In-situ Measurements on suspended Nanoparticles with X-rays, Visible Laser Light and Infra-red Light

One of the aims of the Institute of Radiochemistry, Forschungszentrum Dresden-Rossendorf, is to investigate the transport of environmental contaminants as colloids (nanoparticles). The methods established in the institute that refer to colloid research are:

Characterization of colloids: Photon correlation spectroscopy (PCS), laser-induced breakdown detection (LIBD), microfiltration/ultrafiltration, ultracentrifugation, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
Studying colloid composition/mineralogy and in-situ binding states of contaminants on colloids: X-ray absorption spectroscopy (XAS) with synchrotron radiation (Rossendorf Beamline at the ESRF, Grenoble), attenuated total reflection (ATR) FTIR and time-resolved laser fluorescence spectroscopy TRLFS.
Noninvasive methods (i.e. in-situ measurements) are normally preferred to invasive methods. Such non-invasive methods often rely on high energy radiation. Two methods of colloid characterization, PCS and LIBD, and two methods of binding state in-vestigation, EXAFS and ATR-FTIR, are presented in greater detail.
We used PCS to investigate extremely small natural nanoparticles of high concentration as they occur in acid rock drainage solutions. It was shown that the ultrafine nanoparticles are masked by tiny traces of larger particles that dominate light scattering. They can be unmasked by separation steps which makes the small particles detectable. Colloids of extreme low concentration can be detected by LIBD. LIBD on four commercial mineral waters serves as an example.. In the third example the binding state of arsenate onto the small nanoparticles of the acid rock drainage solution mentioned above was studied by EXAFS. It is demonstrated that the arsenate is initially bound as a bidentate binuclear inner-sphere surface complex to the iron-rich ultrafine nanoparticles of the solution. However, the gradual transformation of the colloidal material to a more aggregated precipitate (within months) results in the incorporation of the arsenate into the interior of the Fe hydroxy sulphate crystal structures. Finally, an example is given where the adsorption of uranium(VI) on ferrihydrite colloids in near-neutral mine water in the presence of carbonate, i.e. the formation of uranyl-ferrihydrite and uranyl-carbonate-ferrihydrite surface complexes, was tested by ATR-FTIR.