Physisorption of molecular oxygen on single-wall carbon nanotube bundles and graphite

TL;DR

This study compares oxygen adsorption on single-wall carbon nanotubes and graphite, revealing higher binding energies on nanotubes due to van der Waals forces, with no evidence of chemisorption.

Contribution

It provides the first detailed kinetic and energetic comparison of oxygen physisorption on SWNTs and graphite using experiments and molecular mechanics calculations.

Findings

Oxygen desorbs at higher temperatures from SWNTs than graphite.

Binding energy for O2 on SWNTs is 18.5 kJ/mol, higher than 12.0 kJ/mol on graphite.

Adsorption is confirmed to be purely physisorption, with no chemisorbed species detected.

Abstract

We present a study on the kinetics of oxygen adsorption and desorption from single-wall carbon nanotube (SWNT) and highly oriented pyrolytic graphite (HOPG) samples. Thermal desorption spectra for SWNT samples show a broad desorption feature peaked at 62 K which is shifted to significantly higher temperature than the low-coverage desorption feature on HOPG. The low-coverage O2 binding energy on SWNT bundles, 18.5 kJ/mol, is 55% higher than that for adsorption on HOPG, 12.0 kJ/mol. In combination with molecular mechanics calculations we show that the observed binding energies for both systems can be attributed to van der Waals interactions, i.e. physisorption. The experiments provide no evidence for a more strongly bound chemisorbed species or for dissociative oxygen adsorption.