Journal of Student Research 2019

Journal of Student Research 112 the size of the magnetite NPs–the smaller the anionic precursor, the smaller the magnetite. [6] These are the reasons for using ferric and ferrous chloride over other precursors to create IONPs, trying to reduce their size to make them SPIONs. The flexibility of co-precipitation is that it allows for comparing small, variable changes to produce different MNPs. Other common alternative methods to co-precipitation are microemulsion and thermal decomposition reaction. The microemulsion method takes two immiscible liquids, and through the reaction, the nanoparticles have a film of surfactant molecules surrounding them to keep them from aggregating. [7] While a thermal decomposition reaction takes the decomposition of the metal precursors and heat is applied to disrupt their tentatively stable nature. [8] This experiments reasons for choosing co-precipitation over microemulsion or thermal decomposition reaction were the ability to control numerous variables and apply them biomedically. It is more difficult to control the size distribution through the thermal decomposition reaction; however, it is more difficult to apply the microemulsion method biomedically.

113 Toward Magnetic Nanoparticle Synthesis and Characterization for Medical Applications 2) Base addition: Next add the choice of base. For this experiment, three different bases were used; 1M sodium hydroxide, 0.7M ammonia (NH 3 ), and ammonium hydroxide (NH 4 OH). The rate of addition can be varied, from dropwise by burette or quick addition. Lastly, continue stirring at 400 RPMs for 30minutes. The pH should end between 11 and 13. For reference, the reaction that occurred with the addition of the ammonium hydroxide is: 3) Separation: The solution was then magnetically separated by placing a magnet underneath the flask for 15 minutes. Next the supernatant was decanted— keeping the magnet underneath. For greater separation, the ferrofluid was lastly centrifuged for 2 minutes at 2000 RPMs, again magnetically decanted the supernatant. 4) Surface Modification: The remaining ferrofluid was then transferred to a falcon tube to be surface modified. Eight milliliters of 25% tetramethylammonium hydroxide [N(CH 3 ) 4 +OH] was added to the falcon tube. 5) Washing: The second to last step was washing the IONPs with 50 mL of DI water 3 to 4 times to bring the pH down to neutral 7. 6) Characterization: Attempted to suspend the solution for characterization by Malvern Zetasizer. Dynamic light scattering (DLS) requires the nanoparticles to stay suspended in solution and not settle to the bottom. You may have noticed the characterization section of the methods’ section lacks finality on the IONPs size and to determine if they were SPIONs. It was discovered after compiling all the data and pictures that noticed that the IONPs aggregated and settled on the bottom of the cuvette, indicating that they were not correctly suspended for characterization by Malvern Zetasizer. While proceeding with my experiment, I became fully aware of how essential it was to minimize IOMNPs exposure to air until they were adequately surface modified. Early runs began in an open beaker and moved to a stoppered flask connected to vacuum flask under light vacuum to attempt to minimize oxidation. This vacuum interfered with the length of time it took to magnetically separate from under 15 minutes to over 30 minutes. Second, using a magnetic stir bar may have interfered with size distribution, as more would accumulate on the stir bar and during the removal of the stir bar with a magnet. Lastly, not monitoring the pH between the six significant steps had me questioning if early parts of the experiment were being done incorrectly and restarting when it was not necessary as proved when I started testing using pH paper. All three of these major issues could have been rectified by using a 3-neck round bottom flask: This would allow for a pH probe to monitor in 2FeCl 3 + FeCl 2 + 8NH3 + 4H 2 O → Fe 3 O 4 + 8NH 4 Cl . [10]

Table 1: Iron Oxide Nanoparticle Synthesis Steps. [9]

Synthesis of magnetic nanoparticles can be broken down to 6 steps: Solution Preparation, Base Addition, Separation, Surface Modification, Washing, and Characterization. (Numbers correspond with Table 1) 1) Solution preparation: First prepared ferrous-chloride tetrahydrate (FeCl 2 *4H 2 O) and ferric chloride hexahydrate (FeCl 3 *6H 2 O) solutions in separate flasks with a molar ratio of 2:1. Next, combined the two solutions into one stoppered flask and stirred at 400 RPMs for 5 minutes. The pH should be between 1 and 3.

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