Organosilica membranes are a promising candidate for pervaporation
dehydration owing to their tunable molecular sieving characteristics and excellent hydrothermal stability. Herein, we report a facile modification using an atmospheric-pressure
water vapor plasma to enhance the pervaporation performance of organosilica membranes. The surface of methyl-terminated organosilica membranes was treated by
water vapor plasma to develop an ultrathin separation active layer suitable for pervaporation
dehydration. The surface hydrophilicity was increased by
water vapor plasma due to oxidative decomposition of methyl groups to form
silanol groups. The plasma-modified layer had a thickness of several nanometers and had a
silica-like structure due to the condensation of
silanol groups. The plasma-modified organosilica membranes exhibited an improved molecular sieving property owing to the formation of highly cross-linked
siloxane networks with a pore size of approximately 0.4 nm. The membranes also exhibited an excellent permselectivity in the
dehydration of
alcohols due to the nanometer-thick separation active layer with controlled pore size and increased hydrophilicity. The plasma-modified membranes showed high H2O permeance exceeding 10-6 mol m-2 s-1 Pa-1 with permeance ratios for H2O/EtOH and H2O/IPA of 517-3050 and >10 000, respectively, in the
dehydration of 90 wt % aqueous solutions at 50 °C, which is among the highest permselectivities for
silica-based membranes. Furthermore, the plasma-modified membranes displayed highly efficient
dehydration performance for a H2O/MeOH mixture. The H2O permeance and H2O/MeOH permeance ratio in the
dehydration of a 90 wt % MeOH aqueous
solution at 50 °C were (2.3-3.0) × 10-6 mol m-2 s-1 Pa-1 and 31-143, respectively, which exceeded the permeance-selectivity trade-off of conventional membranes including polymeric,
silica-based, and
zeolite membranes. The results indicate that the proposed plasma-assisted approach can enhance the pervaporation performance of organosilica membranes via the modification under atmospheric pressure and at room temperature.