High-purity Single-walled Carbon Research Articles

High Purity Single Wall Carbon Nanotube by Oxygen-Containing Functional Group of Ferrocene-Derived Catalyst Precursor by Floating Catalyst Chemical Vapor Deposition.

Single wall carbon nanotubes (SWCNTs) were synthesized using oxygen-containing ferrocene derived catalysts. The mechanism of synthesizing carbon nanotubes was clarified by the catalyst’s exothermic or endothermic decomposition processes. By monitoring the decomposition process of ferrocene-derived catalyst precursors with and without sulfur, we found that the types of oxygen function groups closely influence catalyst formation and nanotube growth. The ferrocene-derived catalyst precursors have a different oxygen containing groups, which are hydroxyl (–OH, ferrocenenemethanol) and carbonyl (C=O, acetylferrocene, and 1,1′-diacetylferrocene). The sulfur chemical state (S 2p) on synthesized catalyst particles using acetylferrocene and 1,1′-diacetylferrocene has more sulfate () than others, and there also is a carbon state (C-S-C). The catalyst particle using ferrocenemethanol predominant formed metal–sulfur bonds (such as S2− and ). The hydroxyl group (–OH) of ferrocenemethanol enhanced the etching effect to remove amorphous carbon and prevented oxidation on the catalyst particle surfaces; however, the carbonyl group (C=O) of acetylferrocene reacted with the catalyst particles to cause partial oxidation and carbon dissociation on the surface of the catalyst particles. The partial oxidation and carbon contamination on catalyst particles controlled the activity of the catalyst. The DFT study revealed that the ferrocene-derived catalyst precursor was dissociated according to following process: the functional groups (such as CH3CO and COH) => first Cp ligands => second Cp ligands. The pyrolysis and release of Fe ions were delayed by the functional groups of ferrocene-derived precursors compared to ferrocene. The thermal-decomposition temperature of the catalyst precursor was high, the decomposition time was be delayed, affecting the formation of catalyst particles and thus making smaller catalyst particles. The size and composition of catalyst particles not only affect the nucleation of CNTs, but also affect physical properties. Therefore, the IG/ID ratio of the CNTs changed from 74 to 18 for acetylferrocene and ferrocene, respectively. The purity also increased from 79 to 90% using ferrocene-derived precursors.

An efficient strategy for the purification of cloth-like single walled carbon nanotube soot produced by arc discharge

High purity single walled carbon nanotubes (SWCNTs) were prepared from arc discharge produced cloth-like soot by a new purification strategy, in which liquid oxidation and steam oxidation were combined with a freeze-drying process to remove the metallic and carbonaceous impurities. The process gives a product of >98% purity, which is acquired from a gram-scale dirty raw soot with an overall yield of ∼75% of the SWCNTs. The purity of the samples was characterized by thermogravimetric analysis, scanning and transmission electron microscopy, Raman and Vis–NIR spectroscopy, and magnetometry. A highly pure SWCNT sample with relative purity of 170.4% and I G/ I D value of 78.92 is achieved. Experiments showed that HNO 3/HCl refluxing combined with freeze-drying is the key process that renders the crude SWCNTs hydrophilic with a large surface area, and thus remarkably increases the efficiency of the steam treatment to remove most of the carbonaceous impurities.

Variation of single wall carbon nanotube dispersion properties with alkyl amide and halogenated aromatic solvents

Organic solvents from the alkyl amide and halogenated aromatic classes have been analyzed as dispersion agents for high purity single wall carbon nanotubes (SWCNTs). The resulting dispersions from two novel SWCNT solvents, N,N,N′,N′-tetramethylmalonamide (TMMA) and 1-chloronaphthalene (1-CLN), have been compared to the well-established solvents, N,N-dimethylacetamide (DMA) and 1,2-dichlorobenzene (DCB). Optical absorption spectroscopy on a series of high purity SWCNT concentrations was used to obtain solvent-dependent dispersion limits, extinction coefficients, and dispersion stability. The variation in SWCNT optoelectronic properties was measured for each solvent dispersion as a function of ultrasonication time and the results demonstrate that under conventional ultrasonication times the halogenated aromatic solvents (DCB and 1-CLN) can significantly affect the SWCNT optical absorption. A post-dispersion analysis was performed on samples, after removal of the solvents, by Raman spectroscopy to monitor structural changes in the SWCNTs. The spectroscopy results for the halogenated aromatic solvents are consistent with formation of a sonopolymer and subsequent interaction with the SWCNTs. In comparison, the alkyl amide solvents (DMA and TMMA) show similar dispersion limits with no significant change in absorbance as a function of ultrasonication, and can easily be removed without affecting the SWCNTs.

Lithium Ion Capacity of Single Wall Carbon Nanotube Paper Electrodes

The electrochemical cycling performance of high purity single wall carbon nanotube (SWCNT) paper electrodes has been measured vs lithium metal for a series of electrolyte solvent compositions. The addition of propylene carbonate (PC) into the conventional ethylene carbonate (EC):dimethyl carbonate (DMC) cosolvent mixture enabled a reversible lithium ion capacity of 520 mAh/g for high purity SWCNTs. The free-standing SWCNT electrode (absent of polymer binder or metal substrate support) with this electrolyte combination demonstrates enhanced cycleability, retaining >95% of the initial capacity after 10 cycles. The first cycle hysteresis, common in these materials, is shown to vary dramatically with solvent selection and illustrates the importance of the solid−electrolyte−interface (SEI) formation on SWCNT capacity. The effect of galvanostatic charge rate (i.e., C-rate) on lithium ion capacity shows a 2× improvement [in capacity per current] over reported values for conventional graphite anode materials. The...

Single Wall Carbon Nanotube – LiCoO2 Lithium Ion Batteries

ABSTRACTThe electrochemical cycling performance of high purity single wall carbon nanotube (SWCNT) paper electrodes has been measured for a series of electrolyte solvent compositions. The effects of varying the galvanostatic charge rate and cycling temperature on lithium ion capacity have been evaluated between 25-100 °C. The measured reversible lithium ion capacities for SWCNT anodes range from 600-1000 mAh/g for a 1M LiPF6 electrolyte, depending on solvent composition and cycling temperature. The solid-electrolyte-interface (SEI) formation and first cycle charge loss are also shown to vary dramatically with carbonate solvent selection and illustrate the importance of solvent alkyl chain length and polarity on SWCNT capacity. SWCNT anodes have also been incorporated into full battery designs using LiCoO2 cathode composites. An electrochemical pre-lithiation sequence, prior to battery assembly, has been developed to mitigate the first cycle charge loss of SWCNT anodes. The pre-lithiated SWCNT anodes show reversible cycling at varying charge rates and depths of discharge with the cathode system. The summary of data shows that the structural integrity of individual SWCNTs is preserved after cycling, and that free-standing SWCNT paper electrodes represent an attractive material for lithium ion batteries.

Synthesis of high purity single-walled carbon nanotubes in high yield.

A simple method for the synthesis of high purity single wall carbon nanotubes has been developed by using nickel formate as a precursor for the formation of nearly mono-dispersed nickel seed-nanoparticles as catalysts in the CVD growth process.