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Chemical Structure and Visible-Light Activated Photocatalytic Effect of Iron-containing Glass Prepared from Slag

In recent years, disposal of general garbage exhausted from households is one of the serious environmental problems. Ishikawa et al. reported that iron-containing glass ceramics prepared from household waste slag denoted as Slag + 10Na2O + xFe2O3 (SlagNaFex) showed photocatalytic effect under visible-light irradiation after the samples were heat treated at 800 °C for 100 min. It was turned out that the photocatalytic effect of SlagNaFex after heat treatment is closely related to the precipitated amount of α-Fe2O3 nanoparticles [1]. In this study, a relation between chemical structure of Fe and photocatalytic effect of Slag + xFe2O3 (SlagFex, x = 0, 5, 10 in mass%) was investigated by means of Mössbauer spectroscopy, XRD, UV-Vis and ESI-MS. SlagFex was prepared by conventional melt-quenching method. Mixture of slag collected from Tamagawa incineration plant and Fe2O3 was placed in a platinum crucible, and was melted at 1400 °C for 1 h in the electric furnace. Dark brown samples were obtained by dipping the bottom of the crucible in ice. Each sample was heat-treated at 800 °C for 100 min or 1000 min after being purverized. Photocatalytic activity of SlagFex before and after heat treatment was evaluated by soaking 40 mg of the powdered samples into 20 mL methylene blue (MB) aqueous solution with the concentration of 20 μmol/L. The MB concentration and decomposition products were detremined by UV-Vis and ESI-MS, respectively. 57Fe Mössbauer spectra (57FeMS) were recorded by constant acceralation method at both room temperature and 80 K, using 57Co(Rh) and -Fe as a source and a reference. X-ray diffraction (XRD) patterns were obtained between 2of 10 and 80 °, by using Cu-K rays ( = 0.1541 nm). As shown in Fig. 1, MB concentration in aqueous solution decreased when it was reacted with SlagFex under the visible-light irradiation. The largest first-order rate constant, k of 1.3×10-3 min-1 was recorded for SlagFe5 after heat treatment at 800 °C for 100 min. According to ESI-MS the MB solution after the degradation test showed a peak at m/z of 257, indicating that MB was decomposed into Azure A. XRD patterns of heat-treated SlagFex showed that the peaks assinged to iron oxides (Fe3O4 andγ-Fe2O3) and CaFeAlSiO6. 57Fe MS of heat treated SlagFex measured at 80 K (Fig. 2) are composed of magnetically relaxated of sextets and doublet peaks of Fe(III). The doublet with quadrupole splitting of 1.00 mms-1 and isomer shift of 0.46 mm s-1 are assinged to paramagnetic CaFeAlSiO6 and the another doublet to superparamagnetic component, γ-Fe2O3. In comparison with previous study, SlagFex showed relatively smaller photocatalytic effect than SlagNaFex containing Na [1]. It is concluded that the smaller nanoparticles of γ-Fe2O3 precipitated in SlagFex is effective to promote photocatalytic effect under visible-light irradiation.

iron-containing glass ceramics, Slag, photocatalytic effect, Mössbauer spectroscopy, XRD, UV-Vis, ESI-MS

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