Effect of the added amount of organically-modified montmorillonite on the catalytic carbonization of polypropylene into cup-stacked carbon nanotubes

• Catalytic carbonization of polypropylene (PP) into cup-stacked carbon nanotubes (CS-CNTs).
• The yield and morphology of CS-CNTs were modulated by organically-modified montmorillonite (OMMT) content.
• OMMT influenced the degradation products of PP and the coalescence and reconstruction of NiO nanoparticles.

For the first time, cup-stacked carbon nanotubes (CS-CNTs) with high quality were efficiently synthesized by a one-pot approach through the carbonization of polypropylene (PP) under the combined catalysis of organically-modified montmorillonite (OMMT)/NiO. The effects of the added amount of OMMT on the yield, morphology, microstructure, phase structure and thermal stability of carbon nanomaterials (including CS-CNTs and carbon nanofibers (CNFs)) were fully investigated by scanning electron microscope, transmission electron microscope (TEM), high-resolution TEM (HRTEM), X-ray diffraction, Raman spectroscopy and thermal gravimetric analysis. Furthermore, the effects of OMMT on the degradation products of PP and the coalescence and reconstruction of NiO nanoparticles before the growth of CS-CNTs and CNFs were analyzed by gas chromatography, gas chromatography–mass spectrometry and HRTEM. It was found that after adding a low amount of OMMT, a relatively large amount of light hydrocarbons and a small amount of aromatics were produced during the degradation of PP, which promoted the coalescence and reconstruction of NiO nanoparticles into rhombic shape. Subsequently, the reshaped NiO catalysts catalyzed the light hydrocarbons and aromatics into long, straight and smooth-surface CS-CNTs with narrow length and diameter distributions. This approach offers a new potential way to largely transform waste polymer materials into valuable CS-CNTs.

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