Reactions and reversible hydrogenation of single-walled carbon nanotube anions
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Single-walled carbon nanotube (SWNT) radical anions will react with tetrahydrofuran and generate ethylene, enolates, and a partially hydrogenated nanotube backbone. The experimental evidence suggests that there are sp3 C–H binding interactions. The total gravimetric content of hydrogen on a sample averages from 3.5% to 3.9% w/w, about four times the total amount observed for nanotubes hydrogenated via traditional Birch reduction reactions. Furthermore, the hydrogen desorbs at temperatures up to 400 °C less than those observed for the hydrogenated SWNTs formed after the Birch reduction. Finally, the first room temperature electron spin resonance spectrum of a nanotube radical ion is also reported. I. INTRODUCTION
Hydrogenated carbon nanotubes are typically prepared by metal reduction reactions via two distinct methods: the modified Birch reduction in ammonia1–3 and the reaction with alkali metal naphthalides in tetrahydrofuran (THF).4–8 The reduced carbon nanotube materials were found to undergo what appeared to be a limited hydrogenation via a reaction with methanol.1 Alternatively, the reduced carbon nanotube materials were utilized for a series of diverse sidewall functionalization reactions, including in situ polymerization reactions.2,3,5–8 Utilizing similar alkali metal reduction chemistries, Teprovich et al.9 showed that a lithium-doped fullerene could reversibly store 5 wt% hydrogen with a 6:1 molar ratio of Li:C60 via a chemisorption mechanism. In this study, it was observed that under controlled conditions, the reaction of sodium naphthalide with purified laser-generated singlewalled carbon nanotubes (SWNTs) in THF leads to an efficient hydrogenation of the nanotube backbone. Through a series of isotope labeling experiments, we were able to establish that an unstable SWNT radical anion intermediate mimics the known reactivity of organolithium reagents with THF.10–12 Here, THF was susceptible to deprotonation by a SWNT radical anion intermediate. The final isolated product was a novel hydrogenated nanotube material that contained 3.5–3.9% w/w hydrogen. II. EXPERIMENTAL DETAILS A. General
All reactions were performed under a nitrogen atmosphere using standard Schlenk line techniques. The isotope-labeled a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.298 2806
http://journals.cambridge.org
solvents used in this study were purchased from Cambridge Isotope Laboratories, Inc. (Andover, MA), and used without further purification. Dry THF was distilled from sodium– benzophenone under nitrogen. B. Temperature programmed desorption apparatus
The temperature programmed desorption (TPD) apparatus and calibration have been described in detail previously.13 TPD measurements were performed on ;2 mg samples evacuated to 10 8 Torr at room temperature and then heated at 1 °C/s to 700 °C. The desorbing species were monitored as a function of temperature with mass spectrometry. C. Raman spectroscopy
Raman spectroscopy was performed using the 2.54 eV (488 nm) line of an Ar i
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