Chemical Synthesis of ZnO Nanocrystals

Nano-crystalline ZnO particles were synthesized using alcoholic solutions of zinc acetate dihydrate through a colloidal process. Five types of capping agents: 3-aminopropyl trimethoxysilane (Am), tetraethyl orthosilicate (TEOS), mercaptosuccinic acid (Ms), 3-mercaptopropyl trimethoxysilane (Mp) and polyvinylpyrrolidone (Pv) were added at the first ZnO precipitation time (1
^st
PPT) to limit the particle growth. The first three capping agents effectively capped the ZnO nanoparticles and limited the growth of the particles, while the last two capping agents caused agglomeration or larger clusters in the solutions. Particles synthesized were in the size range of 10nm to 30nm after capping, and grew to 60nm and 100nm in 3 weeks and 6 weeks respectively during storage at ambient conditions. Refluxing time was found to only affect the 1
^st
PPT time. Washing by methanol and water and slow drying are very important in converting Zn(OH)
2
into ZnO. XRD analyses revealed that single crystal ZnO nanoparticles were achieved with crystal size 53-55nm. Photoluminescence (PL) spectra showed high intensity in UV emission and very low intensity in the visible emission, which indicates a good surface morphology of the ZnO nanoparticles with little surface defect. Optical absorption spectra showed absorption at wavelength of 380nm from the uncapped ZnO, corresponding to the band-gap of bulk ZnO. While capped ZnO absorbed at shorter wavelength (350nm) indicating a much smaller particle size.