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 S10, the SEM image of AO-Fc after uranium extraction (Figure S10a) and uranium elution (Figure S10b) 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 before uranium adsorption of adsorbent (AO-Fc) (Figure 8). 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 confirming the presence of uranium on AO-Fc (Figure 8a). As shown in Figure S11a, 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 from Figure S11b, 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. Further, the uranium-loaded adsorbent was analyzed by FTIR and the results were compared (Figure 8b), the uranium-loaded spectra showed 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-Fc54,55.