Preparation and characterization of (3-aminopropyl)triethoxysilane-coated magnetite nanoparticles

https://doi.org/10.1016/j.jmmm.2004.01.094Get rights and content

Abstract

Magnetite nanoparticles coated with (3-aminopropyl)triethoxysilane, NH2(CH2)3Si(OC2H5)3, were prepared by silanization reaction and characterized by X-ray diffractometry, transmission electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy and magnetization measurements. Both uncoated and organosilane-coated magnetite exhibited superparamagnetic behavior and strong magnetization at room temperature. Basic groups anchored on the external surface of the coated magnetite were observed. The superparamagnetic particles of coated magnetite are able to bind to biological molecules, drugs and metals and in this way remove them from medium by magnetic separation procedures.

Introduction

Modified magnetic materials are nowadays well-known and have been investigated intensively due to their potential applications in many areas, such as biology, medicine and the environment. These applications include enzyme and protein separations, RNA and DNA purifications [1], [2], [3], magnetic resonance imaging (MRI) techniques for cancer diagnosis, and cancer therapy such as magnetically controllled drug carriers and hyperthermia [4], [5], [6], [7], [8]. Another important example is removal of toxic elements from industrial wastes [9], [10], [11], [12]. Modified magnetic materials are composed of an iron oxide core coated with organic or inorganic molecules, which form a chemical bond with the core surface. The iron oxide core is obtained as a fine powder containing nanometer-sized particles and presents superparamagnetic behavior. Functional groups tailored for specific tasks are anchored as an organic molecule shell around of the core. These particles are capable of forming stable aqueous suspensions and may be easily redispersed after agglomeration in the presence of a magnetic field.

In the present study, we report the preparation of superparamagnetic magnetite particles that were coated with (3-aminopropyl)triethoxysilane, NH2(CH2)3Si(OC2H5)3. This organosilane can bind to a metal oxide by adsorption or covalent bonding, and through the active amino group in its structure is able to combine with biomolecules, drugs and metals. This paper provides a detailed study of the preparation and characterization of the silanized magnetite nanoparticles.

Section snippets

Preparation of magnetic nanoparticles and coating procedure

Magnetite particles were prepared by the coprecipitation method, by adding a 5mol/l NaOH solution into a mixed solution of 0.25mol/l ferrous chloride and 0.5mol/l ferric chloride (molar ratio 1:2) until obtaining pH 11 at room temperature. The slurry was washed repeatedly with distilled water. Then particles were magnetically separated from the supernatant and redispersed in aqueous solution at least three times, until obtaining pH 7. After that, the surface of these particles was coated with

Preparation of magnetic nanoparticles

The coprecipitation process to obtain magnetite particles, Fe3O4, through reaction (1) was carried out in an aqueous medium. Magnetite nanoparticles are very sensitive to oxygen, and in the presence of air some might undergo oxidation to Fe(OH)3 as shown in reaction (2) [13], or to maghemite (γ-Fe2O3) phase according to reaction (3). The formation of hematite (α-Fe2O3) is more difficult than that of the maghemite phase, occurring only under thermal dehydration conditions. Furthermore, small

Conclusions

In this work, an easy and effective method of preparation of modified magnetite nanoparticles with APTES in order to produce a superparamagnetic material with the required properties for technological applications is described. The results showed that heating of magnetite nanoparticles during the silanization reaction did not affect either particle size or their magnetic properties. The APTES-magnetite nanoparticles exhibited superparamagnetic behavior and their value of saturation

Acknowledgements

This work was partially supported by the Brazilian agencies FAPESP and RENAMI/CNPq.

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