Park Joonho, Kim Heejin, Han Sang Soo, Jung Yousung
†Graduate School of EEWS (WCU), Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea.
‡Center for Nanocharacterization, Korea Research Institute of Standards and Science, Daejeon 305-340, Korea.
J Phys Chem Lett. 2012 Apr 5;3(7):826-9. doi: 10.1021/jz300047n. Epub 2012 Mar 7.
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.
减少人为碳排放是一个亟待关注的问题。金属有机框架材料（MOFs）已成为一种有前景的新型碳捕获材料平台，其中Mg-MOF-74因其开放的镁位点而对二氧化碳具有化学特异性亲和力。在此，我们通过金属取代（M = Mg、Ca以及第一过渡金属元素）来调节二氧化碳与M-MOF-74的结合亲和力，结果表明，与Mg-MOF-74相比，Ti-MOF-74和V-MOF-74的亲和力可提高6 - 9 kJ/mol。电子结构计算表明，主要亲和力趋势的起源是开放金属位点的局部电场效应，该效应使二氧化碳得以稳定，但如在弱配位键中那样，从二氧化碳的孤对电子向过渡金属的空d能级的正向电子给予作用，使得Ti和V具有比Mg、Ca和Sc更高的结合强度。
