Abstract:
A method for making the metal oxide includes the following steps: mixing a metal nitrate with a solvent of octadecyl amine, and achieving a mixture; agitating and reacting the mixture at a reaction temperature for a reaction period; cooling the mixture to a cooling temperature, and achieving a deposit; and washing the deposit with an organic solvent, drying the deposit at a drying temperature and achieving a metal oxide nanocrystal. The present method for making a metal oxide nanocrystal is economical and timesaving, and has a low toxicity associated therewith. Thus, the method is suitable for industrial mass production. The metal oxide nanocrystal material made by the present method has a readily controllable size, a narrow size distribution, and good crystallinity.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a method for making nanocrystal and, particularly, to a method for making metal oxide nanocrystal. 
     2. Discussion of Related Art 
     Nanocrystals are defined as nanometer sized, single crystalline fragments of the corresponding bulk crystals. The term “nanometer-sized” is typically used to refer to particles with an approximate size range between about 1 nanometer (nm) to about 1000 nm in diameter. More typically, “nanometer-sized” refers to an approximate size rang between about 1 nm-100 nm in diameter. Metal oxide nanocrystals play important roles in many different branches of science and technology, such as catalyzer material, lithium cell, and electronic and optical devices. 
     Synthesis of high quality metal oxide nanocrystals has a critical role in this very active field. The conventional method includes metal organic salt reduction method, hydro-thermal method, and sol-gel method. However, the metal organic salt reduction method requires the use of metal precursors, which are extremely toxic, expensive, and unstable at room temperature, the hydro-thermal method is restricted by product apparatus, and the sol-gel method is not good at control of the size and the size distribution of nanocrystal. 
     However, there is ongoing demand for a simple, timesaving, low toxic, easy for mass product method for making metal oxide nanocrystal with good size control, narrow size distribution, and good crystallinity. 
     SUMMARY OF THE INVENTION 
     A method for making the metal oxide nanocrystal includes the following steps: mixing a metal nitrate with a solvent of octadecyl amine, and achieving a mixture; agitating and reacting the mixture at a reaction temperature for a reaction period; cooling the mixture to a cooling temperature, and achieving a deposit; and washing the deposit with a organic solvent, drying the deposit at a drying temperature and achieving a metal oxide nanocrystal. 
     Compared with the conventional method, with the inorganic metal salt and octadecyl amine as the raw material, the present method for making metal oxide nanocrystal is economical, timesaving and low toxic, and thus is suitable for industrial mass production. The metal oxide nanocrystal made by the present method has good size control, narrow size distribution and good crystallinity, and therefore has significant advantages for applications in catalysis, ceramics, energy storage, magnetic data storage, sensors, ferrofluids, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present method can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the present method. 
         FIG. 1  is a transmission electron microscope (TEM) image of nickel oxide nanocrystal according to a first embodiment; 
         FIG. 2  is a TEM image of mangano-manganic oxide nanocrystal according to a second embodiment; 
         FIG. 3  is a TEM image of mangano-manganic oxide nanocrystal according to a third embodiment; 
         FIG. 4  is a TEM image of mangano-manganic oxide nanocrystal according to a fourth embodiment; 
         FIG. 5  is a TEM image of cerium dioxide nanocrystal according to a fifth embodiment; 
         FIG. 6  is a TEM image of cerium dioxide nanocrystal according to a sixth embodiment; 
         FIG. 7  is a TEM image of zinc oxide nanocrystal according to a seventh embodiment; 
         FIG. 8  is a TEM image of cobaltous oxide nanocrystal according to an eighth embodiment; 
         FIG. 9  is a TEM image of cobalt oxide nanocrystal according to a ninth embodiment; and 
         FIG. 10  is an X-ray diffraction (XRD) image of metal oxide nanocrystal according to the above embodiments. 
     
    
    
     The exemplifications set out herein illustrate at least one preferred embodiment of the present method, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made, in detail, to the drawings to describe embodiments of the present method. 
     One method for making the metal oxide includes the following steps: mixing 0.1-1 gram (g) of a metal nitrate with about 10 milliliters (ml) of octadecyl amine, and forming a mixture; agitating and reacting the mixture at a temperature of 120-300° C. for a period of 1-60 minutes (m); cooling the mixture to a temperature of 70-90° C., and achieving a deposit; washing the deposit with an organic solvent such as ethanol, drying the deposit at a temperature of 40-80° C., and finally achieving a metal oxide nanocrystal with a diameter of 10-200 nanometers (nm). 
     Another method for making the metal oxide includes the following steps: mixing 0.1-1 g of a metal nitrate with 10 ml octadecyl amine as solvent, and forming a mixture; agitating and reacting the mixture at a temperature of 120-300° C. for a period of 1-5 m, and achieving a reactant; filling the reactant into a reaction chamber, and crystallising the reactant at a temperature of 180-220° C. for a period of 20-24 hours (h); cooling the reactant to a temperature of 70-90° C., and achieving a deposit; washing the deposit with an organic solvent such as ethanol, dry the deposit at a temperature of 40-80° C., and finally achieving a metal oxide nanocrystal with a diameter of 10-200 nm. In the present method, the crystallising step is an alternative step, which can make the morphology of the nanocrystal more perfect. 
     A change to the reaction condition of the present method can influence the morphology and the size of the metal oxide. A concentration of the mixture with the metal nitrate and octadecyl amine has an influence on the morphology of the metal oxide nanocrystal, for example, a grain-shaped metal oxide nanocrystal is easily achieved with a lower concentration, and a stick-shaped metal oxide nanocrystal is easily achieved with a higher concentration. The reaction period and reaction temperature has an influence on the size of the metal oxide nanocrystal, for example, a stick-shaped (i.e., oblong) metal oxide with a smaller diameter is easily achieved with a higher reaction temperature, and a shorter reaction period. 
     The present method is further illustrated by the following examples, which are not to be construed in any way as imposing limitation upon the scope thereof. On the contrary, it is to be clearly understood that resort may be had to various other aspects, embodiments, modifications, and equivalents thereof which, after reading the description herein, may suggest themselves to one of ordinary skill in the art without departing from the spirit of the present method or the scope of the appended claims. 
     EXAMPLE 1 
     One gram of nickel nitrate (Ni(NO 3 ) 2 ·6H 2 O) solid is dissolved in 10 milliliters (ml) octadecyl amine, and a mixture is achieved. The mixture is agitated and reacted at a temperature of 180° C. for 10 m and then is cooled to the temperature of 80° C., and a deposit is achieved. The deposit is washed with ethanol and dried at the temperature of 60° C. Referring to  FIG. 1 , a nickel oxide (NiO) nanocrystal with a diameter of about 20 nm is achieved. 
     EXAMPLE 2 
     0.1 ml of manganous nitrate (Mn(NO 3 ) 2 ) (i.e., manganese (II) nitrate) solution with 50% is mixed in 10 ml octadecyl amine, and a mixture is achieved. The mixture is agitated and reacted at the temperature of 200° C. for 10 m and then is cooled to the temperature of 80° C., and a deposit is achieved. The deposit is washed with ethanol and dried at the temperature of 60° C. Referring to  FIG. 2 , a mangano-manganic oxide (Mn 3 O 4 ) nanocrystal with a diameter of about 10 nm is achieved. 
     EXAMPLE 3 
     1 ml of manganous nitrate (Mn(NO 3 ) 2 ) solution with 50% is mixed in 10 ml octadecyl amine, and a mixture is achieved. The mixture is agitated and reacted at a temperature of 200° C. for 10 m and then is cooled to the temperature of 80° C., and a deposit is achieved. The deposit is washed with ethanol and dried at the temperature of 60° C. Referring to  FIG. 3 , a mangano-manganic oxide (Mn 3 O 4 ) nanocrystal with a diameter of about 6 nm is achieved. 
     EXAMPLE 4 
     3 ml of manganous nitrate (Mn(NO 3 ) 2 ) solution with 50% is mixed in 10 ml octadecyl amine, and a mixture is achieved. The mixture is agitated and reacted at a temperature of 220° C. for 1 m and then is cooled to the temperature of 80° C., and a deposit is achieved. The deposit is washed with ethanol and dried at the temperature of 60° C. Referring to  FIG. 4 , a mangano-manganic oxide (Mn 3 O 4 ) nanocrystal with a length of about 30 nm and a width of about 6 nm is achieved. 
     EXAMPLE 5 
     1 g of cerium nitrate (Ce(NO 3 ) 3 ·6H 2 O) solid is dissolved in 10 milliliters (ml) octadecyl amine, and a mixture is achieved. The mixture is agitated and reacted at a temperature of 250° C. for 8 m and then is cooled to the temperature of 80° C., and a deposit is achieved. The deposit is washed with ethanol and dried at the temperature of 60° C. Referring to  FIG. 5 , a cerium dioxide (CeO 2 ) nanocrystal with a diameter of about 30 nm is achieved. 
     EXAMPLE 6 
     0.2 g of cerium nitrate (Ce(NO 3 ) 3 ·6H 2 O) solid is dissolved in 10 milliliters (ml) octadecyl amine, and a mixture is achieved. The mixture is agitated and reacted at a temperature of 120° C. for 2 m, and a reactant is achieved. The reactant is filled into a reaction chamber and is crystallised therein at a temperature of 200° C. for 24 h. Thereafter, the reactant is cooled to the temperature of 80° C., and a deposit is achieved. The deposit is washed with ethanol and dried at the temperature of 60° C. Referring to  FIG. 6 , a cerium dioxide (CeO 2 ) nanocrystal with a diameter of about 10 nm is achieved. 
     EXAMPLE 7 
     0.2 g of zinc nitrate (Zn(NO 3 ) 2 ·6H 2 O) solid is dissolved in 10 ml octadecyl amine, and a mixture is achieved. The mixture is agitated and reacted at a temperature of 200° C. for 1 h and then is cooled to the temperature of 80° C., and a deposit is achieved. The deposit is washed with ethanol and dried at the temperature of 60° C. Referring to  FIG. 7 , a zinc oxide (ZnO) nanocrystal with a diameter of about 100 nm is achieved. 
     EXAMPLE 8 
     0.5 g of cobalt nitrate (Co(NO 3 ) 2 ·6H 2 O) (i.e., cobalt (II) nitrate) solid is dissolved in 10 ml octadecyl amine, and a mixture is achieved. The mixture is agitated and reacted at a temperature of 250° C. for 20 m and then is cooled to the temperature of 80° C., and a deposit is achieved. The deposit is washed with ethanol and dried at the temperature of 60° C. Referring to  FIG. 8 , a cobaltous oxide (CoO) (i.e., cobalt (II) oxide) nanocrystal with a diameter of about 150 nm is achieved. 
     EXAMPLE 9 
     1 g of cobaltous nitrate (Co(NO 3 ) 3 ·6H 2 O) solid is dissolved in 10 milliliters (ml) octadecyl amine, and a mixture is achieved. The mixture is agitated and reacted at a temperature of 120° C. for 5 m, and a reactant is achieved. The reactant is filled into a reaction chamber and is crystallised therein at a temperature of 200° C. for 24 h. Thereafter, the reactant is cooled to the temperature of 80° C., and a deposit is achieved. The deposit is washed with ethanol and dried at the temperature of 60° C. Referring to  FIG. 9 , a cobalt oxide (CO 3 O 4 ) nanocrystal with a diameter of about 120 nm is achieved. 
     Referring to  FIG. 10 , the metal oxides, according to the above embodiments, have perfect or at least near-perfect morphologies. 
     While certain embodiments have been described and exemplified above, various other embodiments will be apparent to those skilled in the art from the foregoing disclosure. The present invention is not limited to the particular embodiments described and exemplified but is capable of considerable variation and modification without departure from the scope of the appended claims.