Nano-sized particles, processes of making, compositions and uses thereof

Abstract

The present invention describes methods for preparing high quality nanoparticles, i.e., metal oxide based nanoparticles of uniform size and monodispersity. The nanoparticles advantageously comprise organic alkyl chain capping groups and are stable in air and in nonpolar solvents. The methods of the invention provide a simple and reproducible procedure for forming transition metal oxide nanocrystals, with yields over 80%. The highly crystalline and monodisperse nanocrystals are obtained directly without further size selection; particle size can be easily and fractionally increased by the methods. The resulting nanoparticles can exhibit magnetic and/or optical properties. These properties result from the methods used to prepare them. Also advantageously, the nanoparticles of this invention are well suited for use in a variety of industrial applications, including cosmetic and pharmaceutical formulations and compositions.

1 . A method of preparing zinc oxide nanoparticles, comprising:
 (a) mixing a zinc acetate precursor with an organic solvent comprising at least one organic stabilizing ligand to form a reaction mixture;   (b) subjecting the mixture of step (a) to a temperature of from about 300° C. to about 400° C. for a time sufficient to allow formation of zinc oxide nanoparticles and decomposition of the zinc acetate; and   (c) extracting the zinc oxide nanoparticles of step (b) into a hydrocarbon solvent at a temperature lower than the temperature of step (b) by precipitation with a flocculating agent.   
     
     
         2 . The method according to  claim 1 , wherein the temperature of step (b) is about 320° C. to about 400° C. 
     
     
         3 . The method according to  claim 1 , wherein the temperature of step (b) is about 360° C. 
     
     
         4 . The method according to  claim 1 , wherein the organic solvent of step (a) comprises a trialkylamine. 
     
     
         5 . The method according to  claim 4 , wherein the trialkylamine is trioctylamine. 
     
     
         6 . The method according to  claim 1 , wherein the organic stabilizing ligand is selected from the group consisting of sulfonic acid, sulfinic acid, phosphonic acid, phosphoric acid, a carboxylic acid, and a thiol. 
     
     
         7 . The method according to  claim 1 , wherein the organic stabilizing ligand is oleic acid. 
     
     
         8 . The method according to  claim 1 , wherein the zinc acetate precursor is anhydrous. 
     
     
         9 . The method according to  claim 1 , wherein, in step (a), the zinc acetate precursor is mixed with the organic solvent at room temperature to form the reaction mixture. 
     
     
         10 . The method according to  claim 1 , wherein, in step (b), the mixture is brought to said temperature in a time period of from about 10 minutes to about 30 minutes. 
     
     
         11 . The method according to  claim 10 , wherein, in step (b), the mixture is brought to said temperature in a time period of from about 10 minutes to about 15 minutes. 
     
     
         12 . The method according to  claim 1 , wherein the mixture of step (b) is maintained at said temperature for a time period of from about 45 minutes to about 1 hour to allow the formation of the zinc oxide nanoparticles. 
     
     
         13 . The method according to  claim 1 , wherein in step (c) the hydrocarbon solvent comprises pentane, hexane, heptane, octane, or dodecane. 
     
     
         14 . The method according to  claim 1 , wherein in step (c) the flocculating agent comprises a polar organic solvent. 
     
     
         15 . The method according to  claim 14 , wherein the polar organic solvent comprises methanol, ethanol, propanol, or butanol. 
     
     
         16 . The method according to  claim 1 , wherein, in step (c), the zinc oxide nanoparticles are extracted into an alkane solvent by precipitation with an alcohol or ketone. 
     
     
         17 . The method according to  claim 16 , wherein the zinc oxide nanoparticles are extracted into hexane solvent by precipitation with ethanol, followed by centrifugation and redispersion in hydrocarbon solvent. 
     
     
         18 . The method according to  claim 1 , wherein the extracted zinc oxide nanoparticles of step (c) are stable, monodisperse, and have uniform size. 
     
     
         19 . The method according to  claim 1 , wherein the zinc oxide nanoparticles have a size of about 2 nm to about 20 nm. 
     
     
         20 . The method according to  claim 1 , wherein, following step (b), the organic solvent is subjected to a second temperature of at least about 100° C. for a time sufficient to obtain zinc oxide nanoparticles having a specific diameter of about 10 nm to about 40 nm. 
     
     
         21 . The method according to  claim 1 , further comprising the step of subjecting the extracted zinc oxide nanoparticles obtained in step (c) to oxidation to obtain further oxidized zinc oxide nanoparticles. 
     
     
         22 . The method according to  claim 1 , wherein the extracted zinc oxide nanoparticles comprise nanorods, nanotriangles, or nanospheres. 
     
     
         23 . The zinc oxide nanoparticles according to  claim 22 . 
     
     
         24 . The method according to  claim 1 , wherein the nanoparticles comprise nanospheres, wherein the molar ratio of the zinc acetate precursor to the at least one organic stabilizing ligand in step (a) is greater than about 1:3. 
     
     
         25 . The method according to  claim 24 , wherein the organic solvent of step (a) comprises an alcohol or hydrocarbon solvent. 
     
     
         26 . The method according to  claim 25 , wherein the alcohol is 1-hexadecanol, or wherein the hydrocarbon solvent is 1-octadecene. 
     
     
         27 . A method of preparing zinc oxide nanorods, comprising:
 (a) mixing a zinc acetate precursor with an organic solvent comprising a carboxylic acid to form a reaction mixture, wherein the molar ratio of the zinc acetate precursor to the carboxylic acid in step (a) is less than about 1:2;   (b) subjecting the mixture of step (a) to a temperature of from about 300° C. to about 400° C. for a time sufficient to allow formation of zinc oxide nanorods and decomposition of the zinc acetate; and   (c) extracting the zinc oxide nanorods of step (b) into a hydrocarbon solvent at a temperature lower than the temperature of step (b) by precipitation with a flocculating agent.   
     
     
         28 . The method according to  claim 27 , wherein the carboxylic acid is oleic acid. 
     
     
         29 . The method according to  claim 27 , wherein the organic solvent of step (a) comprises a trialkylamine. 
     
     
         30 . The method according to  claim 29 , wherein the trialkylamine is trioctylamine. 
     
     
         31 . The method according to  claim 27 , wherein the nanorods have diameters of about 2 nm to about 10 nm. 
     
     
         32 . The method according to  claim 27 , wherein the nanorods have aspect ratios of about 1:5 to about 1:40. 
     
     
         33 . The zinc oxide nanorods according to  claim 27 .