Structure and size effects in catalysis by immobilized nanoclusters of iron oxides

The activities of catalysts containing -Fe₂O₃ or γ-Fe₂O₃ nanoparticles supported on two types of silica (silica gel and layer silica) are tested in 3,4-dichlorobutene-1 isomerization and benzene alkylation by allyl chloride. γ-Fe₂O₃ particles supported on layer silica are the most active catalysts for both reactions. The high activity is associated with features of inverse spinel structure of γ-ferric oxide. The particle size and their location on the surface or interplane cavity of layer silica affect the catalytic activity.     

Effect of composition on rheological behavior of iron oxides produced by hydrothermal method

The aim of the present work was to investigate the rheological properties of different iron oxides (Fe₃O₄, NiFe₂O₄, ZnFe₂O₄ and Ni_0.5Zn_0.5Fe₂O₄) aqueous suspensions. The oxides were produced through mixing the respective metallic sulfates within a closed isothermal reactor at 100 °C and at pH ≈12, in an oxidant environment (provided by H₂O₂ 0.63% w/v). The reactor was coupled with an adequate real-time data (RTD) acquisition system enabling measurement of temperature, pH and pressure. Obtained RTD data showed that once the isothermal conditions are reached, the pressure slowly decreases over time, which is a result of O₂ consumption through oxidation of Fe²⁺ to Fe³⁺. To characterize the suspensions as a function of temperature and shear rate, the steady rheology was used. The results revealed that the effect of temperature on viscosity of all suspensions was insignificant while steady rheology showed pseudoplastic behavior for all ferrites. The magnitude of viscosity and pseudoplasticity turned out to be in agreement with the hydrodynamic diameters of particles complying with the order: NiFe₂O₄>Fe₃O₄>Ni_0.5Zn_0.5Fe₂O₄>ZnFe₂O₄. Finally, the rheological behavior of suspensions was attributed to the concentration of OH groups on the surface of particles and this hypothesis was effectively supported by DRX, FTIR and TGA/DTA measurements.     

Decolorization of synthetic dyes by hydrogen peroxide with heterogeneous catalysis by mixed iron oxides

Heterogeneous catalysts based on magnetic mixed iron oxides (MO·Fe₂O₃; M: Fe, Co, Cu, Mn) were used for the decolorization of several synthetic dyes (Bromophenol Blue, Chicago Sky Blue, Cu Phthalocyanine, Eosin Yellowish, Evans Blue, Naphthol Blue Black, Phenol Red, Poly B-411, and Reactive Orange 16). All the catalysts decomposed H₂O₂ yielding highly reactive hydroxyl radicals, and were able to decolorize the synthetic dyes. The most effective catalyst FeO·Fe₂O₃ (25 mg mL⁻¹ with 100 mmol L⁻¹ H₂O₂) produced more than 90% decolorization of 50 mg L⁻¹ Bromophenol Blue, Chicago Sky Blue, Evans Blue and Naphthol Blue Black within 24 h. The fastest decomposition proceeded during the first hour of the reaction. In addition to dye decolorization, all the catalysts also caused a significant decrease of chemical oxygen demand (COD). Individual catalysts were active in the pH range 2–10 depending on their structure and were able to perform sequential catalytic cycles with low metal leaching.     

Comparison of catalytic decomposition of hydrogen peroxide and catalytic degradation of phenol by immobilized iron oxides

Immobilized iron oxides on silica matrixes in fluidized bed reactors, including SiG1, SiG2, C1, and the commercial catalyst FeOOH, were used in the catalytic decomposition of H₂O₂ and the catalytic degradation of phenol. They were characterized using XRD, SEM, N₂-sorption, and elucidation of the kinetics of dissolved iron by oxalic acid in dark surroundings. XRD patterns reveal that SiG1, SiG2, and C1 exhibit amorphous structures, and FeOOH exhibits the poor crystallinity of goethite. The SEM images reveal that the surfaces of all the iron oxides are smooth and that the iron oxides are aggregated by the iron oxide floc. The N₂-sorption isotherm indicates that SiG1 and SiG2 are non-porous materials, and that C1 and FeOOH are typical type II and typical type IV materials, respectively. A kinetic model for iron dissolved by oxalic acid is established. The order of apparent first-order dissolution rate constants (k_c) is SiG1 > SiG2 > FeOOH  C1. The immobilized iron oxides, SiG1 and SiG2, are weakly bonded to the support (silica sand) in the presence of oxalic acid. The decomposition of H₂O₂ follows pseudo-first-order kinetics. The number of active sites for the decomposition of H₂O₂ is similar among all iron oxides at a particular k_app (1.8 × 10⁻³ min⁻¹). There are no interactions between phenol and iron oxides in the absence of hydrogen peroxide at pH 4. SiG1 and SiG2 exhibit much higher catalytic activities in phenol degradation than either C1 or FeOOH. The reactivity of iron oxides in catalyzing the phenol degradation by H₂O₂ relates to the tendency of iron to be dissolved by oxalic acid. The intermediates of phenol degradation, such as catechol and oxalic acid, promote the dissolution of iron from SiG1 and SiG2 by reductive and non-reductive pathways and lower the pH values. The catalyses of SiG1 and SiG2 involve heterogeneous and homogeneous reactions.     

I. Adsorption mechanism of chlorophenols on iron oxides, titanium oxide and aluminum oxide as detected by infrared spectroscopy

The adsorption of 2-chlorophenol, 2,3- and 2,4-dichlorophenols and 2,4,6-trichlorophenol in liquid and gas phase on iron, titanium and aluminum oxides seem to proceed in a similar way. Higher adsorption of chlorophenols either from gas phase or from aqueous solution was observed on -Fe₂O₃ than on -FeOOH. The low adsorption of chlorophenols from aqueous solution on oxide surfaces suggests that hydrophobic chlorophenols cannot effectively compete with water for the absorption on hydrophilic oxide surface sites. The adsorption of chlorophenols on iron, titanium and aluminum oxides was followed by the adsorption isotherm, HPLC and diffuse reflectance FT-IR (DRIFT) spectroscopy. The adsorption of the chlorophenols on the oxides under study is related to the amount of interfacial water content on the iron oxide. The alumina–chlorophenolate surface complex was found to be weak when compared with either the iron or titanium analogs as seen by the C---O stretching vibrations, leading to a lower adsorption on alumina than on iron and titanium oxides.     

Photocatalytic degradation of organics in water in the presence of iron oxides: Influence of carboxylic acids

The effects of four carboxylic acids: malic, citric, tartaric and oxalic acids on the leaching of iron from two commercial iron oxides (hematite, α-Fe₂O₃, and magnetite, Fe₃O₄) have been investigated. The variables studied were the doses of iron oxides and carboxylic acids used as well as aqueous pH, temperature and the presence of hydrogen peroxide and/or UV-A radiation. On the whole, Fe₃O₄ led to higher amounts of leached iron than α-Fe₂O₃, and oxalic acid was the most effective carboxylic acid used. The importance of iron leaching has been considered to explain the photodegradation of bisphenol A (BPA) by UV-A/iron oxides systems. The influence of the presence of hydrogen peroxide and/or titania on the efficiency of these oxidation systems was also investigated. At the conditions tested, advanced oxidation with the UV-A/iron oxide/oxalic acid/H₂O₂/TiO₂ system led to the lowest BPA half life (<15 min) among those processes studied.     

铸铁表面的不锈钢粉末喷涂技术

介绍了铸铁表面喷涂不锈钢粉末的预加工、喷涂工艺及喷涂后加工,并对涂层的性能做了测试,取得了较好的试验效果     

An efficient electron transfer at the Fe/iron oxide interface for the photoassisted degradation of pollutants with H2O2

Fe-200 was synthesized through the calcination of iron powder at 200 °C for 30 min in air. On the basis of characterization by X-ray diffraction and X-ray photoelectron spectroscopy, Fe-200 had a core–shell structure, in which the surface layer was mainly composed of Fe₂O₃ with some FeOOH and FeO, and the core retained metallic iron. The kinetics and mechanism of the interfacial electron transfer on Fe-200 were investigated in detail for the photoassisted degradation of organic pollutants with H₂O₂. Under deoxygenated conditions in the dark, the generation of hydroxyl radicals in aqueous Fe-200 dispersion verified that galvanic cells existed at the interface of Fe⁰/iron oxide, indicating the electron transfer from Fe⁰ to Fe³⁺. Furthermore, the effects of hydrogen peroxide and different organic pollutants on the interfacial electron transfer were examined by the change rate of the Fe³⁺ concentration in the solution. The results indicated that hydrogen peroxide provided a driving force in the electron transfer from Fe²⁺ to Fe³⁺, while the degradation of organic pollutants increased the electron transfer at the interface of Fe⁰/iron oxide due to their reaction with OH.     

Rare earth and transition metal based entropy stabilised perovskite type oxides

Multicomponent oxides with perovskite type of structure containing up to 10 different cations in equiatomic amounts have been synthesised for the first time. Out of eleven systems synthesised, only six systems crystallised as single phase perovskite type compounds with random and homogenous cation distribution on the respective sites. The formation of phase pure 10-cationic system, (Gd_0.2La_0.2Nd_0.2Sm_0.2Y_0.2)(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)O₃, in contrast to the multiphase mixtures observed in five of the lower entropy systems (containing 6 cations) indicates a possible role of entropy in the stabilisation of a single phase crystal structure. The entropy driven structural stabilisation effect is further supported by the reversible phase transformation, from single phase to multiple phase upon cyclic heat treatment, observed in the (Gd_0.2La_0.2Nd_0.2Sm_0.2Y_0.2)MnO₃ system. This type of entropic signature has been observed in rocksalt based high entropy oxide systems. However, it has not been reported before for perovskite based compounds, as shown in this study.     

国外铁氧化物研究现状

综述了铁氧化物的不同制备方法,包括Fe(OH)2氧化法、缓慢或强制水解Fe3+盐溶液法、凝胶-溶胶法、水热法等方法。指出目前国外铁氧化物的研究趋势是纳米铁氧化物的制备,以及制备过程中开发特殊的添加剂或模板合成特定晶型和形态的晶体,以满足不同领域的应用要求。     

永平矿和胶东杂矿混用制干法铁红实践

通过试验确定了原料配比及其它工艺参数。实践证明,在合理的原料配比和工艺条件下,可以生产出质量上乘的干法氧化铁红。     

Catalytic activities of binary metal oxides containing iron for hydrocracking of benzyl phenyl ether and diphenyl ether

Hydrocracking of benzyl phenyl ether and diphenyl ether has been carried out over a series of iron catalysts (Fe₂O₃, Fe₂O₃Al₂O₃, Fe₂O₃ZnO, Fe₂O₃ZrO₂, Fe₂O₃MgO and Fe₂O₃SiO₂) and reference catalysts ($\text{CoOMoO}{}_3\text{Al}{}_2\text{O}{}_3$, $\text{NiOMoO}{}_3\text{Al}{}_2\text{O}{}_3$ and SiO _Al₂O₃) to search for active and selective catalysts, and to elucidate the catalyst properties of relevance for CO bond cleavage. Among the iron catalysts, Fe₂O₃ZnO, Fe₂O₃ZrO₂ and Fe₂O₃MgO exhibited relatively high activities and selectivities. The important property of catalysts relevant to hydrocracking of the ethers is the ability to accomplish hydrogenation. Acidic properties of the catalysts cause condensation and rearrangement of the reactants. The features of the iron catalysts are compared with those of molybdenum catalysts, and the reaction mechanisms discussed.     

Electrodeposited amorphous iron(III) oxides as anodes for photoelectrolysis of water

Deposition of amorphous iron(III)-oxide films on a conducting glass substrate was achieved via a cathodic bias in a 0.1 M hydrated ammonium iron(II) sulfate ((NH₄)₂Fe(SO₄)₂·6H₂O) solution at −1.6 V versus Ag/AgCl. Analysis by X-ray absorption near edge structure confirmed the iron(III) feature of the amorphous films. The deposited films exhibited n-type semiconducting characteristics by showing photoresponses under an anodic bias. The Mott–Schottky method and cyclic voltammetry were employed to characterize the semiconducting properties of the deposited films, which included the band gap (2.2 eV), the potentials of the conduction and valence band edges and flat band (−0.6, +1.6 and −0.58 V versus Ag/AgCl at pH 7, respectively), and the donor density (1 × 10²²/cm³). The deposited iron(III)-oxide films were suitable to serve as an anode for water splitting under illumination.     

A facile synthesis strategy of fungi-derived porous carbon-based iron oxides composite for asymmetric supercapacitors

Transition metal oxides (TMOs) have been considered as potential anode materials for asymmetric supercapacitors due to their high theoretical capacities. However, undesirable electric conductivity limits the further application in future energy storage. Here, a honeycomb-like architecture of FeOx embedded in the fungi-derived porous carbon-based material (FeOx/C) for asymmetric supercapacitor was reported. The facile synthesis strategy of fungi-derived porous carbon-based iron oxides was using the carbon derived from fungi and the process of carbothermal reduction to form the iron oxide compound. This carbon-encapsulated iron oxide compound provides highly specific surface area (The specific surface area of Fe–O–C-650 was largest (up to 219.0905 m²/g) compared with samples of Fe–O–C-550(144.0304 m²/g), Fe–O–C-750(201.7352 m²/g), Fe–O–C-850(163.2206 m²/g).), an abundance of redox sites, sufficient efficient channels for fast transportation of ions, excellent electrical conductivity, and stable skeleton. Under the three-electrode test system, the FeOx/C electrode delivers excellent specific capacitance of 565F/g at 1 mV/s and impressive cycling performance with capacitance retention of 100% after 3000 cycles. And the NiO electrode delivers a high specific capacitance of 425 F/g at a high current density of 5 mV/s. In addition, the FeOx/C//NiO asymmetric supercapacitor was assembled which exhibits remarkable specific capacitance of 111F/g at 10 mV/s and gravimetric energy density of 36 Wh/kg as well as gravimetric power density of 800W/kg with capacitance retention of 100% after 20,000 cycles, approaching those of ions capacitors.     

石英砂表面负载铁氧化物的方法和特性

以石英砂(0.5mm)为载体,建立流化床-Fenton系统,在pH值为3.5、Fe²⁺/H₂O₂摩尔比为2:1和进水量为试验装置设计进水量的1/3～1/2条件下,连续加入Fenton试剂,使得铁氧化物在载体表面结晶。这是因为凹凸不平的石英砂和均匀的流化状态有利于铁氧化物的覆膜,同时具有高效传质的流化床进一步强化覆膜过程。通过XRD分析可知,铁氧化物的主要成分是FeOOH、Fe₂O₃、FeO和Fe₂(SO₄)₃。同时将此系统用于处理有机硅废水和合成制药废水,在优化操作条件下,COD和TOC的去除率可达80%和85%,总铁(Fe³⁺)的消减量达26%。     

Removal of residual organic matter from secondary effluent by iron oxides adsorption

Residual organic matter (ROM) removal is an important issue in wastewater reclamation and reuse processes. Use of iron oxide particles (IOPs) as adsorbents for further treatment of the secondary effluent was investigated to mainly remove non-biodegradable residual organic matter under various operating conditions. ROM removal by IOP adsorption was evaluated in terms of the changes of UV absorbance, COD, and DOC concentrations in feed (secondary effluent) and treated water. The respective relationship of UV removal with COD and DOC removal efficiencies exhibited somewhat different profiles, possibly due to the influence of ROM properties on adsorptive removal mechanisms by IOP, such as hydrophobicity and coordinative capability. The types of IOPs such as ferrihydrite, geothite, and hematite were compared, and it was found that amorphous ferrihydrite was most effective in ROM removal. Maximum ROM removal was occuring at a solution pH of approximately 6.0, which might be ascribed to the ability of ligand exchange related to the association and dissociation of ROM molecules and IOPs at differing pH levels. Substantial reduction in the oxidation state (OS) of the treated water at high ROM removal indicated the coordination of highly oxidized groups in ROM at the IOP surface, such as carboxylic groups.     

Electronic and chemical properties of mixed-metal oxides: basic principles for the design of DeNOx and DeSOx catalysts

Correlations between the electronic and chemical properties of perovskites, molybdates, and metal-doped MgO or CeO₂ are examined. Simple models based on band-orbital mixing can explain trends found for the interaction of these catalytic materials with adsorbates: the less stable the occupied levels of a mixed-metal oxide, the higher its chemical reactivity. Metal↔oxygen↔metal interactions are common in mixed-metal oxides and can lead to substantial changes in the electronic and chemical properties of the cations. This is particularly true in the case of ABO₃ perovskites (A=Pb, Ca, Sr, Li, K, Na; B=Ti, Zr, Nb), and it is an important phenomenon that has to be considered when mixing AO and BO₂ oxides for catalytic applications. In systems like Ce_1−xZr_xO₂ and Ce_1−xCa_xO₂, the structural stress induced by the dopant (Zr or Ca) leads to perturbations in the electronic properties of the Ce cations. The trends in the behavior of metal-doped MgO illustrate a basic principle in the design of mixed-metal oxide catalysts for DeNO_x and DeSO_x operations. The general idea is to find metal dopants that upon hybridization within an oxide matrix remain in a relatively low oxidation state and at the same time induce occupied electronic states located well above the valence band of the host oxide. Electronic effects should not be neglected a priori when explaining the behavior or dealing with the design of mixed-metal oxide catalysts.     

Synthesis and structures of high-entropy pyrochlore oxides

Multicomponent oxides with pyrochlore structure (A₂Zr₂O₆O’) containing up to 7 different cations with equiatomic amounts have been successfully synthesized, which broadens pyrochlore solid solutions to high entropy pyrochlore oxides. XRD and Raman results indicate that all compositions possessed single-phase pyrochlore structure and the HAADF-STEM images with corresponding EDS mapping demonstrate that all cations were randomly and homogeneously distributed. This new class of high-entropy pyrochlore oxides may open a new research direction in pyrochlore-based materials.     

生物炭负载铁氧化物复合材料的制备及在水处理中的应用

纳米铁氧化物能够更高效地去除水中多种有机和无机污染物质,但易团聚失活、易流失等问题限制了其在水处理中的实际应用。生物炭（biochar,BC）作为一种新型的多孔材料具有比表面积大、碳结构稳定、原料来源广、成本低等优点,是负载纳米铁氧化物的理想载体。近年来,BC负载铁氧化物复合材料（铁氧化物/BC）在水处理领域表现出巨大的应用潜力而备受关注。本文重点介绍和总结了铁氧化物/BC的制备方法,及其吸附、催化氧化去除水中磷、有机污染物、重金属及砷的应用、机理和影响因素;并介绍了其在污泥脱水、光催化消毒等水处理环节的应用。在此基础上,从进一步提高去除污染物性能、实际应用经济和技术可行性、扩展材料应用范围等方面提出了今后研究的方向。