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

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-Mössbauer 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). Mössbauer 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 Fe^IIIO₄ tetrahedra, and the latter had δ of 0.36 mm s^?1 and internal magnetic field (H _int) 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, H _int and Γ of 0.34 mm s^?1 and 37.9 T and 1.32 mm s^?1 was observed from the Mössbauer 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)_0.5O_2.5 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 Fe_1.833(OH)_0.5O_2.5 precipitated in soda-lime silicate glass matrix.     

Degradation of passive layers of iron studied by conversion electron Mössbauer spectroscopy

Integral electron Mössbauer spectroscopy (ICEMS) and additionally some electrochemical methods were used to characterize the passivation process of iron (low carbon steel) in sulfate, sulfate+sulfite (a possible model solution of acid rain) solutions and in phospate buffer. The phase compositions and thicknesses of the passive layers formed due to the electrochemical polarizations were analyzed in dependence on the duration of the anodic passivations and on the pH of the used electrolytes. The passive layer, as determined from the Mössbauer spectra, consists mainly of -FeOOH, however in sulfite containing sulfate aqueous solution at pH 3.5 Fe₃C and despite ex-situ circumstances FeSO₄·H₂O was detected after the shortest polarization time. The film thickness, which was found to grow nearly linearly with polarization time in pure sulfate solution and in phospate buffer, reached a maximum of 60–160 nm (depending on pH) in sulfate+sulfite solution after a passivation time of about 4 hours. It has been proved, that HSO₃ ^–-ion, which is contained by acid rain, initiate pit formation under acid conditions and so enforces the corrosion of iron. The experimental results furthermore suggest, that not the whole oxidic layer is responsible for the passivity but only a very thin intermediate layer formed between an inner oxide layer of a cubic structure and the rhombic oxide (-FeOOH) cover.     

Synthesis and visible light photocatalytic activity of β-AgVO3 nanowires

β-AgVO₃ nanowires are synthesized by the hydrothermal method. The synthesis yields nanowires with a monoclinic phase structure. Typical nanowires have diameter of about 200–700 nm and length up to 300 μm. Photocatalytic degradation of Rhodamine B dye is investigated. It is found that the β-AgVO₃ nanowires possess excellent catalytic degradation activity owing to its effective visible light absorption and well crystallization. The highly photocatalytic activity suggest its possible application in the organic pollutant treatment under visible light irradiation.     

Archaeological pottery from Nasca culture studied by Raman and Mössbauer spectroscopy combined with X-ray diffraction

In the present paper, we report on a study of archaeological fragments from Nasca ceramics using Raman and Mössbauer spectroscopy combined with X-ray diffraction (XRD). By combining results obtained by these methods it is possible to quantitatively determine the paints composition, temperature and environment during the firing. The samples were collected from the Ceremonial Centre of Cahuachi in Southern coast of Peru. Raman spectroscopy allows us to determine the composition of the different pigments used in the preparation of Nasca ceramic. The results show that the composition of the white pigments is formed by rutile and anatase while the black and red pigments are formed by amorphous carbon and hematite, respectively. The Mössbauer spectra were measured at room temperature (RT) and show the presence of components associated with Fe³⁺ indicating an oxidizing environment during the manufacturing process of the ceramic. The analysis is complemented by data obtained by X-ray diffraction suggesting firing temperatures around 950 °C, in agreement with Raman measurements.     

Controllable preparation of nanosized TiO_2 thin film and relationship between structure of film and its photocatalytic activity

~~Controllable preparation of nanosized TiO_2 thin film and relationship between structure of film and its photocatalytic activity@魏刚$College of Material Science and Engineering,Beijing University of Chemical Technology! Beijing 100029,China @张元晶$College of Material Science and Engineering,Beijing University of Chemical Technology! Beijing 100029,China @熊蓉春$College of Material Science and Engineering,Beijing University of Chemical Technology! Beijing 100029,China~…     

Synthesis and visible light photocatalytic activity of Ag spot-coated TiO2–60 wt% SrO composite powders

Nano-sized TiO₂–60 wt% SrO composite powders were synthesized from titanium isopropoxide and Sr(OH)₂·8H₂O by use of a sol–gel method. Ag spot-coated TiO₂–60 wt% SrO composite powders containing 3, 5, or 7 wt% Ag were synthesized by hydrothermal-assisted attachment, by use of Ag hydrosol in a high-pressure bomb at 250 °C and 450 psi. Nano-sized Ag particles approximately 5–25 nm in diameter adhered to the TiO₂–60 wt% SrO₂ composite powders. The photocatalytic activity of Ag spot-coated TiO₂–SrO powders in the degradation of phenol showed that all were highly active when irradiated with UV light. TiO₂–60 wt% SrO composite powder spot-coated with 5 wt% Ag was more photocatalytically active under visible light than TiO₂–SrO composite powder.     

Local structure and valence of impurity ions in oxides by TDPAC and Mössbauer emission spectroscopy

The features of time-differential perturbed angular correlation (TDPAC) in studies on local chemical structures around impurity atoms are described in comparison with those of Mössbauer emission spectroscopy with four typical examples of recent applications to metal oxide systems, namely,⁹⁹Rh⁹⁹Ru in -Fe₂O₃ and YBa₂Cu₃O_7– and¹¹⁷Cd¹¹⁷In in MO (M=Mn, Co, Ni) and BaRu_2/3Cd_1/3O₃.     

Influence of surface treatment on microstructure of stainless steels studied by Mössbauer spectrometry

Examination of surface microstructure of stainless steels is presented. Transmission Mössbauer spectrometry and Conversion Electron Mössbauer Spectrometry which provide information from the bulk and surface regions, respectively, were used. We concentrate on structural modifications that were caused by surface treatments including grinding, polishing, and electrolytic etching. Scanning Electron Microscopy with Energy Dispersive Spectrometry was adopted for visualization of surface differences. Formation of magnetic phases was revealed in the surface regions of X6CrNiTi1810 steel while no substantial effect of surface treatment was found in the ATABOR steel. Bulk regions in both steels are not affected by surface treatment.

     

The X2Σ+ state of LiCa studied by Fourier-transform spectroscopy

The paper reports on a successful observation of high resolution Fourier transform spectra of LiCa. The fine structure of the ground state was observed and attributed to effective spin-rotation interaction. The experimental observations are described by two models using potential energy curves. One of them takes into account the fine structure splitting by means of effective constants, the other by means of a R dependent function γ(R), built in the radial Schr?dinger equation. Ab initio calculations were performed for γ(R) which comes close to the experimental function.     

Development and application of parallel-plate avalanche counter for in-beam Mössbauer spectroscopy

For Mössbauer -rays in the in-beam Mössbauer experiments using various beams such as heavy ion, secondary short-lived isotope, and neutron beams, it is important to develop a detector. A parallel-plate avalanche counter (PPAC) is the most suitable gas counter for on-line measurements, because PPAC collects the internal conversion electrons emitted by the Mössbauer effect even under high -background. We evaluated the influences of the pressure and flow rate of the counter gas against the counting efficiency of PPAC, and determined the optimum conditions for use in the in-beam Mössbauer experiments.     

Coprecipitation of iron and platinum(IV) hydroxo complexes as probed by Mössbauer spectroscopy

Stabilization of ⁵⁷Fe compounds in matrices of solid solutions of platinum(IV) superoxo- and hydroxo complexes was probed by Mössbauer spectroscopy. The ratio Fe^III/Fe^IV in these matrices is 20/1.     

Hydrothermal in situ preparation of phthalocyanine–TiO2 nanocomposites for photocatalytic activity under visible light irradiation

Research on Chemical Intermediates - In this study, phthalocyanine (Pc)–TiO2 nanocomposites were prepared via in situ hydrothermal method. The metal-free, zinc(II), cobalt(II), nickel(II) and...     

Pressure-induced phase transition of Fe2TiO4: X-ray diffraction and Mössbauer spectroscopy

X-ray diffraction and Mössbauer spectroscopy were employed to investigate structural stability of Fe₂TiO₄ under high pressure. Measurements were performed up to about 24 GPa at room temperature using diamond anvil cell. Experimental results demonstrate that Fe₂TiO₄ undergoes a series of phase transitions from cubic (Fd3?m) to tetragonal (I4₁/amd) at 8.7 GPa, and then to orthorhombic structure (Cmcm) at 16.0 GPa. The high-pressure phase (Cmcm) of Fe₂TiO₄ is kept on decompression to ambient pressure. In all polymorphs of Fe₂TiO₄, iron cations present a high-spin ferrous property without electric charge exchange with titanium cations at high pressure supported by Mössbauer evidences.     

Lithium-induced conversion reaction in wüstite Fe1−xO studied by 57Fe Mössbauer spectroscopy

Fe_1−xO wüstite as negative electrode material for Li-ion batteries has been studied. The aim of this work is to get a better understanding of the insertion mechanism involved during reduction/oxidation processes. Electrochemical tests have been done in Swagelock™ cells and shown a high specific capacity of 800 A h/kg for the first discharge. X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy provide us valuable information on both local and long range order. Hence, Li reaction with wüstite induces formation of highly divided metallic iron (α-Fe and nano-Fe) and Li₂O with a small amount of Fe₂O₃ occurring in a diffusion layer at the surface of the primary particles. Based on the X-ray and Mössbauer spectroscopic analyses, a core–shell model is proposed in order to explain the irreversible capacity of about 1 Li observed at the first cycle. It involves cation diffusion induced by lithium acting as an ‘electronic pressure’.