Incorporation of Pb and Ni into disordered iron oxides structures: a joint neutron total scattering and EXAFS study

Incorporation of Pb and Ni in maghemite (a disordered iron oxide) will be studied on samples obtained by means of two different synthesis routes (sol-gel), both with the aim of removing Pb and Ni from waters polluted with heavy metals. Both the synthesis routes are effective in incorporating the two heavy metals, and in retaining them in the structure after acidic leaching. What is not clear is how (with which mechanism) and where (in which crystallographic site) they are actually incorporated. Previous studies (with X-ray total scattering) did not provide a clear answer to those questions, as X-ray PDF is not chemically sensitive, and the amount of metal was probably not large enough. We are aiming at using neutron total scattering to gain a different scattering contrast with respect to X-rays, and to couple it with EXAFS data, to be collected at Diamond. EXAFS will provide the chemical sensitivity and the local environment for Pb and Ni, while neutron (and X-ray) PDF can be used to understand medium range environment. The crystallisation mechanism from the amorphous xerogels will also be studied, using gel samples heated at different temperatures (chosen from previous TG measurements).