Unravelling the Structure of Chemisorbed CO2 Species in Mesoporous Aminosilicas: A Critical Survey
authors Afonso, R; Sardo, M; Mafra, L; Gomes, JRB
nationality International
journal ENVIRONMENTAL SCIENCE & TECHNOLOGY
keywords CARBON-DIOXIDE CAPTURE; SOLID-STATE NMR; AMINE-MODIFIED SBA-15; REVERSIBLE ADSORPTION; CRYSTAL-STRUCTURE; MOLECULAR-SIEVE; GRAFTED SBA-15; POROUS SILICA; FLUE-GAS; ADSORBENTS
abstract Chemisorbent materials, based on porous aminosilicas, are among the most promising adsorbents for direct air capture applications, one of the key technologies to mitigate carbon emissions. Herein, a critical survey of all reported chemisorbed CO2 species, which may form in aminosilica surfaces, is performed by revisiting and providing new experimental proofs of assignment of the distinct CO2 species reported thus far in the literature, highlighting controversial assignments regarding the existence of chemisorbed CO2 species still under debate. Models of carbamic acid, alkylammonium carbamate with different conformations and hydrogen bonding arrangements were ascertained using density functional theory (DFT) methods, mainly through the comparison of the experimental C-13 and N-15 NMR chemical shifts with those obtained computationally. CO2 models with variable number of amines and silanol groups were also evaluated to explain the effect of amine aggregation in CO2 speciation under confinement. In addition, other less commonly studied chemisorbed CO2 species (e.g., alkylammonium bicarbonate, ditethered carbamic acid and silylpropylcarbamate), largely due to the difficulty in obtaining spectroscopic identification for those, have also been investigated in great detail. The existence of either neutral or charged (alkylammonium siloxides) amine groups, prior to CO2 adsorption, is also addressed. This work extends the molecular-level understanding of chemisorbed CO2 species in amine-oxide hybrid surfaces showing the benefit of integrating spectroscopy and theoretical approaches.
publisher AMER CHEMICAL SOC
issn 0013-936X
year published 2019
volume 53
issue 5
beginning page 2758
ending page 2767
digital object identifier (doi) 10.1021/acs.est.8b05978
web of science category Engineering, Environmental; Environmental Sciences
subject category Engineering; Environmental Sciences & Ecology
unique article identifier WOS:000460709100052

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