Effects of the mechanical activation of zinc carbonate hydroxide on the formation and properties of zinc oxides

The nanocrystalline ZnO powders were obtained by mechanochemical treatment of zinc carbonate hydroxide. The mechanical activation was carried out in a planetary ball mill (Fritsch–Premium line–Pulversette No 7) by varying of the milling speed. The phase and structural transformation was investigated by X-ray diffraction (XRD) and infrared spectroscopy (IR). The morphology of the obtained ZnO powders was characterized by scanning electron microscopy (SEM). The crystallite size of the samples calculated from XRD and the SEM observation were in the range from 8 to 50 nm. The optical properties were investigated by UV–vis spectroscopy. The photocatalytic activity was studied with respect to the photodegradation of Malachite green (MG) under UV-light irradiation. The milling speed of 500 rpm led to full amorphization of the initial zinc carbonate hydroxide. After heat-treatment at 400 °C of X-ray amorphous sample single ZnO powder (20 nm) was obtained. The direct synthesis of ZnO nanoparticles (8 nm) was achieved at milling speed of 1000 rpm for short time (90 min). The mechanochemically synthesized ZnO powders possess good optical and photocatalytic properties. The additional heat-treatment improved the photocatalytic activity and the transparency of ZnO powders in the visible spectral range.

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► The nanocrystalline ZnO powders were obtained by mechanochemical treatment of zinc carbonate hydroxide at different milling speed.
► The milling speed of 1000 rpm led to direct synthesis of ZnO nanopowders (8 nm).
► The milling speed of 500 rpm induced the amorphization of zinc carbonate hydroxide.
► Heat-treatment at 400 °C of the amorphous sample produced the formation of ZnO nanoparticles (20 nm).
► Heat-treatment of mechanochemically treated samples improved the optical and photocatalytic properties of ZnO powders.