Iron metal has sub-micrometer particles known as Nano-iron particles. Both water and air (oxygen) make Iron highly reactive. Iron also has a low magneto-crystalline anisotropy. Traditionally, in Fischer–Tropsch synthesis, Iron is the catalyst because it is very reactive. There are several methods to manufacture Iron nanoparticles.

Nanoparticles contain a very large surface area. Magnetism's unique form, known as super para-magnetism, is exhibited by iron nanoparticles. Material's customizability makes it exciting. High coercitivity is important for magnetic recording media, which is an iron nanoparticles' major practical application. Meanwhile, very low coercivity is needed in the core materials of the transformer. Iron nanoparticles are the best catalyst in coal liquefaction. There are many biomedical applications, including the magnetic separation and labeling of biological materials and specific delivery of drugs. They also help in MRI Contrast Enhancement and in selectively heating cancerous tumors and in the removal of heavy metals.

Introduction

Iron is the Period 4 element of the periodic table. It is the 4th most abundant element found in the crust of Earth. It is also found in minerals like magnetite and hematite. Iron is a ductile, malleable, and strong metal. In macroscopic applications like rusting, the reactivity of Iron is important, but at the nanoscale, it dominates due to its very potent catalytic and magnetic properties. Both water and oxygen make Iron highly reactive, Iron oxidizes quickly for creating free iron ions due to its large surface area, and it oxidizes more quickly in nanoparticles than the bulk material in nanoparticles. Use is limited to inert environments. They are not toxic.

Different and rare optical, chemical and magnetic properties are possessed by the nanoparticles owing to their small sizes. Generally, magnetic nanoparticles are very interesting, and the magnetic material that's more useful is Iron as it got the highest value of room temperature of any element and got a high enough Tc, which makes it of no concern in a broad range of the practical applications. Also, it is a magnetic material that is very soft.

Low magneto-crystalline anisotropy is possessed by Iron, which makes nanoparticles of Iron the best material to function with. Superparamagnetic behavior is seen by sufficiently small magnetic nanoparticles, and the maximum volume of the particle, which at a certain temperature can be superparamagnetic, varies with the magneto-crystalline anisotropy, directly. Iron's magnetic characteristics make it the best choice in magnetic recording media. Iron needles of high magnetism in nanosize allow the removable electronic media's development whose convenience and high capacity are we so used to today. Although in a non-oxidizing environment, iron nanoparticles' extreme reactivity can be very useful. Iron nanoparticles are the catalyst in so many reactions Iron nanoparticles act as a catalyst in so many ideal reactions, but in the syntheses of Fischer-Tropsch, Iron is the catalyst of choice because it is highly reactive, both in general and this specific reaction. Iron's use as a catalyst involves carbon-carbon bonds and breaking and making.

How to Synthesis Iron Nanoparticles

Fe(II) or Fe(III) salt reduction with sodium borohydride can synthesize nanoparticles of Iron in an aqueous medium.

Several methods can be used to synthesize Iron nanoparticles, for instance, methods like thermal decomposition of iron pentacarbonyl, etc., and some mechanical ones. Methods like Sol-gel or colloid chemical are the kind of wet chemical processes that can be used to prepare iron nanoparticles.

Properties of Iron Nanoparticles

A range of remarkable chemical, magnetic, and optical properties because of finite size effects are possessed by the nanoparticles. The best property is the nanoparticle's large surface area. Surface free energy is a large amount of energy, which means altered properties of magnetism and added reactivity in nanoparticles. In Iron's case, optical effects aren't that much interesting; meanwhile, the other characteristics have been discussed for some time. In Iron's case, most of the interest is in the effect resulting from electronic interactions: magnetism.

Magnetic Properties

Super para-magnetism is exhibited by nanoparticles of 10-20 nm that are made from a ferri- or ferromagnetic material. In between ferromagnetism and super para-magnetism, a transition temperature lies, which increases with the increase in size. Coercivity appears when the spins aren't allowed to realign due to less thermal energy below a particular temperature, which is termed the "blocking temperature," and the behavior is ferromagnetic when the temperature is below that range.

In magnetic recording, nanoscopic iron needles also have an application. The highest coercivity or lowest (zero) coercivity detected in a material, based on its size, is examined by the iron nanoparticles. 3d electrons that lead to iron magnetism. Coatings of iron nanoparticles with different oxides don't only lessen the iron nanoparticles' Ms values, but the coercivity is also strongly affected, which results in very high coercivity yielded at low temperatures, and with an increase in temperature, coercivity decreases. A continuous, thin shell of gold would offer an effective barrier against oxygen or any other oxidizing agent. Towards oxidation, gold is inert, which makes it an ideal coating.

Chemical Properties

High reactivity with different oxidizing agents, particularly with air, dominates the chemistry of iron nanoparticles. Nanoparticles, when handled in a solid or liquid dispersant, slow oxygen diffusion to the nano-particles surface, and the reaction of oxidation is generally moderated. Iron's reactivity is not always detrimental. The reason for being a catalyst in a limited number of reactions is that surface of Iron oxidizes in ambient conditions, willingly.

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Application Areas of Iron Nanoparticles

Some applications include the treatment of contaminated ground of many types, for instance, contaminated by organochlorine pesticides, polychlorinated biphenyls (PCBs), chlorinated organic solvents, coatings, nanowires, certain alloys, and nanofibers. The main applications are:

Magnetic and Electrical Applications

Material's customizability makes it exciting. Practically and commercially, Iron nanoparticles' largest application is in the world of magnetic recording media. Nanoparticles of Iron have the ability to have either very low or very high coercivity via subsequent processing and synthetic procedure.

Iron nanoparticles are used to obtain a really high capacity of different advanced magnetic tapes, like camcorders and backup tapes of computers. These particles of Iron are elongated, large, permanent, and hard magnets, whereas Iron has an image of being a very soft material. Shape anisotropy is the reason behind it. Magnet emanates external magnetic fields that store energy. This is an ideal system for magnetic storage mediaand an ideal situation for digital information storage. Another benefit is that the hysteresis loop contains the amount of energy that's needed to reverse the magnetization. Superparamagnetic iron particles that are hysteresis-free have some characteristics which very much attract electrical and magnetic applications.

Soft magnetic material is required for many applications. The magnetic properties desirable in a transformer core and of iron nanoparticles, include high ss values, high susceptibility, and low loss of energy. For such applications, nano-crystalline Iron displays a remarkable balance of characteristics.

Catalytic Applications

It is used in the conversion of coal (or natural gas) to synthesis gas, via the steam process. That gas includes a mixture of H2 and CO. Then, conversion of synthesis gas into hydrocarbons via Fischer–Tropsch synthesis, in which at high pressure and temperature, the synthesis gas is made to pass over a catalyst. While in the commercial process, Iron acts as a catalyst often, but nanoparticulate Iron does not. The latest study showed nanoparticles of Iron and its catalytic activity. The iron nanoparticle has six times more catalytic activity than conventional material and displayed a strong selectivity for methane production.

Many of the catalysts traditionally used for this purpose are expensive, while Iron-based catalysts could be produced inexpensively. Nanoscale iron has been researched as a catalyst for coal liquefaction. Formation and the breaking of these bonds can be catalyzed by Iron. Reactivity is moderated by a surfactant presence on iron particles. Iron nanoparticles have catalyzed some other reactions too, including the alkene's hydroformylation, naphthalene's hydrogenation, N2 conversion from nitrogen compounds during coal pyrolysis, and trichloroethylene's degradation, carbon nanotubes growth, and gallium nitride nanostructures growth.

Biomedical Applications

Iron Magnetic nanoparticles have a number of applications in bio-medicine, that includes the magnetic separation and labeling of biological materials, and the delivery of a drug that's directed. Iron, however, provides promising benefits over its oxides because of its higher magnetic moment in the zero-valent state. In the cases of drug delivery that's directed and magnetic separation, a gradient of the magnetic field is used to apply a force to the particles that are directly proportional to the particle's magnetization, the benefit of having higher magnetization is noticeable. An extra benefit that Iron has is that it is softer than any of its oxides so that at larger sizes, super para-magnetism of Iron is maintained (and therefore higher particle moments) than is possible with its oxides. Delivery of drugs that are directed magnetically operates in a similar way but involves magnetic particles' intravenous injection, followed by the magnetic field gradient applications in the area where the delivery is desirable.

MRI Contrast Enhancement

Magnetic resonance imaging (MRI) is based upon nuclear magnetic resonance (NMR). Iron oxides that are superparamagnetic have been commercialized as contrast enhancers for MRI and provide a huge amount of benefits beyond their stronger magnetizations. Different ways can help in functionalizing the particles to offer some very particular interactions with biological samples like, by enhancing the blood or endocytosis. Of course, in similar ways, zero-valent Iron could be used, and a very improved agent of magnetic contrast would be represented. Strong fields of magnetism are used in MRI scans, and the magnetization of superparamagnetic particles is expected to be saturated. Another clear benefit is metallic Iron has double saturation as most strongly magnetic oxides.

Hyperthermia

As a treatment in medicine, hyperthermia depends upon heating tissue locally for almost 30 minutes to more than 428C for destroying the tissue, specifically tumors. For decades, magnetic particle heating has been researched as a probable approach to specifically heating tumors that are cancerous. The best way of heating is using the magnetic particles and the hysteresis in ferri-magnetic (or Ferro) particles to obtain heat. This energy expenditure manifests itself as heat, and a specific area of tissue can be heated if particles are localized appropriately.

Super magnetic particles are employed as another approach to heating by magnetic particles. Reorientation in ferrofluid can occur through two mechanisms, Neel relaxation (within the particle, rotation of the moment), and Brownian relaxation (particle's rotation). An ideal material would have a low anisotropy and high ss value, which obviously explains Iron's magnetic properties perfectly. Possible detrimental side effects can be avoided (including heart arrhythmias, tissue inductive heating, or muscular stimulation), frequencies between 0.05 and 1.2 MHz are usually used, and fields are kept to below 15 kAm1.

For removing heavy metal

Water contamination by heavy metals is one of the serious environmental pollutions. The application of Iron oxide-based nanomaterial is more attractive here due to their significant characteristics, for instance, magnetic properties, high surface area, and small size.

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Conclusion

Nano-iron particles are sub-micrometer particles of iron metal. Iron's reactivity is rapid with both water and air (oxygen). The remarkable properties of both Iron and nanoparticle are combined together. Traditionally, the catalyst of choice in Fischer–Tropsch synthesis and coal liquefaction has been Iron. Its most significant practical application is in the universe of magnetic recording media. There are many biomedical applications, including MRI Contrast Enhancement, selectively heating cancerous tumors, and the removal of heavy metals. 

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References

https://www.azonano.com/article.aspx?ArticleID=3288

https://en.wikipedia.org/wiki/Iron_nanoparticle

https://sci-hub.tw/https://doi.org/10.1002/smll.200500006

https://sci-hub.tw/10.1166/jnn.2017.14196