Tuning Metal–Organic Frameworks with Open-Metal Sites and Its Origin for Enhancing CO2 Affinity by Metal Substitution
Joonho Park, Heejin Kim, Sang Soo Han, and Yousung Jung
J. Phys. Chem. Lett., 2012, 3 (7), pp 826–829
Publication Date (Web): March 4, 2012
Copyright © 2012 American Chemical Society
Reducing anthropogenic carbon emission is a problem that requires immediate attention. Metal–organic frameworks (MOFs) have emerged as a promising new materials platform for carbon capture, of which Mg-MOF-74 offers chemospecific affinity toward CO2 because of the open Mg sites. Here we tune the binding affinity of CO2 for M-MOF-74 by metal substitution (M = Mg, Ca, and the first transition metal elements) and show that Ti- and V-MOF-74 can have an enhanced affinity compared to Mg-MOF-74 by 6–9 kJ/mol. Electronic structure calculations suggest that the origin of the major affinity trend is the local electric field effect of the open metal site that stabilizes CO2, but forward donation from the lone-pair electrons of CO2 to the empty d-levels of transition metals as in a weak coordination bond makes Ti and V have an even higher binding strength than Mg, Ca, and Sc.
Keywords: carbon capture and sequestration; CO2 physisorption; MOF-74; CO2 binding nature; forward donation; PBE+D2
For further details: http://pubs.acs.org/doi/abs/10.1021/jz300047n