SYNTHESIS AND CHARACTERIZATION OF A (ZN,TI)-SUBSTITUTED LAYERED SILICATE

The incorporation of Ti-IV into the framework of zinc-substituted fluo rohectorite is reported. Various spectroscopic techniques point to the substitution of Ti-IV into predominantly the octahedral rather than t etrahedral sublattice of the smectite framework, For clay particles pr epared from a reactant composition with Ti/Ti+Si=0.063 (ZTFH), energy- dispersive X-ray analysis of the particles observed by transmission el ectron 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 cl ay particles is predominantly in an octahedral coordination. This is s upported by electron paramagnetic resonance (EPR) spectra of an orient ed film sample in which Ti-IV is reduced to Ti-III by heating the samp le to 450 degrees C in 30 Torr of CO. The observed single-ion Ti-III E PR spectrum shows dramatic dependence of the orientation of the clay f ilm in the magnetic field. This orientation dependence is consistent w ith 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 con sistent 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 tha t Ti-III ions are at a distance of 0.30-0.35 nm from Li-I ions, a dist ance that is consistent with these two ions occupying adjacent sites i n the octahedral sheet. The MAS NMR spectrum of the zinc/titanium-subs tituted 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 int erpreted as due to variations in the octahedral sheet composition. The refore Ti-IV appears to have a strong preference for occupation of the octahedral sites in the zinc-substituted fluorohectorite framework.