TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The step (b) is carried out at 50 - 400 (preferably 200 - 400, particularly 250 - 400) degreesC. The mixture is brought to 100 degreesC in 10 - 30 (preferably 10 - 15) minutes and maintained for 45 minutes - 1 hour to form the nanoparticles. The nanoparticles are extracted into hexane solvent by precipitation with ethanol, followed by centrifugation and redispersion in hydrocarbon solvent. After step (b), the organic solvent is subjected to a second temperature of at least about 100 degreesC to obtain nanocrystals of larger specific diameter. The method further involves subjecting the extracted metal oxide nanoparticles obtained in to oxidation to obtain further oxidized metal oxide nanoparticles. The oxidation involves exposing the metal oxide nanoparticles to air or trimethylamine-N-oxide to obtain the further oxidized metal oxide nanoparticles. For preparing iron oxide nanoparticles the mixture is heated to 200 - 260 (preferably 250) degreesC. For preparing manganese oxide nanoparticles the mixture is heated to 300 - 350 (preferably 320) degreesC. The manganese oxide nanoparticles are further oxidized by exposing to air or trimethylamine-N-oxide to obtain oxidized Mn3O4 nanoparticles. For preparing zinc oxide nanoparticles the mixture is heated to 300 - 400 (preferably 360) degreesC.Preferred Components: The organic solvent comprises an alkylamine or an ether (preferably trialkylamine of formula (CH3(CH2)n)3N), trialkylphosphine. The organic stabilizing ligand is a long chain alkyl molecule with at least one carboxylic acid functional group(s) of formula CxHy(CO2H)z selected from sulfonic acid, sulfinic acid, phosphonic acid, phosphoric acid, carboxylic acid and thiol. The organic stabilizing ligand is a carboxylic acid (preferably oleic acid). The metal acetate is selected from zinc acetate, iron acetate, manganese acetate, cobalt acetate, ruthenium acetate, copper acetate, scandium acetate, titanium acetate, vanadium acetate, chromium acetate, chromium acetate dimer, molybdenum acetate, molybdenum acetate dimer, yttrium acetate, zirconium acetate, hafnium acetate and nickel acetate. The hydrocarbon solvent is selected from pentane, hexane, heptane, octane, or dodecane. The flocculating agent comprises a polar organic solvent (preferably alcohol or ketone, particularly methanol, ethanol, propanol or butanol). The extracted nanoparticles comprise an organic outside coating. The nanoparticles formed at the second temperature comprise a specific diameter of from about 10 - 40 nm. The Mn3O4 nanoparticles comprise a crystal size of 6 - 20 (preferably 6 - 7) nm. The zinc oxide nanoparticles have size of 2 - 20 (preferably 12 - 20)nm. The zinc oxide nanoparticles comprise nanorods.n=4 - 12 (preferably 7);x=6 - 30;y=8 - 59;z=1 - 3. EXAMPLE - Dry manganese acetate (4 mmol) was added to a mixture of trioctylamine (15 ml) and oleic acid (3 g) at room temperature. The reaction mixture was heated to 320degreesC over 10 - 15 minutes. The solution was maintained at 320degreesC for 1 hour under nitrogen flow. The obtained nanocrystals were cooled to room temperature and extracted into hexane to obtain manganese oxide.