Low-temperature (150 °C) carbon nanotube growth on a catalytically active iron oxide–graphene nano-structural system Enkeleda Dervishi a,⇑ , Alexandru R. Biris b , Joshua A. Driver a , Fumiya Watanabe a , Shawn Bourdo a , Alexandru S. Biris a,⇑ a Center for Integrative Nanotechnology Sciences, University of Arkansas at Little Rock, Little Rock, AR 72204, USA b National Institute for Research and Development of Isotopic and Molecular Technologies, Cluj-Napoca, Romania article info Article history: Received 16 August 2012 Revised 6 November 2012 Accepted 9 December 2012 Available online 30 January 2013 Keywords: Graphene Iron oxide catalyst Low-temperature growth Carbon nanotube Chemical vapor deposition abstract In this work, we report the growth of carbon nanotubes (CNTs) at temperatures as low as 150 °C on an iron oxide–graphene, multicomponent, nano-structural system. A radio-frequency generator and an elec- trical furnace are separately used to heat the decorated graphene samples in an argon/hydrogen environ- ment without adding any external hydrocarbon source. Few-layer graphene sheets are decorated with iron oxide nanoparticles using a simple one-step process and thoroughly characterized by electron microscopy. The synthesis temperature is varied between 150 and 500 °C, and nanotube’s presence is confirmed by transmission and scanning electron microscopy. We find that, while the graphene deco- rated with 5 nm iron oxide nanoparticles forms nanotubes at the lowest temperature (150 °C), the dec- orated samples with larger nanoparticles (15 nm) only initiate nanotube growth at 400 °C or higher, indicating a strong size-dependence on the catalytic activity of these nanoparticles. This low-tempera- ture, facile technique opens the door to a wide range of applications for these novel nanoparticle/graph- ene-nanotube systems in areas varying from nano-electronics and energy harvesting to bio-nano. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction Since the discovery of CNTs, numerous efforts have been fo- cused on finding technological approaches to lower their corre- sponding synthesis temperature, which could make the growth of these nanomaterials more practical for various applications especially in the nano-electronic and field emission areas [1–4]. More specifically, since complementary metal–oxide–semiconduc- tor (CMOS) devices are generally fabricated at temperatures below 400 °C, lowering the CNT growth temperature is imperative for their incorporation in hybrid, complex electronic devices [5]. How- ever, the most common growth temperatures for CNTs, depending on the catalyst system and the synthesis conditions, range between 700 and 1000 °C [6–9]. Compared to other synthesis techniques, chemical vapor deposition (CVD) remains the most popular meth- od and has been widely used to synthesize CNTs at lower temper- atures in controlled conditions resulting in nanomaterials with excellent morphologies and characteristics [10]. More recently, several groups have been working to synthesize CNTs at very low temperatures (below 300 °C) with and without the presence of cat- alyst systems. Wang et al. have reported the growth of multiwalled carbon nanotubes (MWCNTs) at 160 °C by the decomposition of polyethylene glycol using a hydrothermal synthesis without the addition of catalyst Fe/Co/Ni [11]. Since this reaction requires 20 h, it is time-consuming and complex. Wang et al. were able to improve the quality and yield of MWCNTs by increasing the syn- thesis temperature to 180 °C [12]. Vohs et al. reported the lowest synthesis temperature (175 °C) for MWCNTs, using CCl 4 as a pre- cursor along with metal-encapsulated dendrimers as catalysts in a 24-h treatment at 27.6 MPa [13]. However, this method was re- ported to produce relatively low-quality nanotubes and could have limited practicality for industrial applications, since it requires high pressure and a lengthy synthesis time. Moreover, low-quality MWCNTs or nanorods were synthesized on various catalysts, such as Fe, Au, or Ag, utilizing tetrachloroeth- ylene as the carbon feedstock; reactions were performed in the presence of benzene and potassium and kept at 200 °C for 27 h [14]. Vertically aligned MWCNTs have been synthesized using a photo-thermal chemical vapor deposition technique on a Ti/Fe cat- alyst film at temperatures as low as 370 °C [5]. Others have dem- onstrated the growth of CNTs by CVD method on catalyst systems, such as Ni supported on zeolite and Ti/Fe on SiO 2 at tem- peratures between 350 and 600 °C using methane [15]. Addition- ally, Sharma et al. have reported in situ observations of nanotube growth at 450 °C over Ni or Co catalysts [10]. New nanomaterials composed of 1- and 2-dimensional carbon structures with improved electronic and mechanical properties 0021-9517/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcat.2012.12.013 ⇑ Corresponding authors. Fax: +1 501 683 7601. E-mail addresses: exdervishi@ualr.edu (E. Dervishi), asbiris@ualr.edu (A.S. Biris). Journal of Catalysis 299 (2013) 307–315 Contents lists available at SciVerse ScienceDirect Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat