Fabrication of cation exchange sponges based on melamine-formaldehyde sponges

The development of efficient and reusable cation exchange materials is essential for water purification and ion extraction processes. This study introduces innovative cation-exchange sponges fabricated using a melamine-formaldehyde (MF) sponge as a support. The sponge was dip-coated in a solution of polystyrene in dichloromethane and subsequently sulfonated under controlled temperature and time. Results demonstrated that a polystyrene concentration of 10% (w/v) with sulfonation at 40 °C for 2 h yielded a cation-exchange capacity (CEC) of 1.07 meq/g, beyond which performance declined due to pore blockage. Extending the sulfonation duration to 3 h increased the CEC to 1.27 meq/g, while a longer duration (4 h) caused a slight decrease attributable to polymer degradation. Response Surface Methodology (RSM) was employed to systematically optimize the process parameters, leading to a maximum CEC of 1.45 meq/g under ideal conditions (47 °C for 3.5 h). Structural characterization via SEM and FTIR confirmed that the enhanced porosity provided a greater surface area and improved access for ion diffusion, while the incorporated sulfonic acid groups served as the primary cation exchange sites. This synergistic effect between the optimized structure and tailored chemistry was directly responsible for the high CEC achieved. The sponge's monolithic, open-pore structure facilitates easy handling and eliminates clogging and high-pressure drops associated with granular resins. This unique combination of high capacity, straightforward fabrication, and excellent hydrodynamic performance positions this material as a highly promising candidate for next-generation water treatment technologies.