Synthesis and characterization of a (Zn, Ti)-substituted layered silicate

V LUCA, D J MACLACHLAN, Russell Francis Howe, R BRAMLEY

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Abstract

The incorporation of Ti-IV into the framework of zinc-substituted fluorohectorite is reported. Various spectroscopic techniques point to the substitution of Ti-IV into predominantly the octahedral rather than tetrahedral sublattice of the smectite framework, For clay particles prepared from a reactant composition with Ti/Ti+Si=0.063 (ZTFH), energy-dispersive X-ray analysis of the particles observed by transmission electron microscopy indicates that Ti accounts for ca. 6% of the Ti+Si. X-Ray absorption near-edge spectra indicate that the Ti-IV in these clay particles is predominantly in an octahedral coordination. This is supported by electron paramagnetic resonance (EPR) spectra of an oriented film sample in which Ti-IV is reduced to Ti-III by heating the sample to 450 degrees C in 30 Torr of CO. The observed single-ion Ti-III EPR spectrum shows dramatic dependence of the orientation of the clay film in the magnetic field. This orientation dependence is consistent with the principal g-tensor axis of the Ti-III site being perpendicular to the clay layers. The EPR parameters of this Ti-III species are consistent with Ti-III occupying an octahedral site. Three-pulse electron spin-echo modulation data taken at the Ti-III EPR line position shows modulation at the Li-7 nuclear frequency and simulation indicates that Ti-III ions are at a distance of 0.30-0.35 nm from Li-I ions, a distance that is consistent with these two ions occupying adjacent sites in the octahedral sheet. The MAS NMR spectrum of the zinc/titanium-substituted fluorhectorite consists of an intense Q(3) resonance at -96.4 ppm and a weak shoulder at ca. -92.5 ppm. These two resonances are interpreted as due to variations in the octahedral sheet composition. Therefore Ti-IV appears to have a strong preference for occupation of the octahedral sites in the zinc-substituted fluorohectorite framework.

Original languageEnglish
Pages (from-to)557-564
Number of pages8
JournalJournal of Materials Chemistry
Volume5
Issue number4
DOIs
Publication statusPublished - Apr 1995

Keywords

  • spin echo envelope
  • titanium silicalite
  • NMR-spectroscopy
  • chemical-shifts
  • MAS-NMR
  • modulation
  • resonance
  • zeolites
  • XANES
  • EXAFS

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