## 3 Results and Discussion
### Loading the Anion Exchange Resin with the ReNSs  
After completing the anion exchange resin followed by the reduction of ReO4- ions, the anion exchange resin changed its color from yellow to black. This, parallel with shifts of vibration bands associated with amino functionalities (see the previous section), suggested the stabilization of ReNSs in the polymeric matrix. Simultaneously, the concentration of Re in the resultant Re@NCat was 10.0 \(\pm\) 0.5 mg g\({}^{-1}\), i.e., \(\approx\)1% (\(w/w\)) per catalyst mass (based on the ICP-OES analysis of this material). The morphology of the resultant Re@NCat was firstly investigated using the SEM imaging. The acquired photomicrographs are displayed in Figure 3.  
As can be seen in Figure 3A,B, synthesis of the VBC-co-DVB suspension copolymer was successful. The obtained resin is characterized by the spherical shape morphology, \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Interactions**} & \multicolumn{3}{c}{**Characteristic Band Location/Shift (cm\({}^{-1}\))**} \\ \cline{2-3}  & **A-X Resin** & **A-X Resin + ReO4-** & **Re@NCat** \\ \hline N–H stretching & 3394 & 3369 & 3297 \\ C=N aromatic deformation & 1540 & 1544 & 1546 \\ R–N–CO–N–R stretching & 1648 & 1649 & 1658 \\ N–C–N stretching & 1357 & 1359 & 1349 \\ N+–H aromatic stretching & 2472 & 2454 & - \\ H–bridge & - & 2794 & 2796 \\ \hline \hline \end{tabular} \(\Lambda\):X: anion exchange.  
\end{table} 
Table 1: The location of FT-IR bands found in the anion exchange resin (polymeric base) before and after sorption of ReO4- ions, as well as in the resulting Re@NCat. Figure 3: SEM photomicrographs of the Re@NCat sample. (**A**) The CIM-functionalized anion exchange resin, (**B**) the Re@NCat, (**C**) the surface morphology of the Re@NCat. with the size ranging from 0.2 to 0.4 mm. Since the VBC-co-DVB copolymer was obtained in the presence of toluene (a good solvent for monomers), the synthesized resin was characterized by the expanded gel structure. This was reflected by the apparent smooth surface of the grains (Figure 3A,B) that after magnification (Figure 3C) revealed a complex nature attributed to the swelling of polymeric chains in toluene [33; 34]. Simultaneously, Figure 3C displays the photomicrograph captured using the back scattered electrons (BSE) technique that revealed a clear phase contrast between the polymeric matrix (dark area) and ReNSs (bright spots). This indicated that ReNSs were indeed incorporated into the structure of the anion exchange resin. In parallel, adsorption-driven synthesis provided a proper dispersion of ReNSs. However, due to the apparent size of ReNSs, the SEM analysis was not sufficient to investigate them. Therefore, to evaluate the morphology of the resultant ReNSs, the Re@NCat sample was cut into ultra-thin slices and was subjected to the TEM analysis. In reference to TEM photomicrographs (Figure 4A,C), it appeared that the applied synthetic route resulted in a successful fabrication of spherical in shape ReNSs and their loading in the polymeric matrix. Generally, diameters of synthesized ReNSs spanned the range of 1-15 nm. However, larger structures (10-15 nm in size) were also noted near the surface of the Re@NCat (Figure 4A), while the inner part of the polymer's grain contained much smaller particles (1-3 nm) or their agglomerates (\(\approx\)5 nm) (Figure 4C). This effect was predicted as all previous observations proved that the average size of NSs obtained using this method strongly depends on the concentration gradient at the solid-liquid interface [15; 29]. Nevertheless, the average size of ReNSs found inside the polymer's grain was 3.45 \(\pm\) 1.85 nm. Figure 4: (**A,C**) TEM photomicrographs supplied with (**B**) SAED and (**D**) EDX spectra of the Re@NCat sample. The inset in panel D is a magnification of the EDX spectrum recorded in the range of 2–10 keV. The EDX spectrum (see Figure 4D) clearly showed that investigated NPs were based on Re.