This protocol details a facile, one-pot synthesis of manganese oxide (MnO) nanoparticles by thermal decomposition of manganese(II) acetylacetonate in the presence of oleylamine and dibenzyl ether. MnO nanoparticles have been utilized in diverse applications including magnetic resonance imaging, biosensing, catalysis, batteries, and waste water treatment.
Compared to other synthesis methods, thermal decomposition generates uniform metal oxide nano-particles with tight control over particle size, shape, and chemical composition. This technique is an easy one pot synthesis that uses three reagents, a metal precursor, an organic solvent and a stabilizer. It can produce different types of nano-particles including manganese oxide and iron oxide.
Demonstrating the procedure will be Celia Martinez De La Torre, a graduate research assistant in my laboratory. Before beginning an experiment, place a four neck 500 milliliter round bottom flask onto the heating mantle. And secure the middle neck with a metal claw clamp.
Add magnetic stir bar to the round bottom flask and place a glass funnel in the middle neck of the flask. Make sure the safety and input stopcocks are open. Add 1.51 grams of manganese II acetylacetonate through the funnel into the round bottom flask.
And add 20 milliliters of allylamine and 40 milliliters of di-benzyl ether to the flask. Attach a condenser to the left neck of the flask and use a metal claw clamp to secure the condenser to the flask. Add the glass elbow adapter to the top of the condenser and attach the rotovap trap to the right neck of the round bottom flask.
Lace the glass elbow adaptor on top of the rotovap trap. And fold the rubber stopper on the middle neck of the round bottom flask. So the sides cover the neck of the flask.
Use plastic conical joint clips to secure the glassware neck connections. And place the temperature probe into the smallest neck in the brown bottom flask. Use a neck cap and an O-ring to tighten and secure the probe and the reaction mixture without touching the glass.
And connect the temperature probe to the input of the temperature controller. Connect the heating mantle to the output of the temperature controller and turn on the stir plate to begin vigorous stirring of the solution. Open the air free nitrogen tank to slowly begin flowing nitrogen into the system and use the regulator to adjust the flow until a steady stream of bubbles forms in the middle of mineral oil bubbler.
Then turn on the cold water in the fume hood to the condenser and close this For nanoparticle synthesis turn on the temperature controller to start the reaction. And monitor the changes that occur in the temperature throughout the experiment. At 280 degrees Celsius turn off the nitrogen tank and close the right stopcock.
The temperature will be held at 280 degrees Celsius for 30 minutes. During this time, the reaction color will change to a green tone indicating manganese oxide formation. When the reaction is cool to room temperature, turn off the temperature controller, stir plate and water and decant the manganese oxide nano-particles solution into a clean 500 milliliter beaker.
Add two times the volume of 200 proof ethanol to the beaker. And split the nanoparticle mixture equally between four centrifuge tubes. After capping sediment the nano-particles by centrifugation and discard the brown clear supernatant.
Add five milliliters of hexane to each tube. And re-suspend the nano-particles by vortexing. Add any extra nano-particles solution and the 200 proof ethanol to the tubes until each is three quarters full and centrifuge the nano-particles again.
Re-suspend each tube of nano-particles in five milliliters of hexane with vortexing and pool the four tubes of solution into two tubes. Bring the volume in each tube up to three quarters full with 200 proof ethanol and centrifuge the nano-particles again. Discard the nearly colorless and clear a supernatant.
And re-suspend the nano-particles in five milliliters of hexane with vortexing. Pour the entire volume of both tubes into a 20 milliliter glass scintillation vile. And evaporate the hexane in a fume hood overnight.
The next morning place the vile at 100 degrees Celsius for 24 hours to dry out the nano-particles before using a spatula to break up the powder. To assess the nano-particle size and surface morphology, use a mortar and pestle to pulverize the manganese oxide nano-particles into a thin powder, and add five milligrams of the powder to a 15 milliliter conical centrifuge tube. Add 10 milliliters of 200 proof ethanol to the tube and bath sonicate the nanoparticle mixture for five minutes until the nano-particles are fully re-suspended.
Immediately upon re-suspension, add three five microliter drops of nano-particle solution into a 300 mesh copper grid support film of carbon type B.After air drying assess the nanoparticle shape and size by TEM according to standard protocols with a beam strength of 200 kilovolts a spot size of one and a 300 X magnification. To determine the nanoparticle bulk composition, use a spatula to transfer some of the fine nanoparticle powder onto an x-ray diffraction sample holder. And collect the x-ray diffraction spectra of the manganese oxide particles according to standard protocols.
Use a two theta range from 10 to 110 degrees to view the manganese oxide and manganese to three oxide peaks. To determine the nanoparticle surface composition add dry manganese oxide nanoparticle powder to an FTIR sample holder and collect the FTIR spectrum of the nano-particles according to standard protocols between the 4, 400 inverse centimeter wavelength range with a four centimeter resolution. Ideal TEM images consist of individual dark rounded octagonal nano-particles with minimal overlap.
If a high concentration of manganese oxide nano-particles are suspended in ethanol, or too many drops of nano-particles suspension are added to the T and grid each image will consist of large agglomerations of nano-particles. If a low nano-particle concentration is prepared in ethanol the nano-particles will be separated but too sparsely distributed on the TEM grid. Overall, a decrease in the ratio of allylamine di benzyl ether yields smaller manganese oxide nano-particles with less variation in size, except when allylamine alone is used producing similar size nano-particles to the 30 30 ratio.
X-ray diffraction can be used to determine the crystal structure and phase of the nano-particles. The x-ray diffraction sample peaks can then be matched to x-ray diffraction peaks from known compounds. To facilitate estimation of the nanoparticle composition, here FTIR spectrum manganese oxide nano-particles after background correction can be observed.
All spectra show the symmetric and asymmetric methylene peaks associated with groups. In addition to the aminal radicle bending vibration peaks associated with groups. Furthermore, all nanoparticle FTIR spectra contain manganese oxygen and manganese oxygen manganese bond vibrations around 600 inverse centimeters which confirmed the composition found through x-ray diffraction.
To ensure an accurate temperature reading, the temperature probe do not touch the glass. The level of silicone oil and rate of nitrogen flow should also be carefully monitored. Metal oxide nano-particles can be made hydrophilic through polymer or lipid encapsulation to enhance their biocompatibility.
Targeting agents can be also touch to light nanoparticle accumulation in vivo.
