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

Abstract

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 V 4+/V 5+, Cr 3+, Mn 2+, and Fe 3+ for octahedral Ti 4+, and Co 2+ for tetrahedral Si 4+ in the ETS-10 framework. All ETMS-10 samples showed lower bandgap energies ( E g = 3.79–3.90 eV) than unmodified ETS-10 ( E g = 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 Ti 4+, and different d electron configurations of transition metal ions substituted in the ETS-10 framework.