Pressure‐Induced Hydration and Insertion of CO₂ into Ag‐Natrolite

Abstract

CO2 insertion under pressure: In silver-exchanged natrolite, a low and technically achievable onset pressure-induced hydration has been established at 0.4 GPa accompanied by an approximately 5 % expansion in the unit-cell volume (see figure). This unique property has been utilized to trap CO2 under pressure in nominally non-penetrating natrolite pores.

Pressure- and Temperature-Induced Insertion of N2, O2 and CH4 to Ag-Natrolite

“…Concomitantly with our previous high-pressure studies of the Ag-NAT, we found that the onset pressure of the first PII exponentially increases as a function of the kinetic diameter of molecules as PTM ( Figure 4 a) [ 9 , 13 ]. In terms of the kinetic diameter, the water molecule can be most permeable in the angstrom scale channel and therefore, the pressure required for an over-hydrated state is as low as 0.4(1) GPa.…”

“…Compared with the a - and b- axes, the c -axis slightly decreases at the pressure of the first PII (−1.0(1)% in the N 2 run; −0.5(1)% in the O 2 run; −0.8(1)% in the CH 4 run). This phenomenon of axes changing when PII occurs is related to expansion and becoming more circular in the channel window [ 9 ]. In the N 2 run, all axes slightly increase within ~0.5% at 2.15(5) GPa, the onset pressure of the second PII.…”

“… ( a ) Onset pressure of pressure-induced insertion vs. kinetic diameter of molecule as PTM; ( b ) normalized volume plot in a presence of different PTMs (N 2 , O 2 , CH 4 , CO 2 , H 2 O, Xe and Kr) [ 9 , 13 ]. …”

“…However, numerous high-pressure studies of natrolite (Na 16 Al 16 Si 24 O 80 ·16 H 2 O) have recently been carried out using pressure-induced hydration (PIH) and pressure-induced insertion (PII) accompanying abnormal volume expansion under applied pressures. A notable quantity of studies reported potential for various applications, such as in sequestration of cations and molecules (e.g., Cs + , Sr 2+ , Pb 2+ and CO 2 ) and trapping of noble gases (e.g., Ar, Kr and Xe), resulting in the insertion of chemical species by widening the window of natrolite pores using pressure; the noble gases then remain trapped by narrowing the channel opening after pressure release [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. With respect to the crystal structure, the PIH and PII are a consequence of the auxetic behavior of the natrolite framework, which is visualized using a rotating-squares model of framework topology [ 14 ].…”

“…Among the various cation-exchanged natrolites, the silver-exchanged form (Ag-NAT) absorbs water and CO 2 molecules at comparatively low pressures (0.4(1) GPa and 0.8(1) GPa, respectively), whereas natural natrolite absorbs both at 1.0(1) GPa. The onset pressure of pressure-induced insertion (PII) arises from the circular geometry of the channel window, and we have suggested that one of the possible materials for CO 2 storage under crustal conditions [ 9 ]. We investigated the pressure-induced insertion (PII) of N 2 , O 2 and CH 4 gases inside microchannels of the Ag-NAT in order to explore potential material for (ir)reversible gas storage by controlling the pressure and temperature.…”