## 3 Results and Discussion
### Impact of Hydrothermal Synthesis Under Different Conditions
Moreover, the carefully controlled Fe\({}^{3+}\)/H3 BTC ratio employed in this synthesis effectively postpones the formation of iron oxide precipitates during the reaction process. This delay in precipitation enables the production of a substantially pure MIL-100(Fe) material without the interference of iron oxide impurities after a synthesis duration of 12 h.  
This statement directly emphasizes the impact of the lower water solvent concentration and iron ions on the purity of the resulting MIL-100(Fe). It compares the purity obtained using MF-S1 to that achieved with diluted conditions, demonstrating the potential suitability of this procedure. In order to better assess the quality and purity of MIL-100(Fe)-synthesized MOFs, FTIR analysis was applied. Figure 2 compares FTIR spectra of MIL-100(Fe) samples synthesized hydrothermally under different synthesis conditions. All batches exhibit a quite similar spectrum. The region from 1200 cm\({}^{-1}\) to 700 cm\({}^{-1}\) in the infrared spectrum is called the fingerprint region. In Figure 2, characteristic peaks of MIL-100(Fe) samples can be observed, in particular the shift in the C=O stretching vibration peak from 1761 cm\({}^{-1}\) (trimesic acid) to 1621 cm\({}^{-1}\), corresponding to the coordination of trimesic acid with Fe (III), thus indicating the successful synthesis of MIL-100(Fe). [33]  
However, the peak observed at 1710 cm\({}^{-1}\) is described as the stretching vibration of an uncoordinated carboxylate; this indicates the presence of a non-reacted linker in the MOF [10]. For synthesis protocol 2 and synthesis protocol 3, the observed peak of 548 cm\({}^{-1}\) is the vibrational band of the Fe-O bond in Fe\({}_{2}\)O\({}_{3}\), thus indicating the presence of iron oxide [34]. These results are supported by the XRD spectrum (Figure 2). The broad band between 3700 and 2700 cm\({}^{-1}\) is associated with the v [O-H] stretching vibrations, originating from the water molecules' coordination with the open metal site center in the  
Figure 2: FTIR Spectra of MIL-100(Fe) samples synthesized hydrothermally under different synthesis conditions. MIL-100(Fe) structure. Furthermore, a peak at 1037 cm\({}^{-1}\), more evident in MF-S0 than the other batches, probably ascribed to unreacted products, can also be identified. The bands at 711 cm\({}^{-1}\) and 760 cm\({}^{-1}\) appear due to C-H stretching vibrations. Peaks at 1378 cm\({}^{-1}\) and 1456 cm\({}^{-1}\) appear due to C-O vibrations and the O-H bending, respectively. The stretching vibration of C=O is found around 1622 cm\({}^{-1}\). The appearance of these characteristic bands match with previous reports for MIL-100(Fe) [16]. The combined analysis of XRD and FTIR, presented in Figures 1 and 2, respectively, allows for a comprehensive evaluation of the quality and purity of samples synthesized under different conditions. Based on this analysis, the order of purity and crystallinity is established as MF-S1 \(>\) MF-S2 \(>\) MF-S3 \(>\) MF-S0. This trend reveals that MF-S0 and MF-S3 exhibit lower crystallinity and purity compared to other samples. Consequently, only MF-S1 and MF-S2, identified as superior candidates based on their structural integrity and chemical homogeneity, were selected for further investigation through BET surface area analysis. Assessing the potential of materials for gas storage hinges on having a deep understanding of their pore architecture, particularly the distribution of pore sizes. To delve into this aspect, we employed nitrogen adsorption isotherms at 77 K to characterize the prepared materials. This technique provides valuable insights into the total pore volume and how effectively different sized gas molecules can be accommodated within the material's intricate pore network. Figure 3 shows the nitrogen adsorption isotherms and pore size distribution of MIL-100(Fe) sample MF-S1. The adsorption isotherm showed a steep increase at relative pressures below 0.2 and then became nearly saturated thereafter.