Solvent Effects in the Synthesis of Highly Charged Foams of Poly(4-styrenesulfonate-co-glycidylmethacrylate) for Efficient Adsorption of Methylene Blue Enhanced by Aromatic–Aromatic Interactions

Water-resistant porous solid foams expressing a high amount of benzene sulfonate moieties have been fabricated to enhance the adsorption of cationic aromatic pollutants from wastewaters by aromatic–aromatic interactions. Copolymers of sodium 4-styrene sulfonate (NaSS) and glycidyl methacrylate (GMA) have been obtained and submitted to thermal treatment at 270 °C for 15 min. The influence of the solvent used in the copolymerization step on foamability and foam stability, when formed, has been studied. The use of water as cosolvent with N,N-dimethyl formamide (DMF) inhibited foam formation. The use of DMF or DMF/dimethyl sulfoxide (DMSO) = 1:1 as solvents allowed the expansion of copolymers, but the resulting foams are unstable in water, forming hydrogels. However, using DMF/DMSO = 5:1 as solvent, stable water-resistant foams showing NaSS molar fractions of 43, 57, and 68% are obtained, showing high maximum capacity of 244, 435 and 588 mg g⁻¹ and outstanding pseudo-second-order kinetic constants of 1.78, 4.49 and 5.64 g mg⁻¹ min⁻¹ toward adsorption of methylene blue (MB), between 2 and 5 orders-of-magnitude higher than referenced adsorbents. This is due to the highly exposed benzene sulfonate active sites / adsorbent mass ratio that induces strong aromatic–aromatic interactions with the cationic aromatic dye.