title: Rapid exchange between atmospheric CO2 and carbonate anion intercalated within magnesium rich layered double hydroxide.
abstract: The carbon cycle, by which carbon atoms circulate between atmosphere, oceans, lithosphere, and the biosphere of Earth, is a current hot research topic. The carbon cycle occurring in the lithosphere (e.g., sedimentary carbonates) is based on weathering and metamorphic events so that its processes are considered to occur on the geological time scale (i.e., over millions of years). In contrast, we have recently reported that carbonate anions intercalated within a hydrotalcite (Mg0.75Al0.25(OH)2(CO3)0.125·yH2O), a class of a layered double hydroxide (LDH), are dynamically exchanging on time scale of hours with atmospheric CO2 under ambient conditions. (Ishihara et al., J. Am. Chem. Soc. 2013, 135, 18040-18043). The use of (13)C-labeling enabled monitoring by infrared spectroscopy of the dynamic exchange between the initially intercalated (13)C-labeled carbonate anions and carbonate anions derived from atmospheric CO2. In this article, we report the significant influence of Mg/Al ratio of LDH on the carbonate anion exchange dynamics. Of three LDHs of various Mg/Al ratios of 2, 3, or 4, magnesium-rich LDH (i.e., Mg/Al ratio = 4) underwent extremely rapid exchange of carbonate anions, and most of the initially intercalated carbonate anions were replaced with carbonate anions derived from atmospheric CO2 within 30 min. Detailed investigations by using infrared spectroscopy, scanning electron microscopy, powder X-ray diffraction, elemental analysis, adsorption, thermogravimetric analysis, and solid-state NMR revealed that magnesium rich LDH has chemical and structural features that promote the exchange of carbonate anions. Our results indicate that the unique interactions between LDH and CO2 can be optimized simply by varying the chemical composition of LDH, implying that LDH is a promising material for CO2 storage and/or separation.
authors.affiliation: International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS) , 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Pathik
authors.initials: P
authors.lastname: Sahoo
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Ishihara
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Yamada
authors.forename: Kenzo
authors.initials: K
authors.lastname: Deguchi
authors.forename: Shinobu
authors.initials: S
authors.lastname: Ohki
authors.forename: Masataka
authors.initials: M
authors.lastname: Tansho
authors.forename: Tadashi
authors.initials: T
authors.lastname: Shimizu
authors.forename: Nii
authors.initials: N
authors.lastname: Eisaku
authors.forename: Ryo
authors.initials: R
authors.lastname: Sasai
authors.forename: Jan
authors.initials: J
authors.lastname: Labuta
authors.forename: Daisuke
authors.initials: D
authors.lastname: Ishikawa
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Hill
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Ariga
authors.forename: Bishnu Prasad
authors.initials: BP
authors.lastname: Bastakoti
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Yamauchi
authors.forename: Nobuo
authors.initials: N
authors.lastname: Iyi
keywords: anion exchange; carbon dioxide; carbonate; clay mineral; isotope; layered double hydroxide