Surface properties of amphiphilic carbon nanotubes and study of their applicability as basic catalysts

Abstract

Amphiphilic hybrid carbon nanotubes (CNTs) containing a hydrophobic undoped section connected to a hydrophilic N-doped segment were synthesized. These amphiphilic hybrid CNTs were characterized by elemental analysis, nitrogen physisorption (BET), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), CO₂ adsorption coupled with microcalorimetry and X-ray photoelectron spectroscopy (XPS). The point of zero charge (PZC) for the different materials was also determined. The presence of basic sites on the surface of N-doped nanotubes is evidenced both from the CO₂ adsorption measurements and the PZC determinations. Their catalytic activity in the aldol condensation of furfural derivatives and acetone was evaluated. The results of the catalytic tests show significant specific activities (amount of reactant converted per gram of solid) when compared with strong basic solutions of NaOH. A clear correlation between the characterization data and the catalytic behavior was found. Furthermore, the selectivity values towards the two main reaction products, C₈ and C₁₃ aldol condensation adducts, are close to that of the NaOH solution. All together, these findings suggest these materials might be useful basic catalysts.