## 4 Application of Fe-MOF in Advanced Oxidation Processes
### Photo-Based AOPs
This indicates that the heterojunction of WO\({}_{3}\)-MIL-53(Fe) can effectively separate and utilize the pair e\({}^{-}\)-h\({}^{+}\)[172]. Another alternative is to consider the MOFs semiconductor-like properties, which promote photogenerated charges to be separated and photocatalytic activities to be enhanced through the hierarchical hybrid by coupling of different MOFs. Thus, MIL-100(Fe) and MIL-53(Fe) with strong visible light absorption were coupled in a hybrid composite (denoted as MIL-100(Fe)@MIL-53(Fe)) by electrostatic attraction at pH 6, due to the fact that MIL-101 was negatively and MIL-53 positively charged [123]. These hybrid MOFs exhibited higher degradation activity and a reduction in the iron released in comparison with single Fe-MOFs. In recent years, graphite carbon nitride (g-C\({}_{3}\)N\({}_{4}\)) has been considered an excellent photocatalytic degrader of pollutants due to its excellent visible light response, stable chemical properties and metal-free properties; however, this material exhibits a low specific surface area. For this reason, in several studies, MOFs have been designed using g-C\({}_{3}\)N\({}_{4}\) to obtain ideal photocatalysts able to overcome their disadvantages enhancing the photocatalytic surface activity. In the literature, it has been reported that several examples in which co-catalytic synergy between MOFs (ZIF-8, UiO-66, MIL-53, MIL-100, CuBTC, MIL-88B and BUC-21) and g-C\({}_{3}\)N\({}_{4}\) with different morphologies (sheet, rod and tube) have been tested showing excellent behavior in different degradation processes [173; 174; 175; 176]. This kind of heterostructure can provide the following advantages: (i) increased adsorption performance toward targeted models through the development of a large surface area; (ii) accelerated charge transport across the interface and shorter charge transport distances; and (iii) photocatalytically active sites are distributed uniformly. The strong \(\pi\)-\(\pi\) interactions of MOFs (with aromatic rings of organic ligands) and g-C\({}_{3}\)N\({}_{4}\) (triazine rings), together with the abounding surface electrostatic interactions will enable them to achieve close contact, heterojunction construction, and electron transfer effectively [178]. Recently, [PERSON] et al. [179] modified g-C\({}_{3}\)N\({}_{4}\) by calcination using melamine and cyanuric acid (named CM) based on previous studies, and it was determined that these materials induced stronger optical absorption and increased the lifetime of photoexcited charge compared to unmodified g-C\({}_{3}\)N\({}_{4}\)[180; 181]. Thus, a x% Fe-MOF/CM was prepared with a different mass of MIL-Fe(53) (%) by the self-assembly synthesis method using a co-catalyst CM. It was demonstrated that the best results were obtained when 3% Fe-MOF/CM was selected and the addition of hydrogen peroxide had a synergistic effect enhancing the separation of photogenerated electrons (e\({}^{-}\)) and holes (h\({}^{+}\)) effectively. In this variant of Fenton, the photo-Fenton process, using Fe-MOFs and implementing radiation, UV or sunlight, the production of radicals was improved [182] due to \(\equiv\)Fe\({}^{3+}\) being constantly reduced (Equation (20)) [183]. As mentioned above, another strategy is the modification of organic linkers in the synthesis of Fe-MOF such as the introduction of an amino group. Thus, NH\({}_{2}\)-MIL-88B(Fe) or NH\({}_{2}\)-MIL-101(Fe) exhibited a dual excitation pathway (-NH\({}_{2}\) and Fe-O center) and was tested with excellent results in the Cr(VI) reduction and the toluene degradation. This kind of photocatalyst could be improved by coupling with g-C\({}_{3}\)N\({}_{4}\). Several examples have been reported in the literature, such as NH\({}_{2}\)-MIL-88B(Fe), NH\({}_{2}\)-MIL-53(Fe) and NH\({}_{2}\)-MIL-101(Fe) composites used as photocatalysts to remove several pollutants (Cr (VI) reduction, methylene blue dye, tetracycline, ciprofloxacin, carbamazepine, bisphenol A, p-nitropenol,... ) with great efficiency [184; 185; 186].