Bio-inspired fabrication of composite membranes with ultrathin polymer–silica nanohybrid skin layer

An innovative approach was developed to fabricate composite membranes with ultrathin polymer–inorganic nanohybrid skin layer. The in situ formation of silica nanoparticles within the bulk polymer (poly(vinyl alcohol)) was enabled by the templating and catalysis of inorganic-precipitating polymer (protamine), and the size, morphology as well as spatial distribution of silica nanoparticles were conveniently controlled by the confined space constructed from the cross-linked PVA network. The silica nanoparticle size varied from 14.3 to 8.0 nm by altering the annealing temperature of the cross-linked PVA membranes from 293 to 373 K. Incorporating silica particles destroyed the crystallinity, decreased the glass transition temperature (Tg) and increased the fractional free volume of the nanohybrid skin layer. The sorption experiment indicated the preferential sorption of the nanohybrid films toward water, and the water sorption increased only slightly as the silica content increasing. After the PVA–silica nanohybrid was fabricated into ultrathin skin layer on the polysulfone (PSF) hollow fiber support layer, the PVA–silica/PSF composite membrane exhibited the highest permeance of 8.99 × 10−9 m3 (STP)/m2 s Pa and an infinite separation factor (larger than 2 × 106) for 0.3 wt.% water in propylene gas feed at 298 K, when the silica content was 3.4 wt.%.