**3.2 Microwave-assisted method**

Microwave-assisted synthesis methods make use of the interaction of electromagnetic waves with polar solvent ionic species (**Figure 10**). MIL-101(Fe) was synthesized at 150°C using dimethyl formamide, with a yield of 20% and particle sizes similar to 200 nm [51]. Increasing the concentration of water or the pH reduced crystal size. Microwave heating at 210°C was also used to synthesize Cr-Mil-101 MOF. Zr-based MOFs exhibit excellent chemical and thermal stability, resulting in strong coordination interactions of zirconium Zr(IV) ions with organic ligands [52]. The microwave was also used to help in the synthesis of Cr-MIL-101 at 95 °C and for a shorter duration of 9 minutes to generate MOF-5. A solvothermal method for preparing pure phase MIL-140 is likely to result in superior chemical stability with less preparation time than conventional electric heating strategies. In 2013, Ren et al. used this process to produce highly crystalline UiO-66 MOF octahedral-shaped crystals for H2 storage capacity [53].
