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

Abstract

To solve the tradeoff between permeability and selectivity of polymeric membranes, organic−inorganic hybrid membranes composed of poly(vinyl alcohol) (PVA) and γ-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, 29Si 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 Tg, and in particular improved pervaporation properties. Permeation flux increased from 20.3 g/(m2 h) for pure PVA membrane to 137.1 g/(m2 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.