Preparation of stable magnetic nanofluids containing Fe3O4@PPy nanoparticles by a novel one-pot route
© Zhao and Nan; licensee Springer. 2011
Received: 31 October 2010
Accepted: 16 March 2011
Published: 16 March 2011
Stable magnetic nanofluids containing Fe3O4@Polypyrrole (PPy) nanoparticles (NPs) were prepared by using a facile and novel method, in which one-pot route was used. FeCl3·6H2O was applied as the iron source, and the oxidizing agent to produce PPy. Trisodium citrate (Na3cit) was used as the reducing reagent to form Fe3O4 NPs. The as-prepared nanofluid can keep long-term stability. The Fe3O4@PPy NPs can still keep dispersing well after the nanofluid has been standing for 1 month and no sedimentation is found. The polymerization reaction of the pyrrole monomers took place with Fe3+ ions as the initiator, in which these Fe3+ ions remained in the solution adsorbed on the surface of the Fe3O4 NPs. Thus, the core-shell NPs of Fe3O4@PPy were obtained. The particle size of the as-prepared Fe3O4@PPy can be easily controlled from 7 to 30 nm by the polymerization reaction of the pyrrole monomers. The steric stabilization and weight of the NPs affect the stability of the nanofluids. The as-prepared Fe3O4@PPy NPs exhibit superparamagnetic behavior.
Nanofluids, which contain nanoparticles dispersed in base fluids, have been proposed as a new kind of heat transfer medium because they can improve the heat transport and energy efficiency and may have potential applications in the field of heat transfer enhancement . Magnetic nanofluids, suspension containing magnetic nanoparticles, such as magnetite (Fe3O4), iron (Fe), nickel (Ni), and cobalt (Co), show both magnetic and fluid properties and have important applications in industries [2, 3]. Fe3O4 nanoparticles are always used to form magnetic nanofluids because of their broad potential and practical technological applications and fundamental scientific significance [3–10]. Recently, heat transfer enhancements were reported for γ-Fe2O3 magnetic nanofluids . However, long-term stability of nanofluids is a major concern for the engineering applications [11–13]. Nanoparticles tend naturally to aggregate and sediment in the base fluid. Also, stable solution with large volume concentration is not easy to obtain. Therefore, technique breakthroughs are needed to produce well-dispersed and long-term stable nanofluids. Use of functionalized nanoparticles is a promising approach to achieve long-term stability of nanofluid .
Organic-inorganic nanocomposites with an ordered structure show new functional hybrids of organic and inorganic materials. Incorporation of nanosized particles in organic polymeric materials has been extensively studied because they combine the advantages of the inorganic materials and the organic polymers. Moreover, new properties of these hybrids can also show up because of synergetic effects, which can be scarcely obtained from the individual components. Combination of various conducting polymers with magnetic iron-oxides is more and more intensively investigated, because materials possessing both high magnetic susceptibility and high conductivity can be used in different applications, such as nonlinear optics, electrical, and magnetic shielding, magnetic electrocatalysis, and as microwave absorbers .
This study reports on the synthesis of stable nanofluids with a novel one-pot hydrothermal route, in which Fe3O4 coated by PPy NPs were contained. FeCl3·6H2O was used as the iron source and the oxidant to polymerize pyrrole monomers. Trisodium citrate was used as the reducing reagent. The procedure was carried out at low temperature and without any protection atmosphere. To our knowledge, this is the first report to direct synthesis of Fe3O4@PPy nanofluids. The mechanism of suspension was proposed.
Pyrrole monomer, iron (III) chloride hexahydrate (FeCl3·6H2O), sodium hydroxide (NaOH), trisodium citrate (Na3cit), and sodium dodecyl sulfate (SDS) were purchased from Sinopharm Chemical Reagent Company. Pyrrole monomer was distilled under reduced pressure, and other reagents were of analytical grade and used as received without further treatment. All solutions were prepared with twice-distilled water.
In a typical experiment, NaOH 0.0800 g (2.0 mmol) and 0.0230 g SDS (0.008 M) were dissolved into a 9 mL aqueous solution containing 0.1 M Na3cit (C6H5Na3O7·2H2O) under constant stirring. 1.0 mL of FeCl3 solution (1.0 M) and 0.3 mL pyrrole monomer were added into the solution. The whole mixture was stirred vigorously for 5 min to give a homogeneous solution. Subsequently, the solution was transferred into a 50 mL Teflon-lined stainless steel autoclave, and maintained at 160°C for 24 h. Afterward, the autoclave was allowed to cool down to room temperature naturally, and the resulting black Fe3O4@PPy nanofluid was produced. The deposit was obtained by magnetic separation method, and washed with distilled water and absolute ethanol for several times. The as-prepared black precipitate was dried under vacuum at 50°C for 24 h.
X-ray powder diffraction (XRD) measurements were performed on a Bruker D8 Advance X-ray Diffractometer with Cu Kα radiation (λ = 1.5418 Ǻ). The 2θ range used in the measurement was from 20° to 70°. Standard transmission electron microscopy (TEM) measurements were performed on a JEOL-2010 TEM at an acceleration voltage of 200 kV. Samples were first ultrasonically dispersed in deioned water and drop-cast onto copper grids. Magnetic characterization was carried out at room temperature using a vibrating sample magnetometer (VSM, Lakeshore 7307, USA). Infrared spectrum (FT-IR) measurements were performed on a Nicolet Aexus 470, with scanning from 4000 to 400 cm-1 by using KBr pellets under ambient temperature.
Results and discussion
Stability of the as-synthesized Fe3O4@PPy nanofluids
Effects of different amounts of pyrrole monomer on the structure and size of the as-prepared nanoparticles
Comparison of d-spacing values of the as-synthesized samples with standard JCPDS Fe3O4 data
Magnetic property of the as-prepared samples
Effects of trisodium citrate (Na3cit) on the structure of the sample
Formation mechanism of the stable fluid
A steric stabilization effect is always used to explain the stability of particles suspended in the base fluid . This steric stabilization effect arises from the fact that polymers coating on the surface of NPs occupy a certain amount of space. Thus, the space becomes compressed when nanoparticles are brought too close together. An associated repulsive force makes separate nanoparticles from each other and restrains the aggregation of nanoparticles. On the other hand, the weight of the NPs affected the stability of the nanofluids as shown in Figure 1.
In the present experiments, SDS was also used as a dispersant. The size of the Fe3O4 NPs became smaller with SDS (these results are not shown here). Compared with surfactants, the steric effect by polymers onto the surface of NPs is a better way to stabilize NPs suspended in the based fluid . The PPy-coated Fe3O4 NPs have the steric stabilization effect and achieve a better and larger solubility of NPs in water because of the solubility rule of similarity. Thus, stable nanofluids containing magnetic Fe3O4 NPs can be produced with the help of PPy.
The nanofluids containing Fe3O4@PPy NPs can be used to enhance heat transfer, as magnetic nanofluids and other special applications, as PPy is one of the conducting polymers. This facile method can be used to prepare other organic-inorganic NPs.
A facile and novel method for preparing nanofluids containing Fe3O4@PPy was presented, in which one-pot route was used. The nanofluid can keep long-term stability and very good dispersing. Fe3O4@PPy NPs can still keep dispersing well after the nanofluid has been standing for 1 month and no sedimentation is found. The Na3cit acted as a reductant and a dispersant to form Fe3O4 NPs. Fe3+ ions remained in the solution adsorbed on the surface of the Fe3O4 NPs. The polymerization reaction of the pyrrole monomers took place with these Fe3+ ions as the initiator. The particle size of the as-prepared Fe3O4@PPy can be easily controlled from 7 to 30 nm by adjusting the amount of pyrrole monomer. The steric stabilization and weight of the NPs affect the stability of the nanofluids. The as-prepared Fe3O4@PPy NPs exhibit superparamagnetic behavior with various saturation magnetizations.
Figure 1. XRD patterns of the as-synthesized Fe 3 O 4 NPs.
Figure 2. (a) Survey XPS spectrum of the as-synthesized Fe3O4 NPs. (b) High-resolution XPS Fe2p spectrum.
Figure 3. TEM images of the Fe 3 O 4 NPs.
X-ray powder diffraction
transmission electron microscopy
vibrating sample magnetometer.
The financial support from the National Science Foundation of China (20753002) and the Natural & Scientific Grant of Jiangsu Province (BK2009181), China, is gratefully acknowledged.
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