Deciphering CO2 Adsorption Mechanisms at the Atomic Scale in Cellulose and Chitosan Aerogels

resumo

Biopolymer-based aerogels have emerged as promising CO2 adsorbents for large-scale implementation due to their abundance, renewability, and low cost. However, the CO2 capture mechanisms of these materials remain poorly understood. In this study, we exploit the structural similarity between cellulose and chitosan to investigate how surface chemistry governs the CO2 adsorption mechanisms using a combination of solid-state nuclear magnetic resonance (ssNMR) spectroscopy and density functional theory (DFT) modeling. We reveal that cellulose aerogels adsorb CO2 exclusively via physisorption, whereas chitosan aerogels exhibit both physisorption and chemisorption. Chemical shift analysis, supported by DFT calculations, identifies two chemisorbed species in chitosan: carbamic acid (159.0 ppm) and ammonium carbamate (164.5 ppm). Additionally, ssNMR relaxation measurements reveal three distinct physisorbed CO2 states (solid, liquid, and gas-like) in both aerogels. By systematically tailoring the amine density (i.e., the interchain distance) in chitosan, we elucidate its influence on the CO2 chemisorption speciation. Based on well-established principles of polysaccharide chemistry, we engineered a blended cellulose dialdehyde–chitosan aerogel with reduced amino group density. In this material, only the carbamic acid peak was observed, demonstrating that ammonium carbamate formation requires closely spaced amino groups. These findings highlight the critical role of surface functional groups and amine density in dictating the CO2 adsorption pathways. Our study provides valuable atomic level insights into the structure–function relationships of biopolymer-based sorbents, facilitating their optimized design for CO2 capture technologies.

autores

Daniel Pereira, Mirtha A. O. Lourenço, Mariana Sardo, Armando J. D. Silvestre, Ildefonso Marin-Montesinos* and Luís Mafra*

Grupos

G1 - Materiais Porosos e Nanossistemas
G4 - Materiais Renováveis e Economia Circular

Projectos

CICECO - Aveiro Institute of Materials (UIDB/50011/2020)

CICECO - Aveiro Institute of Materials (UIDP/50011/2020)

Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)

Rede Nacional de Ressonância Magnética Nuclear (PTNMR)

Unveiling CO2 chemisorption mechanisms in solid adsorbents via surface-enhanced ex(in)-situ NMR (NMR4CO2)

Rationale design of sustainable porous organosilicas for optimal CO2 uptake from biogas (GRACE)

agradecimentos

This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 (DOI 10.54499/UIDB/50011/2020), UIDP/50011/2020 (DOI 10.54499/UIDP/50011/2020), and LA/P/0006/2020 (DOI 10.54499/LA/P/0006/2020), financed by national funds through FCT/MCTES (PIDDAC). The NMR spectrometers are part of the National NMR Network (PTNMR) and are partially supported by Infrastructure Project 022161 (cofinanced by FEDER through COMPETE 2020, POCI and PORL, and FCT through PIDDAC). This work has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant Agreement 865974). FCT is also acknowledged by D.P. for a Ph.D. Studentship UI/BD/151048/2021 (DOI: 10.54499/UI/BD/151048/2021). M. A. O. L. for a Junior Researcher Position (DOI: 10.54499/2021.01158.CEECIND/CP1659/CT0022) and M. S. for an Assistant Research (DOI 10.54499/2020.00056.CEECIND/CP1589/CT0005). M. A. O. L. further acknowledges funding from the European Union’s Horizon Europe research and innovation programme under grant agreement no. 101090287. The authors acknowledge the support of LCA-UC (Laboratory for Advanced Computing at University of Coimbra) and Oblivion Supercomputer (University of Évora) funded by FCT I.P. under the project Advanced Computing Project CPCA/A0/432327/2021 (platform Navigator) and 2022.15931.CPCA.A1 (platform Oblivion).