Structural and spectroscopic studies of alkali-metal exchanged stilbites

Abstract

The structural, infrared (IR) and Raman spectroscopic properties of alkalimetal exchanged (Na + , K + , Rb + , Cs +) zeolites with the stilbite (STI) framework have been studied by Rietveld analysis of high-resolution synchrotron X-ray powder diffraction data, micro-Raman and synchrotron IR spectroscopy at ambient conditions. Ordered arrangements of the extra-framework cations (EFCs) and H 2 O molecules were found at the intersection of the 10-and 8-ring channels as well as framework distortions and deformations of the channel system caused by the EFCs distributions. The T(5)-T(5) distances along the chains of the structural building units range from 8.921(1) to 8.979(5) Å and scale with the size of EFCs in Na-, K-, Rb-, Cs-STI. Furthermore, our spectroscopic studies show a systematic increase of characteristic band frequencies for the 4-and 5-ring breathing vibration modes in the far-IR spectral region with the size of the EFCs. The frequencies of the ring vibrational bands in the

Removal of Barium from Solution by Natural and Iron(III) Oxide-Modified Allophane, Beidellite and Zeolite Adsorbents

“…The IR bands at 1120 cm −1 , 1022 cm −1 , 986 cm −1 and 798 cm −1 correspond to Si–O stretching vibrations in beidellite and quartz, whereas the IR band at 747 cm −1 is most likely related to the stretching mode of Al–O–Al linkage [ 36 ]. The MIR spectra of ZEO and FeO-ZEO display strong adsorption in the hydroxyl stretching region at 3537 cm −1 and 3321 cm −1 and a weak one at 3615 cm −1 , which are attributed to hydroxyl stretching vibrations in zeolitic water in natrolite and stilbite [ 37 ]. Numerous and intense IR bands in the lattice vibration region between 1200 and 900 cm −1 are due to Si–O–Si and Si–O–Al stretching vibrations.…”

“…Numerous and intense IR bands in the lattice vibration region between 1200 and 900 cm −1 are due to Si–O–Si and Si–O–Al stretching vibrations. The IR band at 720 cm −1 corresponds to the 4-membered rings in the tetrahedral framework of zeolite structures [ 37 ]. IR spectra of the materials obtained after the adsorption experiments ( Supplementary Material Figure S2 ) look similar to those of the unreacted adsorbents, except for the ZEO and FeO-ZEO, which displayed minor modifications in the lattice vibration region.…”