Abstract
Herein we report the synthesis of covalently functionalized carbon nano-onions (CNOs) via a reductive approach using unprecedented alkali-metal CNO intercalation compounds. For the first time, an in situ Raman study of the controlled intercalation process with potassium has been carried out revealing a Fano resonance in highly doped CNOs. The intercalation was further confirmed by electron energy loss spectroscopy and X-ray diffraction. Moreover, the experimental results have been rationalized with DFT calculations. Covalently functionalized CNO derivatives were synthesized by using phenyl iodide and n-hexyl iodide as electrophiles in model nucleophilic substitution reactions. The functionalized CNOs were exhaustively characterized by statistical Raman spectroscopy, thermogravimetric analysis coupled with gas chromatography and mass spectrometry, dynamic light scattering, UV–vis, and ATR-FTIR spectroscopies. This work provides important insights into the understanding of the basic principles of reductive CNOs functionalization and will pave the way for the use of CNOs in a wide range of potential applications, such as energy storage, photovoltaics, or molecular electronics.
Highlights
The first objective of our work is to investigate the effects of intercalation in carbon nano-onions (CNOs) by the intrusion of metallic potassium
The reductive approach via potassium intercalation has already been widely investigated on several carbon nanomaterials, such as graphene, graphite, fullerenes, and carbon nanotubes,[36−43] as well as other postgraphene materials such as black phosphorus or molybdenum disulfide.[44−47] Its advantages in terms of an increase in reactivity and in yield of the reaction have been demonstrated by several studies of interest,[48,49] paving the way for the translation of this approach to CNOs
We carried out a combination of different in situ and ex situ characterization techniques supported by extensive theoretical calculations
Summary
Chemical functionalization has been extensively explored in order to modify the interfacial properties and modulate the solubility of CNOs, representing the most promising route for controlling their processability.[11,12,29,30] Their degree of functionalization is commonly associated with the size and strain of the CNOs. Typically, small-size CNOs (5−10 nm) are more reactive than larger-sized ones due to their higher curvature, leading to an increase in the pyramidalization of the C atoms.[28] Different synthetic procedures for CNO functionalization have been investigated using always neutral CNOs; the unambiguous characterization of the covalent functionalization in CNOs remains challenging. When it comes to other carbon allotropes, one of the probably most efficient routes for functionalization is the reduction using alkali metals
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