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Title: Overcoming double-step CO 2 adsorption and minimizing water co-adsorption in bulky diamine-appended variants of Mg 2(dobpdc)

Alkyldiamine-functionalized variants of the metal–organic framework Mg 2(dobpdc) (dobpdc 4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) are promising for CO 2 capture applications owing to their unique step-shaped CO 2 adsorption profiles resulting from the cooperative formation of ammonium carbamate chains. Primary,secondary (1°,2°) alkylethylenediamine-appended variants are of particular interest because of their low CO 2 step pressures (≤1 mbar at 40 °C), minimal adsorption/desorption hysteresis, and high thermal stability. Herein, we demonstrate that further increasing the size of the alkyl group on the secondary amine affords enhanced stability against diamine volatilization, but also leads to surprising two-step CO 2 adsorption/desorption profiles. This two-step behavior likely results from steric interactions between ammonium carbamate chains induced by the asymmetrical hexagonal pores of Mg 2(dobpdc) and leads to decreased CO 2 working capacities and increased water co-adsorption under humid conditions. To minimize these unfavorable steric interactions, we targeted diamine-appended variants of the isoreticularly expanded framework Mg 2(dotpdc) (dotpdc 4- = 4,4''-dioxido-[1,1':4',1''-terphenyl]-3,3''-dicarboxylate), reported here for the first time, and the previously reported isomeric framework Mg-IRMOF-74-II or Mg 2(pc-dobpdc) (pc-dobpdc 4- = 3,3'-dioxidobiphenyl-4,4'-dicarboxylate, pc = para-carboxylate), which, in contrast to Mg 2(dobpdc), possesses uniformally hexagonal pores. By minimizing the steric interactions between ammonium carbamate chains, these frameworks enable amore » single CO 2 adsorption/desorption step in all cases, as well as decreased water co-adsorption and increased stability to diamine loss. Functionalization of Mg 2(pc-dobpdc) with large diamines such as N-(n-heptyl)ethylenediamine results in optimal adsorption behavior, highlighting the advantage of tuning both the pore shape and the diamine size for the development of new adsorbents for carbon capture applications.« less
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  1. Univ. of California, Berkeley, CA (United States). Dept. of Chemistry
  2. Harvard Univ., Cambridge, MA (United States). Dept. of Chemistry and Chemical Biology
  3. ExxonMobil Research and Engineering Company, Annandale, NJ (United States)
  4. Univ. of California, Berkeley, CA (United States). Dept. of Chemistry. Dept. of Chemical Engineering; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division
Publication Date:
Grant/Contract Number:
AC02-05CH11231; AR00040; SC0001015; F32GM120799
Accepted Manuscript
Journal Name:
Chemical Science
Additional Journal Information:
Journal Volume: 9; Journal Issue: 1; Journal ID: ISSN 2041-6520
Royal Society of Chemistry
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States); ExxonMobil Research and Engineering Company, Annandale, NJ (United States)
Sponsoring Org:
USDOE Advanced Research Projects Agency - Energy (ARPA-E); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); ExxonMobil Research and Engineering Company (United States); National Inst. of Health (NIH) (United States)
Country of Publication:
United States
OSTI Identifier: