Role of Surfaces in the Magnetic and Ozone Gas-Sensing Properties of ZnFe₂O₄ Nanoparticles: Theoretical and Experimental Insights

Abstract

The magnetic properties and ozone (O₃) gas-sensing activity of zinc ferrite (ZnFe₂O₄) nanoparticles (NPs) were discussed by the combination of the results acquired by experimental procedures and density functional theory simulations. The ZnFe₂O₄ NPs were synthesized via the microwave-assisted hydrothermal method by varying the reaction time in order to obtain ZnFe₂O₄ NPs with different exposed surfaces and evaluate the influence on its properties. Regardless of the reaction time employed in the synthesis, the zero-field-cooled and field-cooled magnetization measurements showed superparamagnetic ZnFe₂O₄ NPs with an average blocking temperature of 12 K. The (100), (110), (111), and (311) surfaces were computationally modeled, displaying the different undercoordinated surfaces. The good sensing activity of ZnFe₂O₄ NPs was discussed in relation to the presence of the (110) surface, which exhibited low (-0.69 eV) adsorption enthalpy, promoting reversibility and preventing the saturation of the sensor surface. Finally, the O₃ gas-sensing mechanism could be explained based on the conduction changes of the ZnFe₂O₄ surface and the increase in the height of the electron-depletion layer upon exposure toward the target gas. The results obtained allowed us to propose a mechanism for understanding the relationship between the morphological changes and the magnetic and O₃ gas-sensing properties of ZnFe₂O₄ NPs.