Hybrid Organic-Inorganic Membrane: Solving the Tradeoff between Permeability and Selectivity

To solve the tradeoff between permeability and selectivity of polymeric membranes, organic-inorganic hybrid membranes composed of poly(vinyl alcohol) (PVA) and gamma-glycidyloxypropyltrimethoxysilane (GPTMS) were prepared by an in situ sol-gel approach for pervaporative separation of benzene/cyclohexane mixtures. The structure of PVA-GPTMS hybrid membranes was characterized with FTIR, Si-29 NMR, SEM, TEM, and XRD. Energy-dispersive X-ray Si-mapping analysis demonstrated homogeneous dispersion of silica in the PVA matrix. Compared with pure PVA membranes, the hybrid membranes exhibited high thermal stability and lower T-g, and in particular improved pervaporation properties. Permeation flux increased from 20.3 g/(m(2) h) for pure PVA membrane to 137.1 g/(m(2) h) for PVA-GPTMS hybrid membrane with 28 wt % GPTMS content, and separation factor increased from 9.6 to 46.9 correspondingly. The pervaporation results of PVA-GPTMS hybrid membranes are all above the upper bound tradeoff curve (Lue, S. J.; Peng, S. H. J. Membr. Sci. 2003, 222, 203), while that of pure PVA membrane is obviously below the curve. Positron annihilation lifetime spectroscopy (PALS) was employed to elucidate the enhancement of permeation flux in polymer-based pervaporation membranes, and a size-selective mechanism was proposed to explain the enhancement of the separation factor.