Enhanced MeOH Selective Pervaporation of Carbon-Polyimide-POSS Membranes via Water Plasma Treatment: Synergistic Effects of Microporosity and Hydrophilicity

Methanol (MeOH), as one of the most environmentally friendly fuels and critical raw materials in industrial processes, plays a pivotal role in sustainable chemical engineering. The efficient, energy-saving recovery and purification of MeOH is of significant environmental and economic importance. Membrane-based pervaporation (PV) process offers promising prospects in this field. Carbonized polyhedral oligomeric silsesquioxane (POSS)-polyimide (PI) (carbon-POSS) membranes with excellent molecular sieving capabilities and chemical stability demonstrate significant potential for the PV separation of MeOH from solvent mixtures. However, their separation performance is inherently constrained by the pore structure-dominated molecular sieving behavior. Thus, tailoring the surface chemistry while maintaining the intrinsic structural advantages to improve the separation efficiency presents a significant challenge. In this study, carbon-POSS membranes were fabricated by carbonizing norbornene (NB)-functionalized POSS-PI-phenyl hybrids (POSS-PI-Ph-NB, PPN). The membrane carbonized at 700 °C (PPN-700), exhibits high microporosity and MeOH permeance. A short, 4 s water plasma treatment of PPN-700 significantly enhanced its hydrophilicity while preserving the high microporosity. The resulting WP-PPN-700 membrane demonstrated synergistic effects of molecular sieving and adsorption-diffusion mechanisms, achieving outstanding MeOH permeances exceeding 10–6 mol m–2 s–1 Pa–1, with impressive MeOH/IPA and MeOH/toluene selectivities of 500 and 2000, during the PV of MeOH/IPA (10/90 wt %) and MeOH/toluene (10/90 wt %) mixtures, respectively. Furthermore, the WP-PPN-700 membrane exhibited excellent stability across a range of feed compositions and mixed solvent systems. These findings provide valuable insights and innovative strategies for the development of advanced PV membrane technologies that facilitate efficient MeOH recovery.