Synthesis of ZnO nanoparticles

Chemical synthesis of ZnO nanoparticles has mostly been tried in alcoholic media like ethanol, methanol or propanol. In alcoholic media growth of oxide particles is slow and controllable. Different solutions were prepared by dissolving 0.2725 g of ZnCl2 (10−1 M, 20ml), 0.4 g NaOH (10−1 M, 100 ml) and thioglycerol in methanol. Thioglycerol (TG) solution was slowly added to NaOH solution while it was continuously stirred. The resulting solution was stirred for one hour before adding ZnCl2 solution to it. After three hours of constant stirring a milky white solution was obtained. Size selective precipitation was carried out using acetone as a non-solvent. The precipitate was washed in methanol and methanol was allowed to evaporate at room temperature to obtain ZnO nanoparticles in white powder form. By changing the thioglycerol concentration we could vary the particle size from 2.6 nm to 3.3 nm. Water was added to increase the size further up to 4.0 nm.

To prepare of ZnO NPs, in a typical experiment, a 0.45 M aqueous solution of zinc nitrate (Zn(NO3)2.4H2O) and 0.9 M aqueous solution of sodium hydroxide (NaOH) were prepared in distilled water. Then, the beaker containing NaOH solution was heated at the temperature of about 55 ºC. The Zn(NO3)2 solution was added dropwise (slowly for 40 min) to the above heated solution under high speed stirring. The beaker was sealed at this condition for 2 h. The precipitated ZnO NPs was cleaned with deionized water and ethanol then dried in air atmosphere at about 60 ºC. Morphology of the sample was investigated using SEM and TEM. Parts (a) and (b) of Figure 2 show the typical SEM images of the sample. These images demonstrate that a bulk quantity of flower-like bunches exist. Each bunch is gathered of closely packed nanometer scale rods and forms radiating structures.