Transition metal ion substitution in titanosilicate ETS-10 for enhanced UV light photodegradation of methylene blue

Partial isomorphous substitution of transition metal (M = V, Cr, Mn, Fe, Co) ions in the titanosilicate ETS-10 framework (ETMS-10 with M/Ti ≈ 0.06 mol mol−1) was carried out in efforts to enhance the photocatalytic activity of ETS-10 in the degradation of methylene blue (MB) under UV light (280–400 nm) irradiation. XRD, UV–vis, and EDX analyses suggested substitution of V4+/V5+, Cr3+, Mn2+, and Fe3+ for octahedral Ti4+, and Co2+ for tetrahedral Si4+ in the ETS-10 framework. All ETMS-10 samples showed lower bandgap energies (Eg = 3.79–3.90 eV) than unmodified ETS-10 (Eg = 3.96 eV), and exhibited absorption features in the visible light region. These samples showed higher photocatalytic activities in photodegradation of MB (pseudo-first-order reaction rate constants, k = 0.016–0.055 min−1) than unmodified ETS-10 (k = 0.008 min−1), and the activities decreased in the order: ETCoS-10 > ETCrS-10 ≈ ETFeS-10 > ETMnS-10 ≈ ETVS-10 > unmodified ETS-10. This was hypothesized to be due in part to the lower bandgap energies of ETMS-10 samples compared to that of unmodified ETS-10, as well as the introduction of midgap states with transition metal ions replacing Ti4+, and different d electron configurations of transition metal ions substituted in the ETS-10 framework.

► V, Cr, Mn, and Fe substitute for Ti, whereas Co substitutes for Si in ETS-10.
► Eg for all ETMS-10 was red shifted (3.79–3.90 eV) compared to Eg of ETS-10 (3.96 eV).
► ETMS-10 samples showed higher photocatalytic activities than unmodified ETS-10.