Super-Hydrated Zeolites: Pressure-Induced Hydration in Natrolites

• Published in: Chemistry : a European journal Vol. 19; no. 33; pp. 10876 - 10883
• Main Authors: Seoung, Donghoon, Lee, Yongmoon, Kao, Chi-Chang, Vogt, Thomas, Lee, Yongjae
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 12.08.2013; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Cations; Channels; Chemical composition; Chemistry; Diffraction; high-pressure chemistry; Hydration; ion exchange; natrolites; Porosity; Potassium; Vibration; X-ray diffraction; X-rays; Zeolites; X-ray diffraction; high-pressure chemistry; zeolites; ion exchange; natrolites
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201300591

High‐pressure synchrotron X‐ray powder diffraction studies of a series of alkali‐metal‐exchanged natrolites, A16Al16Si24O80⋅n H2O (A=Li, K, Na, Rb, and Cs and n=14, 16, 22, 24, 32), in the presence of water, reveal structural changes that far exceed what can be achieved by varying temperature and chemical composition. The degree of volume expansion caused by pressure‐induced hydration (PIH) is inversely proportional to the non‐framework cation radius. The expansion of the unit‐cell volume through PIH is as large as 20.6 % in Li‐natrolite at 1.0 GPa and decreases to 6.7, 3.8, and 0.3 % in Na‐, K‐, and Rb‐natrolites, respectively. On the other hand, the onset pressure of PIH appears to increase with non‐framework cation radius up to 2.0 GPa in Rb‐natrolite. In Cs‐natrolite, no PIH is observed but a new phase forms at 0.3 GPa with a 4.8 % contracted unit cell and different cation–water configuration in the pores. In K‐natrolite, the elliptical channel undergoes a unique overturn upon the formation of super‐hydrated natrolite K16Al16Si24O80⋅32 H2O at 1.0 GPa, a species that reverts back above 2.5 GPa as the potassium ions interchange their locations with those of water and migrate from the hinge to the center of the pores. Super‐hydrated zeolites are new materials that offer numerous opportunities to expand and modify known chemical and physical properties by reversibly changing the composition and structure using pressure in the presence of water. Zeolite under pressure: Super‐hydrated zeolite, K16Al16Si24O80⋅32 H2O, undergoes a unique transformation above 2.5 GPa whereby the potassium ions interchange their locations with those of water, whereas the elliptical channel reverts its major–minor axes, resembling a “chatterbox motion” (see graphic). Alkali‐metal‐exchanged natrolites under pressure reveal structural changes that far exceed what can be achieved by varying temperature and chemical composition.