrant further investigation.…”