Microwave Absorbing Ferrite Thin Films for Microwave Heating of Microstructured Reactors

Abstract

Nanocrystalline Ni0.5Zn0.5Fe2O4 thin films have been synthesized with various grain sizes by sol–gel method on polycrystalline silicon substrates. The morphology and microwave absorption properties of the films calcined in the 673–1073 K range were studied by using XRD, AFM, near–field evanescent microwave microscopy, coplanar waveguide and direct microwave heating measurements. All films were uniform without microcracks. The increase of the calcination temperature from 873 to 1073 K and time from 1 to 3h resulted in an increase of the grain size from 12 to 27 nm. The complex permittivity of the Ni-Zn ferrite films was measured in the frequency range of 2–15 GHz. The heating behavior was studied in a multimode microwave cavity at 2.4 GHz. The highest microwave heating rate in the temperature range of 315–355 K was observed in the film close to the critical grain size of 21 nm in diameter marked by the transition from single– to multi–domain structure of nanocrystals in Ni0.5Zn0.5Fe2O4 film and by a maximum in its coercivity.

Potential of Different Enzyme Immobilization Strategies to Improve Enzyme Performance

“…Recent reports137 have hinted at the possibility of utilizing magnetic nanoparticles in the fields of biomolecule recognition or drug release, and some of the proposed materials have already been tested in microwave heating, obtaining very interesting materials 138. Thus, if we could combine not only the possible advantages of mesoporous mixed‐metal oxide materials with magnetic properties which would enable the user to easily separate the catalyst from the reaction medium or to provide perfectly controlled heating by microwaves, the development of on‐demand enzymatic catalysts for a wide range of reactions would be a palpable reality within reach of the scientific community.…”