Spectroscopic characterization of alkali-metal exchanged natrolites

Abstract

Synchrotron infrared (IR) and micro-Raman spectroscopic studies have been performed on zeolite natrolites as a function of the non-framework composition at ambient conditions. This establishes the spectroscopic characterization of the ion-exchanged natrolites in the alkali-metal series both in the as-prepared hydrated (M-NAT-hyd, M = Li, Na, K, Rb, and Cs) and some stable dehydrated forms (M-NAT-deh, M = Rb and Cs). The former series exhibits non-framework cation-size dependent opening of the helical channels to span ca. 21° range in terms of the chain rotation angle, ψ (or ca. 45° range in terms of the chain bridging angle, T-O2-T). For these hydrated phases, both IR and Raman spectra reveal that the degree of the red-shifts in the frequencies of the helical 8-ring channel as well as the 4-ring unit is proportional to the ionic radius of the non-framework cations. Linear fits to the data show negative slopes of -55.7 from Raman and -18.3 from IR in the 8-ring frequencies and ionic radius relationship. The spectroscopic data are also used to identify the modes of the dehydration-induced "collapse" of the helical 8-ring channels as observed in the stable anhydrous Rb-NAT-deh and Cs-NAT-deh. In addition, we demonstrate that the spectroscopic data in the hydrated series can be used to distinguish different water arrangements along the helical channels based on the frequency shifts in the H-O-H bending band and the changes in the O-H stretching vibration modes.

Spectroscopic and Computational Characterizations of Alkaline‐Earth‐ and Heavy‐Metal‐Exchanged Natrolites

“…This could be because of the different electrical field within the helical 8ring unit owing to the different electric charges in monovalent (Na + -, Ag + -) and divalent (Ca 2 + -, Sr 2 + -, Ba 2 + -, Cd 2 + -, Pb 2 + -) natrolites. In accordance with previous spectroscopic studies on alkali-metal forms of natrolites, [8] we confirm that the systematic redshift of the frequency related to the helical 8-ring vibrational mode in both the Raman and IR spectra depends on the cation size (Figure 4 a,b): the peak position of this band shifts progressively to lower frequencies as the size of the EFC increases. These systematic redshifts can be approximated by linear functions with slopes of À54.6 for the Raman and À18.5 for the IR active modes (solid curves as shown in Figure 4 a,b).…”

“…The structural models of Ca 2 + -and Ag + -exchanged natrolites were chosen, as these materials are analogous to mineral scolecite (Ca 8 and exhibit an ordered distribution of EFCs and water molecules in the Cc and Fdd2 space groups, respectively. [5] The geometrical optimizations were performed through density-functional theory (DFT) calculations using the pseudo-potential plane-wave method.…”

“…Furthermore the variations in the H 2 O stretching and bending modes are understood on the basis of structural changes. [8] Herein, we extend our spectroscopic characterizations of monovalent ion-exchanged natrolites to divalent alkaline-earth and heavy metal cations, and develop systematic correlations between structural and spectroscopic parameters as a function of these EFCs. To help interpret certain vibrational bands from synchrotron IR and micro-Raman spectroscopy experiments, we perform molecular dynamics simulations on selected natrolites to complement the established X-ray structural models with H-positions.…”

Meierite, A New Barium Mineral With A Kfi-Type Zeolite Framework From the Gun Claim, Yukon Canada

“…The Raman spectrum of meierite is shown in Figure 7. Based on previous Raman spectroscopic studies of various zeolites (Dutta & Zaykoski 1988, Smirnov et al 1994, Knops-Gerris et al 1997, Goryainov & Smirnov 2001, Yu et al 2001, Liu et al 2012, Yang et al 2013, we made a tentative assignment of major Raman bands for meierite. The O-H stretching vibrations bands are located between 3100 and 3680 cm -1 .…”

Rongibbsite, Pb2(Si4Al)O11(OH), a new zeolitic aluminosilicate mineral with an interrupted framework from Maricopa County, Arizona, U.S.A.

“…Raman spectroscopy has been extensively employed to gain comprehensive structural information of various zeolitetype and feldspar-type aluminosilicate materials (e.g., Dutta , 1992Smirnov et al 1994;Wopenka et al 1998;Goryainov and Smirnov 2001;Yu et al 2001;Mozgawa et al 2004;Putnis et al 2007;Fisch et al 2008;Liu et al 2012). Presented in Figure 6 is the Raman spectrum of rongibbsite.…”