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Membrane separation has become one of the key separation technologies, which play vital roles in food and medicine production, chemical industries, water treatment, etc. Inspired by natural cell membranes with stimuli-responsive channels, artificial stimuli-switchable membranes have drawn growing attention in various fields. Among them, CO2-switchable membranes are highly appealing because of the great features of CO2 as being abundant, nontoxic, environment-friendly, free of contamination in use and good reversibility. In this Highlight article, we review the recent development of CO2-switchable membranes in aqueous medium in separation fields, showcasing applications such as controlled release, oil–water separation, self-cleaning of membranes and size-/charge-based separation. We present the working principles and challenges of CO2-switchable membranes, and also give our opinion on possible opportunities for future research directions and applications. [ABSTRACT FROM AUTHOR]

A “smart” graphene oxide (GO) based nanofiltration membrane was prepared through electrostatic and π–π interaction-driven complexation with poly(N,N-diethylaminoethyl methacrylate) bearing a pyrene end group (Py-PDEAEMA). The composite membranes show a number of attributes potentially appealing for water treatment. First, they display reversible, gas-tunable water permeability between the pore closure state under CO2 stimulation and the pore opening state upon Ar bubbling. The water permeability remains much higher than that of a pure GO membrane even at the pore closure state. Secondly, the separation of organic dye molecules from water using this membrane is similarly efficient as that using a pure GO membrane despite the much higher water permeability. Finally, as a result of CO2-induced reversal of the charge sign, the composite membrane shows an excellent trade-off between rejection of some salts like MgCl2 and water permeability, with both much higher rejection and permeability compared to a pure GO membrane. This study of a CO2-responsive, GO-based nanofiltration membrane, the first of its kind, demonstrates new perspectives in developing smart separation membranes for water purification. [ABSTRACT FROM AUTHOR]

We report a smart polymer membrane whose pore can be switched between the “closed” and “open” state just by passing CO2 and Ar in solution respectively. Compared with other stimuli, such as pH or temperature change, gas is an environmentally friendly and cost-effective stimulus for reversibly tuning the pore size and imparting the size selectivity of the membrane. [ABSTRACT FROM AUTHOR]

Inspired by marine mussel's adhesive system and facilitated transport membranes, we proposed a novel strategy to simultaneously improve the MOF–polymer interface and CO2 separation performance by coating polydopamine (PDA) on the surface of ZIF-8. PDA@ZIF-8 played multiple roles in enhancing the membrane performance. First, the inherent high permeability of ZIF-8 with ultra-microporosity was anticipated to optimize the fractional free volume and enhance the gas permeability of MMMs. Second, the PDA coating can mitigate the interfacial defects and improve the adhesion between ZIF-8 and the polymer matrix. Finally, the abundant –OH and amino groups in PDA have strong interaction with CO2 molecules, which can effectively facilitate CO2 transport. The membrane separation performance for pure gases (CO2 and N2) of the PDA@ZIF-8 incorporated Pebax membrane was investigated and compared with that of the ZIF-8-incorporated membrane without the PDA coating. An anti-tradeoff effect was obtained by addition of PDA@ZIF-8. In particular, the Pebax/PDA@ZIF-8-15 MMM showed the best gas separation performance with a CO2 permeability of 267.74 Barrer and a CO2/N2 selectivity of 62.65, surpassing Robeson's upper bound from 2008. [ABSTRACT FROM AUTHOR]

Zeolitic imidazolate framework-8 (ZIF-8) with different sizes and morphologies were successfully synthesized using a membrane dispersion reactor (MDR). The MDR synthesis applied in this paper was expected to be an efficient and economical way to synthesize ZIF materials. [ABSTRACT FROM AUTHOR]

We report a smart polymer membrane whose pore can be switched between the "closed" and "open" state just by passing CO 2 and Ar in solution respectively. Compared with other stimuli, such as pH or temperature change, gas is an environmentally friendly and cost-effective stimulus for reversibly tuning the pore size and imparting the size selectivity of the membrane.