## 2 Cu-Based Catalyst-Activated PMS Processes
### Cu-Based Designed Catalyst Materials
#### 2.4.1 Cu-Based MOFs  
Regarding MOFs, these materials are composed of metal ions coordinated with organic ligands, forming a highly porous three-dimensional structure. These materials are notable for their high stability and tunable internal structure [104; 105]. Due to the wide variety of MOFs, they can be classified according to their structure and composition. This review focuses on copper-containing MOFs, commonly referred to as Cu-MOFs. They are usually composed of copper ions or groups coordinated with organic linkers, creating a robust and tunable framework. The synthesis of Cu-MOFs can be achieved through several methods, each of which offers different advantages and is suitable for different applications. The choice of the synthesis method depends on the desired properties of the MOF, the specific application, and the scalability requirements. The most employed techniques for synthesizing Cu-MOFs are:  
* Solvothermal synthesis: This is the most widely used method to produce Cu-MOFs. In this technique, the copper salts and organic linkers are dissolved in a solvent and heated in a sealed container (often an autoclave) at elevated temperatures, typically in the range of 80\({}^{\circ}\) C to 220\({}^{\circ}\) C. The solvothermal conditions facilitate the self-assemblyof the metal ions and organic linkers into the desired structural structure [106]. This method allows for precise control over the size, morphology, and crystallinity of the MOFs by adjusting parameters such as temperature, reaction time, and solvent type. MW-assisted synthesis: This offers a fast and energy-efficient approach to producing Cu-MOFs. This method involves the use of MW radiation to heat the reaction mixture, significantly reducing the synthesis time compared to conventional solvothermal methods. MW-assisted synthesis can improve the nucleation and growth rates of MOFs, leading to high-quality crystalline materials with uniform particle sizes [107]. The rapid heating and cooling cycles provided by MW irradiation also help to minimize the formation of defects within the MOF structure. Electrochemical synthesis: This is an emerging technique for producing Cu-MOFs, where an electric current is applied to drive the assembly of the framework. In this method, a copper anode is dissolved to release copper ions in an electrolyte solution containing organic linkers. The electric field promotes the interaction between the copper ions and the linkers, which results in the formation of the MOF on the electrode surface [108]. Electrochemical synthesis is advantageous for producing thin films of MOF directly on conductive substrates, which makes it suitable for applications in sensors and electronic devices. Sonochemical synthesis: This uses ultrasonic waves to induce chemical reactions and facilitate the formation of copper MOFs. The ultrasonic waves generate high temperatures and localized pressures within the reaction mixture, improving the reaction kinetics and promoting the formation of the MOF structure [109]. This method is known for its simplicity, fast reaction times, and ability to produce MOFs with unique morphologies and improved surface areas. Mechanochemical synthesis: This involves the use of mechanical force to induce chemical reactions between copper salts and organic linkers. This technique typically employs grinding or ball milling to physically mix and activate the reactants, leading to the formation of the MOF structure without the need for solvents or high temperatures [110]. Mechanochemical synthesis is environmentally friendly and scalable, which makes it a promising approach for the large-scale production of Cu-MOFs. However, it is also possible to combine several of these synthesis processes to improve the properties of Cu-MOFs. Additionally, another advantage of combining these processes is that the synthesis times and solvent volumes can be reduced, resulting in a material with better properties compared to using a single process.