Effect of Fe<sub>3</sub>O<sub>4</sub> loading on the conductivities of carbon nanotube/chitosan composite films
Effect of Fe3O4 loading on the conductivities of carbon nanotube/chitosan composite films
Carbon letters. 2012. Apr, 13(2): 126-129
Copyright ©2012, Korean Carbon Society
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
  • Received : February 12, 2012
  • Accepted : March 19, 2012
  • Published : April 30, 2012
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About the Authors
Jason Marroquin
Department of Mechanical Engineering, College of Engineering, Kyung Hee University, Yongin 446-701 Korea
H. J. Kim
Ocean Development System Laboratory, Korea Research Institute of Ships and Ocean Engineering, Taejon 305-600, Korea
Dong-Ho Jung
Ocean Development System Laboratory, Korea Research Institute of Ships and Ocean Engineering, Taejon 305-600, Korea
Kyong Yop Rhee
Industrial Liaison Research Institute, Department of Mechanical Engineering, Kyung Hee University, Yongin 446-701, Korea

Nanocomposite films were made by a simple solution casting method in which multi-walled carbon nanotubes (MWCNT) and magnetite nanoparticles (Fe 3 O 4 ) were used as dopant materials to enhance the electrical conductivity of chitosan nanocomposite films. The films contained fixed CNT concentrations (5, 8, and 10 wt%) and varying Fe 3 O 4 content. It was determined that a 1:1 ratio of CNT to Fe 3 O 4 provided optimal conductivity according to dopant material loading. X-ray diffraction patterns for the nanocomposite films, were determined to investigate their chemical and phase composition, revealed that nanoparticle agglomeration occurred at high Fe 3 O 4 loadings, which hindered the synergistic effect of the doping materials on the conductivity of the films.
1. Introduction
Carbon nanotubes (CNTs) are one-dimensional nanomaterials that are considered as ideal reinforcing agents for polymer matrices because of their unique structure and properties [1 , 2] . Electrically conductive composites filled with CNTs have attracted increasing attention for a variety of applications, such as static-charge dissipation [3] , electromagnetic interference shielding [4] , and actuators [5] . However, CNTs are often in bundles or they are entangled because of very strong intertubular van der Waals attractions, which is the current bottleneck in their application [6] .
Chitosan (CS) is a linear polysaccharide synthesized by the deacetylation of chitin, a natural polymer found in the exoskeleton of crustaceans. CS is widely used in biomedical applications, drug delivery, food industry, biotechnology, pharmaceuticals, biomedicine, packaging, wastewater treatment, cosmetics, etc. [7 , 8] . Another advantage of CS is its solubility in acidic aqueous media. Natural polymers modified with suitable nanofillers have now found potential applications as electrochemical sensors and electrodes [9 - 13] . CS can be made to possess amphiphilic properties giving it a unique capacity to solubilize hydrophobic CNTs in aqueous solution [14 , 15] . A key characteristic of the CNT/CS composite is its conductivity, as defined by the charge transfer from one conductive particle to another. Because conduction of electrical charge is established when a network of conductive CNTs reaches a critical percolation threshold density that provides direct electrical contact between particles, the effective conductivity of a CNT/CS composite depends upon many factors, such as size, shape, density, and distribution of CNTs within the CS matrix, as well as chemical interactions between the two materials [16 - 18] .
A Fe 3 O 4 /CNT/CS composite is expected to have diverse properties because each component contributes different chemical and physical properties to the composite. A Fe 3 O 4 /CNT/CS composite may find applications in drug delivery, tumor treatment, enzyme en-
Lager Image
Effect of Fe3O4 loading, expressed as a weight percentage relative to the carbon nanotube (CNT) content, on the conductivity of (a) 5% CNT/chitosan (CS), (b) 8% CNT/CS, and (c) 10% CNT/CS nanocomposite films.
gineering, batteries, electro-magneto rheological fluids, electromagnetic shielding and magnetic recording. In this study, Fe 3 O 4 / CNT/CS nanocomposite films were prepared by the solution casting method. The main objective was to investigate the synergistic effect of Fe 3 O 4 and CNTs on the electrical properties of the nanocomposites. The films were prepared with different concentrations of Fe 3 O 4 at fixed quantities of CNTs in order to determine the optimal metal loading for improving conductivity. Subsequently, the electrical conductivity and X-ray diffraction (XRD) patterns were determined for the nanocomposite films.
2. Experimental
CS (average molecular weight = 350 000 gmol -1 , 90% degree of deacetylation was purchased from Sigma Aldrich. Raw multiwalled CNTs (MWCNTs, CM-95), synthesized using the chemical vapor deposition method, were purchased from Hanhwa Nanotech Co. Ltd., Korea. The MWCNTs had diameters of 10-15 nm, tube length of 10-20 μm and a purity of 95%. Magnetite (Fe 3 O 4 ) nanopowder, (<50 nm particle size [transimission electron microscopy], ≥98% trace metals basis) was purchased from Sigma Aldrich. Acetic acid was used to dissolve CS in distilled water.
CS nanocomposite films containing Fe 3 O 4 and CNTs were prepared by the solution casting method [19] . The concentrations of the functional additives (Fe 3 O 4 and CNT) were changed in order to evaluate the synergistic effect of Fe 3 O 4 and CNTs in the nanocomposite films. Electrical conductivities of the films were measured at room temperature using a ring probe method with a high resistivity meter (MCP-HT 450, Mitsubishi). Wide angle XRD patterns of the Fe 3 O 4 /CNT/CS nanocomposite films were recorded with a Rigaku Rotaflex (RU-200B) X-ray diffractometer using Cu Kα radiation with a Ni filter. The tube current and voltage were 300 mA and 40 kV, respectively, and 2θ angular regions between 0 and 40° were explored.
3. Results and Discussion
The CS composites were characterized in relation to their conductivity as a function of the CNT to Fe 3 O 4 ratio. This was important because the establishment of a highly conductive CNT/CS film requires a network of effective tube-tube contacts. The quality of such a network is ultimately defined by the nanotube concentration and the relative extent of homogeneous (i.e.,
Lager Image
X-ray diffraction patterns of chitosan (CS), carbon nanotubes (CNTs), Fe3O4, and the nanocomposite films.
well-distributed within the matrix) to heterogeneous distribution (i.e., formation of aggregates). The nanotube dimensions limit the effectiveness of electron tunneling across tube-tube contacts. It was also expected that Fe 3 O 4 addition would be beneficial to the electrical conductivity of the CNT and the subsequent composite because of the inherent electrical conductivity of Fe 3 O 4 . Furthermore, the nanoparticles could facilitate electron transfer between nanotubes while being dispersed in the polymer matrix because the composite would acquire more conductive channels and subsequently, a higher metallic character.
Fig. 1 a shows how the effect of Fe 3 O 4 loading, expressed as a weight percentage relative to the CNT content, affects the conductivity of the nanocomposite film. The results clearly indicate the dependence of conductivity on the Fe 3 O 4 to CNT ratio. The conductivity improved with increasing Fe 3 O 4 content, reaching a maximum at 100% loading, with a subsequent decrease with higher Fe 3 O 4 content. It is clearly established that a 1:1 ratio of Fe 3 O 4 to CNT in the CS nanocomposite film is the optimal loading for conductivity enhancement. This behavior in conductivity was observed at CNT concentrations of 5, 8, and 10%, as shown in Figs. 1 a-c, respectively.
The diffraction patterns of CTS, CNTs, Fe 3 O 4 and the nanocomposite films are shown in Fig. 2 . In the diffraction pattern
Lager Image
X-ray diffraction patterns of the nanocomposite films with increasing Fe3O4 loading. CNT: carbon nanotube, CS: chitosan.
of CS, one main peak was observed at 2θ = 20° (maximum intensity) corresponding to a characteristic peak of CS chains aligned through intermolecular interactions [19] . The characteristic sharp peak of CNTs at 2θ = 26° represents C (002), which is attributed to the ordered arrangement of concentric cylinders of graphitic carbon in the nanotube [16] . This crystalline peak is not present in the nanocomposite samples, suggesting the dispersion of CNTs into the CS matrix (17). XRD patterns for the Fe 3 O 4 nanoparticles displayed characteristic peaks (2θ = 30.1°, 35.5°, 43.1°, 53.4°, 57.0°, and 62.6°). These peaks are consistent with those found in the Joint Committee on Powder Diffraction Standards (JCPDS) database (PDF No. 65-3107). Patterns for the Fe 3 O 4 /CNT/CS composites revealed the presence of such peaks, indicating that the Fe 3 O 4 particles in the composites were pure Fe 3 O 4 with a spinel structure.
Fig. 3 clearly shows how increasing Fe 3 O 4 loading in the composites resulted in increasing corresponding peak intensities. The figure further shows that neither the CNTs nor CS induced a phase change in Fe 3 O 4 . Furthermore the results show how the increase in Fe 3 O 4 concentration broadened the main peaks, specifically the (400) peak above a Fe 3 O 4 to CNT ratio of 1:1, which indicates a higher average particle size of Fe 3 O 4 due to increased agglomeration of the nanoparticles. The average particle size, calculated using Scherrer’s formula, was approximately 30.79 nm and 46.61 nm for the 1:1 and 2:1 ratios of Fe 3 O 4 to CNT, respectively. Hence the decrease in conductivity at higher Fe 3 O 4 to CNT ratios was attributed to the agglomeration of the nanoparticles, which hindered the effectiveness of the conductive channels between CNTs; this consequently reduced the conductivity percolation threshold of the composites.
4. Conclusions
Fe 3 O 4 /CNT/CS nanocomposite films were successfully prepared using a simple solution casting method. A synergistic effect of Fe 3 O 4 and CNTs on the electrical conductivity of the nanocomposite films was observed, where by an optimal loading of Fe 3 O 4 resulted in a ratio of 1:1 relative to the CNT content of the nanocomposite film. XRD patterns revealed that higher Fe 3 O 4 to CNT ratios increased the agglomeration of the Fe 3 O 4 nanoparticles, which hindered the synergistic effect on the conductivity.
This work was financially supported by the National R&D project of ‘Development of Energy Utilization of Deep Ocean Water’ supported by the Korean Ministry of Land, Traffic and Maritime Affairs.
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