Synthesis of magnetic iron oxide nanoparticles

The synthesis of magnetic iron oxide nanoparticles (IONPs) typically consists of procedures for generating uniform, ultracrystalline particles with a magnetic nature. The following is a breakdown of the steps of synthesis, as common as they are.

Product

Nano Magnetic Beads (100-500 nm)

Fe2O3 Nanoparticles

Fe3O4 Nanoparticles (High-temperature Pyrolysis Method)

Zn1-xFe2O4 Nanoparticles

Dextran Coated Fe3O4 Nanoparticles

Fe3O4 Nanoparticles (Co-precipitation Method)

MnxZn1-xFe2O4 Nanoparticles

Hydrothermal Method

The ferrous/ferric (sulfate and chloride) salts were synthesized as precursors in two series of IONPs and alkaline NaOH was precipitated. In series I prepared 1:2 ferrous (FeSO₄·7H₂O) and ferric sulfate (Fe₂(SO₄)₃·nH₂O) solutions of 0.3 M and 0.5 M respectively, and stirred for 30 min until a pure ferrous/ferric ion solution was present. To this 5 M NaOH solution was added drop by drop to the above ferrous/ferrous mixture solution till pH10 was reached and stirred for 30 min. This solution was then put into an autoclave and stored in an oven for 18 h at three different temperatures (100, 130 and 190 °C) before being naturally cooled down to room temperature. The resulting black solid product was centrifuged (4500 rpm for 10 min) and washed several times with distilled water and ethanol and dried at 80 °C for 14 h.The second series of IONPs were produced using ferrous and ferric chloride precursors (in 1:2 ratio) under identical experimental conditions as above.

Fig. 1. Synthesis of magnetic iron oxide nanomaterials by hydrothermal method

Co-precipitation Method

As shown in the Fig. 2, for the preparation of magnetite Fe₃O₄ nanoparticles by chemical co-precipitation in modified manner with reprint procedure. This consisted of taking FeCl₃·6H₂O (7 g, 0.52 M) and FeSO₄·7H₂O (3.6 g, 0.26 M) in 50 ml distilled water. Then the two solutions were added and stirred at a molar concentration of 2:1. After 15 min, this orange solution is cooled to 60 °C with 450 rpm stirring. Further, 50 ml of 10% NH₄OH solution was added slowly to the solution and poured over it and agitated on a magnetic stirrer at 60 °C with 450 rpm for 90 min. Once the solution turned black, the process of heating and stirring was stopped. Then, the magnetic bar was removed. After that, the resulting black suspension was placed over a permanent magnet to separate the precipitate from the solution so that the precipitation process can be carried out quickly and effectively. After 15 min, the colorless solution was then separated by magnetic decantation. Then, the precipitate was washed 7 times using distilled water until the odor of NH₄OH disappeared. Repeated washing is carried out to reduce the amount of salt derived from other reactions dissolved in the sample. The washed solution was then dried using a hot plate at 80 °C for 48 h. The dried solution was then mashed using a mortar and pestle to become Fe₃O₄ fine powder.

Fig. 2. Synthetic sketch of Fe₃O₄

Microemulsion Method

The precursor solution (solution I) contains 2 : 1 mole ratio of iron salts, Fe(NO₃)₃·9H₂O (20 mL of 0.4 M), and FeSO₄·7H₂O (20 mL of 0.2 M) dissolved in 80 mL of a mixture of Tween-80/butan-1-ol/n-heptane. This mixture results in the formation of a reverse microemulsion. Solution II contains 80 mL of Tween-80/butan-1-ol/n-heptanes and 50 mL of 25% aqueous NH₃. These solutions were whisked at 300 rpm for 30 minutes at room temperature. Solution II was mixed with solution I and the mixture was stirred continuously at 1000 rpm for 150 minutes at 30, 50 and 80 °C, after which the precipitate was washed numerous times in distilled water and acetone to flush out the ammonia and the surfactant. Finally, the magnetic Fe₃O₄ nanoparticles were dried in a vacuum oven.

Fig. 3. Synthesis procedure of Fe₃O₄ nanoparticles by microemulsion (W/O) method

Sol-Gel Method

The iron oxide nanoparticle was synthesized by following modified sol–gel method. Fig. 4 shows the schematic presentation of Fe₂O₃ nanoparticle synthesis by sol–gelmethod. As a precursor solution (200 mL, 0.1 M) iron nitrate (Fe(NO₃)₃) was used and it wasgelated by addition of (800 mL, 0.1 M) citric acid (C₆H₈O₇) solution. Here citric acid act asligand molecule and distilled water was used as a solvent. The iron salt solution was addedto the citric acid solution drop by drop under vigorous stirring. The mixture solution wasthen heated to a temperature of 70 °C and vigorous stirring was maintained until the gelformation. The gel was heated further to evaporate the remaining water. The dried gelwas then annealed at 250 °C for 2 h. Finally, the calcined mass was grinded by mortar andpestle to get Fe₂O₃ nanoparticle powder.

Fig. 4. Synthesis of Iron oxide nanoparticles by sol–gel method

Thermal Decomposition

Thermal decomposition is based on the breakdown of metal precursors (acetylacetonates, carbonyls or oleates) at high temperatures (150–300 °C) with organic solvents that are hot (250–300 °C) like octadecene or benzyl ether. Dispersants and hydrophobic ligands such as oleic acid, lauric acid, oleylamine and hexadecyl amine are needed to stabilize formed nanoparticles and inhibit their association. This process of synthesis is broken into three parts.

1. A solvent mixture of organometallic precursors, surfactants, and stabilisers are heated uniformly to the precursor's nucleation or decomposition temperature.
2. And then the solution is hotted up to the solvent boiling point and the nano crystals will form.
3. The last stage is growth phase where the solution is refluxed for sometime and brought to room temperature.

Schematic example of this kind of synthesis is shown in Fig. 5.

Fig. 5. Synthesis of magnetite nanoparticles by thermal decomposition

Sonochemical Method

First 1 g of FeCl₂ is dissolved in 100 mL of distilled water. Then 20 mL of NH3 solution 2 M is slowly added to the solution, under ultrasonic waves (60 W) for 3 min. A black precipitate is obtained confirming the synthesis of Fe₃O₄. The precipitate of Fe₃O₄ is then centrifuged and rinsed with distilled water, followed by being left in an atmosphere environment to dry. Fig. 6 shows the schematic diagram for experimental setup used for this sonochemical reaction.

Fig. 6. Schematic diagram for the experimental setup used for the sonochemical reactions

References

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