Researchers at IMEM-CNR have created a composite nanostructure made of zinc oxide (ZnO) tetrapod-shaped crystals and nanometric magnetite (Fe3O4) nanoparticles with super-paramagnetic properties, i.e. thanks to their small size they behaves like a ferromagnetic material only when an external magnetic field is applied. In the obtained composite nano-material several useful properties are contemporary present and combined together in a single multifunctional structure.
By means of the proper synthetic procedure such this two kind of nanostructures are combined together in a stable form, preserving the properties of both the original materials, without any substantial cross-interference among them.
This means that the obtained ZnO-Fe3O4 nanocomposite retains the superparamagnetic properties together with an unchanged ZnO strong UV emission and free active surface, as well as its semiconducting or piezoelectric properties. Therefore, it can be potentially employed in different technological fields, such as photocatalytic systems, gas-sensing devices, water splitting and bio-medical applications (i.e. drug delivery, photodynamic therapy).
Among these, filter-free photocatalysis application for the degradation of pollutant species has been evaluated as a case study. On one hand, indeed, the degradation rate of two organic dyes by means of ZnO-Fe3O4 nanostructures has been measured and it outperformed that of bare ZnO tetrapods. On the other hand, superparamagnetic properties permit an easy on-demand recovery from the treated water by magnetic field, without the need for further downstream filtering processes. Filtering is indeed a slow process in this kind of application because on one hand very small nanostructures are generally used to maximize the active surface availability, while on the other hand their small size makes their filtering difficult.
Although this kind of application is just an example of the potentialities of such a multifunctional composite nanostructure, a short video has been made to highlight these concepts and it can be seen at:
https://www.youtube.com/watch?v=kcY1564woLo
Other kinds of application may take advantage of the multiple functional properties of these two materials. For example, as a further perspective, the combination of magnetic and piezoelectric properties in one single nanomaterial paves the way to the realization of new-concept systems with piezo-magnetic transducing functionalities.
M. Villani, T. Rimoldi, D. Calestani, L. Lazzarini, V. Chiesi, F. Casoli, F. Albertini and A. Zappettini, "Composite multifunctional nanostructures based on ZnO tetrapods and superparamagnetic Fe3O4 nanoparticles", Nanotechnology 24 (2013) 135601 (doi:10.1088/0957-4484/24/13/135601).
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