An evaluation of microwave-assisted fusion and microwave-assisted acid digestion methods for determining elemental impurities in carbon nanostructures using inductively coupled plasma optical emission spectrometry

Abstract

It is common for as-prepared carbon nanotube (CNT) and graphene samples to contain remnants of the transition metals used to catalyze their growth; contamination may also leave other trace elemental impurities in the samples. Although a full quantification of impurities in as-prepared samples of carbon nanostructures is difficult, particularly when trace elements are intercalated or encapsulated within a protective layer of graphitic carbon, reliable information is essential for reasons such as quantifying the adulteration of physico-chemical properties of the materials and for evaluating environmental issues. Here, we introduce a microwave-based fusion method to degrade single- and double-walled CNTs and graphene nanoplatelets into a fusion flux thereby thoroughly leaching all metallic impurities. Subsequent dissolution of the fusion product in diluted hydrochloric and nitric acid allowed us to identify their trace elemental impurities using inductively coupled plasma optical emission spectrometry. Comparisons of the results from the proposed microwave-assisted fusion method against those of a more classical microwave-assisted acid digestion approach suggest complementarity between the two that ultimately could lead to a more reliable and less costly determination of trace elemental impurities in carbon nanostructured materials.

Validation of alkaline oxidation as a pre-treatment method for elemental quantification in single-walled carbon nanotubes

“…These are notoriously difficult to eliminate and may affect the physical properties of the sample. 7,8 Even though ''puried'' CNTs are available commercially, it is sometimes challenging to nd trustworthy information regarding the content of metals and/or the lot-to-lot compositional homogeneity. [9][10][11][12] While this may not constitute a critical issue in applications such as mechanical reinforcement of polymers, in other cases such as electrocatalysis, it can lead to erroneous data interpretation.…”

“…15,18 Concurrent with these advances, some of us proposed alkaline oxidation (or "fusion") as an alternative approach to disintegrate CNTs for ICP-based analyses. 8 This treatment is normally applied to samples that are impervious to strong acids. Among these are refractory materials such as carbides 19,20 and borides, ceramics, 21 mineral ores, 22,23 marine sediments 24,25 and human bones.…”

Comparative study for carcinogenicity of 7 different multi-wall carbon nanotubes with different physicochemical characteristics by a single intraperitoneal injection in male Fischer 344 rats

“…However, because the obtained data on the size distribution are similar to those obtained from aqueous suspension of MWCNTs containing Tween 80 (Takaya et al, 2010), it is suggested that the size distributions are not practically different regardless of the vehicle, if MWCNTs are sufficiently dispersed. For the determination of the metal contents of MWCNTs, the elution of metals from MWCNTs requires the strong acidic condition at a high temperature (Fenoglio et al, 2008;Patole et al, 2016), and metals are not eluted in the aqueous solution under the neutral pH. It is thus suggested that the metal contents of MWCNTs in 2% CMC solution (administering to rats) are dependent on the concentration of MWCNTs.…”

Chemical and Structural Analysis of Carbon Materials Subjected to Alkaline Oxidation

“…fusion) is also capable to digest different types of carbons. 7 The ICP-OES readings from the fusion procedure were compared with those of microwave-assisted acid digestion, but the outcome was not entirely conclusive. In a follow-up study, we validated fusion for ICP-OES by resorting to a chemically certified reference material (CRM), the SWCNT-1, and a lithium (meta)borate salt.…”