Assembly of Defect-Free Microgel Nanomembranes for CO2 Separation

Yu Hoshino; Tomohiro Gyobu; Kazushi Imamura; Akira Hamasaki; Ryutaro Honda; Ryoga Horii; Chie Yamashita; Yuki Terayama; Takeshi Watanabe; Shoma Aki; Yida Liu; Junko Matsuda; Yoshiko Miura; Ikuo Taniguchi

doi:10.1021/acsami.1c06447

Assembly of Defect-Free Microgel Nanomembranes for CO₂ Separation

ACS Appl Mater Interfaces. 2021 Jun 30;13(25):30030-30038. doi: 10.1021/acsami.1c06447. Epub 2021 Jun 17.

Authors

Yu Hoshino^{1

2}, Tomohiro Gyobu¹, Kazushi Imamura¹, Akira Hamasaki¹, Ryutaro Honda¹, Ryoga Horii¹, Chie Yamashita^{1

2}, Yuki Terayama¹, Takeshi Watanabe^{1

2}, Shoma Aki^{1

2}, Yida Liu¹, Junko Matsuda^{3

4}, Yoshiko Miura¹, Ikuo Taniguchi³

Affiliations

¹ Department of Chemical Engineering, Faculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
² Japan Carbon Cycle Lab., Inc., 4-1 Kyudaishinmachi, Nishi-ku, Fukuoka 819-0388, Japan.
³ International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
⁴ International Research Center for Hydrogen Energy, Kyushu University, Fukuoka 819-0395, Japan.

PMID: 34139838
DOI: 10.1021/acsami.1c06447

Abstract

The development of robust and thin CO₂ separation membranes that allow fast and selective permeation of CO₂ 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 CO₂ 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 CO₂ 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 CO₂ permeation (850 GPU, α_CO2/N2 = 25) against post-combustion gases. Acid-containing microgel membranes doped with amines show highly selective CO₂ 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 post-combustion gases and atmospheric air.

Keywords: CO2 separation; deformable microgel; microgel membrane; micropatterned membrane; self-assembly.