Overcoming Catalyst Residue Inhibition of the Functionalization of Single-Walled Carbon Nanotubes via the Billups–Birch Reduction

Abstract

The Billups-Birch Reduction chemistry has been shown to functionalize single-walled carbon nanotubes (SWCNTs) without damaging the sidewalls, but has challenges in scalability. Currently published work uses a large mole ratio of Li to carbon atoms in the SWCNT (Li:C) to account for lithium amide formation, however this increases the cost and hazard of the reaction. We report here the systematic understanding of the effect of various parameters on the extent of functionalization using resonant Raman spectroscopy. Addition of 1-iodododecane yielded alkyl-functionalized SWCNTs, which were isolated by solvent extraction and evaporation, and purified by a hydrocarbon wash. The presence of SWCNT growth catalyst residue (Fe) was shown to have a strong adverse effect on SWCNT functionalization. Chlorination-based SWCNT purification reduced the amount of residual Fe, and achieve a maximum I/I ratio using a Li:C ratio of 6:1 in a reaction time of 30 min. This result is consistent with published literature requiring 20-fold mole equivalents of Li per mole SWCNT with a reaction time of over 12 h. This new understanding of the factors influencing the functionalization chemistry will help cut down material and process costs, and also increase the selectivity of the reaction toward the desired product.

The State of HiPco Single-Walled Carbon Nanotubes in 2019

“…Thermogravimetric analysis (TGA, Figure 5) corroborated the results from EDS elemental analysis, with a final residue of 30 wt% and 18.4 wt% for the Rice University and NoPo HiPco samples, respectively. Given that the TGA was performed in air, these numbers account for the formation of iron oxides during heating [17,22], and the actual iron content in both samples are on the order of 21 wt% and 12.9 wt%, respectively, which is in good agreement with the EDS analysis ( Table 1). The nature of the weight loss plot for the two samples was also different, which also helps describe the carbon content in the samples.…”

“…We have previously reported that in order for A common figure of merit I G /I D (degree of order) was employed for the purposes of evaluating the defect density across different diameters [23]. We have previously reported that in order for meaningful I G /I D values, a number of measurements need to be made across a sample [17]. Table 2 gives the I G /I D value (with associated error) for both samples as a function of the excitation wavelength.…”

“…HiPco SWCNTs continue to be the de-factor standard even in 2019; however, things are quickly turning as a result of the reactor, associated IP, and all remaining stock of HiPco SWCNTs being sold by Rice University to Atom OptoElectronics, Inc. [16] as the sole-supplier of the remaining materials (at $899/g compared to the $150-250 when available directly from Rice University). The expiration of the core patents for the HiPco process combined with a typical 25-30 wt% residual metal catalyst impurity [17], create the potential for a new source of less expensive, high-quality HiPco SWCNTs available globally.…”

The safe handling of bulk low-density nanomaterials

“…3 Average EDS analysis of 4 aliquots taken from a large batch of SWCNTs. Each EDS analysis was taken of 4 areas giving the standard deviation showed defect sites [19,20]. Figure S3 (see ESM) shows representative Raman spectra (633 nm) for the four aliquots.…”

From Newspaper Substrate to Nanotubes—Analysis of Carbonized Soot Grown on Kaolin Sized Newsprint

“…Despite the potential application of both single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) for a broad range of research and commercial fields extending from electronics to medicine [1,2], their purity is of paramount importance with many of the end-uses [3]. As a result, we have, among other things, concentrated much of our research efforts in developing purification methods to remove amorphous carbon, catalyst residue and defects [4][5][6]. Conversely, one of the most commonly raised value enhancements of materials by CNTs is the modification of elastomer properties [7], where purity can actually be detrimental in some cases.…”