Impact of Inorganic Hydroxides on ZnO Nanoparticle Formation and Morphology

ZnO nanopartides (NPs) were synthesized by a seeded polyol process in di(ethylene glycol) (DEG) using zinc acetate as a precursor in the presence of inorganic hydroxides (NaOH, KOH, LiOH). The precursor was transformed into ZnO in DEG without solid intermediates as shown by Fourier transform infrared spectroscopy. Both Raman and photoluminescence spectroscopies confirmed the presence of defects in the ZnO crystal structure which generated visible light emission when excited with UV light. The molar ratio of seeds/precursor affects ZnO particle growth, and at a high ratio (10/1) growth of ZnO NPs is practically prevented, giving ZnO with a narrow particle size distribution. By decreasing the precursor concentration from 1.0 to 0.01 M, ZnO particle size decreased from 50-200 nm to 20-60 nm; however, the degree of agglomeration was increased. Type of cation plays only a minor role in the ZnO NPs formation. By increasing the hydroxide/precursor molar ratio from 1/1 to 5/1, the ZnO particle size is reduced from 50-200 nm to 20-40 nm. Therefore, the hydroxide/precursor molar ratio has a significant role in the formation of ZnO because it defines the concentration of OH- ions, which is the key factor in this process.