User:Khlein/sandbox/Iron Nanoparticles

Zero-Valent Iron nanoparticles are ultrafine iron particles with a diameter ranging between 1 to 100 nanometers with a wide variety of uses, such as water remediation, depending on how the particles are synthesized. What makes these particles so unique is their high reactivity to both inorganic and organic substances caused by their high levels of surface energy and magnetic properties. Based on the method of synthesizing, the chemical properties of these particles can vary depending on the specific need such as the type of contaminant that is reduced.

Synthesis of Zero-Valent Iron Particles

Although there are many ways to synthesize them including using iron filings and milling them down or using plant extracts, the most common method of synthetization is through chemical reduction due to its accessibility. Consequently, the reduction of these nanoparticles results in the hydrolysis of Borohydride. In turn, the synthesis requires a surplus of the toxic chemical.

In these reactions, Fe(II) or Fe(III), usually in the form of iron salts, is reduced in an aqueous solution using sodium borohydride (${\ce {NaBH4}}$).

Example of possible reactions:

${\ce {FeCl2 + 2NaBH4 + 6C2H6O -> Fe + 2NaCl + 2B(OH)3 + 5H2 + 12CH4}}$

${\ce {2FeCl3 + 6NaBH4 + 18H2O -> 2Fe^0 + 6NaCl + 6B(OH)3 + 21H2}}$

External Factors

pH Effect on Nano Particles:

During these reactions, it has been observed the reactivity of these zero-valent iron nanoparticles is inversely proportional to the pH of the solution. More reactive particles were fabricated when reduced in an acidic solution with pH levels ranging from 2-3.

Feeding Rate of Borohydride:

In order to create more reactive nanoparticles, an excess of borohydride is optimal. In order to satisfy this condition, a molar ratio of 1:3 (Fe2+: BH4-) is used along with a high feeding rate of 1 drop every 2 seconds. It has been observed that these techniques were highly significant in the production of highly reactive particles.

Type of Solvent:

The most popular type of solvent used is ethanol. When ethanol reacts with borohydride, it does so at a significantly lower rate than with water. In turn, this allows for the reduced particles to be exposed to oxygen for longer periods of time by decreasing the rate of mass oxidation. Due to the prevention of oxidation, ethanol also often employed as a mean of storage of these particles.

Properties

The properties of zero-valence iron nanoparticles is heavily dependent on how it is manufactured. Zero-valence iron nanoparticles is very reactive, approximately 10-1000 times more reactive than granular zero-valence iron. These particle have a core-shell structure with the core consisting of zero-valent iron (${\ce {Fe^0}}$) whereas the outer is comprised of mixed valent iron (Fe(II) or Fe(III)) oxide shell (FeOOH). This iron-oxide shell, while enclosing the center, does not hinder electron transfer from the iron core. This shell also allows for a higher stability then if there was no outer shell. Due to their high reactivity to oxygen and water, these particles tend to agglomerate. This can be combatted; however, through capping with a variety of materials both organic and inorganic. Although, capping slightly decreases the reactivity of the particles, it does increase the stability and longevity of these particles.

Applications

Ground Water Remediation

Zero-valent iron particles are widely implemented for their high reduction potential (−0.447 V (Fe/Fe(II)) of water contaminants in remediation of ground water. This high level of surface energy makes these particles particularly suitable at removing both organic and inorganic pollutants from water. These particles are injected into affected areas using small injection wells. The nanoparticles move through the environment, causing redox reactions with pollutants to occur. The reactions cause an insoluble precipitate to form with the pollutants, resulting in cleaner water as these pollutants' movements are hindered.

Water Treatment and Purification

Water from sewage plants contains many different harmful particles such as phosphates, ammonia nitrogen, and chemical oxygen. Since iron nanoparticles are excellent at reducing ions, they are utilized to help purify the water and remove contaminants. In a study, these particles were able to remove up to 98% of phosphate, 84.32% of ammonia nitrogen, and 82.35% of chemical oxygen. .

Algae Bloom Removal

Blue-green algae are photosynthetic cyanobacteria that are highly resistant to different weather conditions. They tend to grow in still water with phosphate ions and nitrate ions dissolved in it. These types of algae have been known to cause skin irritation as well as vomiting, headaches, and even liver problems. When introduced to iron nanoparticles, the reduction reaction begins to take place. After they were added, it was evident the amount of algae began to diminish along the levels of phosphate and nitrate dissolved in the water.

Examples of Contaminants:

Organic:

Iron nanoparticles are quite effective at remediating organic pollutants including:

• Orange II (${\ce {C16H11N2NaO4S}}$)

• Chrysoidin (${\ce {C12H13ClN4}}$)

• Tropaeolin O (${\ce {C12H9N2NaO5S}}$)

• N-nitrosodiumethylamine (${\ce {C4H10N2O}}$)
• TNT (${\ce {C7H5N3O6}}$).

Inorganic:

Chlorinated Methanes:

• Carbon Tetrachloride (${\ce {CCl4}}$)
• Chloroform (${\ce {CHCl3}}$)
• Dichloromethane (${\ce {(CH2Cl2)}}$

Pesticides:

• DDT ${\ce {(C14H9Cl5)}}$
• Lindane${\ce {(C6H6Cl6)}}$

Heavy Metals:

• Mercury (${\ce {Hg^2+}}$)
• Nickel (${\ce {Ni^2+}}$)
• Cadmium (${\ce {Cd^2+}}$)
• Lead (${\ce {Pb^2+}}$)
• Chromium (${\ce {Cr^6+}}$)

External links

• www.example.com