As a result of the continuous development in the field of materials science, our life experience has changed significantly. Nanomaterials, due to their special properties at nano-scale, are increasingly used to improve the performance of various devices. Although we are witnessing to a tremendous development of the material chemical diversity, zinc oxide remains an important multifunctional material. Due to its properties and its low toxicity, ZnO is widely used in different industrial applications such as: phosphor for photonic devices; catalyst for light conversion into useful chemical energy; nanostructured mixed-oxide for sensing of various pollutants or matrix for slow delivery of different drugs and pesticides. Along with the continuous demand for technologically valuable materials, simpler, inexpensive and environmentally friendly synthesis techniques are also needed. In this respect, our research shows that the preparation of pure zinc oxide nanoparticles (ZnO-NP) is possible without any calcination stage using a facile precipitation route at room temperature. By changing different preparative conditions such as, reagents molar ratio and precipitation pH, our method was optimized to obtain pure ZnO-NP with sizes between 5-50 nm. On the other hand, by varying the volume of reactants, the reaction mechanism was significantly changed leading to completely different reaction products.
The changes of the morpho-structural and optical properties of samples were investigated by X-Ray diffraction, infrared spectroscopy, scanning electron microscopy, mineralogical optic microscopy, optical and photoluminescence spectroscopy. Depending on the synthesis conditions, three different crystalline phases were obtained: zinc oxide, zinc hydroxide and layered zinc acetate. Pure zinc oxide phase was obtained at pH values between 7- 8 and fixed reagents molar ratio. A better understanding of the crystalline phases formation was achieved using theoretical calculation (DFT) with a good match of the results with the experimental ones. Spherical nano-particles gathered in aggregates with various sizes were obtained for hexagonal ZnO structures while sheet-like morphology was observed for the layered zinc acetate structures. Luminescent studies showed that the emission of ZnO-NP is in green spectral domain (~548 nm) due to VO → VB transitions while the blue emission of the layered acetate structures is much more complex due to Zni contributions.
Audience Take Away:
- About a facile, low-cost synthesis route for the preparation of ZnO-NP
- Role of pH on the formation of ZnO, Zn(OH)2 and layered ZnAc
- Correlation between molar ratio of reagents and morphology of the nano-particles
- Dependence of the luminescent emission on the lattice and defects type