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 Fe3+, 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.

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► Cr3+, Fe3+, Co2+ substitute for the octahedral V sites in the AM-6 framework.
► Eg of AM-6 decreased from 3.82 eV to 3.62–3.78 eV upon TM substitution.
► New visible light absorption features were observed upon TM substitution in AM-6.