Effect of Storage Time on the Structure and Performance of Hybrid Polysulfone Membranes with Graphene Nanoplatelets

This study investigated the impact of time on the structure and performance of hybrid polysulfone (PSU) membranes containing graphene nanoplatelets (GNP), synthesized in 2022. FTIR, SEM, TGA, and BET were used to analyze structural and functional changes after two years of storage. The membranes exhibited distinct behaviors depending on GNP concentration and usage conditions. Pristine membranes showed larger average pore size (16-17 nm) and lower surface area (4.7-16.9 m²·g^-1), whereas compacted membranes exhibited smaller pores (3.6-5.4 nm) and higher surface area (up to 322.7 m²·g^-1). Compaction and storage drastically reduced hydraulic permeability, attributed to fouling, nanoparticle agglomeration, and oxidative degradation of the polymeric matrix. Furthermore, pristine membranes were tested after two years and ruptured during compaction and permeability tests, revealing mechanical fragility caused by aging. FTIR results suggested chemical degradation, with changes in absorption band intensities. SEM micrographs displayed stress marks, cracks, and biological contamination on used membranes, while pristine membranes showed less resilient morphology. TGA analyses revealed a reduction in maximum degradation temperature, indicating thermal stability loss. BET results highlighted the impact of usage and time on pore redistribution and surface area. This research emphasizes the need to optimize storage conditions and explore strategies to improve membranes' thermal and mechanical stability. Future studies should investigate chemical modifications to the polymeric matrix and evaluate new additives to mitigate degradation during long-term storage.