Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

The overall goal of this procedure is to synthesize non centered and metal terminated transition metal carbide nanoparticles. This is accomplished by first encapsulating mono metallic or bio metallic transition metal oxide nanoparticles in silica shells via a reverse microemulsion. The second step is to carbonize the nanoparticles using a tube furnace.

In this step, molecular hydrogen reduces the encapsulated metal oxide nanoparticles by removing lattice oxygens as molecular water at higher temperatures. Methane then decomposes at the metal surface and intercalates into the lattice forming the carbide. The final step is to remove the silica shells using a room temperature solution containing aqueous fluoride media.

Ultimately transmission electron microscopy and other analyses such as powder x-ray diffraction and x-ray photo electron spectroscopy are used to show that the nanoparticles are phase pure carbides, non centered, and metal terminated. The main advantages of this technique over existing methods such as wet impregnation on carbon black are encapsulation in a carbon nitride matrix is that the particle size and composition can be finely tuned prior to the heat treatments and the resulting nanoparticles can be dispersed on any high surface area catalyst support without exposing the support to harsh car rising or neutralizing conditions. To prepare the reverse microemulsion first, add 240 milliliters of anhydrous and heptane to a clean oven dried one liter round bottom flask containing an oven dried magnetic stir bar using a clean oven dried graduated cylinder, then add 54 milliliters of polyoxyethylene Laurel Ether to the Nhat obtain under constant stirring add 7.8 milliliters of ultrapure deionized water under constant stirring.

Using a pipette add 0.1 to 0.5 milliliters of reagent grade ammonium hydroxide to the emulsion if it is desired. To reduce the hydrolysis time, seal the flask with a rubber stopper and paraform wax and let the reverse micro emulsion mix for at least 10 minutes. Next, prepare a metal al oxide precursor alcohol and and heptane solution.

By first placing the clean oven dried 250 milliliter round bottom flask into a dry nitrogen glove box, add 12 milliliters of 5%weight per volume. Tantalum isop prop oxide in isopropanol using a clean, dry syringe at this stage, other metal el oxides can also be added using a clean oven dried cannula. Transfer 120 milliliters of anhydrous and heptane to the 250 milliliter flask containing the metal elk IDE solution.

Next, using a clean oven dried cannula, transfer the metal elk oxide alcohol and heptane solution into the reverse micro emulsion under constant stirring over the span of 10 minutes. After four hours, use a clean dry syringe to inject 1.4 milliliters of reagent grade ammonium hydroxide into the solution dropwise. Then using another clean dry syringe, inject 1.2 milliliters of reagent grade tetraethyl ortho silicate dropwise.

After 16.5 hours, remove the rubber stopper and use a clean, dry, graduated cylinder to add 300 milliliters of methanol to the solution under constant stirring. After 10 minutes of stirring, remove the stir bar and allow the solution to settle after one hour, decant the liquid phases into an organic waste container and collect the solid phase silica encapsulated metal oxides in clean 50 milliliter centrifuge tubes before further processing as described in the text protocol to carbonize the silica encapsulated metal oxide powder in a methane hydrogen atmosphere, load the calcium silica encapsulated metal oxide powder into an unglazed Illumina crucible boat and place into a quartz tube furnace. Flush the quartz tube furnace with nitrogen for at least 30 minutes to remove oxygen.

Also, perform a leak check by spraying all joints with soapy water carborize the silica encapsulated metal oxide powder using a two degree Celsius per minute heating rate to 850 degrees Celsius for four hours under 120 standard cubic centimeters per minute, or SCCM of hydrogen and 33 SCCM of methane to form silica encapsulated metal carbides. After four hours, stop the flow of methane and hold the powder at 850 degrees Celsius for one hour in just 120 SECM of hydrogen to scavenge any excess surface carbon for silica dissolution in ammonium by fluoride for acid stable metal carbides. Weigh out 200 milligrams of silica encapsulated metal carbides and put them in a 30 milliliter sealable polypropylene container with a Teflon coated magnetic stir bar.

If it is desired to support the nanoparticles on a high surface area catalyst support such as carbon, black or carbon nanotubes, weigh out the material and add it to the sealable polypropylene container. Next, add 20 milliliters of ultrapure deionized water and begin mixing to form a suspension. Weigh out five grams of ammonium bi fluoride or a VF and then added to the stirring mixture.

Once added seal, the polypropylene container dissolution of A BF in water is endothermic, so the temperature of the solution will drop to ensure complete dissolution of the silica and good dispersion of the nanoparticles on the catalyst support. Stop the reaction after 16 hours by adding reagent grade ammonium hydroxide dropwise to neutralize the A BF solution to a pH of six to seven. Take caution as this reaction is exothermic empty the neutralized mixture into a centrifuge tube and centrifuge at 2056 times G for 10 minutes.

Shown here a representative transmission electron microscopy images of both multiply coated and singly coated early transition metal oxide nanoparticles encapsulated in silica shells. Here, representative transmission electron microscopy images show silica encapsulated metal carbide nanoparticles post carbonization with different metal carbide nanoparticle size distributions. A representative scanning transmission electron microscope image of non centered and metal terminated tungsten carbide nanoparticles dispersed on a carbon black support after the silica shells have been removed is shown here.

After watching this video, you should have a good understanding of how to synthesize non centered metal terminated transition metal carbide and nitrate nanoparticles using a reverse micro motion mediated silicon capsulation approach.