Heterogeneous Nucleation of ZnO Using Gelatin as the Organic Matrix

The presence of dissolved gelatin in the sol state during the crystallization of ZnO has a substantial influence on its morphology. The gelatin behaves as a matrix where the ZnO is heterogeneously nucleated. The experimental conditions used during crystallization are very mild consisting of a diluted aqueous buffered solution of zinc nitrate and gelatin at a pH close to neutral and 37 °C. This bio-friendly environment is essential for the integrity of the protein. In the absence of gelatin, nearly spherical ZnO nanoparticles of a diameter of about 20 nm were obtained. By the presence of dissolved gelatin at a concentration of 1.2 mg/mL, the morphology of ZnO is drastically changed to twinned hexagonal plates with (002) faces of about 460 nm diameter and 40 nm thick. Oxide materials with this shape are especially interesting for piezoelectric applications. A mechanism of nucleation and crystal growth is proposed.