Encapsulation of molecular nitrogen in multiwall CNx nanotubes

Multiwall CNx nanotubes have been grown in the result of acetonitrile decomposition over Fe catalyst (CVD method). The random nanotubes samples have been produced by classical technique using catalyst nanoparticles formed by iron bimaleate thermolysis. The aligned nanotubes have been synthesized by aerosol assisted CVD method where ferrocene was used as a catalyst source. X-ray photoelectron spectroscopy (XPS) showed the random sample contains two kinds of nitrogen, while additional high-energy peak was detected in the N 1s-spectrum of the aligned CN, nanotubes. X-ray absorption spectra measured near the N K-edge (NEXAFS) of the samples exhibited three peaks for both type of CNx nanotubes. The relative intensity of the high-energy peak was found to be much higher in the spectrum of aligned nanotubes. Assignment of the NEXAFS peaks was made using results of quantum-chemical calculations on carbon tube model incorporating pyridinic, three-fold coordinated and molecule nitrogen. The high-energy peak was shown to correspond to N-2 molecules and its absence in the XPS spectrum of random CNx nanotubes indicates the gaseous nitrogen is mainly concentrated in the interior region of nanotubes. The larger encapsulation of molecules in the aligned CNx nanotubes could be due to the higher diffusion of nitrogen atoms trough the catalytic particles formed directly in the CVD process. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.