Catalytic activity of K10 montmorillonite in the chemical vapor deposition of multi-wall carbon nanotubes from methane

Abstract

The catalytic activity of K10 montmorillonite (K10Mt) as a substrate during the chemical vapor deposition (CVD) of carbon nanotubes (CNT) was investigated. The influence of free iron present in the structure of K10Mt during CNT synthesis was investigated. The synthesis was carried out both on samples containing free iron and after its chemical extraction. The structural and microstructural parameters of the samples were characterized by scanning electron microscopy with X-ray dispersion spectroscopy (SEM/EDS), energy dispersive transmission electron microscopy (TEM/EDS), X-ray fluorescence spectroscopy, X-ray diffraction (XRD), infrared spectroscopy (FTIR), and Raman spectroscopy, and X-ray photoelectron spectroscopy. It was found that K10Mt, before Fe removal, was covered with coarser forms of carbon with rounded shapes characteristic for pyrolytic carbon deposits, while after chemical purification the K10Mt particles were covered with regular forms of CNT. During the CVD process at 850 °C, multi-walled carbon nanotubes about 1 μm in length were formed on the surface of pure K10Mt. Under the conditions of synthesis, the K10-Mt/CNT nanocomposites were formed. After extraction of free iron from K10Mt, the most likely nucleation sites for CNT growth were Mg- and Fe-containing compounds structurally integrated with the K10Mt substrate, such as iron phosphides, magnesia, and magnesium aluminate.