carbon nanotubes with improved biocompatibility prepared by ...

CARBON NANOTUBES WITH IMPROVED BIOCOMPATIBILITY PREPARED BY TEMPLATE SYNTHESIS, WHICH COMBINES CATALYST- FREE CHEMICAL VAPOR DEPOSITION (CVD) AND CHEMICAL DOPING PROCESS 1

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Tariq Altalhi, Milena Ginic-Markovic, Stephen Clarke, Peter Fredericks, Dusan Losic 1

School of Physical and Chemical Science, Flinders University, SA 5042, Adelaide, Australia 2 School of Physical & Chemical Sciences, Queensland University of Technology, Brisbane, QLD 4001, Australia 3 Ian Wark Research Institute, The University of South Australia, Mawson Lakes Campus, Mawson Lakes 5095 SA, Adelaide, Australia. Email: [email protected]

ABSTRACT Carbon nanotubes (CNTs) due to their unique electrical, thermal, chemical and mechanical properties have been extensively studied in terms of both fundamental and practical applications including electronics, energy storage, catalysis, fuel cells, solar cells, molecular separation, sensors, biosensors, and drug delivery. The diameter and morphology of CNTs are determined to be a key factor to govern the properties of CNT and extensive research has been directed to the growth of CNT structures with controllable dimensions. However, the presence of additional doping elements into CNT structure including nitrogen, boron, and phosphor also could considerable alter their conductivity, biocompatibility and chemical properties. In this work, we present several synthetic approaches to prepare multi-walled carbon nanotubes (MWCN) with controlled dimensions, with catalyst, catalyst-free and chemically doped with selected element (N). Our method is based on chemical vapour deposition (CVD) using nanoporous alumina (PA) as a template. The catalyst free carbon nanotubes (0-CNTs) and nitrogen doped (N-CNTs) were prepared in custom designed system set out with an ultrasonic generator, by the pyrolysis of liquid aerosol of toluene along with pyridine, over nanoporous alumina. The synthesis of 0-CNT/PA and N-CNT/PA composites with controllable nanotube dimensions such as diameters (30-150 nm), length, (2-20 µm), and chemistries (nitrogen doped) is demonstrated. The doped CNTs and un-doped CNTs have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, and Raman spectroscopy. The results suggest that nitrogen groups were incorporated into the CNTs graphitic sheets, which decrease the graphitic sp2 content to less crystalline structure compared to un-doped CNTs. We observed an increasing trend in solubility of prepared CNTs with additional doping element N: catalyst free doped CNTs> catalyst free undoped CNTs>catalyst CNTs, as a result of an increase in hydrophilicity. Hence, we predict that these catalyst-free grown N-CNTs will show significantly improved biocompatibility with minor cytotoxicity as a result of their structural properties (diameter and length), absence of catalyst and high level of solubility with less tendency of conglomeration compared to catalyst based MWCNTs or SWCNTs produced using conventional fabrication methods. These prepared N-CNT has potential to be applied as biocompatible CNT for number of biomedical and pharmaceutical applications. Key words: carbon nanotubes, doped carbon nanotubes, carbon nanotube membranes

T. Altalhi, M. Ginic-Markovic, S. Clarke, P. Fredericks, D.Losic INTRODUCTION Carbon nanotubes (CNTs) due to their unique electrical, thermal, chemical and mechanical properties have been extensively studied in terms of both fundamental and practical applications including electronics, energy storage, catalysis, fuel cells, solar cells, molecular separation, sensors, biosensors [Paradise & Goswami (2007); Klumpp et al. (2006); Holt et al. (2006)]. In the biomedical filed CNTs provide new opportunity for imaging and the medical therapy with high performance and efficacy [Shi Kam (2004); Chen et al (2008)]. However, the unique characteristics of CNTs also raise alarms about their possible health effects, as both the small size and large surface area are parameters which could cause potential toxicity [Foldvari, & Bagonluri (2008)]. If nanotubes are used in new products (food, cosmetics, medications), then they are likely to get in contact with the human body and access the inner organs through the respiratory and digestive tracts. Although, there are exciting prospects for the application of CNTs in medicine, concerns over adverse and unanticipated effects on human health have also been raised. Many studies have been performed to evaluate the toxicological effects of CNTs both in vitro and in vivo and majority of these studies demonstrated that CNT exhibited a low toxicity. In general, toxicity and biocompatibility of CNT depend on several factors including: their fabrication, presence of impurities (metal from catalysts, fullerene and amorphous carbon), CNTs structure (diameter and length), dispersion and aggregation status (size of bundles and aggregates), functionalization, immobilization, their administration and cellular uptake [Donaldson & Tran (2002); Hussain et al (2009)]. Toxicity from catalysts likes Cr, Ni, Fe and other impurities from the synthesis of CNTs are recognized as the most critical parameter to influence CNTs toxicity [Yan et al. (2007)]. CNTs stimulate inflammatory reactions, but some studies showed that this reaction can be diminished by purification of CNTs. Even though post-production processes eliminate the most of the metal catalyst impurities, CNTs still contain residual metal up to 15% by mass. Using acid treatment, oxidation, annealing and filtering etc, it is possible to reduce the content of iron to 0.23 % [Tejral et al. (2009)]. Therefore, there is a considerable need to develop new synthetic methods for fabricating CNTs which are more biocompatible, addressing issues such as elimination of catalysts, increasing CNT water solubility and adjusting optimal diameters and lengths. Template synthesis using nanoporous alumina membrane is recognised as an elegant approach to fabricate CNTs with controlled diameters, length and shapes suitable for many applications. In this study we present the template synthesis of multi walled CNTs with controlled physical and chemical properties to demonstrate fabrication of biocompatible CNTs with minor toxicity to the biological system. The schematic of the fabrication method is presented in Figure 1 showing the model of PA pore structure before and after the growth of CNT structure inside the pores. PA template was used to grow different CNTs including catalyst, catalyst free and doped CNTs. The structural and chemical composition of fabricated CNT/PA composite membranes were investigated by various characterisation techniques including scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The dispersion stability of un-doped (catalyst and catalyst free) and doped CNTs suspensions were explored in two different media in hydrophilic media (ethanol) and hydrophobic (toluene) after sonication process, which is a crucial assessment of the cytotoxicity of nanomaterials.

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T. Altalhi, M. Ginic-Markovic, S. Clarke, P. Fredericks, D.Losic

Fig. 1: Figure caption a-b) Schematic of fabrication doped CNT/PA composites by CVD growth of carbon nanotubes inside of porous alumina oxide pores, c) scheme of nitrogen doped CNT EXPERIMENTAL Materials A high purity (99.997 %) Al foil supplied from Alfa Aesar (USA) was used as the substrate for fabrication PA. The chemicals used in this work including oxalic acid, phosphoric acid anhydrous pyridine (20 % and 50 %), cupric chloride, chromic oxide, toluene 99.8 %; were supplied from Sigma/Aldrich and Chem Supply (Australia). Synthesis of nanoporous alumina membrane (PA) PA membranes were prepared using a two-step anodization process as previously described [ Masuda &. Fukuda (1995); Losic &. Lillo (2009)]. Briefly, the Al foil was cleaned in acetone and then electrochemically polished in a 1:4 volume mixture of HClO4 and C2H5OH by a constant voltage of 20V for 2 minutes to achieve a mirror finished surface. Anodization process was performed using an electrochemical cell equipped with a cooling stage at a temperature of -1 ºC. The first anodization step was performed under 40-80 V for 2-8 hours in 0.3M H2C2O4. Afterwards, the formed porous oxide film was chemically removed by a mixture of 6 wt % of H3PO4 and 1.8 % H2CrO4 for a minimum of 3-6 hours at 75 ºC. The second anodization step was performed under the same condition as the first anodization. The thickness of prepared porous layer is controlled by anodization time (2-8 h) and the pore diameters by anodization voltage (from 40-100 V). After anodization, the remaining Al layer was removed from the oxide films using CuCl2/HCl solution followed by chemical etching in 5 % H3PO4 at 25 ºC for 2-3 hours remove the bottom barrier layer of PA (pore opening), and prepare freestanding PA membrane with through hole morphology. The etching process was controlled by time, but the process was also additionally monitored with the method for controlled dissolution of the bottom barrier layer using a two-electrode system as described previously [Losic &. Lillo (2009); Masuda &. Fukuda (1995)].

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T. Altalhi, M. Ginic-Markovic, S. Clarke, P. Fredericks, D.Losic Catalyst- free of un-doped and doped CNT using PA template The synthesis of CNT inside of pores of PA membranes was performed using CVD system consisting of aerosol system, supplied with an ultrasonic generator and tubular electric furnace equipped with a quartz tube (42.75 mm in diameter, 1000 mm long), temperature controller, gas controller and particle generator [Che et al. (1998)]. Doped carbon precursors were introduced into the reaction tube as a mist by utilizing a particle generator with argon as carrier gas (flow rate 1 L/min-1). In the present work different experimental conditions including carbon precursors (nitrogen doped precursor), reaction temperature and reaction time were investigated to optimize fabrication process and the quality accompanied with doping percentage of fabricated doped CNT/PA composite. We prepared following CNTs: Toluene (carbon source) as example of undoped CNT (0-CNTs), toluene and pyridine (with different percentage 20 % to 50 % v/v of pyridine in toluene) solution as example of nitrogen doped, N-CNTs. The 850 °C was used as an optimal temperature for the most experiments presented in this work. The reaction time for CNT growth was 15 minutes. When growth process was completed the tube furnace was slowly cooled to room temperature (cooling time was approximately 24 h). The resulting un-doped carbon nanotubes (0-CNTs) and nitrogen doped carbon nanotubes (N-CNTs) composites were soaked in 48 % HF at room temperature for 30 minutes to remove the porous alumina membranes and obtain the un-doped 0-CNTs and nitrogen containing CNTs as an insoluble part. The tubes were then washed several times with distilled water to remove the residual HF and dried at 75 °C overnight. Characterizations Structural characterization of the prepared PA and CNT/PA composites and liberated CNTs was carried out by Scanning Electron Microscopy (SEM) using XL30 ESEM from Philips and Transmission Electron Microscopy (TEM, Philips CM 200). Before inserting sample grids into the microscope, the samples were sonicated in ethanol, then dropped on the cupper grids and dried at room temperature. XPS analysis X-ray photoelectron spectroscopy was conducted with a Kratos Axis Ultra with a delay line detector. The X-Ray source produces photons with an energy of 1486.7 eV and monochromatic line Al Kα. The power used was 130 W. The analyzed area was a rectangle 7 x 3mm in size. XPS wide spectra were acquired using pass energy of 160 eV at the step size for the high resolution spectra of 100 meV and 500 meV for the survey spectra. Raman spectra were obtained with 632.8 nm excitation wavelength on Renishaw Model 1000 Raman microprobe spectrometer. A survey scan was collected for each sample in the spectral range 3200-200 cm-1. More accurate data were then collected with the grating centered at 1400 cm-1 giving a spectra range of about 1000 – 1800 cm-1. Note that for these spectra the bands are relatively broad hence the error in band position is at least ±1 cm-1. RESULTS AND DISCUSSION Structural characterization of prepared PA and CNT/PA composite The typical structures of PA membranes used as template and prepared by two-step electrochemical anodization of Al foil in 0.3 M oxalic acid are presented in Figure 2. The cross-sectional SEM image of PA membrane shows a perfectly straight and densely packed array of nanopores across the whole structure (Figure 2a). The thickness of the

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T. Altalhi, M. Ginic-Markovic, S. Clarke, P. Fredericks, D.Losic PA membrane is about 40 µm (Fig. 2a), but by selecting the anodization time (from 20 min to 8 hours) we prepared PA membranes with desired thicknesses ranging from 100 µm. SEM images of the top PA surface (Figures 2b-c) show pore structures with diameters about 50 ± 10 nm and hexagonal arrangements of the pore cells. The pore diameters from 20 nm to 300 nm can be controlled by varying the anodization potential (20 V to 300 V) and selecting different electrolyte (sulphuric acid, oxalic acid and phosphoric acid), but in this work results on PA membrane prepared by anodization in oxalic acid are presented. Figure 2c presents a high-resolution SEM image of pore structure showing pore with perfectly flat channels. The bottom surface of selfsupporting PA membranes before removal of the barrier layer on the bottom is presented in Figure 2d. In this work we mainly used PA with through-hole morphology using pore opening process but also PA with closed pores were used to demonstrate the growth of CNT is possible with closed pores.

Figure 2. SEM images of PA membranes prepared by electrochemical anodization of Al foil showing a) Cross-section and whole membrane (inset), b) top surface of pores c) high resolution cross-sectional image of pore structure and d) bottom of pore structures showing closed before pore opening Figure 3 shows SEM images of CNTs/PA and un-doped 0-CNT/PA composite membranes. PA does not show any structural differences irrespective of the type of deposition inside; either doped or un-doped CNTs. Cross-sectional image of whole membrane (Figure 3a) clearly shows the formation of nanotube structures inside the PA pores. The Figure 3b with high resolution SEM image shows the morphology of the 0CNTs inside of PA after cracking of the composite structure. The top part of doped NCNTs (Figure 3c) shows the formation of the N-CNTs inside the PA. The Figure 3d reveals high resolution images of liberated N-CNTs by removal of PA template and proves capacity of this method to produce free and liberated CNTs. Using PA membrane with different pore diameters ranging from 100 nm, it is possible to fabricate CNTs with controllable pore diameter and lengths which significantly improve their versatility for many applications including drug delivery.

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T. Altalhi, M. Ginic-Markovic, S. Clarke, P. Fredericks, D.Losic

Figure 3: SEM images of carbon nanotube grown inside of PA template. a) crosssectional image CNT/PA composite (0-CNT) with whole structure in inset. b-c) nitrogen doped carbon nanotubes (N-CNTs) synthetised inside of pores of PA membrane showing cross-sectional image and top surface. d) liberated CNT after removal of PA template We performed (TEM) analysis to determine the morphology of librated CNT with more details, after the removal of PA template. Particular focus was, to determine purity, presence of amorphous carbon, and smoothness of tube walls prepared by different methods. TEM images in Figures 4 a-f show structure of 0-CNTs and N-CNTs prepared by CVD growth inside the pores of PA membrane template from two different concentration of pyridine: 20% and 50% in toluene. The images show that the nitrogen doped and un-doped CNTs display features of multi-walled carbon nanotubes, well aligned in a hollow structure with open or closed ends and with uniform diameter closely matching the pore size of the PA template. Furthermore CNTs are completely free from catalyst particles with wall thickness around 5-10 nm. In addition the doped samples showed high level of purity compared to the un-doped, which are heterogeneous mixture of carbon nanostructures: CNTs and amorphous carbonaceous structures. CNTs doped and un-doped were fabricated under the same experimental conditions with just one difference; use of toluene as a carbon source for un-doped against toluene in presence of pyridine as a precursor for doped one. From the Figure 4 the difference in the obtained structure of doped and un-doped CNTs and the degree of purity is obvious. It has been reported in the literature that structure of the produced CNTs is not affect by precursor but rather by the following fabrication parameters: catalyst, temperature and gas mixture. [Dupuis (2005); Kukovecz et al. (2000); Nagaraju et al. (2002); Lee et al. (2001)]. We believe that radicals generated during the decomposition of nitrogen precursor lead to the etching of by-products; mainly amorphous carbon (CVD layer covering the surface of the CNTs) and some carbon nanostructure. Furthermore, the high concentration (50 % pyridine) causes further 6

T. Altalhi, M. Ginic-Markovic, S. Clarke, P. Fredericks, D.Losic etching of C=C bonds in the sp2-hybridized graphite carbon in the CNTs walls Figure 4f. This finding is in agreement with the role of NH3 in carbon nanotubes growth mechanism.[ Jang et al. (2003)].

Figure 4: TEM image of liberated un-doped and nitrogen doped CNT prepared by using different precursors. a, c and e) un-doped CNTs (0-CNTs) prepared using toluene as precursor showing the presence of amorphous carbon on the surface; b-d) doped CNTs (N-CNTs) prepared using pyridine (20 %) showing the absence of the amorphous carbon and f) improved N-CNTs prepared from higher pyridine concentration (50 %) without of amorphous layer and presence of visible graphitic layers in CNT walls. The influence of doping on CNT morphology was examined by Raman spectroscopy, by comparing peaks of D and G modes of 0-CNTs and N-CNTS (Figures 5a-b). From these graphs it is obvious that even small amount of doping, 20 % pyridine in toluene, can

Figure 5: Raman analysis of un-doped and doped CNT synthesized in PA with catalyst free (toluene) as carbon precursor and (pyridine20 % / toluene) respectively. a) Raman analysis for un-doped 0-CNTs from toluene shows high intensity of G band and less Dband intensity compared to N-CNTs. b) Raman for doped N-CNTs from (pyridine 20 % / toluene)

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T. Altalhi, M. Ginic-Markovic, S. Clarke, P. Fredericks, D.Losic cause the difference in the height of D and G bends compared to the un-doped counterpart. Typically, G mode or tangential mode at 1580 cm-1 corresponds to the movement in opposite directions of two neighbouring carbon atoms in a graphite sheet (sp2 hybridized carbon atoms). The D mode or disorder mode at 1330 cm-1 is caused by sp3–hybridised carbon atoms in the nanotube sidewalls, but is also activated by any defect that breaks the translational symmetry [ Suzuki & Hibino (2011); Rao et al. (1998); Pérez-Cabero et al. (2003)]. After doping the N-CNTs shows less intense Gband at 1995 cm-1 but stronger D-band at 1332cm-1 compared to 0-CNTs as an indication of the presence of amorphous and lattice distortion due to the incorporation of nitrogen atoms in the CNTs structure[ Liu et al. (2005)]. XPS analysis was conducted on the 0-CNTs and N-CNTs (50 % pyridine) to investigate the nature of chemical bonding and the elemental composition, due to the observed differences in the graphitic wall structures from the TEM images. XPS was used in order to determine the extent of nitrogen doping of CNTs and clarify the role of etching by nitrogen. XPS results are summarised in Figure 6 showing survey and selected high

Figure 6: a-b) XPS survey scan and high resolution C 1s spectrum of un-doped carbon nanotubes (0-CNTs), c-d) high resolution spectrum of N 1s and C1s peak of nitrogen doped carbon nanotubes (N-CNTs) prepared using pyridine 50 %.

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T. Altalhi, M. Ginic-Markovic, S. Clarke, P. Fredericks, D.Losic resolution spectra of C and N. The survey spectrum of 0-CNT exhibits three major peaks at 688 eV, 531 eV, and 284eV, corresponding to F 1s, O 1s, and C 1s photoemission respectively (Figure 6a). However, the survey spectrum of N-CNT shows four major peaks at 686 eV, 532 eV, 400 eV, and 284 eV, corresponding to F 1s, O 1s, N 1s and C 1s photoemission respectively. Figure 6b exhibits the deconvoluted C 1s spectrum of the un-doped CNTs (0-CNTs). The characteristics of high resolution XPS spectra of C 1s envelop are four peaks at 284.5± 0.3 eV (graphitic carbon sp2 hybridised C=C), 285.5± 0.3 eV (amorphous carbon sp3 hybridized carbon atom (C–C); , 286.5 is considered oxygen-containing functional groups such as, C-O bonding) and 291.5 ± 0.3 eV have been assigned to the π–π* inter-band,. [Pinault et al (2005); Orikasa, et al. (2006)]. In the deconvoluted C1s spectrum of doped CNTs the peak at 286.5± 0.3 eV, is assigned to the carbon bonded to nitrogen [ He et al. (2005); Morant, et al. (2006); Estrade-Szwarckopf (2004); Pels et al. (1995); Yang, et al. (2005)]. Figures 6b-d shows elemental analysis of C 1s peaks for 0-CNTs and N-CNTs respectively. Doping CNTs with nitrogen leads to decline in the C=C (sp2 hybridized graphitic structure) from 82.6% of un-doped CNTs to 77.12% for N- CNTs and also increase sp3 hybridized structure from 9.41% of un-doped to 14.08 % for the doped NCNTs. This suggests a lower degree of graphitic ordering of nitrogen doped CNT samples prepared by CVD using pyridine sources, which is in agreement with the TEM images and Raman analysis. Figure 6d reveals deconvoluted N 1s spectrum of N-CNTs which proves the presence of the N atoms within the graphite structure bonded to the C atoms, and comprises of three peaks, pyridine nitrogen sp3-hybridized nitrogen (398.2 EV), pyrrolic nitrogen to sp2-hybridized nitrogen or graphitic (400.46eV) and quaternary nitrogen (401.95 eV) [Ayala et al. (2010); Liu et al. (2010)]. Finally, we investigated the solubility of librated un-doped and N-doped CNT which can be used as possible indicator of their biocompatibility. Figure 7 represents photograph of this test showing dispersions in ethanol of doped CNTs with 20 % and 50 % pyridine, un-doped CNT and CNT prepared with catalyst (ferrocene/toluene). From the figure the significant difference between these CNTs is obvious, indicating their different interfacial properties. As we expected from our previous work [Altalhi et al. (2010)] the suspension of N-CNTs Figures 7a-b in ethanol is black and was stable for several months, the 0-CNTs was stable for 72 h , the CNTs dispersion formed with catalyst was stable only for 2h (Figure 7d). Dispersion test on N-CNT in hydrophobic solvent such as, toluene showed that CNTs were aggregated and started to precipitate in several minutes clearly indicating their hydrophilic nature. These results undoubtedly indicate the hydrophilic nature of the doped tubes and catalyst free CNTs, although naturally carbon is hydrophobic. This result agrees with findings of [Kyotani et al.(1996)] who claimed that the carbon lattices of CNTs grown without catalyst posses lower crystallinity and also suffer from many defects. We expect that this structure leads to induced curvature and these defects are increasing more after doping process with N. We observed from XPS results, Raman and TEM images noticeable differences in degree of graphitization of the un-doped carbon nanotubes and the nitrogen doped CNTs. The crystallinity of the graphitic sheets deteriorates with the incorporation of heteroatom into the wall of graphitic sheets. However, reactivity, hyrdrophilicity and roughness [Smart et al. (2006)] increase, leading to the weaker van der Waals interactions between the tubes and to high tendency to form stable suspension. In

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T. Altalhi, M. Ginic-Markovic, S. Clarke, P. Fredericks, D.Losic contrast un-doped CNTs , have slightly better crystallinity and hence trend to coagulate easily as a result of van der Waals interactions which leads to poor solubility and high possibility of expected toxicity.

Figure 7: Photograph of carbon nanotubes suspensions state in ethanol. (a) N-CNTs from (toluene /pyridine20% ) (b) N-CNTs from (toluene/pyridine 50%) (C) un-doped CNTs catalyst free from toluene and (d) un-doped catalyst CNTs from toluene/ferrocene) CONCLUSION In summery we demonstrated the template synthesis of CNTs by CVD using free catalyst process, CNT doped with nitrogen atoms with high level of purity and with controllable morphology which is controlled by selecting PA membranes with desired pore dimensions. The morphology of the un-doped and doped CNTs grown inside of PA template and liberated was verified by SEM, TEM and Raman spectroscopy. These studies show a high degree of graphitic disorder, indicating a lattice distortion of the graphitic network as a result of hetero atoms (N) incorporation in the carbon nanotubes beside the absence of the catalyst role. The XPS results confirm the presence of the nitrogen peak in the CNTs structure and it shows that surface chemistry modifies the CNTs graphitic structure, by decreasing the degree of surface graphitization sp2 (C=C). Moreover, this induce hydrophilic nature of CNTs and hence improves its solubility as a result of creating rough surface which weaken the van der Waals interactions and produce stable suspension of the tubes in aqueous media. We believe that catalyst free CNTs and N-CNTs doped would be more biocompatible when compared to other types of CNTs suggesting that these nanotubes could now be applied in biological systems as promising potential in drug delivery and also capable to show chemical versatility taking the advantages of increasing surface defects as anchoring sites. REFERENCES 1. Altalhi, T., et al., Synthesis of Carbon Nanotube (CNT) Composite Membranes. Membranes, 2010. 1(1): p. 37-47. 2. Ayala, P., et al., The doping of carbon nanotubes with nitrogen and their potential applications. Carbon, 2010. 48(3): p. 575-586.

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T. Altalhi, M. Ginic-Markovic, S. Clarke, P. Fredericks, D.Losic 3. Che, G., et al., Chemical Vapor Deposition Based Synthesis of Carbon Nanotubes and Nanofibers Using a Template Method. Chemistry of Materials, 1998. 10(1): p. 260-267. 4. Chen, J., et al., Functionalized Single-Walled Carbon Nanotubes as Rationally Designed Vehicles for Tumor-Targeted Drug Delivery. Journal of the American Chemical Society, 2008. 130(49): p. 16778-16785. 5. Donaldson, K. and Tran, C.L., Inflammation caused by particles and fibres. Inhal Toxicol, 2002. 14: p. 5–27. 6. Dupuis, A.-C., The catalyst in the CCVD of carbon nanotubes--a review. Progress in Materials Science, 2005. 50(8): p. 929-961. 7. Estrade-Szwarckopf, H., XPS photoemission in carbonaceous materials: A "defect" peak beside the graphitic asymmetric peak. Carbon, 2004. 42(8-9): p. 1713-1721. 8. Foldvari, M. and. Bagonluri, M., Carbon nanotubes as functional excipients for nanomedicines: II. Drug delivery and biocompatibility issues. Nanomedicine: Nanotechnology, Biology and Medicine, 2008. 4(3): p. 183-200. 9. He, M., et al., CVD Growth of N-Doped Carbon Nanotubes on Silicon Substrates and Its Mechanism. The Journal of Physical Chemistry B, 2005. 109(19): p. 9275-9279. 10. Holt, J.K., et al., Fast Mass Transport Through Sub-2-Nanometer Carbon Nanotubes. Science, 2006. 312(5776): p. 1034-1037. 11. Hussain, M.A., Kabir, M.A., and Sood, A.K., On the Cytotoxicity of Carbon Nanotubes. Curr Sci, 2009. 96(5): p. 664-673. 12. Jang, Y.-T., et al., Effect of NH3 and thickness of catalyst on growth of carbon nanotubes using thermal chemical vapor deposition. Chemical Physics Letters, 2003. 372(5-6): p. 745-749. 13. Klumpp, C., et al., Functionalized carbon nanotubes as emerging nanovectors for the delivery of therapeutics. Biochimica et Biophysica Acta (BBA) Biomembranes, 2006. 1758(3): p. 404-412. 14. Kukovecz, A., et al., Catalytic synthesis of carbon nanotubes over Co, Fe and Ni containing conventional and sol-gel silica-aluminas. Physical Chemistry Chemical Physics, 2000. 2(13): p. 3071-3076. 15. Kyotani, T., Tsai, L.-f., and Tomita, A., Preparation of Ultrafine Carbon Tubes in Nanochannels of an Anodic Aluminum Oxide Film. Chemistry of Materials, 1996. 8(8): p. 2109-2113. 16. Lee, C.J., et al., Temperature effect on the growth of carbon nanotubes using thermal chemical vapor deposition. Chemical Physics Letters, 2001. 343(1-2): p. 33-38. 17. Liu, J., Webster, S. and Carroll, D.L., Temperature and Flow Rate of NH3 Effects on Nitrogen Content and Doping Environments of Carbon Nanotubes Grown by Injection CVD Method. The Journal of Physical Chemistry B, 2005. 109(33): p. 15769-15774. 11

T. Altalhi, M. Ginic-Markovic, S. Clarke, P. Fredericks, D.Losic 18. Liu, H., et al., Structural and morphological control of aligned nitrogen-doped carbon nanotubes. Carbon, 2010. 48(5): p. 1498-1507. 19. Losic, D. and Lillo, M., Porous Alumina with Shaped Pore Geometries and Complex Pore Architectures Fabricated by Cyclic Anodization. Small, 2009. 5(12): p. 1392-1397. 20. Masuda, H. and Fukuda, K. Ordered Metal Nanohole Arrays Made by a TwoStep Replication of Honeycomb Structures of Anodic Alumina. Science, 1995. 268(5216): p. 1466-1468. 21. Morant, C., et al., XPS characterization of nitrogen-doped carbon nanotubes. physica status solidi (a), 2006. 203(6): p. 1069-1075. 22. Nagaraju, N., et al., Alumina and silica supported metal catalysts for the production of carbon nanotubes. Journal of Molecular Catalysis A: Chemical, 2002. 181(1-2): p. 57-62. 23. Orikasa, H., et al., Template Synthesis of Water-Dispersible Carbon Nano “Test Tubes” without Any Post-treatment. Chemistry of Materials, 2006. 18(4): p. 1036-1040. 24. Paradise, M. and Goswami, T. Carbon nanotubes - Production and industrial applications. Materials & Design, 2007. 28(5): p. 1477-1489. 25. Pels, J.R., et al., Evolution of nitrogen functionalities in carbonaceous materials during pyrolysis. Carbon, 1995. 33(11): p. 1641-1653. 26. Pérez-Cabero, M., Rodríguez-Ramos, I., and Guerrero-Ruíz, A., Characterization of carbon nanotubes and carbon nanofibers prepared by catalytic decomposition of acetylene in a fluidized bed reactor. Journal of Catalysis, 2003. 215(2): p. 305-316. 27. Pinault, M., et al., Growth of multiwalled carbon nanotubes during the initial stages of aerosol-assisted CCVD. Carbon, 2005. 43(14): p. 2968-2976. 28. Rao, A.M., et al., Raman spectroscopy of pristine and doped single wall carbon nanotubes. Thin Solid Films, 1998. 331(1-2): p. 141-147. 29. Shi Kam, N.W., et al., Nanotube Molecular Transporters: Internalization of Carbon Nanotube−Protein Conjugates into Mammalian Cells. Journal of the American Chemical Society, 2004. 126(22): p. 6850-6851. 30. Smart, S.K., et al., The biocompatibility of carbon nanotubes. Carbon, 2006. 44(6): p. 1034-1047. 31. Suzuki, S. and Hibino, H., Characterization of doped single-wall carbon nanotubes by Raman spectroscopy. Carbon, 2011. 49(7): p. 2264-2272. 32. Tejral, G., Panyala, N.R., and Havel, J., Carbon nanotubes: toxicological impact on human health and environment. J Appl Biomed, 2009. 7: p. 1–13. 33. Yang, Q., et al., The Template Synthesis of Double Coaxial Carbon Nanotubes with Nitrogen-Doped and Boron-Doped Multiwalls. Journal of the American Chemical Society, 2005. 127(25): p. 8956-8957.

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T. Altalhi, M. Ginic-Markovic, S. Clarke, P. Fredericks, D.Losic BRIEF BIOGRAPHY OF PRESENTER Dr Ginic-Markovic completed her PhD at the University of South Australia in Applied Science in November 2000. From 2001-2003 Dr Ginic-Markovic started her post doctoral experience at Ian Wark research Institute, University of South Australia. She was involved in longer term joint research projects developing special thermodynamic methodology to investigate the state of the solvent in the gel network scaffolding. In 2003, Dr Ginic-Markovic moved to Flinders University, where she is working on polymeric nanocomposits, based on carbon nanotubes in different polymer matrices (thermoplastics and liquid crystals). Currently Dr Ginic-Markovic is a Program Manager on The Nanotechnology Desalination Research Project – Low Energy Desalination Membranes” – ARC Linkage project. She is a chief investigator on large research grant recently awarded from: NCED grant, ARC Linkages totalling $3,500,000.

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