Iron filled carbon nanostructures from different precursors S. Costa a , E. Borowiak-Palen a, * , A. Bachmatiuk a , M.H. Rümmeli a,b , T. Gemming b , R.J. Kalenczuk a a Centre of Knowledge Based Nanomaterials and Technologies, Institute of Chemical and Environment Engineering, Szczecin University of Technology, Poland b Leibniz Institute for Solid State and Materials Research Dresden, D-01171 Dresden, Germany article info Article history: Available online 5 June 2008 Keywords: Carbon nanotubes Nanocapsules Biomedical Therapeutics abstract Here, we present a study on the synthesis of different nanostructures with one single-step in situ filling (encapsulation) via carbon vapor deposition (CVD). Ferrocene, acetylferrocene and iron (II) nitrate as iron precursors were explored. The application of each of these compounds resulted in different carbon nanomaterials such as: iron filled multiwalled carbon nanotubes with a low filling ratio (Fe-MWCNT), iron filled nanocapsules and unfilled MWCNT. The as-produced samples were purified by high tempera- ture annealing and acid treatment. The purified materials were characterised using transmission electron microscopy (TEM) and Raman spectroscopy. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Since their discovery, carbon nanotubes (CNT) have been devel- oped and applied in several scientific and technological fields due to their unique physical and morphologic properties. The potential application of CNT has been reported in various fields. One of the most reported fields is their use for energy storage [1–7], once it is necessary to start with a world-wide application of environment friendly electric power sources [1]. The mesoporous character of carbon nanotubes plays an important role in their electrochemical properties. In respect to the other types of carbon forms they have higher rate of electron transfer which makes them more suitable for the applications as nanoscale electric devices [2]. Next very important potential of CNT is their application in the biomedical science what was also widely reported [8,9]. One of their most challenging biomedical applications is their use in cancer therapy by magnetic fluid hyperthermia (MFH). Here, magnetic nanoparti- cles penetrate into the tumour cells where they are heated until the cell-killing effect is reached (41–42 °C). Further, due to their morphology CNT can be used as carrier systems and act as mag- netic nano-heaters, drug delivery systems (DDS) and temperature sensors at the cellular level [10,11]. One of the greatest challenges in such therapy is the ability to control the temperature and the heating process. The application of magnetic-filled CNT seems to be a promising way to overcome this problem. Iron could be a promising candidate due to its ferromagnetic behaviour [12]. The development of CNT therapies as discussed required their produc- tion with a high level purity on a bulk sample. In addition a low le- vel of filling inside the nanotubes is required. Limiting the filling ratio is crucial because there must be free space in the cavity of the tubes for further insertions such as the temperature sensor and the therapeutics. The synthesis of iron filled multiwall carbon nanotubes (MWCNT) has been already reported using different iron contain- ing compounds in solid [13–17] or liquid phase [18–21]. However, a systematic and comparative study of the process is still required. In the current work we compare different single-step routes in situ CVD synthesis of Fe filled nanostructures using different iron sources acting also as catalysts (ferrocene, acetylferrocene and iron (II) nitrate). Applying different process conditions and different iron sources the as-produced materials can exhibit different mor- phological properties: iron filled MWCNT, iron filled carbon nano- capsules and MWCNT with an empty cavity. 2. Experimental The synthesis was carried out using a CVD process with differ- ent iron precursors. Two types of the experimental setups were investigated (Fig. 1). The first apparatus scheme is shown in Fig. 1a. It consists of a dual zone furnace, a bottle containing high pure methane or argon gas, a temperature controller, a flowmeter and a rotary pump. Initially the system was evacuated to about 10 À3 mbar at room temperature. Next, the iron source was subli- mated in the first heating zone (heated just above the sublimation temperature of the compound) and the gas flow of methane direc- ted these vapours to the second heating zone where the formation of the CNT occurs. The second apparatus scheme is shown in Fig. 1b. Here, a single zone furnace is applied. In this CVD route, ethanol/ferrocene vapors were introduced by feeding Ar to the reaction zone. The ethanol/ ferrocene mix was placed in the bubble bottle and buffer gas flow rates of 600 mL/min were used. The temperature of the process at 950 °C was set. Later the product was cooled down to room 0196-8904/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2008.01.040 * Corresponding author. E-mail address: eborowiak@ps.pl (E. Borowiak-Palen). Energy Conversion and Management 49 (2008) 2483–2486 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman