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Visible light activated photo-catalytic effect and local structure of iron silicate glass prepared by sol-gel method

Anatase type TiO is well known as a photo- catalyst activated by the UV light. It will be more effective to develop photo-catalyst which shows photo catalysis under visible light irradiation. Recently, Kubuki et al. revealed that 15Na2O•15CaO•xFe2O3•(70–x)SiO with ‘x’ between 10 and 50 mass% exhibited chemical oxygen demand (COD) decomposing ability. This result implies that iron silicate glass might be utilized as a purifier of polluted water. In this study, we report a relationship between local structure and visible light activated photo-catalytic effect of xFe2O3·(100–x)SiO2 glass prepared by sol-gel method. method. Iron silicate glass with a composition of xFe2O3·(100–x)SiO (in mass %, x = 10-50) were prepared by a sol-gel method. Reagent chemicals of Si(OC2H5)4, Fe(NO3)3·9H2O, 7.8 M HNO3, and C2H5OH were poured into a beaker and well mixed for 2 h at RT. After having been agitated by refluxheat method at 80ºC for 2h, the solution was poured into a glass vial and dried at 60ºC for 3 days to prepare gel samples of dark brown color. It was annealed at 1000ºC for 3 h in air. For evaluation of photo-catalytic effect, 40mg of well-pulverized annealed samples were soaked into 20 ml of methylene blue aqueous solution (MBaq) with a concentration of 20µΜ. Irradiation test was carried out for 2 h at RT in a darkroom using a glass vial irradiated with a visible light having the wavelength range of 420-750 nm. Absorbance (Abs.) of MBag before and after the irradiation test was determined by UV-VIS. 57^Fe-Mössbauer spectra were measured by a constant acceleration mode with a source of Co(Rh) and a reference of α-Fe. Absorption area (A) for the magnetic sextet with isomer shift and internal magnetic field (Hint) of 0.37 mm s^-1 and 51.4 T increased from 0.0 to 10.3 and 100 % with Fe2O3 content (x), indicating an increase in the fraction of hematite (α-Fe2O3). Decrease in the Abs. of MB became larger after 2h-irradiation test with an increase of ‘x’. It is concluded that MB-decomposing ability is associated with the amount of α-Fe phase precipitated in the annealed iron silicate glass.

Iron silicate glass; Sol-gel method; α-Fe2O3; Photo-catalytic effect; UV-ViS; Mossbauer spectroscopy

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