Rapid assembly of carbon nanotube-based magnetic composites
Highlights
► Trapping of α-haemetite on acid-oxidised carbon nanotubes enables magnetic nanocomposites; ► Coating magnetic carbon nanotubes with silica improves chemical stability in low pH solution; ► Silica-coated magnetic carbon nanotube composites still adsorb polycyclic aromatic hydrocarbons; ► Final composites are useful for organic chemical remediation and rapid adsorbate recovery.
Introduction
The functionalisation of carbon nanomaterials can modify their physicochemical properties, making them more suitable for chemical and biological applications. Of particular interest are CNTs with magnetic properties because of their potential applications in biological labelling, drug delivery and magnetic storage media [1], [2], [3].
Various synthetic routes have been developed. Open-ended, template-grown nanotubes were filled with a ferrofluid [4], [5]. Magnetic nanoparticles were also embedded into CNT walls [6]. Correa-Duarte et al. produced a CNT-based magnetic material through a polymer wrapping and layer-by-layer assembly technique [7]. Georgakilas et al. attached magnetic nanoparticles to CNTs via a carboxylic derivative of pyrene immobilised on the surface of the nanotubes [8]. A hydrothermal approach to decorating CNT surfaces with magnetic beads utilising reduction of iron chloride (III) with ethylene glycol, was reported by Jia et al. [9]. However, the methods described above produce composites with magnetic particles loosely bound to CNTs, where they are exposed to the environment, and may either become detached or react directly with the surrounding media. CNTs that are embedded with magnetic particles are strongly bound, but this technique does not prevent the availability of the magnetic nanoparticles to external chemical reactions.
Herein, we report the synthesis of magnetic MWCNT composites through the electrostatic attraction of α-haematite nanoparticles, stably “trapped” within a thin silica shell. The process exploits a set of facile and rapid chemical reactions with acidic groups decorating the CNT surfaces.
Section snippets
Carbon nanotube preparation
MWCNTs (TMSpetsmash, Ukraine, ca. 96% purity) were refluxed in nitric acid (70%) for 8 h at 100 °C in order to remove any residual catalytic particles [10] and surface amorphous carbon and also introduce surface functional groups [10]. The samples were cooled, vacuum-filtered and washed with deionised water until the system reached pH 7 and then dried at 120 °C for 8 h [11]. The acid-oxidised MWCNTs were refluxed in 1.0 M NaOH for 1 h, washed, filtered until a neutral pH in order to remove any fulvic
Results and discussion
The experimental procedure involves three main steps (Fig. 1). First, the treatment of MWCNTs with nitric acid removes catalytic metal impurities within the system and also oxidises the carbon nanotube surface. At this stage it is important to remove the oxidised fragments from the carbon lattice in order to allow covalent bonding directly to the carbon nanotube surface [11]. Second, the immobilisation of α-haematite occurs through electrostatic attraction to the surface carboxylic groups.
Conclusions
Aminosilica-coated magnetic composites of α-Fe2O3 nanoparticles attached to MWCNT surface were successfully prepared via a facile method involving the hydrolysis–polycondensation of gamma-aminopropyltriethoxysilane. The silica coating of the α-haemetite nanoparticles extends partly to the MWCNTs, leaving sites available for surface adsorption of PAH contaminants. Aqueous suspensions of these magnetic composites can be easily separated from the liquid phase using an external magnetic field and
Acknowledgements
The authors acknowledge the RCUK Academic Fellowship (RW) and Dr. Martin Smith from University of Brighton. A.K. acknowledges support of her PhD studentship by the University of Brighton. Y.G. was supported by NSF grant DMR-0945230.
References (28)
- et al.
Magnetic resonance imaging of multifunctional pluronic stabilized iron-oxide nanoparticles in tumor-bearing mice
Biomaterials
(2009) - et al.
Magnetic lymphatic targeting drug delivery system using carbon nanotubes
Medical Hypotheses
(2008) - et al.
Self-assembly of magnetite beads along multiwalled carbon nanotubes via a simple hydrothermal process
Carbon
(2007) - et al.
The surface acidity of acid oxidised multi-walled carbon nanotubes and the influence of in situ generated fulvic acids on their stability in aqueous dispersions
Carbon
(2009) - et al.
Direct confirmation that carbon nanotubes still react covalently after removal of acid-oxidative lattice fragments
Carbon
(2010) - et al.
The effect of stabilizer addition and sonication on nanoparticle agglomeration in a confined impinging jet reactor
Colloids and Surfaces A: Physicochemical and Engineering Aspects
(2009) - et al.
Reversible ordered agglomeration of hematite particles due to weak magnetic interactions
Journal of Colloid and Interface Science
(1986) - et al.
Structural distinctions of Fe2O3–In2O3 composites obtained by various sol–gel procedures, and their gas-sensing features
Sensors and Actuators B: Chemical
(2007) - et al.
Stacking nature of graphene layers in carbon nanotubes and nanofibres
Journal of Physics and Chemistry of Solids
(1997) - et al.
Low-temperature hydrothermal synthesis of multiwall carbon nanotubes
Carbon
(2005)