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Nano structure including pore structure and amine assembly is critical for improving sorption and desorption kinetics for adsorptive CO2 separation. The present work delineates (1) the influence of the nano-scale pore structure of amine-functionalized solid sorbents, and (2) effect of changing the assembly of amine molecules on surface of nano-porous SiO2 on the rates of adsorption and desorption of CO2. 50PEI-MSN sorbent with inverted cone-shaped pores was prepared by using mesoporous silica nanospheres (MSN) with inverted cone-shaped pores for the loading of polyethyleneimine (PEI). Co-structure-directing (CSD) method was used to synthesize the sorbent with arranged amine assembly at nano-scale (2N-CSD). By comparison with 50PEI-SBA15 as a benchmark sorbent, both sorbents have improved sorption and desorption kinetics. There are significant effects of nano pore structure and amine assembly on the sorption and desorption kinetics. The inverted cone-shaped pores in MSN allow loading polymeric amines in their narrower ends and leaving larger pore mouths open for the transport of CO2; 50PEI-MSN shows a maximum sorption rate of 81.4 mg·g-1·min-1 with average sorption rate of 25.4 mg·g-1·min-1 at 80 °C which are 34% and 59% higher than the corresponding values for 50PEI-SBA15; a maximum desorption rate of 38.4 mg·g-1·min-1 with average desorption rate of 11.8 mg·g-1·min-1 ramping from 30 to 95 °C which are 37% and 156% higher than the corresponding values for 50PEI-SBA15. The arranged monolayer-like amine assembly on surface of nanoporous SiO2 likely provides high amine sorption sites through improved accessibility of amine, and 2N-CSD shows a maximum sorption rate of 60.5 mg·g-1·min-1, with average sorption rate of 12.8 mg·g-1·min-1 at 30 °C which are 108% and 205% higher than the corresponding values for 50PEI-SBA15; a lower maximum desorption rate of 9.7 mg·g-1·min-1 and average desorption rate of 9.8 mg·g-1·min-1 ramping from 30 to 95 °C which is 250% higher than the corresponding value for 50PEI-SBA15. The present work demonstrates the importance of tailoring nano-scale pore structure and amine assembly for significantly improving sorption and desorption kinetics of adsorptive CO2 separation.

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Publication history
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Acknowledgements

Publication history

Received: 25 January 2021
Revised: 19 May 2021
Accepted: 20 May 2021
Published: 09 June 2021
Issue date: September 2021

Copyright

© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2021

Acknowledgements

This work was financially supported by the National Key Research and Development Program of China (No. 2016YFB0600902-4), the Fundamental Research Funds for the Central Universities (No. DUT20RC (5)002), and the CUHK Research Startup Fund (No. #4930981).

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