Crystal -Growth Kinetics of Magnetite (FE3O4) Nanoparticles using the Ostwald Ripening Model

Magnetite nanoparticles (Fe3O4) are a type of magnetic particle with huge potential for application as a drug carrier due to their excellent superparamagnetic, biocompatible, and easily modified surface properties. One characteristic of nanoparticles is that they can be controlled by studying the evolution of crystal growth. The purpose of this research is to study the evolution of magnetite-crystal growth and determine the crystal growth kinetics using the Ostwald ripening model. Magnetite nanoparticles were synthesized from FeCl3, citrate, urea, and polyethylene glycol using the hydrothermal method at 220oC for times ranging from 1–12 hours. The characterizations using X-ray diffraction (XRD) indicated that the magnetite began to form after 3 hours synthesis. The crystallinity and crystal size of the magnetite increased with the reaction time. The diameter size of the magnetite crystals was in the range of 10–29 nm. The characterizations using a transmission electron microscope (TEM) showed that magnetite nanoparticles had a relatively uniform size and were not agglomerated. The core-shell nanoparticles were obtained after 3 hours synthesis and had a diameter of 60 nm, whereas the irregular-shaped nanoparticles were obtained in 12 hours and had a diameter of 50 nm. The characterizations using a vibrating sample magnetometer (VSM) revealed that magnetite nanoparticles have superparamagnetic properties. The magnetization saturation (Ms) value was proportional to the degree of crystallinity. The magnetite-crystal growth data can be fitted to an Ostwald ripening model with the growth controlled by the dissolution of the surface reaction (n?4).

Crystal growth; Hydrothermal; Magnetite; Nanoparticles; Ostwald ripening

In conclusion, we have developed a facile, one-pot hydrothermal method for the synthesis of magnetite nanoparticles with a core-shell structure. The magnetite nanoparticles we obtained have monodispersity, no agglomeration, and a diameter of 50–60 nm. The magnetite nanoparticles also exhibited superparamagnetic properties, high saturation magnetization (65 emu/g), and were highly water soluble, which makes them an ideal candidate for drug delivery. The crystal growth kinetics study discovered a correlation among reaction time, crystal size, crystallinity, and magnetization saturation. A longer reaction time will increase the crystals’ sizes and crystallinity. In addition, the value of the saturation magnetization grew with increasing crystallinity. The magnetite-crystal growth data can be fitted to an Ostwald ripening model with the growth being controlled by the dissolution of the surface reaction (n?4), with a percentage error of 2.53%.

Financial support for this study was provided by the Ministry of Research, Technology and Higher Education of the Republic of Indonesia (Kemenristekdikti).

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