TY - JOUR
T1 - Potassium-exchanged natrolite under pressure. computational study vs experiment
AU - Kremleva, Alena
AU - Vogt, Thomas
AU - Rösch, Notker
N1 - Publisher Copyright:
© 2014 American Chemical Society.
PY - 2014/9/25
Y1 - 2014/9/25
N2 - Using density functional theory we modeled the effects of pressure on K-exchanged natrolite, K-NAT, including superhydration and the experimentally observed structural phase transition. Natrolites are composed of T5O10secondary building units (T = Si, Al) linking two Al-and three Si-based TO4tetrahedra which in projection have an average chain rotation angle Ψ with respect to the crystallographic a-and b-axes. Besides an isomer with pore axes orientations characterized by a negative chain rotation angle, found experimentally at moderate pressure, we also examined a superhydrated isomer with pore axes orientations resulting from positive chain rotation angles in the pressure range 1-2.5 GPa. We estimated the critical pressure for possible transformations between various isomers, but we were unable to identify any specific energetic preference for a superhydrated structure with a negative chain rotation angle. Therefore, our computational results suggest that both isomers coexist in the same pressure range and transform into a more compact structure near 4 GPa. We also modeled the pathways for this latter phase transition and found rather similar barrier heights, 43-44 kJ mol-1per K+ion for both isomers, but distinct energy profiles. Thus, based on the modeling results, the isomers of superhydrated K-NAT, with either positive or negative chain rotation angles, may coexist at moderate pressures, calling for new experiments.
AB - Using density functional theory we modeled the effects of pressure on K-exchanged natrolite, K-NAT, including superhydration and the experimentally observed structural phase transition. Natrolites are composed of T5O10secondary building units (T = Si, Al) linking two Al-and three Si-based TO4tetrahedra which in projection have an average chain rotation angle Ψ with respect to the crystallographic a-and b-axes. Besides an isomer with pore axes orientations characterized by a negative chain rotation angle, found experimentally at moderate pressure, we also examined a superhydrated isomer with pore axes orientations resulting from positive chain rotation angles in the pressure range 1-2.5 GPa. We estimated the critical pressure for possible transformations between various isomers, but we were unable to identify any specific energetic preference for a superhydrated structure with a negative chain rotation angle. Therefore, our computational results suggest that both isomers coexist in the same pressure range and transform into a more compact structure near 4 GPa. We also modeled the pathways for this latter phase transition and found rather similar barrier heights, 43-44 kJ mol-1per K+ion for both isomers, but distinct energy profiles. Thus, based on the modeling results, the isomers of superhydrated K-NAT, with either positive or negative chain rotation angles, may coexist at moderate pressures, calling for new experiments.
UR - http://www.scopus.com/inward/record.url?scp=84907450628&partnerID=8YFLogxK
U2 - 10.1021/jp505973r
DO - 10.1021/jp505973r
M3 - Article
AN - SCOPUS:84907450628
SN - 1932-7447
VL - 118
SP - 22030
EP - 22039
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 38
ER -