Dry–wet phase inversion block copolymer membranes with a minimum evaporation step from NMP/THF mixtures

Polyoxometalate-Modified Amphiphilic Polystyrene-block-poly(2-(dimethylamino)ethyl methacrylate) Membranes for Heterogeneous Glucose to Formic Acid Methyl Ester Oxidation

Herein, we present a new heterogeneous catalyst active toward glucose to formic acid methyl ester oxidation. The catalyst was fabricated via electrostatic immobilization of the inorganic polyoxometalate HPA-5 catalyst H8[PMo7V5O40] onto the pore surface of amphiphilic block copolymer membranes prepared via non-solvent-induced phase separation (NIPS). The catalyst immobilization was achieved via wet impregnation due to strong coulombic interactions between protonated tertiary amino groups of the polar poly(2-(dimethylamino)ethyl methacrylate) block and the anionic catalyst. Overall, three sets of five consecutive catalytic cycles were performed in an autoclave under 90 °С and 11.5 bar air pressure in methanol, and the corresponding yields of formic acid methyl ester were quantified via head-space gas chromatography. The obtained results demonstrate that the membrane maintains its catalytic activity over multiple cycles, resulting in high to moderate yields in comparison to a homogeneous catalytic system. Nevertheless, presumably due to leaching, the catalytic activity declines over five catalytic cycles. The morphological and chemical changes of the membrane during the prolonged catalysis under harsh conditions were examined in detail using different analytic tools, and it seems that the underlying block copolymer is not affected by the catalytic process.

New Preparation Methods for Pore Formation on Polysulfone Membranes

This work described the preparation of membranes based on aromatic polysulfones through the phase-inversion method induced by a nonsolvent, generating the phase separation (NIPS) process. Three new techniques, including the nano iron acid etching method, base hydrolysis method of crosslinked polymers, and base hydrolysis method of a reactive component in a binary polymer blend, were developed for pore creation on membranes. The modified polymers and obtained membranes were carefully characterized. The uniform pores were successfully created by base hydrolysis of the crosslinked polymers and obtained at the size of the crosslinker. Moreover, homogeneous pores were created after base hydrolysis of the membranes prepared from binary polymer blends due to the internal changes in the polymer structure. The separation performance of membranes was tested with different inorganic salt solutions and compared with commercially known membranes. These new membranes exhibited high water flux (up to 3000 L/m^-2·h^-1 at 10 bar and at 25 °C) and reasonable rejections for monovalent (21-44%) and multivalent ions (18-60%), depending on the different etching of the hydrolysis times. The comparison of these membranes with commercial ones confirmed their good separation performance and high potential application for water treatment applications.

Stimuli-Responsive Membranes through Sustainable Aqueous Phase Separation

Polymeric membranes are used on huge scales for kidney dialysis, wastewater treatment, and drinking water production. However, almost all polymeric membranes are fabricated by a process reliant on the use of unsustainable, expensive, and reprotoxic dipolar aprotic solvents. In this work, we propose an aqueous phase separation approach for preparing porous membrane films. Poly(4-vinylpyridine) (P4VP), a pH-responsive polymer, is first dissolved at low pH where the polymer is charged and subsequently cast as a thin film. Switching to a high pH where the polymer is uncharged and insoluble results in controlled phase separation and solidification of the polymer into porous membrane structures. This approach gives a large degree of control over membrane structure, leading to symmetric porous microfiltration membranes and asymmetric dense nanofiltration membranes. Moreover, the use of a pH-responsive polymer leads directly to a pH-responsive membrane, where the degree of responsive behavior can be tuned by the degree of cross-linking. Such responsive behavior allows effective cleaning of the membrane, without the use of harsh chemicals. This work outlines an approach toward preparing membranes in a more sustainable fashion-an approach that allows control over the membrane structure and one that naturally leads to advanced membranes with responsive properties.

Free-standing thermo-responsive nanoporous membranes from high molecular weight PS-PNIPAM block copolymers synthesized via RAFT polymerization

Free-standing, fully reversible thermo-responsive nanoporous membranes were fabricated from PS-PNIPAM block copolymers.