Preparation of Silica Nanoparticles Through Microwave-assisted Acid-catalysis

The overall goal of this procedure is to demonstrate the steps required for the synthesis of silicon nanoparticles by microwave assisted techniques using acid catalysts. This is accomplished by first selecting appropriate microwave compatible precursors and solvents to be used within the reaction and to prepare the precursor solution using TE Os hydrochloric acid and acetone. The prepared precursor solution is then irradiated by microwave techniques to yield silicon nanoparticles suspended within the acetone solution.

Ultimately, dynamic light scattering and scanning electron microscopy is used to characterize the prepared nanomaterials for representative differences in size and morphology. The main advantage of this technique over existing methods is that silicon nanoparticle SOS can be quickly and reproducably synthesized by microwave assisted techniques using an acid catalyst where nano nanoparticle diameters can range from 30 to 250 nanometers simply by varying the reaction conditions. For a 25 millimolar reaction solution of teos and acetone, obtain a 50 milliliter plastic conical tube teos, and a prepared one millimolar hydrochloric solution using a micro pipetter at 850 microliters of the one millimolar hydrochloric solution to the plastic conical tube, then add 150 microliters of teos to the tube.

Observe that the mixture of teos and acid are originally admissible, resulting in two clear colorless layers. Vortex the solution. A quick burst will cause the solution to turn slightly cloudy and pale white vortexing.

The solution again will yield a clear colorless solution. Total vortex time is approximately 10 seconds. At this point, the teos is hydrolyzed and in the form of silicic acid, add acetone to the plastic conical tube containing the silicic acid solution and dilute to a total volume of 40 milliliters.

Ensure proper mixing by vortexing the solution. After diluting the solution with acetone, create a microwave method within the provided software for silicon dioxide nanoparticle formation. Typical reaction parameters include power equals to 300 watts, temperature equals to 125 degrees celsius, and time equal to 60 seconds.

Using an external laptop, the temperature, pressure and power profiles can be stored, plotted, and compared with future experiments. Add a stir bar to a 10 milliliter microwave reaction vial, and using a micro pipetter at five milliliters of the silicic acid acetone reaction solution to the microwave vial. A reaction volume of five milliliters should be used to provide adequate head space to accommodate the generation of pressure from superheated acetone.

Place the snap cap on a 10 milliliter vial, ensure the cap is seated properly on the vial to reduce loss of solvents. When superheated place the vial in the microwave reactor, press the start button on the laptop to start the microwave heating procedure. Observe proper placement of the pressure head unit.

Observe that the proper microwave power settings are correct. Once the reaction begins with an increase in reaction, temperature and generation of reaction pressure. When the reaction time has expired, compressed air will quickly cool the reaction.

Remove the reaction vial from the microwave reactor after cooling. For dynamic light scattering or DLS size analysis, add 900 microliters of distilled water to a polystyrene disposable vet. Add 100 microliters of the reaction solution containing silicon dioxide nanoparticle to the vete containing the water and mix Set up procedures for particle measurements by following the dynamic light scattering analyzer software and analyze the solution for particle size to perform the cleanup procedure.

Clean the silicon dioxide nanoparticles by adding one milliliter of the reaction solution to an einor tube centrifuge for 30 minutes to one hour, depending on particle diameter. Carefully decant excess solution from the silicon dioxide nanoparticle pellet. Add one milliliter of fresh acetone and resuspend the nanoparticles by placing in an ultrasonic bath for five to 10 minutes.

Repeat this procedure two more times for adequate removal of residual silicic acid for scanning electron microscopy or SEM. Clean the highly polished single crystal silicon wafers and an ultrasonic bath for approximately 30 minutes prior to use. Place the silicon wafers and piranha solution at a temperature of 80 degrees Celsius for one hour.

After removing from the ultrasonic bath, wash the silicon wafers with distilled water and dry drop cast, clean or not clean solutions of silicon dioxide nanoparticles onto the clean prepared silicon wafer. Place the prepared samples on silicon wafers in the cylindrical tube of the sputter system. Vacuum the cylindrical tube of the sputter system to 40 milour.

Purge the cylindrical tube of the sputter system with argon gas until a pressure of approximately 200 milour is reached. Decrease the pressure to 80 milour and apply 15 milliamps of voltage, keeping it constant as a final step before SEM sputter platinum on the prepared samples for 60 seconds. Temperature pressure and microwave power traces for a representative.

Silicon dioxide nanoparticle microwave assisted reaction are presented here. The microwave reaction plot is divided into three sections, ramping reaction and cooling. A reaction temperature of 125 degrees celsius and reaction time of 60 seconds are used in this representative reaction.

During the ramping portion. The power is maximized at 300 watts so that the reaction temperature can be reached quickly without overshooting the targeted reaction temperature, the reaction begins to pressurize. Once the temperature surpasses the boiling point of the solvent upon reaching the reaction temperature, microwave power is decreased and the power oscillates to maintain the selected targeted temperature.

After the allotted reaction time has expired, the power is reduced to zero watts and compressed air is blown across the reaction vial quickly reducing the temperature and quenching particle growth. Reaction vials containing prepared silicon dioxide nanoparticles ranging in size from 40 to 270 nanometers in diameter are presented here as measured by dynamic light scattering and are zeta averages based on intensity measurements. Reaction solutions are clear and colorless for dioxide nanoparticles with particle diameters less than 125 nanometers.

While solutions are pale white in color for particle diameters greater than 125 nanometers. The three dimensional bar graphs presented here demonstrate the range in size and poly dispersity of silicon dioxide nanoparticles that can be synthesized using these microwave assisted techniques by controlling the initial T os concentration and reaction time at 125 degrees Celsius. The Te OS concentration varies from 10 to 50 millimolar and the reaction time varies from zero to 60 seconds, resulting in silicon dioxide nanoparticle diameters ranging in size from 30 nanometers to over 275 nanometers.

Scanning electron micrographs of silicon dioxide nanoparticles prepared by microwave assisted synthetic techniques are shown here. These micrographs are prepared from solutions of silicon dioxide nanoparticles that were not cleaned by the described cleaning procedures.Here. A glass like silicon film can be observed covering the entire prepared silicon wafer.

At this magnification, the silicon dioxide nanoparticles cannot be observed, although large cracks can be visualized as a result of the evaporation of the acetone from preparation. A more detailed view of the silica film can be observed here, as well as the trapped silicon dioxide nanoparticles. The silica film results from the incomplete conversion of silicic acid to silicon dioxide nanoparticles during the microwave reaction.

As previously noted, as the solvent evaporates, the unreactive silicic acid begins to condense trapping the nanoparticles in the film. The silicon dioxide nanoparticles shown here are prepared from solutions where the reaction solution was cleaned using the provided cleanup procedure by cleaning the reaction solution, the majority of unreactive silicic acid is removed, and individual silicon dioxide nanoparticles can be visualized. After watching this video, you should have a good understanding of how to synthesize silicon nano particles by microwave assisted techniques using acid catalyst, the selection of proper microwave compatible solvents and precursors such as T os, hydrochloric acid and acetone facilitate the the production of silica nanoparticles.