## 3 Results and Discussion
### Effective Activation of PMS with Catalysts for Contaminant Removal  
To thoroughly evaluate the catalytic performance of the prepared FeCo-LDH catalysts for degrading organic pollutants via PMS activation, their efficiency in degrading sulfamethoxazole (SMX) was examined under controlled conditions (catalyst dosage: 0.1 g/L; PMS: 0.3 mmol/L; pH: 6.96; SMX concentration: 10 mg/L). As depicted in Figure 3a, PMS alone exhibited a minimal SMX degradation rate of only 6.99%, with an apparent reaction rate constant of 0.0443 min\({}^{-1}\). However, the catalytic activity improved significantly with an increase in the Co\({}^{2+}\)/Fe\({}^{3+}\) ratio. The basic structure of LDHs is represented as [M\({}_{1-x^{2}+}\)M\({}_{3}\)\({}^{+}\)(OH)\({}_{2}\)(A\({}_{n}\)\({}_{v}\)/n]\(\kappa^{+}\)-mH\({}_{2}\)O. The observed variation in catalytic performance suggests that the optimal M\({}^{2+}\)/M\({}^{3+}\) ratio for LDHs lies between 1 and 3, aligning with previous findings that the synthesis of LDH compounds is most effective when \(0.2\leq x\leq 0.33\)[43; 44]. The XPS images of LDH with different iron to cobalt ratios illustrate the conclusion just made very well (Figures S1-S4), as the peaks represented by iron are completely absent from the Fe2p spectra of the material at the 1:1 ratio, while the elemental peaks of the material at the other two ratios are well presented. Additional experiments investigated the influence of catalyst dosage and SMX concentration on degradation efficiency, with detailed results provided in the Supplementary Information (Figures S5-S7). As shown in Figure 5b, the degradation rate of the system for SMX was 79.2% at an initial pH of 3, and reached nearly 100% at an initial pH of 11, with the degradation rate showing a decreasing trend with increasing pH. Notably, the degradation efficiency remained high regardless of the initial pH. During the reaction, the system's pH quickly stabilized between 4.0 and 6.96 within 10 min after the catalyst addition, regardless of initial pH levels. This behavior contrasts with PMS alone, which cannot neutralize the solution pH due to its intrinsic acidity [45]. The observed pH stabilization is likely attributed to the presence of Co(OH)\({}_{2}\) in the catalyst. When the M\({}^{2+}\)/M\({}^{3+}\) ratio in LDHs falls within the range of 0.5-2, the proximity of M\({}^{3+}\)(OH)\({}_{3}\) octahedra facilitates the formation of M(OH)\({}_{3}\). Conversely, when x < 0.33, hydrotalcite-like layers predominantly generate M(OH)\({}_{2}\) instead [46]. The sequential reactions between Co(OH)\({}_{2}\) on the catalyst surface and H\({}^{+}\) or OH\({}^{-}\) ions in the solution drive the system's pH toward neutrality. To further confirm the broad pH adaptability of FeCo-LDH, different buffer systems were employed to maintain stable pH conditions during the reaction. Specifically, HCOOH-NaOH (pH = 4.0), phosphate (pH = 6.96), and borax (pH = 9.18) buffer solutions were used. Detailed buffer compositions are provided in the Section 2. Figure 5d illustrates the degra  
Figure 4: CV (**a**) and EIS (**b**) patterns of different catalysts. dation trends and pH changes of SMX under various buffered conditions. The results reveal differences in SMX degradation efficiency depending on the pH environment. While acidic conditions initially exhibit faster degradation rates, neutral pH conditions achieve superior overall efficiency. Conversely, alkaline conditions provide more sustained degradation, albeit at a slower initial rate. These findings underscore the robust performance of Fe-Co LDHs across diverse pH environments, with neutral conditions being particularly effective for pollutant degradation. Figure 6 highlights that cobalt leaching peaks during the first 10 min of the reaction, coinciding with the stabilization of the pH.