9912 Chem. Commun., 2011, 47, 9912–9914 This journal is c The Royal Society of Chemistry 2011 Cite this: Chem. Commun., 2011, 47, 9912–9914 Poptube approach for ultrafast carbon nanotube growthw Zhen Liu, a Jialai Wang, b Vinod Kushvaha, c Selcuk Poyraz, a Hareesh Tippur, c Seongyong Park, d Moon Kim, d Yang Liu, a Johannes Bar, a Hang Chen e and Xinyu Zhang* a Received 6th June 2011, Accepted 21st July 2011 DOI: 10.1039/c1cc13359d Microwave irradiation can be used to heat conductive materials and metallocene precursors to initiate ultrafast CNT growth. It takes only 15–30 seconds to grow CNTs at room temperature in air, without the need for any inert gas protection and additional feed stock gases. Carbon nanotubes (CNTs) have drawn a great deal of attention since Iijima discovered this new class of allotropes of carbon. 1 Due to their extraordinary mechanical, thermal and electrical properties, CNTs have huge potential in the applications of composite materials, 2 smart structures, 3 chemical sensors, 4 energy storage 5 and nano-electronic devices. 6 However, the challenges remain in the high cost of CNT raw materials and the difficulty in their processing and applications. For example, vacuum or inert gas protection, high temperature and/or high energy density are always needed for the production of CNT, e.g., arc-discharge, 7 laser ablation 8 and chemical vapor deposition (CVD) 9 approaches, which make the cost of the as-produced CNTs to remain high. In addition, strong van der Waals force induced poor solubility/dispersibility is another factor that restricts the application of CNTs, especially in reinforcing composite materials. 10 As an attempt to address the challenges mentioned above, some reports discussed on embedding CNTs into carbon fibers through the conventional thermal heating process, 11 and CVD methods, 12 which can partially solve the dispersibility issue, but the reaction setup is still costly and complicated, and the process is time-consuming and energy inefficient due to the target-less volumetric heating. As previously developed by our group, conducting polymers can be heated to very high temperature in a short time, and converted to graphitic nanocarbons. 13 Based on this finding, we can use conducting polymers as heating sources towards growth of CNTs through the microwave approach. In a typical process, microwave Poptube precursors, such as ferrocene powder, 14–16 were physically mixed in the solid state with conductive materials, namely conducting polymers, Indium Tin Oxide (ITO) nano-powders, graphite powders, and carbon fibers. Upon microwave irradiation of the conducting materials, they will be heated to spark, arc and rapidly reach the temperature above 1100 1C, 13,17 where the ferrocene could be decomposed to an iron catalyst 18 and cyclopentadienyl that could serve as the carbon source. The microwave initiated CNT growth will take only 15–30 seconds under the microwave irradiation at room temperature in air, without the need for any inert gas protection, and additional feed stock gases, usually required in the CVD approach and other methods. To the best of our knowledge, this is the fastest CNT growth in terms of process duration, and probably the only approach that can be done under ambient conditions. The SEM images revealed the morphologies of the CNTs made from conducting polypyrroleÁCl powder (PPyÁCl) and ITO nanopowders (Fig. 1A and B). Spaghetti-like, hollow CNTs were observed with a few micrometres long (Fig. 1B), when conducting PPyÁCl was used as the heating layer, with outer diameter in the range of 30–50 nm. However, rod-like CNTs with bamboo-shaped inner hollow structures were obtained when ITO nanopowders were used as the heating layer (Fig. 1C and D and the inset), having outer diameters in the range of 150–200 nm. The nature of the conducting layers could play a significant role in controlling the morphology of the CNTs, e.g., the crystallinity and conductivity of the heating layers could affect the crystallinity and dimension of the iron catalyst nanoparticles. The multi-walled nature of the CNTs was evidenced by high resolution TEM (HRTEM, Fig. 1E and F), confirming that the CNTs are composed of B20 layers of coaxially folded graphene sheets. Other metallo- cenes and derivatives can be used as precursors, such as cobaltocene, nickelocene and 1,1 0 -bis-(diphenylphosphino) ferrocene, which are evidenced by the SEM images in Fig. S2 (ESIw). Compared to ferrocene, the 1,1 0 -bis-(diphenylphosphino) derivative has more conjugated rings (four benzene rings) in the structures, which could contribute to the more rigid structures (Fig. S2B, ESIw). The mechanism of the CNT growth is still unclear, although a tip-growth model could be proposed for this Poptube process. This is confirmed by the electron microscope images, since most of the catalyst particles are either at the tip or the middle part of the carbon nanotubes, indicating that the CNT a Department of Polymer and Fiber Engineering, Auburn University, Auburn, AL 36849, USA. E-mail: xzz0004@auburn.edu; Fax: +1-334-844-4068; Tel: +1-334-844-5439 b Department of Civil, Construction, and Environmental Engineering, The University of Alabama, Tuscaloosa, AL 35487, USA c Department of Mechanical Engineering, Auburn University, Auburn, AL 36849, USA d Department of Materials Engineering, The University of Texas at Dallas, Richardson, TX 75080, USA e Nanotechnology Research Center, Georgia Institute of Technology, Atlanta, GA 30332, USA w Electronic supplementary information (ESI) available: Enlarged images and experimental details. See DOI: 10.1039/c1cc13359d ChemComm Dynamic Article Links www.rsc.org/chemcomm COMMUNICATION Downloaded by Auburn University on 08 August 2012 Published on 08 August 2011 on http://pubs.rsc.org | doi:10.1039/C1CC13359D View Online / Journal Homepage / Table of Contents for this issue