Formation Of Fe2 Research Articles

Development of conversion coatings on iron via corrosion in LiPF6 solution

The corrosion process of iron in 1M LiPF6 solution using an ethylene carbonate/diethyl carbonate (EC/DEC) mixture solvent is studied using gravimetric and electrochemical methods. The electrochemical technique employed is electrochemical impedance spectroscopy, EIS, and a special electrode arrangement is used in a pouch cell. The electrochemical and gravimetrical data match reasonably well, indicating a decreasing corrosion rate with time of exposure. The EIS data are analysed using a transmission line model that accounts for the shifts observed in the high frequency limit of the impedance. The data presented suggest that PF6− corrodes Fe to Fe2+ that further evolves to Fe3+, forming porous structures based on FeF3. The formation of Fe3+ has also been confirmed by X-ray photoelectron spectroscopy, XPS analysis. In the presence of non-oxidising salts (e.g., LiBOB, LiBF4), the Fe corrosion rate decreases.

Ore component mobility, transport and mineralization at mid-oceanic ridges: A stable isotopes (Zn, Cu and Fe) study of the Rainbow massif (Mid-Atlantic Ridge 36°14′N)

Ultramafic hosted hydrothermal deposits are ubiquitous along slow-spreading ridges such as the Mid-Atlantic Ridge (MAR; e.g., Ashadzé, Rainbow, Lost City) where they exert a major control on the cycling of economically important elements (e.g., Zn, Cu, Ni). However, the origin of metal mobility in these environments remains unclear. Here we use Zn (δ66Zn), Cu (δ65Cu) and Fe (δ56Fe) stable isotopes to explore the mobility of metals during (1) the serpentinization of the Rainbow massif basement in a seawater dominated system at low temperature (<250 °C) and (2) the subsequent high temperature (>350 °C) mineralization of serpentinites through seawater-derived fluids that interacted with gabbro prior to interacting with serpentinite near hydrothermal sites (stockworks).The Rainbow samples display among the largest range of isotopic variations ever reported for ultramafic rocks (−0.10‰ ≤ δ66Zn ≤ +0.47‰; −0.93‰ ≤ δ65Cu ≤ +0.24‰; −0.15‰ ≤ δ56Fe ≤ +0.25‰). These variations reflect a two-stage process. (1) Serpentinization of the ultramafic basement is accompanied by a decrease in Zn (26–41 ppm) and Cu (1–13 ppm) concentrations and an increase of δ66Zn (+0.30–+0.47‰) in peridotites relative to primitive mantle (Zn ∼ 55 ppm, Cu ∼ 20 ppm, δ66Zn ∼ +0.16‰). Striking correlations between δ66Zn and indices of serpentinization (LOI and Fe/3+ΣFe) show preferential leaching of isotopically light Zn by fluids during the serpentinization of the massif. This isotopic fractionation is controlled by the dissolution of both mantle sulfides and/or spinels and Zn complexation with chlorine in fluids. At this stage, Fe seems to be immobile as attested by correlations between δ56Fe and indices of peridotite fertility (e.g., Al2O3/SiO2). (2) The mineralization of serpentinites near the Rainbow stockwork is accompanied by an increase in Fe/3+ΣFe (>0.7), FeO (up to 19.8 wt%), Zn (≫50 ppm) and Cu (≫20 ppm) concentrations. The δ66Zn and δ65Cu values progressively decrease with indices of serpentinite mineralization (e.g., Zn, Cu, Fe/3+ΣFe), while several samples display abnormally high δ56Fe (up to 0.25‰) relative to primitive mantle (δ56Fe ∼ 0.025‰), suggesting a high mobility of Zn, Cu and Fe in high temperature hydrothermal fluids. These isotopic fractionations can be explained by the local oxidation of sulfur bearing fluids in contact with seawater. This process enhances metal precipitation as well as the formation of Fe3+-bearing phases, such as magnetite, beneath the stockwork, explaining the presence of magnetic anomalies below the Rainbow hydrothermal field. Our study shows that the mobility of metals in hydrothermal fluids can be enhanced by both peridotite interaction with seawater or with fluid that interacted with deeper mafic bodies and then flowed to the surface. These processes may generate hydrothermal deposits with distinct metal signatures.

Effect of Fe doping on structural and optical properties of ZnO films and nanorods

Fe-doped ZnO thin films were successfully prepared via the sol-gel spin coating method. Both X-ray diffraction and X-ray photoelectron spectroscopy analysis displayed that Fe atoms were successfully incorporated into the ZnO thin films and existed in the form of Fe2+ mostly in 1 at.% Fe-doped ZnO films, and mainly existed in the form of Fe3+ in higher concentration of the films. Scanning electron microscopy images demonstrated the decrease in crystallite size with increasing Fe concentration. The room temperature photoluminescence revealed that electrons transition from a shallow level of Zni to top level of valance band increased, while near band edge (NBE) emission reduced with increasing Fe content, which indicated that Fe doping introduce some impurity levels and/or influence on the existing levels and hence affect the type of transition. Furthermore, the behavior of surface carrier transport and interfacial charge transfer are investigated by the photocatalytic activities and electrochemical impedance spectroscopy for undoped and Fe-doped ZnO films and nanorods, to detect the effects of Fe dopant in the form of Fe2+ and Fe3+ ions on photocatalytic performance.

Synthesis and properties of Sn1−xFexO2 nanoparticles obtained by a proteic sol–gel method

Iron-doped SnO2 nanoparticles with chemical formula Sn1−xFexO2−y (x = 0.02, 0.05 and 0.10 at%) were successfully produced by a proteic sol–gel method. Thermogravimetric analysis and differential scanning calorimetry were performed to investigate the thermal behavior of the precursor powders as well as to select the appropriate calcination temperatures for oxide formation. X-ray absorption near-edge spectroscopy studies were carried out to determine the valence state of the transition metal used as dopant. Structural, morphological, and optical properties of the synthesized materials were studied by X-ray diffraction, Mossbauer spectroscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, and ultraviolet-visible spectroscopy. The results confirmed the formation of nanometric spherical particles of single-phased SnO2 with rutile-type tetragonal structure. Iron doping was accomplished in the form of Fe3+ substituting for Sn4+ in the SnO2 matrix, with the creation of oxygen vacancies to achieve charge balance. Band gaps of SnO2 were found to be unaffected by the introduction of iron.

Assembly of Protein Stacks With in Situ Synthesized Nanoparticle Cargo.

The ability of proteins to form hierarchical structures through self-assembly provides an opportunity to synthesize and organize nanoparticles. Ordered nanoparticle assemblies are a subject of widespread interest due to the potential to harness their emergent functions. In this work, the toroidal-shaped form of the protein peroxiredoxin, which has a pore size of 7 nm, was used to organize iron oxyhydroxide nanoparticles. Iron in the form of Fe2+ was sequestered into the central cavity of the toroid ring using metal-binding sites engineered there and then hydrolyzed to form iron oxyhydroxide particles bound into the protein pore. By precise manipulation of the pH, the mineralized toroids were organized into stacks confining one-dimensional nanoparticle assemblies. We report the formation and the procedures leading to the formation of such nanostructures and their characterization by chromatography and microscopy. Electrostatic force microscopy clearly revealed the formation of iron-containing nanorods as a result of the self-assembly of the iron-loaded protein. This research bodes well for the use of peroxiredoxin as a template with which to form nanowires and structures for electronic and magnetic applications.

Fe-doped LaCoO3 perovskite catalyst for NO oxidation in the post-treatment of marine diesel engine’s exhaust emissions

New post-treatment process for marine diesel engine exhaust emissions was proposed by combining NO oxidation and wet scrubbing technology for the simultaneous removal of SOX, NOX and PM. NO, insoluble in aqueous scrubbing absorbent, is preferentially oxidized to NO2, which then turns fully soluble in it. Fe substituted LaCo1-xFexO3 perovskite catalysts were developed for NO oxidation to NO2. The catalysts were prepared by co-precipitation method and analyzed with XRD, XRF, BET, FT-IR, NO-TPD and XPS techniques. Crystal structure change from rhombohedral to orthorhombic was observed with the increased amount of Fe substituted in the B site of the perovskite by XRD analysis. From FT-IR and NO-TPD analysis, nitrate on perovskite species was found to be the active species for NO oxidation. Quantitative analysis was performed within the prepared catalysts. Catalytic activity was measured using a packed bed reactor operated at 150–400 °C, atmospheric pressure and with gas hourly space velocity (GHSV) of 20,000 h-1 using a simulated exhaust gas composed of NO 400 ppm, O2 10% balanced with N2. Formation of Fe4+ cation enhanced the redox property as well as the mobility of the lattice oxygen present in the perovskite catalysts, confirmed by XPS analysis. Reaction mechanism of NO oxidation on Fe substituted LaCo1-xFexO3 was discussed based on Mars-van Krevelen mechanism.

Crystal structural, dielectrical properties and high temperature magnetic phase transition of Sm1-xCaxFeO3 (x=0–0.3)

In the present study, crystal structural, dielectric, ferromagnetic properties and high temperature magnetic phase transition of Sm1-xCaxFeO3 (x = 0–0.3) by the conventional solid-state reaction method were investigated. The crystalline structure, the microstructure, the dielectric property of the Sm1-xCaxFeO3 samples was characterized by x-ray diffraction (XRD) and field emissions canning electron microscopy (FESEM). The dielectric property measurement was performed by a precision impedance analyzer with the frequency range from 40 to 110 MHz. The coexistence of Fe3+/2+ ions in Sm1-xCaxFeO3 samples was investigated with X-ray photoelectron spectroscopy (XPS). The magnetic property of Sm1-xCaxFeO3 was measured with Physical Property Measurement System (PPMS). The result shows that all the peaks for Sm1-xCaxFeO3 samples can be indexed according to the crystal structure of pure SmFeO3 and has a fine crystal structure by XRD. The SEM images indicate that Ca2+ doping significantly increases the grain sizes of SmFeO3 ceramic. The average grain sizes of Sm1-xCaxFeO3 samples range from 0.5 to 2 μm with Ca2+ doping. εr of Sm1-xCaxFeO3 measured at 1 kHz is about 5, 3 and 2.6 times greater than that of SmFeO3, respectively, and the dielectric loss increases by an order of magnitude. The increase of εr is mainly caused by the interaction between the dipole and the space charge orientation polarization. Magnetic measurements show that the M-H of Sm1-xCaxFeO3 samples exhibit saturated magnetic hysteresis loops with the increase of Ca2+, and the Mr of Sm1-xCaxFeO3 (x = 0–0.3) is 20, 31, and 68 times of that of SmFeO3, respectively, suggesting the weakly ferromagnetic behavior. The XPS spectrum indicates the coexistence of Fe2+ and Fe3+ in Sm1-xCaxFeO3 samples. The ratio of Fe2+/Fe3+ presents a growing trend with the increase of Ca2+ doping. It can be attributed to the structural distortion and the formation of Fe2+-O2--Fe3+ super-exchange. The spin recombination temperature (TSR) and Neel temperature (TN) are 437 K, 687 K by measuring the M-T curves. It is noted that both TSR and TN of SmFeO3 samples move towards the low temperature with the increase of x, and the spin recombination disappear when x = 0.3. This is primarily due to the stability of the magnetic structure of SmFeO3 and the interaction of Fe3+-O2--Fe3+ and Sm3+-O2--Fe3+ super-exchange.

Influence of heat-treated Al–Si coating on the weldability and microstructural inhomogeneity for hot stamped steel resistance nut projection welds

Resistance nut projection weldability of Al–Si coated hot stamped steel (HSS) was investigated under the viewpoint of weldable current range and joint strength (pull-out load). The microstructural inhomogeneities in the welds were also studied in order to elucidate the factors affecting the joint strength of the welds. The weldability of the given Al–Si coated HSS was compared with the weldability of an identical HSS without the Al–Si coating (Al–Si coating was polished out) and Zn coated dual phase steel. The weldable current range of Al–Si coated HSS was found to be narrower than that of the other materials. Furthermore, the average pull-out load within the weldable current range of the Al–Si coated HSS was the lowest among the three materials. The reason for poor weld mechanical property of the Al–Si coated hot-stamped steel was attributed to the microstructural inhomogeneities such as unmixed Al–Si coating layer at the edge of the nugget and the second phase Fe3(Al, Si) intermetallic compound. The formation of Fe3(Al, Si) phase was attributed to the solidification segregation of Al and Si during the weld solidification and was confirmed with the numerical analysis of solidification segregation.

Study of Fe-doped V2O5/TiO2 catalyst for an enhanced NH3-SCR in diesel exhaust aftertreatment

Selective catalytic reduction (SCR) with ammonia has been considered as the most promising technology, as its effect deals with the NOX. Novel Fe-doped V2O5/TiO2 catalysts were prepared by sol–gel and impregnation methods. The effects of iron content and reaction temperature on the catalyst SCR reaction activity were explored by a test device, the results of which revealed that catalysts could exhibit the best catalytic activity when the iron mass ratio was 0.05%. It further proved that the VTiFe (0.05%) catalyst performed the best in denitration and its NOX conversion reached 99.5% at 270 °C. The outcome of experimental procedures: Brunauer–Emmett–Teller surface area, X-ray powder diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction and adsorption (H2-TPR, NH3-TPD) techniques showed that the iron existed in the form of Fe3+ and Fe2+ and the superior catalytic performance was attributed to the highly dispersed active species, lots of surface acid sites and absorbed oxygen. The modified Fe-doped catalysts do not only have terrific SCR activities, but also a rather broad range of active temperature which also enhances the resistance to SO2 and H2O.

Binding of proton and iron to lignite humic acid size-fractions in aqueous matrix

The bioavailability of trivalent iron (Fe3+) to plants can be enhanced using fertilizer solutions containing humic acids (HA) as manifested from the increased crop yield at an iron stress conditions. The lignite-derived HA (HAlignite) facilitates higher diffusion of Fe3+ between the soil layers as attributable to more number of reactive sites in the assemblage compared to those from other origins. In the current work, the proton-binding of HAlignite size-fractions (5–10, 10–30, 30–100, and >100 kDa), as segmented based on the molecular weight distribution, and their complexation with Fe3+ have been studied at varying pH ranging from low to high. The protonation or formation of Fe3+-complexes exhibited a comparable pattern despite the differences in the conformational distribution of HAlignite size-fractions. The protonation behavior specified that the behavior of HAlignite size-fractions has similarity with that of a dibasic acid. The results are interpreted using reactive structural units (RSU) concept to show that the carboxyl and phenolic-hydroxyl groups in the HAlignite size-fractions simultaneously available as the Fe3+-binding sites. The stability constants for larger MW fractions of HAlignite (>100 kDa) was the lowest, as attributed to the increased aggregation rate in an aqueous matrix. The trend in conditional stability constants of HAlignite-size fractions and other Fe-chelators point to a better Fe-binding capability of HAlignite (30–100 kDa) size-fraction than the biodegradable alternatives (GLDA, HIDS, EDDS, IDSA, or NTA), while the Fe-interaction was stronger with classical synthetic chelators (EDTA, DTPA, or EDDHA).

The preparation of Fe3+ ion-exchanged mesopore containing ZSM-5 molecular sieves and its high catalytic activity in the hydroxylation of phenol

A series of Fe3+ containing catalysts were synthesized using ion-exchange technique over hierarchically porous ZSM-5 (M-ZSM-5) and micro-mesoporous composite ZSM-5/MCM-41 (ZSM-5/MCM-41), respectively. The prepared catalysts were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, N2 adsorption–desorption, UV–Vis spectroscopy, temperature programmed reduction and inductively coupled plasma-optical emission spectroscopy. The characterization results exhibit that the hierarchically porous ZSM-5 was synthesized with intracrystalline mesopores, while the micro-mesoporous composite ZSM-5/MCM-41 was prepared with the well-ordered mesopores. Furthermore, the results also prove that the existence of iron in the catalysts was mainly presented in the form of Fe3+ ions. Catalytic performances of the samples for phenol hydroxylation were compared by using H2O2 as oxidant. Under the optimized conditions, Fe3+ ion-exchanged M-ZSM-5 (Fe-M-ZSM-5) shows that a phenol conversion of 42.3% obtained with 92.5% selectivity to dihydroxybenzenes, whereas Fe3+ ion-exchanged ZSM-5/MCM-41 (Fe-ZSM-5/MCM-41) give 46.2% phenol conversion and 90.1% dihydroxybenzenes selectivity, which are all better than most reported results. The recyclability tests show that Fe-ZSM-5/MCM-41 with ordered mesoporous structure and bigger surface area has better anti-deactivation performance than Fe-M-ZSM-5. The excellent catalytic performances were due to the improved diffusion performance with newly created mesopores and the highly active Fe3+ species obtained by ion-exchange technique.

Formation of structural defects and strain in electrodegraded Fe‐doped SrTiO3 crystals due to oxygen vacancy migration

AbstractWe report on our investigation of structural defect and strain formation in electrodegraded reduced and oxidized, Fe‐doped SrTiO3 (Fe:STO) single crystals using optical second harmonic generation (SHG) and confocal Raman spectroscopy. SHG and Raman spectra reveal structural and electrochemical inhomogeneity resulting from the formation of Fe4+/oxygen ion and Fe3+/oxygen vacancy aggregation sites along the degraded anode and cathode interfaces, respectively. We show that mixed Fe3+/Fe4+ states and structural strain gradients are generated across the color fronts. These results, as well as oxygen sublattice differences between the anodic and cathodic bulk, present the color front as an interface between two dominant oxygen bonding distortions. The strain near the color front shows a strong dependence on oxygen vacancy concentration and diffusion within the crystals. Our characterization of structural and electrochemical changes due to electric field‐induced strain and oxygen vacancy migration advances knowledge of electrodegradation in perovskite‐based titanate single crystals.

Facile fabrication of mesoporous Fe-Ti-SBA15 silica with enhanced visible-light-driven simultaneous photocatalytic degradation and reduction reactions

A series of mesoporous iron-titanium-containing silica Fe-TiO2-SBA15 (FTS) were constructed via a facile one-pot hydrothermal route and subsequently characterized by X-ray diffraction patterns, UV–vis diffuse reflection spectroscopy, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption-desorption, X-ray photoelectron spectroscopy, and X-ray energy dispersion spectroscopy. By analyses, these samples possessed ordered two-dimensional hexagonal mesoporous structures, mainly involving mixed dual-phases of anatase and rutile TiO2, like commercial titania P25. The UV–vis diffuse reflection spectra demonstrated the presence of Fe species that was further confirmed by the X-ray photoelectron spectra and X-ray energy dispersion spectrum. The existence of Fe species in form of Fe3+ cations played an important role on the phase composition and electronic structure of these samples. With structural and morphological merits, these samples exhibited relatively high photocatalytic efficiency toward the degradation of dye methylene blue (MB) and reduction of Cr(VI) under visible-light irradiation, comparing with P25. In addition, among all candidates, the sample with a Fe/Si molar ratio of 0.03 showed the highest catalytic performance under optimal conditions, especially in the coexistence of both MB and Cr(VI), revealing an obviously synergistic effect when the consumption of both contaminants occurred. Finally, a primary catalytic mechanism was speculated on basis of active species capture experiments.

Barium (II)-doped zinc ferrite-reduced graphene oxide nanohybrids for superior adsorption and magnetic properties

A one-step solvothermal method was used to prepare barium (II)-doped zinc ferrite/reduced graphene oxide (Ba2+-ZF/rGO) magnetic nanohybrid adsorbents. During the solvothermal treatment, Ba2+-ZF nanoparticles were formed from Ba2+, Fe3+and Zn2+ chlorides, which were anchored on the surface of rGO obtained from the reduction of GO with ethylene glycol. TEM and SEM results show that the Ba2+-ZF nanoparticles are uniformly distributed on the rGO sheets without any agglomeration. When used as adsorbents, the Ba2+-ZF-rGO nanohybrid with an rGO content of 35% possesses excellent adsorption capacities for methylene blue at different initial concentrations and the adsorption kinetics can be well-described by the pseudo-second-order kinetic model. The formation of Fe2+ from FeCl3·6H2O and the doping of Ba2+ into the spinel structure dramatically improve the magnetism of the zinc ferrite, which makes the magnetic separability of the nanohybrid outstanding. The Ba2+-ZF/rGO nanohybrid could be used as an efficient, magnetically separable adsorbent for removing organic dyes.

Electro-Fenton degradation of antibiotic ciprofloxacin (CIP): Formation of Fe3+-CIP chelate and its effect on catalytic behavior of Fe2+/Fe3+ and CIP mineralization

This work investigated the effect of the chelation of Fe3+ with a fluoroquinolone (FQ) antibiotic ciprofloxacin (CIP) on the catalytic behavior of Fe3+/Fe2+ and the degradation and mineralization of CIP in electro-Fenton (EF) process using activated carbon fiber (ACF) felt cathode. First of all, effect of initial Fe2+ and Fe3+ concentrations on the degradation and mineralization of CIP in EF process was compared, while the optimal initial Fe2+ and Fe3+ contents were both verified to be 1.50mmoldm−3, in which 73% and 72% of initial TOC were eliminated after 360min electrolysis, respectively. Secondly, Fe3+-CIP chelate was produced during CIP degradation in EF process, whose predominant form was confirmed as 1:2 metal-ligand stoichiometry. The formation of Fe3+-CIP chelate had no obvious inhibition on the degradation and mineralization of CIP due to the efficient Fe3+ reduction on the ACF cathode with excellent catalytic feature. About 17% and 35% of initial 1.50mmoldm−3 Fe3+ were reduced to Fe2+ at 18mAcm−2 in ultrapure water and 200mgdm−3 CIP solutions during 30min pre-aeration of EF process, respectively, while higher Fe2+ concentration was maintained for initial 1.50mmoldm−3 Fe3+ during CIP degradation. Finally, the evolution of F−, NH4+ and NO3− ions released to the acidic medium were determined, as well as the formation of short-chain carboxylic acid (oxalic, oxamic and formic acids). Eight aromatic intermediates were identified using UPLC-QTOF-MS/MS, and a feasible mineralization pathway was proposed.

Simultaneous removal of SO2 and NO from flue gas with [rad]OH from the catalytic decomposition of gas-phase H2O2 over solid-phase Fe2(SO4)3

In typical Fenton-like reaction, ferric sulfate (Fe2(SO4)3) was usually used to produce hydroxyl radical (OH) in the form of Fe3+ in aqueous solution. In this research, it was the first time that OH was obtained from the catalytic decomposition of gas-phase H2O2 over solid-phase Fe2(SO4)3 for simultaneous removal of SO2 and NO. The radical scavenger tests indicated the critical role of OH in NO removal rather than SO2 removal. The operation parameters were systematically investigated. The SO2 removal efficiency was affected by the liquid absorption, whereas the NO removal was mainly affected by the catalytic temperature, H2O2 concentration, H2O concentration and catalyst dosage. 99.8% SO2 and 92.5% NO were achieved under the operation condition where the molar ratio of H2O2 to NO was 2.5. According to the products before and after scrubbing, the removal process of SO2 and NO were speculated. NO removal experiments in NO only system and simultaneous removal system was studied, respectively. The improvement of SO2 on NO removal was elucidated by XPS characterization. SO2 and NO removal efficiencies in 12hours’ test were collected and the evolution of catalyst before and after reaction was studied using FTIR and SEM-EDX.

Reforming sewage sludge pyrolysis volatile with Fe-embedded char: Minimization of liquid product yield

Obtaining high quality syngas from sewage sludge (SS) means transferring a low-grade SS into a high-grade fuel or raw materials for chemical products. In this study, Fe is added to SS in form of Fe2(SO4)3 to produce an effective and self-sufficient catalyst in order to obtain more syngas and minimize liquid products from SS pyrolysis. The Fe-embedded sewage sludge chars (SSCs) were used as catalysts for volatile reforming at 600°C. It has been found that the gas yield increases from 15.9 to 35.8wt% of the SS and that of liquids decreases from 31.9 to 10.2wt% after volatile reforming with Fe-embedded SSC when Fe was added equal to 7 % in the dried SS. In addition, the content of nitrogen-containing compounds in the oily products decreased. After reforming with Fe-embedded SSC, the molar fractions of syngas combustible components, including H2, CH4 and CO, increase, and the higher heating value of the syngas increased to 17.0MJ/Nm3 from the original 12.5MJ/Nm3 obtained from SS pyrolysis at 550°C. Moreover, the volatile reforming seems to reduce the level of some important syngas pollutants, like H2S, HCl and HCN, even though it was also observed an increase of the contents of SO2, NH3, NO2, HCNO and N2O.

Microbial Dissolution of Iron Surface Coatings in Industrial Minerals

The purpose of this work was to investigate the phenomenon of microbial iron reduction in industrial minerals and materials. These materials are generally not pure, often associated with impurities usually in the form of Fe3+. In all cases, the presence of iron affects the colour and the physical properties of the mineral and therefore lowers their industrial value and limits their application. In this study bentonite, kaolin and quartz sand sample were used for the experiments and compared in effectiveness of iron dissolution. The experimental results showed that after 30 days of bioleaching process, bacteria are able to remove 9.29% of Fe occurring in the kaolin sample (K-I) in amorphous form of oxyhydroxides and approximately 12% of Fe from the bentonite sample (B-JP) also in amorphous form of oxyhydroxides. In the quartz sand sample C3-15D, the concentration of Fe decreased by 15% after 15 days of bioleaching process and in the sample C3-30D after 30 days of bioleaching process by 24.7%.

Highly ordered Fe3+/TiO2 nanotube arrays for efficient photocataltyic degradation of nitrobenzene

Highly ordered TiO2 nanotube arrays (TiO2 NTs) were prepared through a facile two-step electrochemical anodization, subsequently, active iron ions were introduced into the TiO2 NTs via a direct impregnation method. The XPS results showed that the iron elements existed in TiO2 NTs in the form of Fe3+ ions. Compared with the undoped TiO2 NTs, the absorption edge of Fe3+/TiO2 NTs showed an overt red shift and the photocurrent improved obviously, which indicated that Fe3+/TiO2 had a much higher photocatalytic activity. The optimal doping content was tested to be 0.1mol/L which could make the photocatalytic activity of TiO2 NTs obviously improves under both visible and ultraviolent light. The prepared samples were adopted as photocatalyst to degrade nitrobenzene (NB). The reaction rate constants ks under UV light were in the order kone-stepTiO2NTs=0.00338<ktwo-steTiONTs=0.00455<kFe3+/TiONTs=0.00736 which showed the superior photocatalysis activity of Fe3+/TiO2 NTs. The final degradation products were probed to be CO2 and H2O, which demonstrated that NB could be completely mineralized to harmless inorganic substance. The mechanism of NB degradation with Fe3+/TiO2 was also discussed and the quenching experiments further confirm that OH, h+ and O2− are active intermediates in the process of photocatalytic degradation.

Formation mechanisms of Fe3\u2212xSnxO4 by a chemical vapor transport (CVT) process

Our former study reported that Fe-Sn spinel (Fe3−xSnxO4) was easily formed when SnO2 and Fe3O4 were roasted under CO-CO2 atmosphere at 900–1100 °C. However, the formation procedure is still unclear and there is a lack of theoretical research on the formation mechanism of the Fe-Sn spinel. In this work, the reaction mechanisms between SnO2 and Fe3O4 under CO-CO2 atmosphere were determined using XRD, VSM, SEM-EDS, XPS, etc. The results indicated that the formation of Fe3−xSnxO4 could be divided into four steps: reduction of SnO2 to solid phase SnO, volatilization of gaseous SnO, adsorption of gaseous SnO on the surface of Fe3O4, and redox reaction between SnO and Fe3O4. During the roasting process, part of Fe3+ in Fe3O4 was reduced to Fe2+ by gaseous SnO, and meanwhile Sn2+ was oxidized to Sn4+ and entered into Fe3−xSnxO4. The reaction between SnO2 and Fe3O4 could be summarized as Fe3O4 + xSnO(g) → Fe3−xSnxO4 (x = 0–1.0).