Synthesis and characterization of vanadosilicate AM-6 with transition metal ions isomorphously substituted in the framework

Isomorphous substitutions of transition metal (TM) ions into the vanadosilicate AM-6 framework have been investigated. X-ray powder diffraction and FTIR spectroscopy showed no impurities due to TM oxides (i.e., cobalt oxide, chromium oxide or iron oxide for Co-AM-6, Cr-AM-6 and Fe-AM-6, respectively) in all TM ion-substituted AM-6 products (TM-AM-6). All TM-AM-6 products showed a red shift of their bandgap energies (3.62-3.78 eV) compared to unmodified AM-6 (3.82 eV). New absorption features in the low energy region of the UV-Vis spectra of AM-6 were observed upon incorporation of the various TM ions, and the intensity of these new features increased with increasing crystal TM/V ratios. These low energy region absorption features suggested the presence of Fe ³⁺, Cr³⁺, and Co²⁺ in Fe-AM-6, Cr-AM-6, and Co-AM-6, respectively. These findings together with shifts to higher frequency of the Raman bands observed for TM-AM-6 relative to unmodified AM-6 suggested successful partial isomorphous substitution in or near the VO₆ chains in the AM-6 framework.