Visible light activated catalytic effect of iron containing soda-lime silicate glass characterized by 57Fe-Mössbauer spectroscopy

Abstract

A relationship between local structure and visible light activated catalytic effect of iron containing soda lime silicate glass with the composition of 15Na2O·15CaO·xFe2O3·(70-x)SiO2, x = 5–50 mass %, abbreviated as NCFSx was investigated by means of 57Fe-Mossbauer spectroscopy, X-ray diffractometry (XRD), small angle X-ray scattering (SAXS), electrospray ionization mass spectrometry (ESI–MS) and ultraviolet–visible light absorption spectroscopy (UV–Vis). Mossbauer spectra of NCFSx glass with ‘x’ being equal to or larger than 30 after isothermal annealing at 1,000 °C for 100 min consisted of a paramagnetic doublet and a magnetic sextet. The former had isomer shift (δ) of 0.24 mm s−1 and quadrupole splitting (Δ) of 0.99 mm s−1 due to distorted FeIIIO4 tetrahedra, and the latter had δ of 0.36 mm s−1 and internal magnetic field (Hint) of 51.8 T due to hematite (α-Fe2O3). The absorption area (A) of α-Fe2O3 varied from 47.2 to 75.9, 93.1, 64.8 and 47.9 % with ‘x’ from 30 to 35, 40, 45 and 50, indicating that the amount of precipitated α-Fe2O3 varied with the Fe2O3 content of NCFSx glass. The precipitation of α-Fe2O3 was also confirmed by XRD study of annealed NCFS glass with ‘x’ larger than 30. A relaxed sexted with δ, Hint and Γ of 0.34 mm s−1 and 37.9 T and 1.32 mm s−1 was observed from the Mossbauer spectra of annealed NCFSx glass with ‘x’ of 45 and 50, implying that the precipitation of non-stoichiometric iron hydroxide oxide with the composition of Fe1.833(OH)0.5O2.5 having the similar structure of α-Fe2O3 and α-FeOOH. A remarkable decrease in the concentration of methylene blue (MB) from 10 to 0.0 μmol L−1 with the first-order rate constant (k) of 2.87 × 10−2 h−1 was observed for 10-day leaching test using annealed NCFS50 glass under visible light irradiation. ESI–MS study indicated that existence of fragments with m/z value of 129, 117 and 207 etc. originating from MB having m/z of 284. This result evidently showed that the MB concentration decreased due to visible light induced decomposition caused by the visible light activated catalytic effect of α-Fe2O3 and/or Fe1.833(OH)0.5O2.5 precipitated in soda-lime silicate glass matrix.