## 3 Results and Discussions
### Performance Testing  
As shown in Table 1, according to Equations (1) and (2), the ion exchange capacity of the best PES membrane was 1.5 meq/g, and the corresponding sulfonation degree was  
Figure 8: AFM figures of selected PES and sPES membranes: 1 \(\upmu\)m \(\times\) 1 \(\upmu\)m AFM images of **(a)** PES and (b) sPES; 0.5 \(\upmu\)m \(\times\) 0.5 \(\upmu\)m surface roughness analysis of **(c)** PES and (d) sPES.  
Figure 7: XPS spectra of selected PES and sPES membranes.  
42%. The ion exchange capacity of the best sPES membrane was 2.67 meq/g, and the corresponding sulfonation degree was 83%.  
More comparisons are shown in Table 2. As shown in Table 2, although there have been many IEMs developed by researchers for ED applications, most of them were fabricated with multiple materials, non-trivial physical or chemical treatments, or crosslinked with some other materials, making the fabrication process complicated or not cost-effective. In contrast, the membranes developed in this work demonstrate competitive performance with simpler, more scalable methods.  
The sPES membrane, with an IEC of 2.67 meq/g, is among the highest reported, indicating excellent ion exchange capabilities essential for efficient ED. While some membranes show higher salt removal rates or current efficiency (CE), it is crucial to consider the feed solution concentration. Higher molarity feed solutions, as used in some studies, can artificially enhance performance metrics. This work uses a moderate feed solution concentration (0.05 mol/L NaCl), offering a more realistic performance assessment.  
The PES membrane shows a salt removal rate of 24% and a CE of 50%, while the sPES membrane achieves a 33% salt removal rate and a CE of 48%. These results are significant, given the lower ionic strength of the feed solution, underscoring the membranes' effectiveness under practical conditions.  
In summary, the developed PES and sPES membranes exhibit high IEC values and competitive performance metrics, demonstrating their potential for practical and scalable  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & **Membrane Material** & **IEC (meq/g)** & **CE (\%)** & **Salt Removal (\%)** & **Feed Solution (mol/L)** & **Reference** \\ \hline PDP-2.0 & PPTA/DS/PPTA & 1.6 & - & 95.1 & 0.08 Na\({}_{2}\)SO\({}_{4}\) & [10] \\
60 PSF-C2 & SPSF/Acrylic & 1.6 & 95.7 & 91.7 & 0.1 NaCl & [11] \\  & crosslink & & & & \\ Z-2 & Zn-MOF/sPPS & - & 75.8 & 94.1 & 0.1 NaCl & [12] \\ SPEEK/PGO-8 & SPEEK/PGO & 2.16 & 78.2 & 67.6 & 0.7 NaCl & [13] \\ Sub-nanoporous PES & PES & - & - & - & 0.1 LiCl, NaCl, & [14] \\  & & & & & KCl, MgCl\({}_{2}\) & \\ SPSU-60 & SPSF/AgNP & 1.55 & 96.9 & 67.5 & 0.5 NaCl & [15] \\ SG-10 & sPES/GO & 1.27 & 97.4 & 99.1 & 0.1 NaCl & [16] \\
40\%sPES-PES & sPES/PES/PVP & 0.52 & 127.5 & 91.9 & 0.1 NaCl & [17] \\ S/P/PANI-0.6 & sPES/PVP/PANI & 0.47 & 94.3 & - & 0.1 NaCl & [31] \\ PAN-PAMPS-2 & PAN/PAMPS & 1.65 & 91 & - & 0.35 NaCl & [32] \\ DES-5 & sPES/S-MoS2 & 1.42 & 69.5 & - & 0.1 NaCl & [33] \\ PVA/BFC-70 & PVA/DVB/AMPS & 1.3 & 87.5 & - & 0.85 NaCl & [34] \\ SPI/PGO-8 & SPI/PGO & 2.37 & 76.4 & - & 0.1 NaCl & [35] \\ SPK/IGO-8 & SPEEK/IGO & 2.23 & 82.9 & - & 0.85 NaCl & [36] \\ SGO-5 & sPES/SGO & 1.7 & 93.1 & - & 0.1 NaCl & [37] \\ S-25/P & sPES/PVP & 0.65 & - & - & 0.1 NaCl & [38] \\
70\%s & SPVDF/PVDF & 0.7 & - & - & 0.1 NaCl & [39] \\ MIL-10 & sPES/MIL-101 & 1.04 & 85 & - & 0.1 NaCl & [40] \\ PM-5 & PVC/St/DVB/SGO & 1.76 & 82.3 & - & 0.085 NaCl & [41] \\ CEM-3 & PAN/PSSO\({}_{3}\)Na/PnBA & 1.47 & 76.8 & - & 0.085 NaCl & [42] \\ S/P K30 & sPES/PVP & 0.54 & 80 & 90 & 0.86 NaCl & [43] \\ CINHz & CI-PES/NH\({}_{2}\)-PES & 2.2 & - & 93.8 & 0.05 NaCl & [44] \\ PES & PES & 1.5 & 50 & 24 & 0.05 NaCl & (This work) \\ sPES & sPES & 2.67 & 48 & 33 & 0.05 NaCl & (This work) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Summary of IEMs developed for ED applications.  
ED applications. Their simple and cost-effective fabrication process further supports their industrial applicability.