**3. Synthesis approaches of MOFs**

The solvothermal synthesis method has been used for the synthesis of MOFs using organic solvents, such as N, N dimethylformamide (DMF), methanol (MeOH), ethanol (EtOH), and acetonitrile [38, 39]. To form and self-assemble MOF crystals, metal components and organic linkers are commonly dissolved in an organic solvent. The heating rate during synthesis is typically less than 220°C, and crystal growth times

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

#### **Figure 7.**

*(a) The popular synthesis methods for synthesis of MOFs; (b) the utility percentages of synthesis methods (reproduced from Ref. [41]).*

range from a few hours to several days. Significant advances in the synthesis of MOFs have been made after two decades. Several useful synthesis techniques for MOFs and their utility have been reported, including electrochemical, microwave-assisted, mechanochemical, and sonochemical methods [40] (**Figure 7a**, **b**).

The ability to manipulate and customize the morphology of mesoporous crystals, as well as their synthetic functionalization, is critical in delivering the desired characteristics and outcomes for MOF materials [42–44]. MOF crystal growth has led to the development of more advanced and tunable methods of synthesis for controlling MOF crystal morphology and size, as well as heavily doped to begin creating hybrid MOF crystals [45]. This section of the time frame that follows provides an overview of some of the key advances in this area of research (**Figure 8**).

#### **3.1 Solvothermal method**

Metal–organic frameworks can be successfully synthesized using solvothermal (**Figure 9**) and hydrothermal strategies, which appear to be very simple and well-known methods modified from zeolite synthesis [48]. In most cases, the metal component and the carboxylic acid linker are bonded in a suitable solvent. The ability to produce large crystals, less expensive, and use a high bandwidth of heat are just a few advantages of using this method over simpler approaches [49]. The DMF solvent is widely recognized

**Figure 8.**

*The time framework for the development of the MOF synthesis methods (reproduced from Ref. [46]).*

#### **Figure 9.**

*Schematic representation of the solvothermal synthesis method for synthesis of metalorganic frameworks (reproduced from Ref. [47]).*

as the best solvent for this purpose. Microwave-assisted applications can help to improve reaction efficiency but are limited by low product yield and long reaction times, high heat, and the use of toxic organic solvents, such as cadmium iodobenzene [50].
