A Vibrational Spectroscopic Study of the Fate of Oxygen-Containing Functional Groups and Trapped CO₂ in Single-Walled Carbon Nanotubes During Thermal Treatment

Abstract

The oxygen-containing functional groups, introduced by common purification procedures, on single-walled carbon nanotubes (SWNTs) made by both the HiPco and laser-ablation (Rice Tubes) techniques are studied by Fourier Transform Infrared (FTIR) spectroscopy from 90 to 1400 K under vacuum. The fate of the functional groups under heating and the physically trapped CO2 generated from the decomposition of these functional groups are investigated. Vacuum heating to ∼1300 K removes most of the oxygen-containing functionalities in the purified samples. The similarities in the infrared spectra of the Rice Tubes after a 1400 K treatment with spectra for the as-received and air/HCl treated HiPco nanotubes suggests the observation of intrinsic SWNT IR bands. Vacuum heating of nitric acid treated HiPco samples leads to the formation of a new feature, tentatively assigned to cyclic anhydride groups, in the 1850 cm-1 region. The cyclic anhydride groups decompose and ultimately disappear after thermal annealing to 600 K. Above 700 K, the quantity of CO2 trapped in HNO3 treated HiPco SWNTs decreases and trapped CO2 is completely released from the nanotubes after 1100 K even though oxygen-containing functionalities are still present on the sample. The Rice Tubes made by the laser ablation technique retain the physically trapped CO2 even after heating to 1400 K.

Adsorption on Carbon Nanotubes Studied Using Polarization-Modulated Infrared Reflection−Absorption Spectroscopy

“…Some of the other features in Figure 1 have been discussed elsewhere. 13,40,41 The broad band at ∼3450 cm -1 indicates the loss of H-bonded sOH groups and/or physisorbed H 2 O. The structure in the 1680-1735 cm -1 range has been assigned to the loss of various carbonyl (>CdO) species.…”

Real Time Dynamics of Laser Activated Interface Processes at the Molecular Scale

“…11). [25] We have also recently shown that NH 3 adsorption appears to be functionality/defect mediated and that pristine single-walled CNTs show no sign of adsorption of ammonia (Fig. 12).…”

“…11 IR peak evolution of nitric acid treated HiPco samples during vacuum heating from 300K to 1300K. [25] Fig. 12 IR of Ammonia adsorption at 94K on nanotubes treated to successively higher temperatures, a process that drives off surface functionality and heals defects.…”

Effect of ozonolysis on the pore structure, surface chemistry, and bundling of single-walled carbon nanotubes

“…However, it is not inaccurate to assume that some degree of removal of surface functionalities and oxygenated defects along the nanotube sidewalls occurred as a result of the thermal treatment. In fact, it has been reported that heating (up to 1400 K) can readily defunctionalize (i.e., deoxygenate) HiPco tubes [14]. The E 1u mode of carbon nanotubes, due to C=C double bonds, at around 1581 cm −1 can be seen in both spectra, whose posi- tion is relatively unaffected by the localized addition and removal of oxygenated groups; however, its intensity changes slightly upon more severe oxidation.…”

“…HCl treatments, especially in the presence of moist air, are known to reduce metal impurities in tubes without necessarily introducing defects in the intrinsic sp 2 carbon framework [14]. Samples of ozone and ozone/H 2 O 2 -treated carbon nanotubes were subsequently placed in ceramic crucibles, and heated in a quartz tube at 700 • C for 2 h (a ramp rate of 10 • C/min) in a continuous flow of argon to prevent sample destruction, prior to cooling to room temperature.…”