Abstract
Chitosan-coated magnetic nanoparticles (CMNP) were obtained at 70 °C and 80 °C in a one-step method, which comprises precipitation in reverse microemulsion in the presence of low chitosan concentration in the aqueous phase. X-ray diffractometry showed that CMNP obtained at both temperatures contain a mixture of magnetite and maghemite nanoparticles with ≈4.5 nm in average diameter, determined by electron microscopy, which suggests that precipitation temperature does not affect the particle size. The chitosan coating on nanoparticles was inferred from Fourier transform infrared spectrometry measurements; furthermore, the carbon concentration in the nanoparticles allowed an estimation of chitosan content in CMNP of 6%–7%. CMNP exhibit a superparamagnetic behavior with relatively high final magnetization values (≈49–53 emu/g) at 20 kOe and room temperature, probably due to a higher magnetite content in the mixture of magnetic nanoparticles. In addition, a slight direct effect of precipitation temperature on magnetization was identified, which was ascribed to a possible higher degree of nanoparticles crystallinity as temperature at which they are obtained increases. Tested for Pb2+ removal from a Pb(NO3)2 aqueous solution, CMNP showed a recovery efficacy of 100%, which makes them attractive for using in heavy metals ion removal from waste water.
Highlights
Chitosan-coated magnetic nanoparticles (CMNP) contain a core of magnetic material usually a mixture of magnetite (Fe3O4) and maghemite (γ-Fe2O3)
The chitosan coating on nanoparticles was inferred from Fourier transform infrared spectrometry measurements; the carbon concentration in the nanoparticles allowed an estimation of chitosan content in CMNP of 6%–7%
The dissolved chitosan in the aqueous phase of the microemulsion does not perturb the mechanism of nucleation and growth of magnetic nanoparticles
Summary
Chitosan-coated magnetic nanoparticles (CMNP) contain a core of magnetic material usually a mixture of magnetite (Fe3O4) and maghemite (γ-Fe2O3) Their chitosan covering provides them with free amino and hydroxyl groups that enable the possibility to bind to a diversity of chemical groups and ions, leading to a number of applications such as protein and metal adsorption [1,2,3], guided drug and gene delivery [4,5], magnetic resonance imaging [6], tissue engineering [7] and enzyme immobilization [8,9,10]. We report here a one-step preparation of CMNP by precipitation at 70 °C and 80 °C in a reverse microemulsion containing chitosan in the aqueous phase These relatively high temperatures were selected due to the known direct effect of temperature on crystallinity, which in turn directly affects the nanoparticles magnetization. Based on our previous reports on preparation of CMNP with low content of chitosan in one step [17,21], appropriate amounts of this polymer were used to minimize the chitosan to magnetic nanoparticles weight ratio
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