Surface Fe3 Research Articles

Hierarchical Zeolite Y Containing Ti and Fe Oxides as Photocatalysts for Degradation of Amoxicillin.

The Ti/hierarchical zeolites Y were obtained by direct and post synthesis methods and loaded with Fe(III) by ion-exchange and impregnation resulting Fe-Ti/hierarchical zeolites Y photocatalysts. The synthesized materials were characterized by XRD, SEM microscopy, N2 physical adsorption, Raman, UV-Vis and XPS and EPR spectroscopy. XRD patterns evidenced the crystalline structure of the zeolite Y in all materials, excepting the samples with higher Fe content. The presence of anatase was evidenced by XRD and Raman spectroscopy in the samples obtained by impregnation while α-Fe₂O₃ was depicted in the Raman spectra of the samples with Ti and lower Fe loading. SEM images and N2 adsorption-desorption isotherms confirmed the formation of mesopores together with microporous crystals of zeolite Y. The UV-Vis spectra proved a red-shifted adsorption band for samples with iron. In all these samples XPS shows Fe3+ as oxide on the surface and EPR Fe3+ in tetrahedral coordination. Different variables such as hierarchical structure, amount of iron, catalyst loading, concentration of pollutant solution, pH value were studied to estimate their effects on performances of photocatalysts in degradation of amoxicillin from aqueous solution in UV and Visible light. A higher adsorption capacity and degradation efficiency of amoxicillin (100%) was noticed for hierarchical materials, especially for higher iron oxide loaded samples.

Identifying the reactive sites of hydrogen peroxide decomposition and hydroxyl radical formation on chrysotile asbestos surfaces

BackgroundFibrous chrysotile has been the most commonly applied asbestos mineral in a range of technical applications. However, it is toxic and carcinogenic upon inhalation. The chemical reactivity of chrysotile fiber surfaces contributes to its adverse health effects by catalyzing the formation of highly reactive hydroxyl radicals (HO•) from H2O2. In this Haber-Weiss cycle, Fe on the fiber surface acts as a catalyst: Fe3+ decomposes H2O2 to reductants that reduce surface Fe3+ to Fe2+, which is back-oxidized by H2O2 (Fenton-oxidation) to yield HO•. Chrysotile contains three structural Fe species: ferrous and ferric octahedral Fe and ferric tetrahedral Fe (Fe3+tet). Also, external Fe may adsorb or precipitate onto fiber surfaces. The goal of this study was to identify the Fe species on chrysotile surfaces that catalyze H2O2 decomposition and HO• generation.ResultsWe demonstrate that at the physiological pH 7.4 Fe3+tet on chrysotile surfaces substantially contributes to H2O2 decomposition and is the key structural Fe species catalyzing HO• generation. After depleting Fe from fiber surfaces, a remnant fiber-related H2O2 decomposition mode was identified, which may involve magnetite impurities, remnant Fe or substituted redox-active transition metals other than Fe. Fe (hydr)oxide precipitates on chrysotile surfaces also contributed to H2O2 decomposition, but were per mole Fe substantially less efficient than surface Fe3+tet. Fe added to chrysotile fibers increased HO• generation only when it became incorporated and tetrahedrally coordinated into vacancy sites in the Si layer.ConclusionsOur results suggest that at the physiological pH 7.4, oxidative stress caused by chrysotile fibers largely results from radicals produced in the Haber-Weiss cycle that is catalyzed by Fe3+tet. The catalytic role of Fe3+tet in radical generation may also apply to other pathogenic silicates in which Fe3+tet is substituted, e.g. quartz, amphiboles and zeolites. However, even if these pathogenic minerals do not contain Fe, our results suggest that the mere presence of vacancy sites may pose a risk, as incorporation of external Fe into a tetrahedral coordination environment can lead to HO• generation.

Surface modification and flotation improvement of ilmenite by using sodium hypochlorite as oxidant and activator

In this study, we have developed a novel method for ilmenite activation. Sodium hypochlorite was used as an oxidant and surface modifier to promote ilmenite flotation. And it has successfully been performed valence transitions of iron atoms on the ilmenite surface, thereby enhancing the action activity between the surface sites of ilmenite and sodium oleate. Eventually the surface Fe3+ content increased from 42.15 to 63.79%. Oxidation by sodium hypochlorite increased the amount of Fe3+ on the ilmenite surface by 21.64% and improved the ilmenite recovery to 95%, while the maximum recovery of ilmenite without sodium hypochlorite addition was only 85%. The activation mechanism of ilmenite by sodium hypochlorite was studied by batch flotation, Zeta potential measurement, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and reaction thermodynamic analysis. The results of potential measurement show that sodium hypochlorite made the Zeta potentials of ilmenite–sodium oleate system more negative mainly due to the enhanced adsorption effect between them. FTIR results indicate that more prominent absorption peak of iron oleate appeared in the FTIR spectrum of ilmenite treated with sodium oleate after sodium hypochlorite oxidation. XPS analyses suggest that more Fe2+ on ilmenite surface supplied electrons to the oxidant and formed more Fe3+. Reaction thermodynamic analyses also show that compared with Fe2+, Fe3+ was more likely to interact with oleate ions and formed more stable species. In summary, sodium hypochlorite can activate ilmenite and improve its flotation.

In situ 3D bacterial cellulose/nitrogen-doped graphene oxide quantum dot-based membrane fluorescent probes for aggregation-induced detection of iron ions

The development of a bio-based fluorescent membrane sensor for iron ions is elaborated. A three-dimensional (3D) network structure of bacterial cellulose (BC) made by layer-by-layer in situ cultivation contained nitrogen doped graphene oxide quantum dots (N-GOQDs). The obtained BC/N-GOQDs were analyzed by SEM, TEM and XPS and demonstrated that the blue emissive N-GOQDs were homogeneously distributed in the BC mats through hydrogen bonding. These materials were found to be useful for the detection of iron ions in aqueous solutions. Experimental data showed the blue-emitting BC/N-GOQDs fluorescent probes exhibited a sensitive response to Fe3+ within a favorable concentration range of 0.5–650 μM with a very good lower limit detection of 69 nM at a signal-to-noise ratio of 3 (S/N = 3). Meanwhile, the BC/N-GOQDs–Fe3+ complexes has good reproducibility after treatment with EDTA. The quenching mechanism was attributed to strong coordination between surface functional groups (–NH2 and –OH) and Fe3+ which was successfully applied in real water samples. Diagram of quenching mechanism of the BC/N-GOQDs nanocomposites towards Fe3+ ions.

Fabrication of an Fe‐Doped SrTiO3 Photocatalyst with Enhanced Dinitrogen Photofixation Performance

SrTiO3 as semiconducting photocatalyst has been extensively investigated due to its band edges meeting the thermodynamic requirements for water splitting, but a few attention has been concentrated on its application in the NH3 synthesis via N2 photofixation process. Herein, Fe‐doped SrTiO3 (FexSr1–xTiO3) products (0 ≤ x ≤ 0.20) were synthesized via a hydrothermal process followed by calcination at 700 °C. All FexSr1–xTiO3 products (0.03 ≤ x ≤ 0.20) deliver an enhanced N2 fixation ability, and FexSr1–xTiO3 (x = 0.10) achieves the best NH3 production activity of 30.1 µmol g–1 h–1, which is 3.2‐hold higher than that of SrTiO3 alone. Once the x value is higher than 0.10, FexSr1–xTiO3 will transform into composites containing Fe‐doped SrTiO3 and α‐Fe2O3, which acts as charge recombination sites, thus causes a decreased N2 fixation activity. Further investigations demonstrate that the surface Fe3+‐doped sites can not only chemisorb and activate N2 molecules, but also promote the interfacial electron transfer from Fe‐doped SrTiO3 to N2 molecules, and thus significantly improve the N2 fixation ability. The present Fe‐doped SrTiO3 products exhibit characteristic features such as stable and efficient N2 fixation ability as well as simultaneous realization of N2 reduction and H2O oxidation without co‐catalyst, which are of significance in artificial photosynthesis with H2O as electron and proton sources.

Effect of Nb modification on the structural and catalytic property of Fe/Nb/M (M = Mn, Co, Ni, and Cu) catalyst for high temperature water-gas shift reaction

Abstract Herein, the catalytic performance of Fe/Nb/M (M = Mn, Co, Ni, and Cu) spinel ferrites prepared by a co-precipitation method for the high-temperature water-gas shift (HT-WGS) was investigated. Incorporation of Nb into the iron oxide lattice was found to moderately improve the catalytic activity. Conversely, the co-doping with Nb and transition metals (Mn, Co, Ni, and Cu) into the iron oxide matrix drastically enhanced the HT-WGS activity. The high lattice strain/disorder and facile Fe3+/Fe2+ redox cycle induced by the enhanced synergism in the Fe/Nb/M ternary catalysts serve as active sites to efficiently catalyze the WGS reaction. The results also indicate that the Nb acts as a textural promoter to improve the thermal stability of the active magnetite phase, while the transition metals act as structural promoters to enhance the WGS activity. The Fe/Nb/Ni exhibited the higher catalytic performance among the co-doped spinel ferrite catalysts. The high lattice strain/disorder, facile reduction of hematite to magnetite and highly facilitated surface Fe3+/Fe2+ redox pair by strong synergistic effect could be responsible for the better activity and stability of Fe/Nb/Ni in HT-WGS reaction. The characterizations of the spent Fe/Nb/Ni after 100 h of reaction revealed that the catalyst exhibited an excellent structural and surface stability during the reaction.

Interaction of Water Molecules with the α-Fe2O3(0001) Surface: A Combined Experimental and Computational Study

The interaction of water with the basal plane (0001) of α-Fe2O3 (hematite) is a fundamental and challenging topic in the fields of surface science and earth science. Despite intensive investigations, many issues remain unclear especially due to the lack of direct spectroscopic evidence. Here, water adsorption on the pristine Fe-terminated α-Fe2O3(0001) surface was investigated by polarization-dependent infrared reflection absorption spectroscopy and X-ray photoelectron spectroscopy in conjunction with calculations from density functional theory. The combined results provide solid evidence that the interaction of water with α-Fe2O3(0001) is dominated by the heterolytic dissociation yielding an OwD species coordinated in atop-configuration to surface Fe3+ and an OsD species resulting from the deuterium/hydrogen transfer to an adjacent substrate O2–. Both isolated hydroxyl groups do not feature any hydrogen bonding, while the intact water molecules were identified as minor species that are bound to surface F...

Modification of polyvinylidene fluoride membrane with different shaped α-Fe2O3 nanocrystals for enhanced photocatalytic oxidation performance

A novel modified polyvinylidene fluoride (PVDF) membranes with adding α-Fe2O3 nanocrystals were prepared for the photocatalytic degradation of organic contaminants. The α-Fe2O3 nanocrystals entrapped PVDF membranes were characterized by XRD, SEM and TEM. The photocatalytic performance and antifouling property were studied by filtration and degradation of Congo red (CR) under visible light irradiation. The results show that the photocatalytic activity of the α-Fe2O3/PVDF membranes were significantly influenced by the morphology of α-Fe2O3 nanocrystals. The PVDF membrane with inclusion of α-Fe2O3 nanorods showed high degradation efficiency (90%) because of the higher surface Fe3+ density. The water flux and degradation kinetics of the composite membrane were also studied.

High-temperature water-gas shift over Fe/Ce/Co spinel catalysts: Study of the promotional effect of Ce and Co

A set of Fe/Ce/Co ferrite spinels was synthesized and characterized to investigate the effect of Ce and Co atomic contents in the catalyst on the high-temperature water-gas shift (HT-WGS) performance. It was found that both the Ce and Co atomic compositions in the Fe/Ce/Co catalyst have a significant influence on the surface and structural properties and thereby HT-WGS activity. The Fe/Ce/Co (10:1:1.5) exhibited the best activity owing to preferable properties among the catalysts with other Ce and Co atomic contents. Besides, it showed an excellent time-on-stream (TOS) stability in HT-WGS for 100h of reaction even at lower steam to CO ratio of 1.5. XRD results suggested that Ce and Co co-doping could make the lattice strain in the magnetite lattice because of difference in the ionic sizes of Fe and dopants. Raman spectroscopy demonstrated that the lattice disorder was introduced with the addition of Ce and Co. The magnitude of the lattice strain/disorder depends on the promoters’ (Ce and Co) atomic composition in the catalyst. Our H2-TPR findings indicate that the degree of reduction for hematite-to-magnetite conversion increased until the Ce and Co atomic concentration reached to 1.0 and 1.5, respectively. The XPS analysis proves that both Ce and Co as dopants have the ability to facilitate the surface Fe3+↔Fe2+ redox cycle over the catalysts because of their redox nature (Ce4+/Ce3+, Co2+/Co3+). We observed the changes in the quantity of surface Fe3+/Fe2+ ratio as a function of the Ce and Co atomic contents. The results also revealed that the surface area, lattice strain/disorder, reducibility, and surface Fe3+/Fe2+ redox pair were the decisive factors for the HT-WGS reaction. A combination of techniques demonstrated that there is a strong synergistic interaction between Fe and dopants (Ce and Co) in the Fe/Ce/Co (10:1:1.5) which could enhance its surface area, lattice strain/disorder, surface Fe3+/Fe2+ redox capability, and thus leading to the elevated HT-WGS activity among other catalysts. XPS investigations on the spent Fe/Ce/Co (10:1:1.5) after 100h of reaction show that the catalyst remains in magnetite phase like the reduced one and is not reduced or oxidized during reaction. Our TEM images confirm that the Fe/Ce/Co (10:1:1.5) catalyst particles are not agglomerating/sintering during the TOS study which is an important characteristic for its long term stability.

Adsorption of CO on the Fe3O4(001) Surface.

The interaction of CO with the Fe3O4(001)-(√2 × √2)R45° surface was studied using temperature-programmed desorption (TPD), scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS), the latter both under ultrahigh vacuum (UHV) conditions and in CO pressures up to 1 mbar. In general, the CO-Fe3O4 interaction is found to be weak. The strongest adsorption occurs at surface defects, leading to small TPD peaks at 115, 130, and 190 K. Desorption from the regular surface occurs in two distinct regimes. For coverages up to two CO molecules per (√2 × √2)R45° unit cell, the desorption maximum shows a large shift with increasing coverage, from initially 105 to 70 K. For coverages between 2 and 4 molecules per (√2 × √2)R45° unit cell, a much sharper desorption feature emerges at ∼65 K. Thermodynamic analysis of the TPD data suggests a phase transition from a dilute 2D gas into an ordered overlayer with CO molecules bound to surface Fe3+ sites. XPS data acquired at 45 K in UHV are consistent with physisorption. Some carbon-containing species are observed in the near-ambient-pressure XPS experiments at room temperature but are attributed to contamination and/or reaction with CO with water from the residual gas. No evidence was found for surface reduction or carburization by CO molecules.

Oxidative coupling of acetaminophen mediated by Fe3 +-saturated montmorillonite

The wide usage of acetaminophen as human medicine has resulted in its ubiquitous occurrence in various environmental compartments. However, the information for the transformation of acetaminophen in soil is still limited. In this study, oxidative coupling of acetaminophen in bulk solution mediated by Fe3+-saturated montmorillonite was observed under different environmental conditions. In the absence of natural phenolic acids, acetaminophen could be fully eliminated from the solution within 72h at pH3.5, acetaminophen dimer was identified as the major reaction product. Reduction of montmorillonite associated Fe3+ coupled with the oxidation of acetaminophen was considered as the main mechanism for acetaminophen transformation on Fe3+-saturated montmorillonite. The clay associated Fe3+ showed higher reactivity than Fe3+ in solution due to the strong complexation between surface Fe3+ and acetaminophen. The cross-coupling reaction between acetaminophen and phenolic acids was also observed when phenolic acids were present in the system. While with the increase of phenolic acid concentration, the competition for the reactive sites between acetaminophen and phenolic acids significantly suppressed acetaminophen removal. These results demonstrated the importance of transition metal saturated clay minerals for the abiotic transformation of anthropogenic micropollutants.

Weakly bound water structure, bond valence saturation and water dynamics at the goethite (100) surface/aqueous interface: ab initio dynamical simulations

BackgroundMany important geochemical and biogeochemical reactions occur in the mineral/formation water interface of the highly abundant mineral, goethite [α-Fe(OOH)]. Ab initio molecular dynamics (AIMD) simulations of the goethite α-FeOOH (100) surface and the structure, water bond formation and dynamics of water molecules in the mineral/aqueous interface are presented. Several exchange correlation functionals were employed (PBE96, PBE96 + Grimme, and PBE0) in the simulations of a (3 × 2) goethite surface with 65 absorbed water molecules in a 3D-periodic supercell (a = 30 Å, FeOOH slab ~12 Å thick, solvation layer ~18 Å thick).ResultsThe lowest energy goethite (100) surface termination model was determined to have an exposed surface Fe3+ that was loosely capped by a water molecule and a shared hydroxide with a neighboring surface Fe3+. The water molecules capping surface Fe3+ ions were found to be loosely bound at all DFT levels with and without Grimme corrections, indicative that each surface Fe3+ was coordinated with only five neighbors. These long bonds were supported by bond valence theory calculations, which showed that the bond valence of the surface Fe3+ was saturated and surface has a neutral charge. The polarization of the water layer adjacent to the surface was found to be small and affected only the nearest water. Analysis by density difference plots and localized Boys orbitals identified three types of water molecules: those loosely bound to the surface Fe3+, those hydrogen bonded to the surface hydroxyl, and bulk water with tetrahedral coordination. Boys orbital analysis showed that the spin down lone pair orbital of the weakly absorbed water interact more strongly with the spin up Fe3+ ion. These weakly bound surface water molecules were found to rapidly exchange with the second water layer (~0.025 exchanges/ps) using a dissociative mechanism.ConclusionsWater molecules adjacent to the surface were found to only weakly interact with the surface and as a result were readily able to exchange with the bulk water. To account for the large surface Fe–OH2 distances in the DFT calculations it was proposed that the surface Fe3+ atoms, which already have their bond valence fully satisfied with only five neighbors, are under-coordinated with respect to the bulk coordination.Graphical abstractAll first principle calculations, at all practically achievable levels, for the goethite 100 aqueous interface support a long bond and weak interaction between the exposed surface Fe3+ and water molecules capping the surface. This result is supported by bond valence theory calculations and is indicative that each surface Fe3+ is coordinated with only 5 neighbors.

Fe-containing carbon obtained from ferrocene: Influence of the preparation procedure on the catalytic performance in FTS reaction

Four different preparation routes were applied to obtain Fe-containing carbon catalysts for Fischer Tropsch Synthesis (FTS) including copolymer assisted co-precipitation of iron precursor, chemical modification of ferrocene, sol-gel and wetness impregnation of iron on polymeric carbon. The effects of the FTS reaction temperature and pressure were also examined. Using ferrocene as a starting precursor and applying sol-gel method to prepare the solid, the syngas is readily converted to C10+ hydrocarbons with a conversion of up to 56% and a productivity of 34mg hydrocarbon.gcat−1.h−1 at 240°C and 20atm. Impregnation method gave a Fe/C based catalyst with the highest exposure of active sites, including surface Fe3+ and Fe2+ redox sites with great properties in FTS. Chemical modification of ferrocene route enables the formation of hematite and maghemite nanoparticles on carbon, which were in situ reduced to magnetite and iron carbides, being the latter mostly active for the water gas shift reaction. It is found that copolymer assisted co-precipitation of ferrocene facilitates the production of large crystals of magnetite, which suffered from sintering and coking exhibiting low performance in FTS. Among these methods, sol-gel based catalyst proved to have superior performance due to the good dispersion of Fe, stable magnetite and iron carbide and Fe-doped nitrogen carbon phases production. Based on spent catalysts characterizations, the synergetic effect between magnetite and the iron carbides phases in the sol-gel based catalyst plays an important role in heavy hydrocarbon formation.

NO reduction by CO over iron‐based catalysts supported by activated semi‐coke

Activated semi‐coke was developed and loaded by iron species and other assistant metals (Co, La, and Ce) using a hydrothermal method to obtain the abatement of NOx emissions from power plants and then used for NO removal by CO. These catalysts were systematically characterized by N2 physisorption, scanning electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and the activity of NOx reduction. The results showed that the activated semi‐coke that was loaded by Fe species could achieve an excellent NOx conversion of 96.5 % at 350 °C with 0.2 g/g (20 wt%) of the precursor content (catalyst denoted as Fe20/ASC). This was ascribed to higher amounts of surface Fe3+ and chemisorbed oxygen. Furthermore, Co was the best promoter among Co, La, and Ce. This enhancement was attributed to the increase of the specific surface area and chemisorbed oxygen, as well as the formation of CoFe2O4. The synergistic effect between Fe and Co species was beneficial for the formation of oxygen vacancies, which could promote the adsorption and dissociation of NO. The in situ DRIFTS results indicated that the reaction for NOx removal by CO over activated semi‐coke supported catalysts mainly occurred between coordinated nitrates/nitryls and the adsorbed COx species.

Role of [FeOx(OH)y] surface sites on the adsorption of β-lactamic antibiotics on Al2O3 supported Fe oxide

In this work, [FeOx(OH)y]/Al2O3 composites with different Fe oxyhydroxy contents, i.e. 10, 20 and 50wt% treated at 150, 200, 300 and 450°C were investigated as adsorbents of β-lactamic antibiotics, i.e. cephalexin, ceftriaxone and especially amoxicillin, from aqueous solutions. The obtained results showed that the nature of the surface Fe3+ species play a fundamental role on the adsorption process. The most efficient adsorption was obtained for the sample 150Fe50A (50% [FeOx(OH)y] supported in Al2O3 treated at 150°C) whereas the thermal treatment at higher temperatures caused a strong decrease on the adsorption capacity. Mössbauer, XRD, FTIR, Raman, TG-MS, SEM, CHN and BET of the composite 150Fe50A suggested an approximate composition of FeO0.65(OH)1.7 whereas at 450°C strong dehydroxylation process takes place to form FeO1.4(OH)0.21. These results combined with competitive adsorption using amoxicillin mixed with phosphate or H2O2 suggest that the antibiotic molecules adsorb by complexation on surface sites likely based on FeOx(OH)y by the replacement of the labile OH ligands.

Development of biomaterial for chromium(VI) detoxification using Aspergillus flavus system supported with iron

This study was aimed to develop the growing Aspergillus flavus biomaterial for Cr(VI) transformation and removal from simulated wastewater. Fe2+ ions have significant implication as it enhanced both chromium removal as well as sticky nature of the biomaterial. The values of Δ, i.e. the differences between the frequencies νas and νs of carboxyl group 146.59, 139.27, 152.38 by Fe(II), Cr(VI) and mix metals ions (Fe(II)+Cr(VI)) inferred the carboxylate ions bidentate coordination. The highest value in case of mix metals ions (Fe(II)+Cr(VI)) inferred that carboxylate groups have coordinated to surface Fe3+ ions increasingly with greatest bridging character. Heat flow value 31.36Jg−1 and 51.02Jg−1 in Fe2+ and Cr(VI) amended material respectively indicated that extremely little amount of the free water content was sorbed.

Sustaining reactivity of Fe0 for nitrate reduction via electron transfer between dissolved Fe2+ and surface iron oxides

The mechanism of the effects of Fe2+aq on the reduction of NO3− by Fe0 was investigated. The effects of initial pH on the rate of NO3− reduction and the Fe0 surface characteristics revealed Fe2+aq and the characteristics of minerals on the surface of Fe0 played an important role in NO3− reduction. Both NO3− reduction and the decrease of Fe2+aq exhibited similar kinetics and were promoted by each other. This promotion was associated with the types of the surface iron oxides of Fe0. Additionally, further reduction of NO3− produced more surface iron oxides, supplying more active sites for Fe2+aq, resulting in more electron transfer between Fe2+ and surface iron oxides and a higher reaction rate. Using the isotope specificity of 57Fe Mossbauer spectroscopy, it was verified that the Fe2+aq was continuously converted into Fe3+ oxides on the surface of Fe0 and then converted into Fe3O4 via electron transfer between Fe2+ and the pre-existing surface Fe3+ oxides. Electrochemistry measurements confirmed that the spontaneous electron transfer between the Fe2+ and structural Fe3+ species accelerated the interfacial electron transfer between the Fe species and NO3−. This study provides a new insight into the interaction between Fe species and contaminants and interface electron transfer.

Sodium Dodecyl Sulfate Modified FeCo2O4 with Enhanced Fenton-Like Activity at Neutral pH

In this work, FeCo2O4 was prepared by a simple coprecipitation method and investigated as a heterogeneous Fenton catalyst. The influences of sodium dodecyl sulfate (SDS) on the structure, surface charge, electron transfer ability, and catalytic activity of FeCo2O4 were investigated. FeCo2O4–S prepared with SDS exhibited much higher catalytic activity for the degradation of methylene blue (MB) in aqueous solution than pure FeCo2O4, which can be attributed to its higher electron transfer ability. The adsorbed SDS accelerated the reduction of surface Fe3+ to Fe2+ by H2O2 and •O2–. The high concentration of surface Fe2+ on FeCo2O4–S during the reaction promoted the decomposition of H2O2 into •OH, which was the main active specie for the degradation of MB. Furthermore, SDS increased the adsorption capacity of the catalyst toward MB, thus facilitating the reaction between adsorbed MB and •OH generated on the catalyst surface.

Ultrathin carbon nanopainting of LiFePO4 by oxidative surface polymerization of dopamine

The common strategy to address the low electronic conductivity of LiFePO4 is to downsize LiFePO4 and to coat the nanocrystal with conductive carbon film. The major issues with existing carbon coating techniques are thickness and quality control. This paper reports a facile carbon coating method which can provide ultrathin, uniform and fully encapsulating carbon coating on LiFePO4. This coating method capitalizes on the redox chemistry of surface Fe3+ on solvothermally synthesized LiFePO4 nanocrystal, to deposit uniform thin films of polydopamine films. The polymer film is easily carbonized into ultrathin carbon film. The carbon coated LiFePO4 exhibits very high rate performance (143 mAh g−1 at current density of 1700 mA g−1) with excellent capacity retention.

Ion transport through homogeneous and heterogeneous ion-exchange membranes in single salt and multicomponent electrolyte solutions

The increasing demand for clean industrial processes has intensified the use of electrodialysis in the treatment of metal containing effluents and encourages the investigation of the different phenomena involved in the transport of metal ions through cation-exchange membranes. Ion sorption, chronopotentiometric and current–voltage characteristics have been obtained to characterize the transport of sodium and iron through homogeneous and heterogeneous cation-exchange membranes. The heterogeneous membranes having a broader pore size distribution showed increased electrical resistances with solutions of trivalent iron, which may be caused by the blockage of the smallest pores by multivalent ions. However, for both types of membranes an unexpected decrease of the electrical resistance with increasing current densities was verified with concentrated solutions of Fe2(SO4)3. This behavior was explained to be a consequence of the dissociation of FeSO4+ ions into more conductive Fe3+ and SO42− ions as the depleting solution layer becomes diluted. When tested with multicomponent mixtures, the homogeneous perfluorosulfonic membranes show an increased preference for Na+ ions at low current densities and, once Na+ ions are depleted from the membrane surface Fe3+ ions are transported preferentially at higher current densities. On the contrary, both Na+ ions and Fe(III) species are responsible for the ion transport through the heterogeneous membranes within the ohmic regime of currents.