Tetraethylenepentamine and (3-aminopropyl)triethoxysilane adsorbed on multi-walled carbon nanotubes for stable water and ethanol nanofluids

Abstract

Two solvent-free methods were combined to modify the surface of multi-walled carbon nanotubes (MWCNTs) with a high concentration of amine functional groups. First, an oxygen-rich plasma polymer (PP) coating was deposited on the MWCNTs. Second, either tetraethylenepentamine (TEPA) or (3-aminopropyl)triethoxysilane (APTS) were adsorbed on the surface of the MWCNTs by vapor functionalization. Results from thermogravimetric analysis of the PP coating reveal that it is composed of small oligomers, some of which are volatile at temperatures as low as 150 °C. Nevertheless, the PP coating can withstand the temperature required for vapor functionalization of the two chosen molecules. The APTS treated MWCNTs are not stable when dispersed in water, but stable in ethanol. As for TEPA treated MWCNTs, it is shown that they are stable in water at pH 2 and 5.5. This confirms that TEPA is adsorbed on the PP coating and completely shields this coating, allowing for the amines to stabilize the MWCNTs in an acidic environment.