Abstract
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.
Highlights
For a long time, ZnO nanostructures have been attracting huge interest due to the prominent applications these materials have to offer
The ε-Zn(OH)2 powder was taken to ball milling; generally, 100 mg of powder were placed in an 80 mL ZrO2 cup with steel casting, 1 mm diameter ZrO2 grinding balls were placed in the cup with a powder/ball mass ratio of 1:100, and 5 mL of ethanol was added to the cup and mixed in order to receive a homogeneous mesh of powder–ball mixture
Transmission electron microscopy (TEM) images were taken using a JEOL JEM-1400 microscope operated at 120 kV; samples were prepared by making a dilute suspension of the powders in isopropanol, placing them dropwise on a 400-mesh carbon-coated copper grid, and vacuum drying the grid
Summary
ZnO nanostructures have been attracting huge interest due to the prominent applications these materials have to offer. There are many examples where ball milling was used to execute various chemical reactions [32,33,34] This solvent-free synthetic method could, be used to study the solid-state phase transformation of ε-Zn(OH) into ZnO nanoparticles. In the study of ZnO, the ball milling technique was mainly used either to grind large micron-sized crystals into nanocrystalline material [35,36] or to grind Zn powder into. ZnO [37,38,39]; mechanochemical synthesis of ZnO nanoparticles directly from ε-Zn(OH) appears to be novel We present such a synthesis of ZnO nanocrystals from ε-Zn(OH) micron-sized crystals; a simple ball milling process was used at ambient conditions. The milling process was studied by looking at all the parameters of the materials: chemical structure, optical properties, average crystallite size, average nanocrystal aggregate size, and photocatalytic activity of the powders
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