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.
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
subject category
Engineering; Environmental Sciences & Ecology
authors
Afonso, R; Sardo, M; Mafra, L; Gomes, JRB
our authors
José R. B. Gomes
Principal Researcher
Luís Mafra
Principal Researcher
Mariana Coutinho Sardo
Assistant Researcher
Rui Afonso
Post-Doc Fellowshipacknowledgements
This work was developed in the scope of the projects CICECO-Aveiro Institute of Materials POCI-01-0145-FEDER-007679 (ref. FCT UID/CTM/50011/2019), PRESS-NMR_MAT - P2020-PTDC/QEQQAN/6373/2014, GAS2-MAT-DNPSENS - POCI-01-0145-FEDER-028747 and Smart Green Homes POCI-01-0247-FEDER-007678, a copromotion between Bosch Termotecnologia S.A. and the University of Aveiro. These projects are financed by Portugal 2020 under the Competitiveness and Internationalization Operational Program and by the European Regional Development Fund (FEDER). The authors are also thankful to Fundacao para a Ciencia e a Tecnologia (FCT) for the Investigator FCT program (LM and JRBG).