## 3 Fe-MOF Synthesis
### Solvothermal Synthesis  
This synthesis technique consists of a chemical reaction, which takes place in a solvent at a temperature above the boiling point of the solvent and occurs at a pressure above 1 bar in a sealed vessel, commonly known as an autoclave [86; 87]. In the case of MOFs, this synthesis involves a mixture of metal ions and organic ligands in a low solvent [88]. To obtain the synthesized MOFs, after the reaction in the autoclave, the obtained product needs to be filtered and dried by evaporation at room temperature [88]. Normally, the solvothermal method uses a highly soluble organic solvent such as acetonitrile, methanol, acetone or dimethylformamide (DMF) [88]. A major advantage of this method is that it can control particle size and shape distribution precisely by adjusting the reaction parameters [87; 89]. Due to these characteristics, it is considered one of the most suitable and widely used conventional techniques for MOF synthesis [7]. In the following table, Table 4, some examples of Fe-MOF syntheses are shown.  
The table reflects the procedure that is normally followed in several studies. As can be seen from this table and Figure 4a, the iron salt and the organic ligand are dissolved in a given solvent. When these reagents are completely released, the mixture is poured into a Teflon-lined steel autoclave reactor. This is placed in an oven in which a constant temperature is set for the duration of the reaction (Table 4). When the reaction is finished, the resulting solid is removed from the Teflon and then cleaned and dried.  
During this synthesis, reagents, their counter anions, reaction time and temperature are mainly highlighted as the key factors. Thus, in the study of [PERSON] et al. [90], three identical syntheses were carried out to obtain MIL-100 (Fe) but the iron salt used changed (FeCl\({}_{3}\), Fe(NO\({}_{3}\))\({}_{3}\) and Fe\({}_{2}\)(SO\({}_{4}\))\({}_{3}\)) and the effect of these counter anions was evaluated. Although the characterisation of these materials was approximately similar, there were some differences in their photocatalytic activity. So, this shows the great complexity of the synthesis of Fe-MOFs.  
Figure 3: Most used synthesis methods to obtain Fe-MOFs [83].  
Figure 4: General scheme of (**a**) solvothermal/hydrothermal synthesis, (**b**) microwave-assisted synthesis, (**c**) electrochemical synthesis, (**d**) sonochemical synthesis, (**e**) mechanochemical synthesis, (**f**) dry-gel synthesis.  
Moreover, the solvothermal method allows the synthesis of a wide variety of Fe-MOFs. Moreover, without altering the overall process of the method, it allows for the easy addition of modifications to the Fe-MOFs, and even the addition of another metal salt, as shown in the work of [PERSON] et al. [91] who synthesized a cobalt-iron bimetallic MOF. This study demonstrated that the Fe-MOF had Co\({}^{2+}\) in its structure as they analysed the 3D structure and detected that the Fe/Co-MOFs presented a herringbone ball shape due to the new coordination that had originated.  
The synthesis process, despite its complexity, has proven viable and growing, as shown in Table 4. Consequently, it is an advance in the synthesis of bimetallic iron catalysts with another metal, improving the catalytic properties of Fe-MOFs in water decontamination processes.