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

A relationship between local structure and visible light activated catalytic effect of iron containing soda lime silicate glass with the composition of 15Na(2)O center dot 15CaO center dot xFe(2)O(3)center dot(70-x)SiO2, x = 5-50 mass %, abbreviated as NCFSx was investigated by means of Fe-57-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 A degrees C for 100 min consisted of a paramagnetic doublet and a magnetic sextet. The former had isomer shift (delta) of 0.24 mm s(-1) and quadrupole splitting (Delta) of 0.99 mm s(-1) due to distorted (FeO4)-O-III tetrahedra, and the latter had delta of 0.36 mm s(-1) and internal magnetic field (H (int)) of 51.8 T due to hematite (alpha-Fe2O3). The absorption area (A) of alpha-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 alpha-Fe2O3 varied with the Fe2O3 content of NCFSx glass. The precipitation of alpha-Fe2O3 was also confirmed by XRD study of annealed NCFS glass with 'x' larger than 30. A relaxed sexted with delta, H (int) and I" 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 Fe-1.833(OH)(0.5)O-2.5 having the similar structure of alpha-Fe2O3 and alpha-FeOOH. A remarkable decrease in the concentration of methylene blue (MB) from 10 to 0.0 mu mol L-1 with the first-order rate constant (k) of 2.87 x 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 alpha-Fe2O3 and/or Fe-1.833(OH)(0.5)O-2.5 precipitated in soda-lime silicate glass matrix.