Surface Properties of Carbon Nanotubes and Their Role in Interactions with Silica

Abstract

Different approaches, including determination of the surface tension via capillary penetration measurements and characterization of the surface chemical composition by means of X-ray photoelectron spectroscopy (XPS), were applied to reveal the surface properties of various CNT types produced from acetonitrile (CH₃CN), cyclohexane (C₆H₁₂) and methane (CH₄). Significant differences were found in the polarity of the CNT surfaces depending on the used precursors. The surface tension of the CNTs increases by utilization of carbon sources in the following order: cyclohexane, methane, acetonitrile. Using XPS analysis a comparatively high contents of nitrogen and oxygen atoms were detected on the surface of the CH₃CN-CNTs. Based on the results of the mass spectrometry, the strong hydrophobic character observed for the C₆H₁₂-CNTs is assumed to originate from polycyclic aromatic hydrocarbons deposited on the nanotubes’ surface during synthesis. The investigation of the deposition of silica on the CNTs by a sol-gel method showed that the polar surface of the CH₃CN-CNTs provided the most favorable condition for the heterogeneous precipitation of silica. In contrast, no precipitation of silica was observed on the hydrophobic C₆H₁₂-CNTs.