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Hierarchical N-doped Carbon as CO Adsorbent with High CO Selectivity from Rationally Designed Polypyrrole Precursor
John W. F. To, Jiajun He, Jianguo Mei, Reza Haghpanah, Zheng Chen, Tadanori Kurosawa, Shucheng Chen, Won-Gyu Bae , Lijia Pan, Jeffery B.-H. Tok, Jennifer Wilcox, and Zhenan Bao J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.5b11955 • Publication Date (Web): 30 Dec 2015 Downloaded from http://pubs.acs.org on December 30, 2015
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Hierarchical N-doped Carbon as CO2 Adsorbent with High CO2 Selectivity from Rationally Designed Polypyrrole Precursor
John W. F. To,a,† Jiajun He,b,† Jianguo Mei,a,c Reza Haghpanah,b Zheng Chen,a Tadanori Kurosawa,a Shucheng Chen,a Won-Gyu Bae,a Lijia Pan,d Jeffery B.-H. Tok,a Jennifer Wilcox,b,* and Zhenan Baoa,* a b
Department of Chemical Engineering, Stanford University, California, 94305, USA
Department of Energy Resources Engineering, Stanford University, California, 94305, USA c
Department of Chemistry, Purdue University, Indiana, 47907 ,USA
d
Collaborative Innovation Center of Advanced Microstructures, Jiangsu Provincial Key Laboratory of Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China *Corresponding Authors:
[email protected],
[email protected] †
These authors contributed equally to this work
Abstract Carbon capture and sequestration from point sources is an important component in the CO2 emission mitigation portfolio. In particular, sorbents with both high capacity and selectivity are required for reducing the cost of carbon capture. Although physisorbents have the advantage of low energy consumption for regeneration, it remains a challenge to obtain both high capacity and sufficient CO2/N2 selectivity at the same time. Here, we report the controlled synthesis of a novel N-doped hierarchical carbon that exhibits record-high Henry’s law CO2/N2 selectivity among physisorptive carbons while having a high CO2 adsorption capacity. Specifically, our synthesis involves the rational design of a modified pyrrole molecule that can co-assemble with the soft Pluronic template via hydrogen bonding and electrostatic interactions to give rise to
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mesopores followed by carbonization. The low-temperature carbonization and activation processes allow for the development of ultra-small pores (d 0.4 (Fig. 2e), corresponding to the major mesopore distribution centered at 6-8 nm (Fig. 2f). The
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mesopores stem from the removal of the block copolymer template.17 SU-MC also has 0.13 cm3 g-1 of microporosity (d < 2 nm, Fig. 2f), which originates from the cleavage of the butanoic acid side chain of the monomer. To tune the pore size distribution, esp., micropore distribution, chemical activation was carried out on SU-MC using KOH as activating agent. A series of hierarchical carbons (SU-MAC-500, 600 and 800) with different micropore size distributions were synthesized by simply varying the activation temperature. The nitrogen sorption isotherms (77 K) (Fig. 2e) of the three SU-MAC samples all showed steep uptakes at low relative pressures, corresponding to the presence of microporous features (d 0.4 (Fig. S6), indicating the presence of mesopores. Using the Brunauer– Emmett–Teller (BET) method,29 the apparent specific surface areas are calculated to be 609, 942, 1500 and 2369 m2 g-1 for SU-MC, SU-MAC-500, SU-MAC-600 and SU-MAC-800, respectively (Figs. S7-10). It can be observed that higher activation temperatures gave rise to higher specific surface areas and larger pore volumes. This is attributed to the enhanced KOH activation reactions at higher temperatures. Note that the activation process led to shrinkage of the original mesopore distribution of SU-MC (Fig. S11), which indicates the thermal instability of the mesostructure under the oxidative activation conditions. Besides, it can also be observed that KOH activation at elevated temperatures created additional pore volumes in the range of 0.7–5 nm (Fig. 2f). Note that SU-MAC-500 possesses an ultramicropore (d
