Iron oxide Nanoparticles Synthesis

Having a diameter of 1 to 100 nm, iron oxide nanoparticles are a type of iron oxide particles that come in two different forms:

• Fe3O4 or magnetite
• The oxidised form of magnetite known as maghemite or γ-Fe2O3

Iron oxide nanoparticles have garnered plenty of interest in nanoresearch owing to their super paramagnetic properties, as well as potential applications in several different fields. Although nickel and cobalt also have good magnetic abilities, they fall short in the manner that they get easily oxidized and are also toxic in nature.

Some of the commonly known applications of iron oxide nanoparticles are in high sensitivity biomolecular MRI (Magnetic Resonance Imaging), sensors, catalysis and terabit magnetic storage devices. All these applications involve coating of nanoparticles using agents like diols, alkyl-substituted amines and long chain fatty acids.

About iron oxide nanoparticles synthesis

The surface chemistry, size distribution and shape of the produced nanoparticles is hugely determined by the exact method of iron oxide nanoparticles synthesis used. The process also has a great impact on the type of impurities or structural defects and the distribution aspect of the nanoparticles. All these factors combined determine the magnetic behaviour of the particles too.

Various attempts have been made of late to devise methods and processes that can deliver monodisperse colloids comprising of iron oxide nanoparticles of more uniformity, in terms of their shape and size. Let's look at some of these iron oxide nanoparticles synthesis methods in brief:

The co-precipitation method of iron oxide nanoparticles synthesis

This is easily the most commonly used method of iron oxide nanoparticles synthesis, and can be subdivided into two kinds:

• The first method involves partial oxidisation of ferrous hydroxide suspensions using different oxidising agents.
• The second one involves ageing of stoichiometric mixtures of ferric and ferrous hydroxides inside in an aqueous media, resulting in spherical magnetite particles that are homogenous in size.

The micro-emulsion method of iron oxide nanoparticles synthesis

Micro-emulsion is the name given to a stable isotropic liquid mixture of two immiscible liquids (like oil and water) comprising of their nano-sized domains, stabilised using surface-active molecules (in the form of an interfacial film). These micro emulsions can be further categorised into water-in-oil or oil-in-water solutions, depending on the continuous and dispersed phases.

A large variety of nanoparticles can be produced using the water-in-oil micro-emulsion. The process involves mixing of water in oil, along with an amphiphilic surface agent. The surfactant helps in lowering the surface tension existing between the oil and water, resulting in a transparent solution. The tiny water droplets function as nanoreactors for iron oxide nanoparticles synthesis. The water pool is spherical in shape and the size of the produced nanoparticles depends greatly on the size of the water pool used. Hence, the physical characteristics of these spherical nanoparticles can be altered and fine-tuned by altering the water pool's size.

Iron oxide nanoparticles synthesis through high temperature decomposition of the organic precursors

This process of iron oxide nanoparticles synthesis involves decomposition of iron precursors using hot organic surface agents, resulting in nanoparticle samples having good crystallinity, narrow size distribution (varying from 5 nm to 12 nm) and good size control. Furthermore, the nanoparticles can be dispersed very easily. The magnetic nanoparticles produced this way are highly useful in biomedical applications such as magnetorelaxometry, magnetic cell separation and magnetic resonance imaging, where the nanoparticle size used plays a very key role in the process.