## 4 Conclusions  
This study investigated the optimal synthesis conditions and post-synthesis washing procedures for the creation of a high-purity and high-performance MIL-100(Fe) metal-organic framework for gas capture and energy storage applications. The following conclusions can be drawn:  
* A high-quality MIL-100(Fe) MOF was successfully synthesized using an HF-free hydrothermal method, demonstrating a sustainable and environmentally friendly approach. Optimized synthesis conditions (Fe\({}^{3+}\)/(H\({}_{3}\)BTC)/water ratio of 1:0.67:56) and a 12 h reaction time were identified as crucial for maximizing the yield and purity of the MOF.
* Washing protocol No. 2 (multiple washes with hot water and ethanol) proved most effective in maintaining high crystallinity, surface area (1162 m\({}^{2}\)/g), and pore volume (0.377 cm\({}^{3}\)/g) while minimizing the presence of impurities. Washing protocol No. 1 (extended immersion in distilled water) enhanced crystallinity but led to a significant decrease in surface area and pore volume. This highlights the importance of optimizing both synthesis and washing procedures for obtaining high-quality MOFs.
* The MOF sample washed with a sequential hot water and ethanol washing procedure (MF-S1-W2) was identified as the most promising candidate for further gas adsorption studies due to its superior crystallinity, purity, and surface area. The optimized MIL-100(Fe) exhibited a remarkable hydrogen adsorption capacity, reaching 0.25 wt.% at 5 \({}^{\circ}\)C and 40 bar. The material demonstrated significant CO\({}_{2}\) adsorption, reaching 32.6 wt.% at 5 \({}^{\circ}\)C and 10 bar and 23.9 wt.% at 30 \({}^{\circ}\)C and 10 bar. Heats of adsorption were calculated to be 5 kJ/mol for H\({}_{2}\) and 20 kJ/mol for CO\({}_{2}\). The MOF also displayed an excellent water vapor adsorption capacity, reaching a maximum of 47.5 wt.% at 20 mbar and 30 \({}^{\circ}\)C. The observed S-shaped adsorption isotherms and minimal hysteresis during desorption indicate the potential of this material for efficient water vapor sorption applications.  
These preliminary results not only suggest valid application potential but also open a promising path for further exploration of the material in clean energy technologies. Future research will focus on optimizing the microstructure and functional properties of the material to better meet the specific demands of gas capture and energy storage applications. Moreover, repeated cycle tests and durability assessments are essential for a comprehensive evaluation of the MF-S1-W2 batch. These will include investigations into structural stability and working adsorption capacity over extended cycling (up to 1000 cycles), which are planned as key components of our upcoming studies to confirm the material's long-term performance and practical viability.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app15116097/s1](https://www.mdpi.com/article/10.3390/app15116097/s1)]([https://www.mdpi.com/article/10.3390/app15116097/s1](https://www.mdpi.com/article/10.3390/app15116097/s1)), Figure S1: SEM image of (a) MF-S1-W2 and (b) MF-S1-W1 samples; Table S1: DLS analysis on MF-S1-W2 sample.  
Conceptualization, L.C. and E.M.; methodology, M.I., L.C. and E.M.; validation, L.C. and E.M.; formal analysis, L.C. and E.P.; investigation, M.I. and E.P.; resources, L.C.; data curation, M.I. and L.C.; writing--original draft preparation, L.C.; writing--review and editing, E.M. and C.M.; visualization, E.M.; supervision, C.M. and L.C. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
Data Availability Statement: The raw data supporting the conclusions of this article will be made available by the authors on request.  
The authors would like to thank [PERSON] and [PERSON] for their precious contributions to the hydrogen and water vapor adsorption measurements.  
The authors declare no conflicts of interest.