Previous studies on CO
2
adsorbents have mainly
addressed
the identification and quantification of adsorbed CO
2
species
in amine-modified porous materials. Investigation of molecular motion
of CO
2
species in confinement has not been explored in
depth yet. This work entails a comprehensive study of molecular dynamics
of the different CO
2
species chemi- and physisorbed at
amine-modified silica materials through the determination of the rotating
frame spin–lattice relaxation times (
T
1ρ
) by solid-state NMR. Rotational correlation times
(τ
C
) were also estimated using spin relaxation models
based on the Bloch, Wangsness, and Redfield and the Bloembergen–Purcell–Pound
theories. As expected, the τ
C
values for the two
physisorbed CO
2
species are considerably shorter (32 and
20 μs) than for the three identified chemisorbed CO
2
species (162, 62, and 123 μs). The differences in molecular
dynamics between the different chemisorbed species correlate well
with the structures previously proposed. In the case of the physisorbed
CO
2
species, the τ
C
values of the CO
2
species displaying faster molecular dynamics falls in the
range of viscous liquids, whereas the species presenting slower dynamics
exhibit
T
1ρ
and τ
C
values compatible with a CO
2
layer of weakly interacting
molecules with the silica surface. The values for chemical shift anisotropy
(CSA) and
1
H–
13
C heteronuclear dipolar
couplings have also been estimated from
T
1ρ
measurements, for each adsorbed CO
2
species. The CSA
tensor parameters obtained from fitting the relaxation data agree
with the experimentally measured CSA values, thus showing that the
theories are well suited to study CO
2
dynamics in silica
surfaces.