## 3 Results and Discussion
### Impact of Washing Procedure
However, washing procedure MF-S1-W1 is able to eliminate the peak at 1710 cm\({}^{-1}\) assigned to C=O stretching vibrations of non-reacted carboxylate, making it the most effective cleaning method. While the other procedures also demonstrated sufficient cleaning ability to remove impurities and unreacted synthesis compounds, MF-S1-W1 stands out as the superior choice. Figure 6b depicts the FTIR spectra of samples subjected to the W1 washing protocol for durations of 5, 10, and 15 days. As the immersion time increased, the peak at 1710 cm\({}^{-1}\), characteristic of C=O stretching in non-reacted carboxylate groups, progressively diminished, indicating its complete removal after 15 days. While positive effects were observed even after 5 days, the complete disappearance of the peak confirms the optimal performance of this washing method with extended immersion periods in distilled water. This extended immersion not only ensures thorough cleaning but also avoids potential harm caused by shorter washing times, making it a more suitable and effective approach. In order to give further details concerning the structure of the solid sorbents under varying washing treatments, BET surface area and pore volume results are summarized in Table 3.  
Table 3 compares the BET surface area and pore volume of the washing protocols used. The samples washed by washing protocol No. 1 at different immersion times (5 days, 10 days, 15 days) showed a decrease in BET surface area and pore volume compared to the MIL-100(Fe) sample washed by washing protocol No. 2, MF-S1-W2. For instance, regarding the results after 15 days of washing, the nitrogen adsorption isotherm changes considerably relative to the MF-S1-W2 sample, indicating a strong decrease in both the surface area (from 1162 m\({}^{2}\)/g to 871 m\({}^{2}\)/g) and the pore volume (from 0.377 to 0.257 cm\({}^{3}\)/g). Figure 6: FTIR spectra of (**a**) samples before and after washing of MIL-100(Fe) produced by protocol No. 1 and (**b**) MIL-100(Fe) samples washed by washing protocol No. 1. This effect may be attributed to reduced pore accessibility resulting from the prolonged removal of species or unreacted precursors during the reflux treatment of MIL-100(Fe). Simultaneously, as confirmed in [23], changes in the material's optical properties indicate microstructural transformations in MIL-100(Fe), likely due to MOF reconstruction caused by extended immersion in water. Consequently, this treatment yields a surface area that remains below 1000 m\({}^{2}\)/g [23]. Therefore, these observations highlight the MF-S1-W2 washing procedure as the preferred option over MF-S1-W1, as it better preserves the structural integrity and porosity of the material while effectively removing residual species. The BET results indicate that although washing protocol No. 1 is increasing the crystallinity of MIL-100(Fe), it has a negative impact on the surface area and porosity. Washing protocol No. 2 showed BET surface area and pore volume comparable to the unwashed samples. This indicates washing protocol No. 2 maintains the BET surface area and porosity. The obtained surface area is comparable to that of the MIL-100(Fe) values listed in Table 4. For context, additional solid sorbents have been included for comparison. Notably, MIL-100(Fe) is recognized for its high surface area, a characteristic that is generally advantageous for enhancing sorption capacity. Furthermore, to assess the morphological and compositional characteristics of the synthesized adsorbent, the results of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses are presented in Figure 7. In Supplementary Material, a comparison of SEM images for MF-S1-W1 and MF-S1-W2 is reported. Furthermore, dynamic light scattering (DLS) measurements for the MF-S1-W2 sample were also carried out. The MIL-100(Fe) crystals exhibit an irregular morphology, deviating from a uniform, well-defined shape.