## 4 Application of Fe-MOF in Advanced Oxidation Processes
### Electrochemical AOP
#### 4.3.1 Electro-Fenton  
In the preparation of MOF-based Fe/C cathodes in which the catalyst is immobilized, the main advantage is that, as the catalyst is fixed on the surface (Figure 10a), it is no longer necessary to recover the catalyst from the medium, which is necessary for homogeneous electro-Fenton processes [196]. Thus, carbon felt electrodes were modified by growing MIL-53(Fe) on the surface of a material using a solvothermal synthesis method obtaining a MIL-53(Fe)-based composite material (MIL-53(Fe) @CF) with MOF elongated crystals uniformly distributed on the carbon felt (CF) [197]. Using MIL-53(Fe) instead of another iron salt, minimal leaching of iron into solutions was detected and the possibility was opened up to operate at natural water pH of around 7. In addition, agglomerates or nanoparticles of iron oxide were not detected after treatment. The obtained good results were ascribed to the large accessible pore volume and higher accessible surface area that favor the H\({}_{2}\)O\({}_{2}\) production and the surface catalyzed reactions. An important challenge in heterogeneous catalysis is the agglomeration of catalysts. To overcome this limitation, recent studies have shown that catalysts with a transition metal nanoparticle core and a graphitized porous carbon shell have remarkably enhanced catalytic activity and stability [196]. In this sense, electro-Fenton processes exhibit excellent performance with MOF-derived micro-/nano-materials as MOF-derived core-shell structured materials. Figure 10: General scheme of the degradation electro-Fenton processes using (**a**) modified cathode with Fe-MOF and (**b**) Fe-MOF in bulk solution. Several examples have been reported in the literature in which novel catalysts were constructed from Fe-MIL. Thus, [PERSON] and [PERSON] designed a magnetic Fe@mesoporous carbon (Fe@MesoC) and flower-like FeCu@C derived from MIL-100(Fe) and (Fe, Cu)-BDC, respectively, that presented a dual reaction site as highly reactive Fenton catalysts for efficient removal of pollutants as sulfanilamide antibiotics [198]. Similarly, [PERSON] et al. designed the synthesis of an S-modified MIL-53 (Fe) catalyst by a sulfurizing process [199] determining the positive effect of S in the catalyst enables quick pH adjustments and promotes the generation of Fe\({}^{2+}\), which, in turn, efficiently activates H\({}_{2}\)O\({}_{2}\) to form OH\({}^{-}\). [PERSON] et al. [200] followed the strategy of adding a carbonized Fe-MOF (CMOF) in porous carbon monoliths (PCM), so it was named CMOF@PCM. Furthermore, their results showed that the MOF precursor to obtaining the CMOF@PCM influenced the final structure of the CMOF@PCM and the catalysis activity to carry out the electro-Fenton process. They synthesized and used several Fe-MOFs (MIL-88(Fe), MIL-100(Fe) and MIL-101(Fe)) to study the influence of the MOF precursor and the functionalization of Fe-MOFs (MIL-88(Fe)-NH\({}_{2}\) and MIL-101(Fe)-NH\({}_{2}\)). From the electrochemical performance study, they were able to determine that the efficiency decreased in the CMIL-100(Fe)@PCM > CMIL-88(Fe)@PCM > CMIL-101(Fe)@PCM. Regarding the influence of the functional groups, it was confirmed that the use of amine-functionalized CMIL-88(Fe)-NH\({}_{2}\)@PCM improved the removal of the pollutant (73.42%) while with the corresponding CMIL-101(Fe)-NH\({}_{2}\)@PCM, this catalytic capacity worsened (53.63%). So, there was no conclusion about the influence of the functional groups on Fe-MOFs. After analyzing these two effects, they selected CMIL-100@PCM as the ideal. Additionally, to examine how the amount of PCM influence the process and pollutant degradation, several MOFs were synthesized in a range of 10-75 wt%. The first thing to note is that the PCM favored the process in comparison to the control process without PCM in which the maximum degradation was only 11.8%. Regarding the amount of PCM to be used, it was observed that when the PCM increased the percentage of elimination improved until a maximum when the amount was 25% PCM.