Direct synthesis of ZnO nanoparticles by a solution-free mechanochemical reaction

This paper presents a study on the synthesis and characterization of ZnO nanoparticles by a two-step synthesis procedure. The first step is the solution-free mechanochemical synthesis of ZnC₂O₄2H ₂O nanoparticles by grinding a powder mixture of Zn(CH ₃COO)₂ and H₂C₂O₄2H ₂O at room temperature for a certain time. The second step is the thermal decomposition of ZnC₂O₄2H₂O nanoparticles at 450 °C to form ZnO nanoparticles. The obtained ZnO nanoparticles have been structurally characterized by x-ray diffraction, indicating a wurtzite structure (hexagonal phase, space group P6₃mc) with high crystallinity. The average grain size of the ZnO nanoparticles is in the range of 24-40nm, depending on the mechanical grinding time. The UV-vis diffuse reflectance spectrum of the ZnO nanoparticles indicates a band gap of about 3.3eV with an onset of absorption at about 3.1eV, showing a weak red shift compared to 3.37eV for the bulk ZnO. X-ray photoelectron spectroscopy and Raman spectra showed a nonadsorption on the surface and a very low concentration of oxygen vacancies, respectively, indicating a high quality of the prepared ZnO nanoparticles. The formation process of the ZnC₂O₄2H ₂O nanoparticles bythe solution-free mechanochemical reaction is discussed.