**3.6 Sonochemical**

The sonochemical synthesis of MOFs is a simple and effective method that involves exposing the mixture to sonogram waves with frequencies ranging from 20 kHz to 10 MHz. The advantages of this approach include the lack of additional heat required, the quick reaction time, and the creation of a narrow size distribution crystallization product (**Figure 14**). The sonochemical synthesis method is suitable for the synthesis of nanoscale crystals because particles are generated instantly inside local solvent cavity regions with a short total lifetime (ms) and dimensions in the 10 nm range. MOFs

*Historical Developments in Synthesis Approaches and Photocatalytic Perspectives… DOI: http://dx.doi.org/10.5772/intechopen.107119*

#### **Figure 13.**

*Schematic representation of solventless synthesis method of metal–organic frameworks (reproduced from Ref. [61]).*

#### **Figure 14.**

*Sonochemical synthesis of the metal–organic framework (reproduced from Ref. [62]).*

produced at room temperature using a sonochemical synthesis method have dimensions in the 10 nm range [63]. Fard et al. demonstrated the creation of a 2D MOF [Pb2(N3) (NO3)L2], (L = 8-hydroxy quinolate) in an aqueous medium [64].

#### **3.7 Electrochemical method**

The electrochemical synthesis method provides an alternative approach to the sonochemical procedure that does not require an external source of heat [65] (**Figure 15**). Joaristi et al [67]. reported the synthesis of HKUST-1 on an anode side with only an isopropanol solution and a copper mesh. MIL-100(Fe) has been synthesized for the first time using a simple nucleation method [68]. The method involves dissolving 1,3,5-benzenetricarboxylic acid in ethyl alcohol and Milli-Q moisture in an electrolytic system under high pressure and temperature. MIL-100(Fe) crystals were grown on pure iron substrates using a Fe electrode at temperatures ranging from 110 to 190°C. Heating a solution of BDC: HNO3: H2O: AA: DMF contributed to UiO-66 anodic/cathodic film deposition on zirconium foil. The anodic deposition has been shown to improve MOF adhesion on zinc metal ions, in a study published in the Journal of Organic Chemistry and Biomaterials (JICB) by researchers at the University of California, Los Angeles [69].

#### **Figure 15.**

*Schematic representation of electrochemical synthesis method of metal–organic frameworks (reproduced from Ref. [66]).*
