Chemical modification of multi-walled carbon nanotubes using a tetrazine derivative
Graphical abstract
Multi-walled carbon nanotubes (MWNTs) have been reacted with 3,6-diaminotetrazine under heating. This process involves series of interactions between tetrazines and carbon nanotubes including π–π interactions, cycloaddition (Diels–Alder) and cross-linking reactions. These interactions resulted in coating of the MWNTs and in the formation of Y-junctions between nanotubes. Long heating (48 h) of MWNTs with the terazine resulted in a partial destruction of nanotubes due to their excessive functionalisation. The new nanocomposites have been studied by TEM, FTIR and Raman spectroscopy.
Introduction
Functionalisation of carbon nanotubes is very important for their further processing and manipulation [1], [2], as currently applications of carbon nanotubes is limited by their low solubility in common solvents and their low miscibility with most materials. Therefore considerable effort has been devoted to the chemical modification of carbon nanotubes. C60 fullerene consists of twelve pentagons and twenty hexagons formed by sp2 hybridised carbon atoms. Cycloaddition reactions are very well known for fullerenes, for example, C60 behaves as an electron-deficient dienophile in Diels–Alder reactions [3], [4], [5], [6], [7] with numerous electron rich dienes such as anthracene, pentacene and cyclopentadiene [8], [9], [10], [11], [12], [13]. The tips and elbows of carbon nanotubes contain pentagon–hexagon pair fragments structurally similar to C60, in addition carbon nanotubes also have 4 and 7 membered rings [14]. All these distortions are responsible for the high reactivity of tips and elbows of carbon nanotubes, carbon nanotubes may also have a number of different side-wall defects. These factors allow us to suggest a possibility of nanotubes modification using 1, 4-disubsituted tetrazines and cycloaddition reactions. Tetrazines are well known to be used as electron-poor diene in [4 + 2] cycloadditions with electron rich dienophiles [15]. It has been previously reported that the cycloaddition reaction [16] of fullerenes and tetrazines results in a monoadduct consisting of the fullerene and a modified tetrazine (−N2) nested atop of the fullerene. More recently the formation of fullerene dimers and new non-classical C62 fullerenes, from the tetrazine–C60 monoadduct upon irradiation with visible light and heat has been reported [17]. All these results demonstrate high complexity of the fullerene–tetrazine systems, which may yield a variety of products. After the addition steps, the sequence is normally completed by loss of dinitrogen in a cyclo-elimination step forming azolydienamines. The main aim of this work is to investigate the interaction of 3,6-diaminotetrazine (datz) with multi-walled carbon nanotubes (MWNTs). We used transmission electron microscopy (TEM), FTIR and Raman spectroscopy for the characterisation of the nanotube composites.
Section snippets
General procedures
The multi-walled carbon nanotubes (MWNTs) were purchased from Nanocyl company. The synthesis of 3,6-Diamino-1,2,4,5-tetrazine (datz) was performed according to published procedure [18].
The transmission electron microscopy (TEM) images were taken on Hitachi H-7000 electron microscope. The TEM was operated at a beam voltage of 100 kV. Samples for TEM were prepared by deposition and drying of a drop of the powder dispersed in ethanol onto a formvar coated 400 mesh copper grid.
FTIR spectra in the
Results and discussion
The reaction was performed using datz as a reagent (Fig. 1). The MWNTs were initially sonicated in ethanol to disperse them. Then datz was added to the mixture. The mixture was heated under reflux. After 8 h of heating, the first sample was taken from the mixture. It was washed three times with THF and ethanol, before being dried in vacuum. A similar procedure was performed after 12, 24, 36 and 48 h of heating. The functionalised MWNTs were analysed by TEM, FTIR and Raman spectroscopy.
Conclusions
We have investigated interactions between MWNTs and diaminotetrazine. In overall this procedure involves several possible interactions. The first step is a π–π interaction, which results in the coating (and cycloaddition) of the nanotubes. The second step is the junction formation, which occurs after 24 and mostly after 36 h of heating. The final step is a partial destruction of the nanotubes, which is very pronounced after 48 h of heating as result of an excessive functionalisation. We believe
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