Grafting the surface of carbon nanotubes and carbon black with the chemical properties of hyperbranched polyamines

Abstract

Controlling the chemistry on the surface of new carbon materials is a key factor to widen the range of their applicability. In this paper we show a grafting methodology of polyalkylamines to the surface of carbon nanomaterials, in particular, carbon nanotubes and a carbon black. The aim of this work is to reach large degrees of covalent functionalization with hyperbranched polyethyleneimines (HBPEIs) and to efficiently preserve the strong chelating properties of the HBPEIs when they are fixed to the surface of these carbon materials. This functionalization opens new possibilities of using these carbon nanotubes-based hybrids. The results show that the HBPEIs are covalently attached to the carbon materials, forming hybrids. These hybrids emerge from the reaction of amine functions of the HBPEIs with carbonyls and carboxylic anhydrides of the carbon surface which become imine and imide bonds. Thus, due to the nature of these bonds, the pre-oxidized samples with relevant number of C=O groups showed an increase in the degree of functionalization with the HBPEIs. Furthermore, both the acid-base properties and the coordination capacity for metal ions of the hybrids are equivalent to that of the free HBPEIs in solution. This means that the chemical characteristics of the HBPEIs have been efficiently transferred to the hybrids. To reach this conclusion we have developed a novel procedure to assess the acid-base and the coordination properties of the hybrids (solids) by means of potentiometric titration. The good agreement of the values obtained for the hybrids and for the free HBPEIs in aqueous solution supports the reliability of the procedure. Moreover, the high capacity of the hybrids to capture Ni²⁺ by complexation opens new possibilities of using these hybrids to capture high-value metal ions such as Pd²⁺ and Pt²⁺.

Hyperbranched polyethylenimines are covalently fixed to the surface of carbon materials, so the chemical characteristics of the amines are transferred to the hybrid materials.

Keywords:

• Carbon nanomaterials
• functionalization
• hyperbranched polyamines

CLASSIFICATION:

• 10 Engineering and Structural materials
• 104 Carbon and related materials
• 105 Low-Dimension (1D/2D) materials
• 212 Surface and interfaces
• 301 Chemical syntheses / processing
• 502 Electron spectroscopy

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

The supplementary material for this paper is available online at http://dx.doi.org/10.1080/14686996.2016.1221728

Acknowledgements

The assistance of Dr Abdelkader Fernández in the dispersion and HRTEM measurements is gratefully acknowledged.