## 3 Results and Discussion
### Characterization
#### 3.1.2 SEM-EDX Analysis  
A crucial factor in the analysis of the prepared TMC material is the composition and elemental distribution within the sample matrix. Elemental analysis via EDX mapping estimation of the composition of a sample spot, but also to visualize the elemental distribution (homogeneous vs. heterogeneous) across the sample region. Several regions of the sample (\(n=5\)) were analyzed, as shown in Figures S16-S49 in the Supplementary Materials, where selected sample images are presented. However, based on the instrumental limitations, the quantification of N is semi-quantitative due to the significant overlap between the N and C K\(\alpha\) line, especially at low N concentrations. In contrast, the mapped images for the elemental distribution may show nitrogen. The average composition for each sample type is listed in Table 2.  
The elemental quantification and mapping were focused on the metal centers, hence, small deviations in the determined wt.% due to K\(\alpha\) overlap of C and N may be less significant compared to samples without metal content. The average composition (wt.%) detected via EDX mapping is broadly corroborated by X-ray photoelectron spectroscopy (XPS) performed in an earlier study for various composites [17]: Al-TMC with ca. 31 wt.% Al and 52 wt.% O; Cu-TMC with 35 wt.% Cu and 42 wt.% O; Fe-TMC with 48 wt.% Fe and 33 wt.% O. Therein, Al-TMC was found to have 1.75 wt.% N, while Fe-TMC contained ca. 1.44 wt.% N. The high N content in Cu-TMC with 4.63 wt.% agrees with the EDX quantification. (cf. Table S3 in the Supplementary Materials of [17]). Specific to Al-TMC is the mostly homogeneous composition across multiple sampling spots with an average of 59 wt.% oxygen and 25 wt.% aluminum. This trend is congruent with most of the Al-O-species coordinated onto the biopolymer framework, and also indicates considerable metal content in the TMCs. Cu-TMC shows a similar trend, except for increased N content  
Figure 1: IR spectra of Alginate, Chitosan, and TMC materials before adsorption. due to the formation of Cu\({}_{2}\)(OH)\({}_{3}\)(NO\({}_{3}\)) salts. Fe-TMC, on the other hand, shows mostly heterogeneous composition within the composite, with areas rich or deficient in Fe. It can therefore be estimated that at least 2-5 wt.% N must be present for detection and the appropriate wt.% needs to be removed from C for a more accurate elemental quantification. The use of SEM-EDX results provides additional information like elemental distribution and surface imaging. For Al-TMC, one exemplary spot is shown in Figure 2.  
Further to the inhomogeneity of the Al distribution, which aligns with the O distribution that is indicative of Al-O coordination, a mainly smooth surface of the particles was detected. The low N content may indicate that the metal oxide particles are mostly on the surface of the composite. In contrast, Cu-TMC observes a more particle-laden, rough surface morphology, in addition to homogeneous Cu elemental distribution (cf. Figure 3). \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Al-TMC** & **Cu-TMC** & **Fe-TMC** \\  & **(wt.\%)** & **(wt.\%)** & **(wt.\%) * \\ \hline O & 59 \(\pm\) 3 & 40 \(\pm\) 3 & 35 \(\pm\) 15 \\ Al & 25 \(\pm\) 4 & N/A & N/A \\ C & 15 \(\pm\) 2 & 12 \(\pm\) 1 & 13 \(\pm\) 3 \\ N & 0 ** & 5 \(\pm\) 1 ** & 1 \(\pm\) 2 ** \\ Cu & N/A & 42 \(\pm\) 4 & N/A \\ Fe & N/A & N/A & 48 \(\pm\) 20 \\ Na & 0 & 0 & 2 \(\pm\) 3 \\ \hline \hline \end{tabular} Note: * Large standard deviation resulted from spots with vastly different elemental composition (e.g., Spot 1 with 76 wt.% Fe and 13 wt.% O vs. Spot 5 with 25 wt.% Fe and 49 wt.% O); N/A: Not applicable. ** Inaccurate at low concentrations due to overlap with C.  
\end{table} 
Table 2: The average composition of the three prepared TMCs.