Aluminum Nanoparticle Synthesis by Reduction of Halides with Na/K
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Aluminum Nanoparticle Synthesis by Reduction of Halides with Na/K Andrew P Purdy, Joel B Miller, Rhonda M Stroud, and Katherine A Pettigrew Chemistry Division, Code 6123, Naval Research Laboratory, 4555 Overlook Av, SE, Washington, DC, 20375
Abstract. Solutions or mixtures of aluminum halides AlX3 (X = Cl, Br, I) or aluminum halide alkoxide (ROAlX2; R= i-Pr, X = Cl, Br) are prepared in toluene, or pentamethyldiethylenetriamine (PMDETA) and treated with a slight excess of 50:50 (wt.%) sodium potassium alloy (Na/K). Upon agitation, the reaction takes place slowly. The reaction appears to be limited by the deposition of insoluble products on the surface of the Na/K since sonication in an ordinary ultrasonic cleaner is necessary to bring the reaction to completion in several hours. Aluminum nanoparticles (NPs) and Na and K halides are formed, and soluble Al compounds, are also formed in some cases. Lithium powder is used instead of Na/K to reduce Al(N(SiMe3)2)3 to Al NPs. In an effort to passivate the surface of the Al particles to oxidation or hydrolysis, various agents are added either during the reaction or afterward. The products are characterized by SEM, XRD, NMR, and TEM, and their stability to water and air is evaluated. Introduction. Nanoparticles of reactive metals such as aluminum present a challenge, both in synthesis, and in protection from oxidation by air and water.1 Aluminum nanoparticles (NPs) have been prepared by evaporation of electrically heated wires,2 catalytic decomposition of AlH3·NR3 adducts, and other methods.3 Passivation of Al NPs has been attempted by polymers, carbon coatings, nitro compounds, fatty acids, and by monolayers of long chain perfluorocarboxylic acids.4 However, the coating methods vary in effectiveness, and in some cases the coatings take a considerable fraction of mass. Nanoparticles of other reactive metals, most notably magnesium, have been prepared for decades by alkali metal reduction of magnesium halides, a material that is known as Reike magnesium.5 A report exists of reactive aluminum nanoparticles made by Rieke methods in xylene or THF.6 In this work, we explored the reduction of aluminum compounds with sodium-potassium alloy (Na/K) or lithium to Al NPs, and both co-reduction with fluorinated organics as well as treatment with glycerol as passivation agents. Experimental. General comments. All air sensitive reagents are handled in the Dri-Lab. All aluminum halides are anhydrous. Aluminum chloride is purified by sublimation from a mixture of AlCl3 with ~10% NaCl and Al flakes. AlBr3, Al(OCHMe2)3, and Al(OC4H9)3 (Aldrich) are used as received and AlI3 (Strem) is sublimed before use. Al(N(SiMe3)2)3 is made by literature methods.8 C6F6 is dried over molecular sieves and glycerol is purified by vacuum distillation. Toluene, ethylenediamine, and pentamethyldiethylenetriamine are distilled from sodium or sodiumbenzophenone ketyl and handled in a Vacuum Atmospheres Dri-Lab. Sodium-
potassium alloy is made in the Dri-Lab by combining an equal mass of each metal
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