Effect of the nanostructure and surface chemistry on the gas adsorption properties of macroscopic multiwalled carbon nanotube ropes

The NO2 adsorption properties of macroscopic multiwalled carbon nanotube (MWCNT) ropes and acid treated MWCNT ropes, obtained by the floating catalyst chemical vapour deposition process, have been examined. The structural characterisation shows that these ropes constitute bundles of MWCNTs. This bundled structure is found to control the electrical and gas adsorption properties of the material. The electrical resistance of these ropes decreases upon exposure to NO2 with a high sensitivity even at room temperature. The adsorption of the NO2 onto MWCNT bundles is found to be more stable with temperature in comparison to isolated MWCNTs revealing the complex nature of the adsorption process. These adsorption sites, which are created within the bundles of carbon nanotubes, are more stable requiring higher desorption energy. The surface of the MWCNT ropes is also modified with acid treatment, which increases the response to NO2 by a factor 100% due to increased polar interactions between the gas molecules and the existing functionalised surface. These results suggest the possibility of using these macroscopic MWCNT ropes as low cost gas sensing materials.