Assembly of Defect-Free Microgel Nanomembranes for CO₂ Separation

Abstract

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.

Direct air capture: process technology, techno-economic and socio-political challenges

“…316 Very recent work on a mobile carrier system appears promising, and likely represents an important avenue for future development. 317 The significant potential of electrochemical processes and devices for direct air capture. Electrochemical gas separation processes can offer higher efficiencies than thermal-or pressure-based separation processes, as they act directly on the target molecules rather than the molecules and the medium they are within.…”

“…316 Very recent work on a mobile carrier system appears promising, and likely represents an important avenue for future development. 317…”

Macroscopic Supramolecular Assembly of Rigid Building Blocks Facilitated by Layer-By-Layer Assembled Microgel Film

“…Similar to hydrogel materials, microgel particles are promising for use in MSA because designated supramolecular functional groups can be programmed into microgel particles during the synthesis stage, − which may enrich application scenarios for MSA due to advantages of microgels’ porous structures and stimulus-responsiveness properties. − It is worth noting that LbL-assembled microgel films have been reported to heal micrometer-sized defects upon exposure to water , because of the high softness and flowability, which is significant features of flexible spacing coating for the MSA process . In this work, the LbL-assembled microgel films composed of negatively charged poly­( N -isopropylacrylamide- co -acrylic acid) microgels (AA-microgel) and a polycation of poly­(allylamine hydrochloride) (PAH) are modified onto rigid millimeter-scaled PDMS building blocks to act as both a flexible spacing coating and a supramolecular interactive surface for assembly of rigid building blocks.…”

Pd Nanoparticle-Loaded Smart Microgel-Based Membranes as Reusable Catalysts

“…The preparation of membranes with tailored properties has become an increasingly important topic in academic and industrial research. − In contrast to conventional modifications of commercially available membranes with polymers, in particular, the use of intelligent microgels offers an enormous advantage for such modifications. , Due to their chemical nature, microgels are able to respond to the external stimuli such as temperature, − pH, − or ionic strength with a change in size. The most popular microgel system in this context is based on the thermoresponsive polymer poly- N -isopropylacrylamide (PNIPAM).…”

“…While the collapsed state is characterized by the microgels becoming hydrophobic, the microgels are strongly hydrophilic in the swollen state. The properties of such systems can be tuned by simple copolymerization with, for example, hydrophobic, hydrophilic, ionic, or pH-sensitive comonomers. − Due to their diverse properties, microgels are used in the uptake and release of drugs, , in sensor technology, or as carriers of inorganic, − organic, , or biological catalysts. − In terms of surface modifications, microgels have been used for cell culture substrates as anti-fouling coatings for membrane modification ,,− or as free-standing microgel membranes with tunable diffusion properties. , Most of the surface modifications for catalytic films published to date involve modification of the substrate with the polymeric material, subsequent immobilization of metal ions, and final reduction of the ion to the metal of interest. − While this approach promises a good loading with nanoparticles (NPs), it can only be applied to chemically resistant substrates. Another drawback is that the size and number of incorporated NPs is difficult to quantify.…”