Unravelling the role of the exchanged Ni amount in zeolites A and X for their thermal transformation into magnetic metal-ceramic nanocomposites

Magnetic zeolites with a Ni content of 4.80 and 6.20 wt%, were prepared by Ni-exchanging zeolites 4 A and 13×, respectively, and thermally treating the Ni-exchanged zeolites at 735–750 °C, under a reducing atmosphere. This thermal treatment gave rise to the formation of Ni0 nanoparticles dispersed in a ceramic matrix, which partially retained the zeolitic structure (about 50%). The obtained nanocomposites were fully characterized using atomic absorption spectrometry, X-rays powder diffraction (with synchrotron source) followed by Rietveld analysis, High-Resolution Transmission Electron Microscopy, N2 adsorption/desorption at −196 °C and magnetic measurements at both room temperature and low temperature. To highlight the effect of nickel content on the final properties of the nanocomposites, the features of the samples produced in this work were compared with the features of the nanocomposites obtained, in previous works, from the same zeolites loaded with a low (approx. 1%) and a high (approx. 15 wt%) Ni content. The most important result obtained here is that only by entering the intermediate Ni content of this work (4.80–6.20 wt%) it was possible to obtain real magnetic zeolites as the final product of the process. The low Ni content gave rise to a poor magnetic response, whereas the high Ni content resulted in the almost total destruction of the zeolite framework.