## 4 Discussion  
The findings of this work show that sodium 4-styrene sulfonate (NaSS) can be polymerized within porous materials, especially filter paper, using dielectric barrier discharge (DBD) plasma. Plasma offers a distinct benefit compared to traditional polymerization techniques like UV or heat-based polymerization, which frequently have drawbacks like inadequate penetration or thermal damage to delicate materials. FTIR measurement shows that the C=C double bonds completely disappear in NaSS, indicating that the DBD plasma successfully triggered polymerization under mild circumstances. This supports the feasibility of DBD plasma for polymerization within porous substrates and is consistent with earlier research using non-thermal plasma for comparable purposes. The PSS crosslinked with 0.5% divinylbenzene (DVB) with the highest methylene blue elimination efficiency indicates greater stability and longevity of the polymer network. This demonstrates how crosslinked PSS can be used in environmental applications where multiple filtration cycles are necessary, such as wastewater treatment. These findings are consistent with the body of research on the effectiveness of crosslinked polymer systems in environmental cleanup. The applications of DBD plasma-synthesized PSS materials for water treatment would require practical considerations such as material durability, filtration efficiency under variable water conditions, commercialization, and potential fouling. Furthermore, while stable in controlled lab settings, the crosslinked structure may face challenges in natural waters containing competing organic and inorganic materials, which could reduce its adsorption capacity for methylene blue (MB). Thus, optimizing DBD plasma treatment for consistent polymerization quality, testing its stability in various water conditions, and assessing capacity for larger treatment systems are essential to advancing this technique for practical environmental applications. Additionally, the durability of the DBD plasma-modified filter paper in continuous flow systems will also be considered. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Trial** & **Filter Paper** & **MB Removal Rate (\%)** \\ \hline First & blank & 47.80 \\  & PSS/DVB(0.5\%) & 68.83 \\ \hline Second & blank & 67.70 \\  & PSS/DVB(0.5\%) & 84.41 \\ \hline Third & blank & 74.30 \\  & PSS/DVB(0.5\%) & 95.80 \\ \hline Fourth & blank & 78.50 \\  & PSS/DVB(0.5\%) & 99.40 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: MB removal rates after four filtration trials using both PSS/DVB and blank filter paper. The uncertainty is determined as roughly \(\pm\)2%. Reusability would be advantageous for real-world applications; therefore, regeneration of the filter material when it reaches adsorption capacity is another considerable factor. The DBD plasma can be generated in various gases, such as N\({}_{2}\), Ar, O\({}_{2}\), air, etc. Although all of them can polymerize monomers to polymers, such as NaSS to PSS, the polymerization process, polymerization efficiency, reaction rate, and properties of polymers vary from different plasmas. Among these, air DBD plasma is the most common plasma due to its lower cost. In our experiments, the DBD plasma was generated in air at ambient conditions. The air-plasma contains reactive oxygen and nitrogen species (ROS and RNS), including ozone (O\({}_{3}\)), radicals (\(\bullet\)NO and \(\bullet\)OH), superoxide anion (O\({}_{2}\)\({}^{-}\)), and electrons, etc. The radicals are believed to be the species that could initiate the polymerization reaction. Other species, including impurities in air, do not significantly affect the polymerization process and the properties of the polymers. Subsequent investigations may concentrate on the feasibility of this methodology for commercial implementations and examine alternative monomers and crosslinkers for constructing customized polymer networks.