There are increasing requirements for highly efficient and solvent-resistant nanoporous membranes in various separation processes. Traditional membranes usually have a poor solvent resistance and a thick skin layer leading to a low permeation flux. Currently, the major challenge lies in fabrication of ultrathin few-nanometers-pore membranes for fast organic filtration. Herein, a facile approach is presented to prepare ultrafine cellulose nanofibers for fabrication of ultrathin nanoporous membranes. The obtained nanofibers have a uniform diameter of 7.5 ± 2.5 nm and are homogeneously dispersed in aqueous solutions that are favorable to the fabrication of ultrathin nanoporous membranes. The resulting cellulose nanoporous membranes have an adjustable thickness down to 23 nm and pore sizes ranging from 2.5 to 12 nm. They allow fast permeation of water and organics during pressure-driven filtration. Typically, the 30 nm thick membrane has high fluxes of 1.14 and 3.96 × 10⁴ L h⁻¹ m⁻² bar⁻¹ for pure water and acetone respectively. Furthermore, the as-prepared cellulose nanofibers are easily employed to produce a novel syringe filter with sub-10 nm pores that have a wide application in fast separation and purification of nanoparticles on few-nanometers scale.

Ultrafiltration (UF) is a size selective pressure-driven membrane separation process increasingly required for high efficient water treatment and suspended solids removal in many industrial applications. This study examined the morphology of as-prepared cellulose nanofibers and then utilized the nanofibers dispersion to fabricate nanofibrous nanoporous membranes with potential wide applications in various fields including water treatment. The nanofibers were prepared using a simple and powerful mechanical high intensity ultrasonication following a pre-chemical treatment of α-cellulose. The cellulose nanofibers’ morphology, crystallinity, and yield were found to be influenced by pre-chemical treatment. Cellulose nanofibrous membranes were fabricated from cellulose nanofibers dispersion on a porous support. A nanoporous structure with an extensive interconnected network of fine cellulose nanofibers was formed on the support substrate. The resulting membranes exhibited typical and high-efficient UF performances with high water fluxes of up to 2.75 10³ L/m²/h/bar. The membranes also displayed high rejections for ferritin and 10 nm gold nanoparticles with a reactive surface area capable of rapidly decolorizing methylene blue from its aqueous solution. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43544.

Stimuli-responsive nanoporous membranes have attracted increasing interest in various fields due to their abrupt changes of permeation/separation in response to the external environment. Here we report ultrathin pH-sensitive nanoporous membranes that are easily fabricated by the self-assembly of poly(acrylic acid) (PAA) in a metal hydroxide nanostrand solution. PAA-adsorbed nanostrands (2.5–5.0 nm) and PAA-Cu^II nanogels (2.0–2.5 nm) grow competitively during self-assembly. The PAA-adsorbed nanostrands are deposited on a porous support to fabricate ultrathin PAA membranes. The membranes display ultrafast water permeation and good rejection as well as significant pH-sensitivity. The 28 nm-thick membrane has a water flux decrease from 3740 to 1350 L m⁻¹ h⁻¹ bar⁻¹ (pH 2.0 to 7.0) with a sharp decrease at pH 5.0. This newly developed pH-sensitive nanoporous membranes may find a wide range of applications such as controlled release and size- and charge-selective separation.

Chitosan (CS)/polyvinylpyrrolidone (PVP)-silica hybrid membranes are prepared to separate the methanol/ethylene glycol (EG) azeotrope. These hybrid membranes are formed in semi-interpenetrating network structure at the molecular scale via sol-gel reactions between CS and tetraethoxysilane (TEOS). The physico-chemical property and morphology of the as-prepared membranes are investigated in detail. They have lower crystallinity, higher thermal stability, and denser structure than the pristine CS membrane and its blending counterpart. The as-prepared hybrid membranes demonstrate excellent performances and a great potential in pervaporation separation of methanol/EG. Silica-hybridization depressed the swelling degree of membranes in the azeotrope, and remarkably enhanced methanol sorption selectivity. The membrane containing 7.77 wt % PVP and 14.52 wt % TEOS has a permeation flux of 0.119 kg m⁻² h⁻¹ and separation factor of 1899. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013