Production of mixed metal oxide nanostructured compounds
A method for the rapid and controlled synthesis of mixed metal oxide nanoparticles using relatively low temperature plasma oxidation of liquid droplets of predetermined mixed metal precursors is disclosed. The resulting nanoparticles reflect the metal precursor stoichiometries and the mixed metal oxide's metastable phase can be controlled. The synthesis of mixed transition metal oxide comprising binary metal oxides, ternary mixed metal oxides, quaternary mixed metal oxides and pentanary mixed metal oxides are demonstrated herein.
1. A method for synthesizing mixed metal oxide nanoparticles consisting of:
(a) providing a first metal precursor;
(b) providing at least a second metal precursor;
(c) providing a solvent selected from the group consisting of a water, polar organic solvent, a non-polar organic solvent, an alcohol, a combustive fuel, acetic acid, methanol, ethanol, propanol, butanol, formic acid, formamide, acetone, ethyl acetate, methyl ethyl ketone, acetonitrile, N, N-dimethylformamide, dimethyl sulfoxide, toluene, carbon tetrachloride, benzene, diethyl ether, hexane, tetrahydrofuran, methylene chloride, and combinations thereof;
(d) mixing the first metal precursor, the second metal precursor, and the solvent to form a metal precursor solution;
(e) injecting the metal precursor solution into an atmospheric microwave plasma flame reactor to expose the metal precursor solution to an oxygen plasma flame to form mixed metal oxide alloy nanoparticles, wherein the plasma flame is held at a temperature less than or equal to 550° C. and wherein the metal precursor solution is exposed to the plasma flame for up to about 60 seconds;
(f) cooling the mixed metal oxide alloy nanoparticles; and
(g) collecting the mixed metal oxide alloy nanoparticles in an air filter collection station positioned downstream of the plasma flame,
wherein the first metal precursor and the at least second metal precursor are each selected from the group consisting of nickel, manganese, iron, cobalt, lanthanum, strontium, calcium, rhodium, zirconium, copper, yttrium, and combinations thereof, and
wherein the first metal precursor and the second metal precursor define a stoichiometry which produces specific metastable phases and the resulting mixed metal oxide nanoparticles have a composition that reflect the stoichiometry of the metal precursors which is essentially free from contaminates.
2. The method of claim 1 wherein the oxygen plasma flame has a jet that is oriented vertically in such a way that the tip of the jet is pointing upwards or is oriented vertically in such a way that the tip of the jet is pointing downwards.
3. The method of claim 1 wherein the first metal precursor or the at least second metal precursor or the first metal precursor and the at least second metal precursor are complexed with an alkoxide group, an oxalate group, an acetyl-acetonate group, a benzoate group, a carbonyl group, an acetate group, a water molecule, a nitrate, a sulfate, a chloride, a phosphate, a carbonate, a bromide, an iodide, and combinations thereof.
4. The method of claim 1 wherein the at least a second metal precursor comprises one metal precursor or two metal precursors or three metal precursors or four metal precursors.
5. The method of claim 1 wherein the mixed metal oxide alloy nanoparticles are nanowires, nanorods, nanospheres or a combination thereof.