The importance of oxygen-containing defects on carbon nanotubes for the detection of polar and non-polar vapours through hydrogen bond formation

Abstract

We report the electrical responses of water vapour and O2 adsorption onto macroscopic multi-walled carbon nanotube (MWCNT) ropes, and compare the results with mats of acid-treated MWCNTs on SiO2 substrates in order to investigate the importance of oxygen-containing defects on CNTs. In the outgassed state both carbon nanotube (CNT) materials exhibit rapid changes in electrical resistance when exposed to dry air, humid air or water vapour at standard temperature and pressure (STP). The measured electrical responses are highly reversible at STP when cycled between humid air, vacuum and dry air. We report a decrease in resistance for the CNT materials in dry air, attributed to O2 p-type doping of the CNTs, whereas there is an increase in resistance when exposed to a humid environment. This latter effect is attributed to the formation of hydrogen bonding from the polar water molecules with the oxygen-containing defects on the CNTs. Our observations indicate that the increase in electrical resistance upon water absorption affects a reduction of the electron-withdrawing power of the oxygen-containing defect groups, thus leading to a reduced hole carrier concentration in the p-type nanotubes.

Electrochemical Modification of Graphene

“…[27] An alternative mechanism that also appears plausible involves water adsorption on the residual oxygen containing groups that reduces the p-type doping. [28] However, our observations suggest that such a mechanism only plays a minor role, most likely due to the high concentration of water used here. Furthermore, a similar shift is observed upon exposure of the bare graphene samples to water (dash-dotted curve in Fig.…”

The synthesis of carbon nanomaterials using chlorinated hydrocarbons over a Fe-Co/CaCO3 catalyst

“…Modification of CNTs has thus led to the creation of new functional and construction materials. 11 Doping of the carbonaceous materials with non-carbon atoms, such as nitrogen, [12][13][14][15][16][17][18][19] boron, [20][21][22][23][24] sulphur, [25][26][27][28][29] oxygen [30][31][32][33][34][35][36] and halogens 11,[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55] has been explored over the past two decades. Modification of the carbon surface and electronic properties has also been explored but the effect of chlorine (Cl) on the morphology of carbon nanomaterials is not well established.…”

Resonant behavior observed in electron field emission from acid functionalized multiwall carbon nanotubes

“…10 They have high electrical and thermal conductivity, making them ideal candidates for use in electrical devices 11,12 such as sensors. 13,14 CNTs can be grown over large areas 15 and at low temperatures, 16 making them perfect for large area applications on temperature-sensitive substrates. Of interest in this work are the FE properties of CNTs.…”