Herein we report that an aqueous solution of temperature-responsive micro- and nanogel particles (GPs) consisting of N-isopropylacrylamide (NIPAm) and N-[3-(dimethylamino)propyl]methacrylamide (DMAPM) reversibly absorbs and desorbs CO(2) via a phase transition induced by cooling and heating cycles (30-75 °C). Below the phase-transition temperature, most of the amines in the swollen GPs are capable of forming ion pairs with absorbed bicarbonate ions. However, above the phase-transition temperature, shrinkage of the GPs lowers the pK(a) and the number of amine groups exposed to water, thereby resulting in almost complete desorption of CO(2). The GPs can reversibly absorb more than the DMAPM monomer and polymer without NIPAm, which indicates the importance of the temperature-responsive phase transition of polymers in determining the degree of absorption. The results show the potential of temperature-responsive polymer solutions as absorbents to sequester CO(2) at a low energy cost.
Hydrogel films composed of temperature-responsive microgel particles (GPs) containing amine groups work as stimuli-responsive carbon dioxide absorbent with a high capacity of approximately 1.7 mmol g(-1). Although the dried films did not show significant absorption, the reversible absorption capacity dramatically increased by adding a small amount of water (1 mL g(-1)). The absorption capacity was independent of the amount of added water beyond 1 mL g(-1), demonstrating that the GP films can readily be used under wet conditions. The amount of CO2 absorbed by the GP films was proportional to their thickness up to 200-300 μm (maximum capacity of about 2 L m(-2) . Furthermore, the films consisting of GPs showed faster and greater absorption and desorption of CO2 than that of monolithic hydrogel films. These results indicated the importance of a fast stimulus response rate of the films that are composed of GPs in order to achieve long-range and fast diffusion of bicarbonate ions. Our study revealed the potential of stimuli-responsive GP films as energy-efficient absorbents to sequester CO2 from high-humidity exhaust gases.
The development of robust and thin CO 2 separation membranes that allow fast and selective permeation of CO 2 will be crucial for rebalancing the global carbon cycle. Hydrogels are attractive membrane materials because of their tunable chemical properties and exceptionally high diffusion coefficients for solutes. However, their fragility prevents the fabrication of thin defect-free membranes suitable for gas separation. Here, we report the assembly of defect-free hydrogel nanomembranes for CO 2 separation. Such membranes can be prepared by coating an aqueous suspension of colloidal hydrogel microparticles (microgels) onto a flat, rough, or micropatterned porous support as long as the pores are hydrophilic and the pore size is smaller than the diameter of the microgels. The deformability of the microgel particles enables the autonomous assembly of defect-free 30−50 nm-thick membrane layers from deformed ∼15 nm-thick discoidal particles. Microscopic analysis established that the penetration of water into the pores driven by capillary force assists the assembly of a defect-free dense hydrogel layer on the pores. Although the dried films did not show significant CO 2 permeance even in the presence of amine groups, the permeance dramatically increased when the membranes are adequately hydrated to form a hydrogel. This result indicated the importance of free water in the membranes to achieve fast diffusion of bicarbonate ions. The hydrogel nanomembranes consisting of amine-containing microgel particles show selective CO 2 permeation (850 GPU, α CO2/N2 = 25) against post-combustion gases. Acid-containing microgel membranes doped with amines show highly selective CO 2 permeation against post-combustion gases (1010 GPU, α CO2/N2 = 216) and direct air capture (1270 GPU, α CO2/N2 = 2380). The membrane formation mechanism reported in this paper will provide insights into the self-assembly of soft matters. Furthermore, the versatile strategy of fabricating hydrogel nanomembranes by the autonomous assembly of deformable microgels will enable the large-scale manufacturing of high-performance separation membranes, allowing low-cost carbon capture from postcombustion gases and atmospheric air.
Hydrogel films composed of temperature‐responsive microgel particles (GPs) containing amine groups work as stimuli‐responsive carbon dioxide absorbent with a high capacity of approximately 1.7 mmol g−1. Although the dried films did not show significant absorption, the reversible absorption capacity dramatically increased by adding a small amount of water (1 mL g−1). The absorption capacity was independent of the amount of added water beyond 1 mL g−1, demonstrating that the GP films can readily be used under wet conditions. The amount of CO2 absorbed by the GP films was proportional to their thickness up to 200–300 μm (maximum capacity of about 2 L m−2). Furthermore, the films consisting of GPs showed faster and greater absorption and desorption of CO2 than that of monolithic hydrogel films. These results indicated the importance of a fast stimulus response rate of the films that are composed of GPs in order to achieve long‐range and fast diffusion of bicarbonate ions. Our study revealed the potential of stimuli‐responsive GP films as energy‐efficient absorbents to sequester CO2 from high‐humidity exhaust gases.
Hydrogelfilme …… aus temperaturresponsiven und mit Amingruppen funktionalisierten Mikrogelpartikeln (GPs) kçnnen als Absorptionsmittel für CO 2 verwendet werden, wie Y. Hoshino et al. in ihrer Zuschrift auf S. 2692 ff. berichten. Die Fähigkeit der GP-Filme, reversibel CO 2 zu absorbieren, ist proportional zur Filmdicke, und ihre Kapazität übertrifft die eines monolithischen Gelfilms. Mit den GP-Filmen steht ein Material zur Verfügung, um CO 2 energieeffizient aus sehr feuchten Abgasen abzutrennen.
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