3.4 Adsorbent stability and interaction with uranyl ions
The morphology of the adsorbent after uranium extraction/elution was analyzed by using SEM analysis. From Figure 10, we see the SEM images after uranium extraction (Figure 10a) and uranium elution (Figure 10b) confirmed that seawater exposed AO-Fc maintained the integrity of structure after reuse of several cycles for a long time of seawater exposure. The detailed chemical composition of the uranium-loaded adsorbent (AO-Fc-U) adsorbent was analyzed by XPS and FTIR analysis and the results were compared with the adsorbent before uranium adsorption (AO-Fc) (Figure 11). The uranium-loaded adsorbent (AO-Fc-U) showed two peaks at 390.9 eV and 380.1 eV assigned to U 4f5/2 and U 4f7/2 confirmed the presence of uranium on AO-Fc (Figure 11a). As shown in Figure 11b, two types of Nitrogen peaks were observed at 400.05 eV and 398.4 eV assigned to N-H and C=N respectively. And also in accordance with Figure 11c, the binding energy of both N-H and C=N shifted to higher binding energy at 400.9 eV and 399.1 eV. The positive shift in N-H and C=N groups confined the coordination of nitrogen and uranium ions. To further analysis the uranium-loaded adsorbent was analyzed by FTIR. Compared with the results (Figure 11d), the uranium loaded spectra showed the shifts at various peaks or increase peak intensity. What is more, in the FTIR spectrum of AO-Fc, two new peaks were observed at 937 cm-1 and 1161 cm-1 confirming the presence of uranium on AO-Fc50,51.