A detailed investigation is presented for the solvent-free mechanochemical synthesis of zinc oxide nanoparticles from ε-Zn(OH)₂ crystals by high-energy ball milling. Only a few works have ever explored the dry synthetic route from ε-Zn(OH)₂ to ZnO. The milling process of ε-Zn(OH)₂ was done in ambient conditions with a 1:100 powder/ball mass ratio, and it produced uniform ZnO nanoparticles with sizes of 10–30 nm, based on the milling duration. The process was carefully monitored and the effect of the milling duration on the powder composition, nanoparticle size and strain, optical properties, aggregate size, and material activity was examined using XRD, TEM, DLS, UV-Vis, and FTIR. The mechanism for the transformation of ε-Zn(OH)₂ to ZnO was studied by TGA and XPS analysis. The study gave proof for a reaction mechanism starting with a phase transition of crystalline ε-Zn(OH)₂ to amorphous Zn(OH)₂, followed by decomposition to ZnO and water. To the best of our knowledge, this mechanochemical approach for synthesizing ZnO from ε-Zn(OH)₂ is completely novel. ε-Zn(OH)₂ crystals are very easy to obtain, and the milling process is done in ambient conditions; therefore, this work provides a simple, cheap, and solvent-free way to produce ZnO nanoparticles in dry conditions. We believe that this study could help to shed some light on the solvent-free transition from ε-Zn(OH)₂ to ZnO and that it could offer a new synthetic route for synthesizing ZnO nanoparticles.

Hierarchical organic structures have gained vast attention in the past decade owing to their great potential in chemical and medical applications in industries such as the food and pharmaceutical industries. In this paper, the crystallization of L-glu hierarchical spheres using inorganic ions, namely calcium, barium and strontium cations, is described. The anti-solvent precipitation method is used for the spherical crystallization. The L-glu microspheres are characterized using various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photo-electron microscopy (XPS) and polarized microscopy (POM). It is shown that without additives, L-glu crystallizes as flower-like structures, very different from the hierarchical spheres crystallized with the charged additives. Based on our results, we suggest a mechanism for the hierarchical sphere formation based on the crystallization and self-assembly of L-glu in emulsion droplets using charged additives.