Effect of the added amount of organically-modified montmorillonite on the catalytic carbonization of polypropylene into cup-stacked carbon nanotubes Jiang Gong a,b , Jie Liu a , Zhiwei Jiang a , Xin Wen a , Xuecheng Chen a , Ewa Mijowska c , Yanhui Wang a , Tao Tang a,⇑ a State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China b University of Chinese Academy of Sciences, Beijing 100039, China c Institute of Chemical and Environment Engineering, West Pomeranian University of Technology, Szczecin ul. Pulaskiego 10, 70-322 Szczecin, Poland highlights  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. graphical abstract article info Article history: Received 8 January 2013 Received in revised form 14 March 2013 Accepted 25 March 2013 Available online 6 April 2013 Keywords: Cup-stacked carbon nanotubes Polypropylene Organically-modified montmorillonite NiO Combined catalysis abstract 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 micro- scope, 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 coales- cence and reconstruction of NiO nanoparticles into rhombic shape. Subsequently, the reshaped NiO cat- alysts 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 trans- form waste polymer materials into valuable CS-CNTs. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Recently, cup-stacked carbon nanotubes (CS-CNTs) as a special and functional nanomaterial have attracted increasing attention due to their stacked morphology consisting of many truncated 1385-8947/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2013.03.112 ⇑ Corresponding author. Tel.: +86 (0) 431 85262004; fax: +86 (0) 431 85262827. E-mail address: ttang@ciac.jl.cn (T. Tang). Chemical Engineering Journal 225 (2013) 798–808 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej