Add time:07/29/2019         Source:sciencedirect.com

Out of many functionalities of zinc oxide, its magnetic properties are only sparsely explored. Herein we report on the evolution of ferromagnetism of undoped ZnO nanoparticles, depending on the zinc source used for the synthesis. We started from mechanochemical synthesis of phase pure nanocrystalline hydrozincite, Zn5(CO3)2(OH)6 (ZnHC) by milling a mixture comprising either Zn(NO3)2·6H2O or ZnCl2, and Na2CO3 for 10 min. Zinc oxide nanoparticles with specific surface over 70 m2/g were obtained by subsequent heating of ZnHC up to 300 °C. Ferromagnetism was observed only for ZnO nanoparticles derived from Zn(NO3)2, while those from ZnCl2 were conventionally diamagnetic. X-ray photoelectron, Raman, as well as electron paramagnetic resonance spectrograms consistently showed significantly higher concentration of oxygen vacancies in the Zn(NO3)2-derived ZnO. We also referred to the difference in the charging states of oxygen vacancies by detailed observation of EPR spectra. Since the formation of ZnO from ZnHC is topotactic, the difference in the lattice imperfection was discussed in terms of the hydration energy of the coexisting NO3− or Cl− anion. The present simple mechanochemical – thermal procedure offers a facile method for obtaining well-dispersed active ZnO nanoparticles. More importantly, the new synthesis method offers possibility of controlling their magnetic properties by choosing anionic species of the starting zinc source.

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