Abstract
Graphite intercalation compounds (GICs) are often used to produce exfoliated or functionalised graphene related materials (GRMs) in a specific solvent. This study explores the formation of the Na‐tetrahydrofuran (THF)‐GIC and a new ternary system based on dimethylacetamide (DMAc). Detailed comparisons of in situ temperature dependent XRD with TGA‐MS and Raman measurements reveal a series of dynamic transformations during heating. Surprisingly, the bulk of the intercalation compound is stable under ambient conditions, trapped between the graphene sheets. The heating process drives a reorganisation of the solvent and Na molecules, then an evaporation of the solvent; however, the solvent loss is arrested by restacking of the graphene layers, leading to trapped solvent bubbles. Eventually, the bubbles rupture, releasing the remaining solvent and creating expanded graphite. These trapped dopants may provide useful property enhancements, but also potentially confound measurements of grafting efficiency in liquid‐phase covalent functionalization experiments on 2D materials.
Highlights
Reductive dissolution of nanocarbons is a versatile and widely used methodology to achieve individualisation, exfoliation and functionalisation of carbon nanotubes (CNTs), fullerenes, and other graphitic nanomaterials;[1] it has been extended, more recently, to graphene analogues, such as carbon nitride[2] and transition-metal dichalcogenides.[3]
In situ X-ray diffraction (XRD) has been used to observe the well-defined stage transitions which occur during the vapour phase insertion of potassium into graphite,[10] whilst operando measurements have been used to study electrochemical intercalation of sodium and diethylene glycol dimethyl ether (DEGDME).[27]
Raman spectroscopy can monitor the level of charge transfer, and intercalation, in graphite, and is a useful complementary technique for characterising graphite intercalation compounds (GICs),[18,25] whilst thermogravimetric analysis (TGA) has been used to calculate the amounts of inserted metal and solvent, and can provide information on structural composition.[17,44]
Summary
Reductive dissolution of nanocarbons is a versatile and widely used methodology to achieve individualisation, exfoliation and functionalisation of carbon nanotubes (CNTs), fullerenes, and other graphitic nanomaterials;[1] it has been extended, more recently, to graphene analogues, such as carbon nitride[2] and transition-metal dichalcogenides.[3]. In situ XRD has been used to observe the well-defined stage transitions which occur during the vapour phase insertion of potassium into graphite,[10] whilst operando measurements have been used to study electrochemical intercalation of sodium and diethylene glycol dimethyl ether (DEGDME).[27] Raman spectroscopy can monitor the level of charge transfer, and intercalation, in graphite, and is a useful complementary technique for characterising GICs,[18,25] whilst TGA has been used to calculate the amounts of inserted metal and solvent, and can provide information on structural composition.[17,44] The decomposition of solvent is observed at surprisingly high temperatures as the GICs are heated, but the structural evolution is often complex and not well understood Most of these studies focus mainly on metal insertion and do not consider de-intercalation behaviour, with only a few offering insights into reversibility of the process[10,27] or stability of the product.[26,45] Since intercalation appears to be strongly dependent on the choice of metal, solvent and host graphite, de-intercalation behaviour might be expected to differ between these systems. Understanding this phenomenon is crucial to obtaining pure functionalised graphenes and may be useful for alternative applications such as Na-ion batteries
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