Fe 2p X-ray Photoelectron Spectroscopy Spectra Research Articles

Impact of Mn2+-Si4+ co-substitution on the electronic structure of Zn0.3Mn0.7Fe2O4 ferrites studied by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) has been employed to explore the electronic structure of Zn0.3Mn0.7+xSixFe2-2xO4 (x = 0.0–0.3) ferrite series. The Si2p XPS spectra insinuated the presence of Si ions in the +4 valence state. The elemental Si0 and suboxide SiOx are present in the system, the former showing an increase and the latter a decrease in atomic percentage upon Mn–Si substitution. It is also inferred that a fraction of Si0 might be residing at the grain boundaries; however, more studies are required to substantiate this. The Fe2p XPS spectra stipulate that ferrous and ferric ions co-occur in the system. The ferrous ions occupy the octahedral sites while the ferric ions dwell on both the octahedral and the tetrahedral sites. The O1s spectra indicate a remarkable increase in the oxygen defects with increasing Mn–Si substitution (x). The Mn2p XPS data indicate that the Mn+2 states show an overall increasing tendency with increasing Mn–Si concentration. Also, the Mn+4/Mn+3 ratio shows an increment with an increase in Mn–Si substitution.

Tailored Alkali Resistance of DeNOx Catalysts by Improving Redox Properties and Activating Adsorbed Reactive Species

SummaryIt is still challenging to develop strongly alkali-resistant catalysts for selective catalytic reduction of NOx with NH3. It is generally believed that the maintenance of acidity is the most important factor because of neutral effects of alkali. This work discovers that the redox properties rather than acidity play decisive roles in improving alkali resistance of some specific catalyst systems. K-poisoned Fe-decorated SO42−-modified CeZr oxide (Fe/SO42−/CeZr) catalysts show decreased acidity but reserve the high redox properties. The higher reactivity of NHx species induced by K poisoning compensates for the decreased amount of adsorbed NHx, leading to a desired reaction efficiency between adsorbed NHx and nitrate species. This study provides a unique perspective in designing an alkali-resistant deNOx catalyst via improving redox properties and activating the reactivities of NHx species rather than routinely increasing acidic sites for NHx adsorption, which is of significance for academic interests and practical applications.

Acid-Free and Selective Extraction of Lithium from Spent Lithium Iron Phosphate Batteries via a Mechanochemically Induced Isomorphic Substitution.

Lithium (Li) is the most valuable metal in spent lithium iron phosphate (LiFePO4) batteries, but its recovery has become a challenge in electronic waste recovery because of its relatively low content and inconsistent quality. This study proposes an acid-free and selective Li extraction process to successfully achieve the isomorphic substitution of Li in LiFePO4 crystals with sodium (Na). The method uses low-cost and nontoxic sodium chloride (NaCl) as a cogrinding reagent via a mechanical force-induced solid-phase reaction. X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), and X-ray photoelectron spectroscopy (XPS) characterizations demonstrated the evidence of Li/Na isomorphic substitution, while XPS spectra of Fe 2p, P 2p, and O 1s revealed that the coordination environment of these elements was not significantly altered. Density functional theory calculations further provided evidence that Na and Li share similar outer electron arrangements and coordination environments, favoring Na over Fe as a replacement for Li in LiFePO4. Additionally, the regeneration of NaCl and the recovery of precipitated Li2CO3 were simultaneously achieved with Na2CO3 as the sole reagent. This concise and efficient acid-free mechanochemical process for Li extraction is a promising candidate for feasible recycling technology of Li from spent LiFePO4 batteries. The proposed process is particularly appealing because of its high selectivity, considerable economic advantages, and environmental benefits.

Preparation, characterisation and enhanced photocatalytic activities of Fe,F co‐doped TiO 2 nanotubes

Fe,F co-doped TiO 2 nanotubes (Fe,F/TiO 2 NTs) were synthesised by the combination of hydrothermal process and impregnation method. The structure and composition of prepared catalysts were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). XRD results confirmed only the presence of the anatase phase in Fe,F/TiO 2 NTs. Well-defined TiO 2 NTs with nearly uniform diameters could be seen from the TEM images. Also, the high-resolution XPS spectra of Fe 2P and F 1s showed that Fe 3+ and F - existed in TiO 2 lattice and on the surface of TiO 2 , respectively. The photocatalytic performances of Fe/TiO 2 NTs and Fe,F/TiO 2 NTs with different Fe concentrations were evaluated by photo-degrading aqueous methyl orange under visible light irradiation, and the results showed that the photoactivity of Fe and F co-doped TiO 2 NTs was enhanced obviously compared with Fe mono-doped TiO 2 NTs and the 0.5% Fe,F/TiO 2 NTs presented the best photocatalytic performance.

Chemical Characterization of Corrosion Films Electrochemically Grown on Carbon Steel in Alkaline Sour Environment

Surface reactivity and the chemical nature of corrosion films electrochemically formed on carbon steel in a 1 M and 500 ppm medium for different growth times were studied by scanning photoelectrochemical microscopy (SPECM) and X-ray photoelectron spectroscopy (XPS). SPECM diagrams corresponding to films grown for times <15 min revealed their heterogeneous and protective nature, while for times >15 min these films showed surface activity and homogeneity in the characterization medium. The XPS spectra of Fe 2p, S 2p, and O 1s on the film surface indicated that and FeO are present in the protective (heterogeneous) films; meanwhile, Fe(OH) and FeS are the chemical species present in nonprotective (homogeneous) films. The O 1s peak analysis using a mix of Gaussian and Lorentzian functions indicated that during film growth both and/or hydroxyl groups are incorporated into the film structure. These results prove that the corrosion film composition was modified as a function of electrochemical oxidation time and this composition is directly related to the passive properties of these films. © 2003 The Electrochemical Society. All rights reserved.

Electronic structure and band gap of the negative charge-transfer material Sr 3Fe 2O 7

We studied the electronic structure of the Sr 3Fe 2O 7 compound using X-ray photoelectron spectroscopy (XPS). The charge-transfer satellites in the Fe 2p XPS spectra were analyzed using standard cluster model calculations. The analysis indicates that Sr 3Fe 2O 7 is in the negative charge-transfer regime, and that the ground state is dominated by the 3 d 5 L configuration (where L denotes an O 2p hole in the oxygen band). These results are similar to those found in the related SrFeO 3 and Sr 2FeO 4 compounds. The band gap of the Sr 3Fe 2O 7 compound is split off by the relatively large value of the p–d transfer integral T σ. The lowest lying excitations are 3 d 5 L +3 d 5 L →3 d 5+3 d 5 L 2 and consequently the band gap is of the p–p type. The band gap in the Sr n+1 Fe n O 3 n+1 series can be understood taking into account the trend in the O 2p bandwidths.

Effect of grinding atmosphere on the leaching of mechanically activated pyrite and sphalerite

The effects of grinding atmosphere, such as highly pure nitrogen (99.999 vol.%) (abbreviated as nitrogen), less air, and air on the leaching of pyrite and sphalerite mechanically activated for 20 and 120 min, respectively, were investigated. The results indicate that the leaching recovery of mechanically activated pyrite varies with the grinding atmosphere, and increases in the sequence of nitrogen, air, and less air. In contrast, the leaching recovery of mechanically activated sphalerite is insensitive to the different grinding atmospheres. The structural changes of the sulfide minerals mechanically activated under different grinding atmospheres were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD) and X-ray diffraction laser particle size analysis. The results show that the XRD spectra and the specific granulometric surface area ( S G) do not vary with the grinding atmosphere, neither do the S2p and Zn2p XPS spectra of mechanically activated sphalerite and Fe2p XPS spectra of mechanically activated pyrite. However, a change was observed in the S2p XPS spectra of pyrite mechanically activated under different grinding atmospheres. The lattice distortion, S G and the elemental sulfur contents of pyrite and sphalerite mechanically activated under nitrogen were also investigated using XRD, X-ray diffraction laser particle size analysis and a gravimetric method, respectively. The results indicate that the elemental sulfur content of mechanically activated pyrite rises significantly and the lattice distortion ratio ( ε) rises only slightly with increasing grinding time. In contrast, the elemental sulfur content of mechanically activated sphalerite remains constant at 0.5 mg/g while the lattice distortion ratio ( ε) increases rapidly with increasing grinding time. Therefore, the formation of lattice defects on the surface of mechanically activated pyrite, and the lattice distortion on the surface of mechanically activated sphalerite may be mainly responsible for the enhancement of the leaching process for the corresponding sulfide minerals.

Electrochemically grown passive films on carbon steel (SAE 1018) in alkaline sour medium

Corrosion films were prepared by applying cyclic potential pulses to the 1018 carbon steel–sour medium interface (1 M (NH 4) 2S, 500 ppm CN −) for 1 min. Electrochemical behavior and surface morphology of these films were determined using electrochemical impedance spectroscopy (EIS), scanning electron microscopy, and scanning photoelectrochemical microscopy (SPECM). EIS diagrams and SPECM images show the passive properties and homogeneity of the films. Furthermore, X-ray photoelectron spectroscopy (XPS) was used to characterize their chemical nature and structure. XPS results show that different oxide and sulfur structures were developed during the electrochemical oxidation of carbon steel in concentrated sour media. The analysis of O 1s data indicated that, during film growth, H 2O and/or hydroxyl groups are incorporated into the film structure. The XPS spectra of Fe 2p show iron bonds with S as iron sulfide (FeS 2 and FeS) and the corresponding peak of O 1s shows those bonds with oxygen as Fe 2O 3 and/or FeO. XPS depth profile analyses for the film showed that the ratio of FeS and FeO increases from film surface to film–carbon steel interface. This corroborates the diffusion of iron ions through the film during its electrochemical growth. The chemical shift through the film for the peak associated with Fe 2p signal proves that transport mechanism of iron ions through the film is carried out by chemical diffusion.

Electronic structure of granular Fe–Al 2O 3 thin films prepared by co-evaporation

We studied the electronic structure of granular Fe–Al 2O 3 thin films using X-ray photoelectron spectroscopy (XPS). The samples were produced by co-evaporation of Fe and Al 2O 3 and have relatively large Fe volume factions (27 and 48%). The Fe 2p XPS spectra show that the Fe precipitates in the granular alloy are in a majority metallic phase. The spectra show also that there is a minority Fe oxide phase and that this phase decreases for the 48% sample. The valence band spectra of granular Fe–Al 2O 3 can be understood as a linear combination of the individual Fe and Al 2O 3 bands, which is consistent with mostly metallic Fe precipitates deduced from the core level Fe 2p XPS spectra. The core level and valence band results suggest the possibility of little interaction between the Fe precipitates and the Al 2O 3 matrix. In turn, this would suggest that there is little interdiffusion as well as relatively well-defined and abrupt grain boundaries. This information is important to understand the transport and magnetic properties of the Fe–Al 2O 3 thin films.