# Magnetic Properties of Nanocomposites
## 4 Ceramic Nanocomposites  
Magnetic metal-ceramic nanocomposites, consisting of a dispersion of transition metal (TM = Fe, Co, Ni) nanoparticles into a ceramic matrix, are being actively studied in view of a variety of applications associated with their porous structure, ranging from environmental issues (e.g., water remediation [45; 46; 47], treatment of pollutants [48; 49; 50; 51; 52]) to catalysis [53; 54; 55; 56] and biomedicine [57; 58]). The magnetic nanocomposites whose magnetic behavior is reviewed in this work were obtained from zeolite precursors by means of a smart and scalable process [14; 59; 60; 61]. Through such a patented process, the final products are obtained by thermal treatment under reducing atmosphere of commercial zeolites (precursors) loaded with TM ions. Treatment temperatures are relatively moderate, as discussed below. During thermal treatment, the starting zeolite structure is almost totally degraded, and the final product of the process is an NC material that contains metallic TM NPs (with sizes ranging from few nanometers or tenths of nanometers) evenly dispersed in a mostly amorphous silica and alumina matrix. This NC is almost completely devoid of the features of the parent zeolite from which it originated; however, it exhibits an irregular residual porosity, associated with the starting zeolite precursor, which can be exploited for a number of applications including water remediation [62] and DNA adsorption and separation [63]. Nanocomposites studied in the literature [14; 59; 60; 61; 62; 63] exhibit magnetic properties [64] owing to the presence therein of Fe\({}^{0}\), Co\({}^{0}\), or Ni\({}^{0}\) ferromagnetic nanoparticles deriving from Fe\({}^{2+}\), Co\({}^{2+}\), or Ni\({}^{2+}\) reduction, respectively. The steps of the preparation process can be summarized as follows: the parent zeolite is first contacted with a solution containing the selected TM ions at a low temperature for a suitable time; the solid is separated from the liquid through filtration and contacted anew with a fresh solution; the above procedure is iterated in order to control the exchange between TM and the cation(s) originally present in the zeolite. Cation-exchange operations are described in the literature [65; 66; 67]. Subsequently, the powders are heated from room temperature up to the target temperature (typically ranging between 600 \({}^{\circ}\)C and 850 \({}^{\circ}\)C) under a reducing atmosphere (created by a flow of a 2% vol. H\({}_{2}\) gaseous mixture with Ar) and are either kept at that temperature for a selected time, or immediately cooled down within the furnace to room temperature. During such thermal treatments under a reducing atmosphere, the following phenomena are known to occur [68; 69]:  
1. Reduction of the TM cation to 0 oxidation number with possible structural damage of the zeolite framework. 2. Migration of the new formed metallic atoms to form metallic clusters located into the cavities of the microporous zeolite structure. 3 Migration of the new formed metallic atoms out of the cavities and channels present in the microporous zeolite structure to form metallic particles located on the outer surface of zeolite grains. 4 Thermal collapse of the microporous zeolite structure. 5 Possible crystallization of ceramic structures. It must be evidenced that it is not said that these phenomena occur in the reported order as they may superimpose each other. As is evident from the short description of the smart and scalable process used, the proposed technique of production of magnetic nanocomposites is very simple and cheap. Despite this, our technique allows strict control of the structure and texture of the nanocomposites by simply operating on a number of key parameters. Such strict control results in a careful tuning of their technological properties. The main key parameters are reported hereafter together with a short explanation of how they work:  
1. **The type of the parent zeolite.