## 2 Cu-Based Catalyst-Activated PMS Processes
### Cu-Based Designed Catalyst Materials
#### 2.4.2 Cu-Based LDHs
This feature allows for greater versatility in modulating their physical and chemical properties, such as ionic exchange capacity, thermal stability, and catalytic activity. Additionally, LDHs have a layered structure that facilitates ionic exchange and the intercalation of organic and inorganic molecules, further expanding their range of potential applications. For instance, in the study of [PERSON] et al. (2019), a Cu\({}_{3}\)Mn-LDH is synthesized via coprecipitation, a commonly used method for LDH synthesis. During this process, hydrogen peroxide is incorporated to slightly modify the structure and enhance PMS activation efficiency. Specifically, using 0.1 g\(\cdot\)L\({}^{-1}\) of Cu\({}_{3}\)Mn-LDH and 0.25 g\(\cdot\)L\({}^{-1}\) of PMS results in the complete degradation of a 10 mg\(\cdot\)L\({}^{-1}\) concentration of BPA in less than 60 min at neutral pH. This material exhibits a bipath degradation mechanism, with the primary pathway being the generation of \({}^{1}\)O\({}_{2}\) and the auxiliary pathway involving free radicals, as determined by electron paramagnetic resonance (EPR) analysis and quenching experiments. The generation of \({}^{1}\)O\({}_{2}\) is the predominant pathway in the degradation of BPA. \begin{table}
\begin{tabular}{c c c c c} \hline  
* BDC: benzene dicarboxylic acid.  
\end{table} 
Table 2: _Cont._Regarding trimetallic LDHs, [PERSON] et al. 's study highlighted the differences between the metal salts involved in the formation of the LDH structure by synthesizing MgCuFe-LDH, MgCuAl-LDH, and a bimetallic MgFe-LDH [128]. From the synthesis of these three LDHs, it was concluded that the two trimetallic LDHs exhibited a higher degradation capacity compared to the bimetallic one. Among the two trimetallic LDHs, MgCuFe-LDH demonstrated the highest degradation rate, with a 2.9% higher rate than MgCuAl-LDH. This is believed to be due to a significant synergistic effect on PMS activation by the Cu and Fe metals, while Mg provided charge balance and structural stability, enhancing the activation reactions of PMS by Cu and Fe. Additionally, like MOFs, another approach to further enhance the stability of these catalysts and enable their use in repeated or continuous processes is the formation of membranes or the incorporation of the catalyst onto physical supports. For instance, [PERSON] et al. demonstrated the effectiveness of CoCu-LDH in removing a contaminant like sulfamethoxazole, achieving more than 86% removal in 1 h [131]. However, when this material was immobilized on a support such as PVDF, resulting in CoCu-LDH@PVDF, there was a significant improvement in catalyst activation. In the same timeframe, a removal rate of 92.8% for sulfamethoxazole was achieved. Furthermore, CoCu-LDH@PVDF showed a removal capacity of over 89% for other drugs such as sulfacetamide, lomefloxacin, and carbamazepine. Another approach is to synthesize these LDHs on the structure of other materials, as in the case of [PERSON] et al., who synthesized a trimetallic CuCo-FeLDH on a biochar structure [132]. As shown in Table 2, the results are very promising, with the material displaying high stability over multiple reuse cycles. The successful degradation of phenanthrene is largely attributed to the synergy between the two materials. The biochar, in addition to acting as a support for the LDH, enhances the activation capacity of PMS, allowing its catalytic activity to operate over a broader pH range than without the biochar. Furthermore, this carbon-based material also contributes to PMS activation due to the functional groups it contains. Additionally, a further advantage of combining CuCoFe-LDH with biochar is that it significantly reduces metal leaching, which enhances the material's stability and addresses one of the common issues associated with LDHs. However, regarding the study of [PERSON] et al. [132], it is important to note that LDHs have some limitations, such as reduced stability upon reuse and insufficient catalytic activity.