Effect of iron counter-ions on the reducibility of the Keggin type molybdophosphoric heteropolyacid: Part II. A theoretical study

Quantum-chemical calculations of the interaction of the molybdophosphoric Keggin heteropolyanion with the iron counter-ion are performed to explain the influence of the latter on the reducibility of iron-doped acid. It is shown that the electron transfer heteropolyanion→iron counter-ion becomes possible only under hydration of the solid. The microscopic mechanism of this transfer is due to the modification of the relative position of the counter ion which enters into strong interaction with terminal oxygens of the heteropolyanion.     

The interaction of water-soluble iron porphyrins with DNA films and the electrocatalytic properties for inorganic and organic nitro compounds

The electrochemistry of water-soluble iron porphyrins (Fe(n-TMPyP)) (where n=2 and 4) was studied as an electrochemically active film on DNA modified glassy carbon, gold, platinum, and transparent semiconductor tin oxide electrodes in solutions of various pH values. The two layers of the modified electrode containing the iron porphyrin and the DNA film were prepared by depositing the iron porphyrin on a DNA film modified electrode. The Fe(4-TMPyP)/DNA film was electrocatalytic reductive for p-nitrobenzoic acid in a weak acidic, or neutral aqueous solution through an Fe^II species, and the electrocatalytic reduction peak potential became more negative than the cathodic peak of the Fe^III/II redox couple. The electrocatalytic reduction properties by the Fe(2-TMPyP)/DNA film as catalysts for nitrite reduction have also been determined, and shown to be active through an Fe^I species and to be pH-dependent. The electrocatalytic oxidation properties of nitrite by Fe(n-TMPyP)/DNA (for n=2 and 4) film have also been determined and shown to be active through an Fe^IV species with the electrocatalytic oxidation efficiency of NO₂⁻ with Fe^IV(O)(n-TMPyP) being higher than with (HO)Fe^IV(O)(n-TMPyP). The electrocatalytic oxidation efficiency of NO₂⁻ by iron porphyrin is pH-dependent. The electrocatalytic reduction of p-nitrophenol by Fe(2-TMPyP)/DNA film are also discussed.     

Halogen substituent effects on the catalytic activity of iron porphyrin complexes for selective air-oxidation of alkanes in the liquid phase

Halogenation of the porphyrin ring of porphyrinatoiron(III) complexes greatly increases their catalytic activity for the selective mild reaction of alkanes with molecular oxygen. The greater the halogen content the greater is the catalytic activity of the complex. Selective reaction of isobutane and propane with molecular oxygen is catalyzed bytetrakis(pentafluorophenyl)porphyrinatoiron(III) azido, hydroxo, or halo complexes under mild conditions of temperature and pressure. No added co-reductant is required in these systems. Catalytic oxidation of isobutane in the presence oftetrakis (pentafluorophenyl)porphyrinatoiron(III) hydroxide at room temperature gavetert-butyl alcohol in 95% selectivity. The catalyst activity was virtually unchanged after over 140 hours at room temperature and over 12,000 turnovers (moles of alcohol produced/mole of metal complex used) of isobutane to the alcohol were observed.     

Comparison of the chemical properties of iron and cobalt porphyrins and corrins

Density functional calculations have been used to compare various geometric, electronic and functional properties of iron and cobalt porphyrin (Por) and corrin (Cor) species. The investigation is focussed on octahedral M(II/III) complexes (where M is the metal) with two axial imidazole ligands (as a model of b and c type cytochromes) or with one imidazole and one methyl ligand (as a model of methylcobalamin). However, we have also studied some five-coordinate M(II) complexes with an imidazole ligand and four-coordinate M(I/II) complexes without any axial ligands as models of other intermediates in the reaction cycle of coenzyme B12. The central cavity of the corrin ring is smaller than that of porphine. We show that the cavity of corrin is close to ideal for low-spin Co(III), Co(II), and Co(I) with the axial ligands encountered in biology, whereas the cavity in porphine is better suited for intermediate-spin states. Therefore, the low-spin state of Co is strongly favoured in complexes with corrins, whereas there is a small energy difference between the various spin states in iron porphyrin species. There are no clear differences for the reduction potentials of the octahedral complexes, but [Co(I)Cor] is more easily formed (by at least 40 kJ mole(-1)) than [Fe(I)Por]. Cobalt and corrin form a strong Cobond;C bond that is more stable against hydrolysis than iron and porphine. Finally, Fe(II/III) gives a much lower reorganisation energy than Co(II/III); this is owing to the occupied d(z2) orbital in Co(II). Altogether, these results give some clues about how nature has chosen the tetrapyrrole rings and their central metal ion.     

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.     

Carbon nanotubes modified with electrodeposited metal porphyrins and phenanthrolines for electrocatalytic applications

Composites consisting of multi-walled carbon nanotubes (MWCNTs) and iron-nitrogen containing compounds as catalysts for the electroreduction of oxygen in acidic media were directly prepared on a glassy carbon (GC) electrode in a bottom-up synthesis. In a first step, MWCNTs were drop-coated in form of an ink onto the electrode. Afterwards the nanotubes were modified with catalytically active films of iron porphyrin (FeTMPP-Cl) or iron phenanthroline (Fe(phen)₃) through a pulsed potential deposition technique. Finally the prepared electrodes were heat-treated in an inert gas atmosphere.By employing cyclic voltammetry and rotating disc electrode measurements it is shown that the activity for the oxygen reduction reaction (ORR) at such composites increases progressively with every applied synthesis step showing the possibility for direct synthesis of a catalyst on an electrode. The activities of FeTMPP-Cl/MWCNT and Fe(phen)₃/MWCNT composites prepared by this technique are higher than that of similar electrocatalysts prepared by wet impregnation and heat treatment. The presented approach opens possibilities for systematic tuning of electrode structures, for example by stepwise build-up of gas diffusion electrodes.     

Oxygen reduction at negatively charged iron porphyrins heat-treated and bridged by alkaline-earth metal ions

An ordered network of tetrasodium tetra(4-sulphonatophenyl)porphyrin iron(III) chloride (FeTPPS₄Na₄), which exhibited a higher catalytic activity for oxygen reduction than Co and Ir(CO)TPPS₄Na₄, was fabricated by complexation with alkaline-earth metal ions. Heat treatment of these complexes enhanced their catalytic activity with the highest performance observed with Ba²⁺-FeTPPS₄. The onset potential for oxygen reduction (E_onset) was 720 mV vs. Ag|AgCl, which is almost the same as that for Pt-impregnated carbon black. The number of electrons, n, transferred during oxygen reduction at a Ba²⁺-FeTPPS₄-coated electrode, as determined by rotating ring-disc experiments, was 3.9 and suggests that oxygen was reduced to water. A neutral solution of FeTPPS₄Na₄ was acidified by the addition of barium ion, and the elemental ratio Fe:S:Ba in the resulting Ba²⁺-FeTPPS₄ complex was approximately 1:4:2.5. This suggests the formation of a highly ordered network with Fe sites bridged with barium ions in addition to the normal salt bridges between sulphonates. Catalytic oxidation reactions with nitric oxide and nitrite ion as the intermediate at the heat-treated Ba²⁺-FeTPPS₄ indicate the formation of Fe(IV) and Fe(IV) π-cation radicals or Fe(V). The agreement between the potential of Fe(IV) π-cation radical formation and E_onset suggests that the redox cycle of the Fe(III)/Fe(IV) π-cation radical provides a sufficient driving force for the observed 4-electron reduction of oxygen at the heat-treated Ba²⁺-FeTPPS₄ electrode.     

Removal of iron from drinking water by electrocoagulation: Adsorption and kinetics studies

The present study provides an electrocoagulation process for the removal of iron from drinking water with aluminum alloy as the anode and stainless steel as the cathode. The studies were carried out as a function of pH, temperature and current density. The adsorption capacity was evaluated with both the Langmuir and the Freundlich isotherm models. The results showed that the maximum removal efficiency of 98.8% was achieved at a current density of 0.06 A dm⁻², at a pH of 6.5. The adsorption of iron preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules. The adsorption process follows second-order kinetics. Temperature studies showed that adsorption was endothermic and spontaneous in nature.     

A review of the electrochemical corrosion behaviour of iron aluminides

The objective of this review is to outline the aqueous corrosion research activities being undertaken on iron aluminides. Key results are extracted and reviewed from publications covering the past 25 years of research activity in aqueous corrosion behaviour of iron aluminides. This review deals with phenomena, which are related with electrochemical corrosion such as passivation and repassivation kinetics, breakdown of passivity, chemistry of the passive film and mechanism of passivation. The role of constituent elements and the effect of alloying elements on the corrosion behaviour of iron aluminides have also been discussed. To assess corrosion resistance of iron aluminides a comparative study was put up with that of stainless steels.     

间氯苯基卟啉-氨基酸及其锌配合物的合成与表征

合成了2种新型的尾式卟啉－氨基酸化合4物及其锌配合物,用元素分析,UV,IR,^HNMR确证了其结构,并测试了其荧光光谱。     

Electrochemical and spectral studies on the catalytic oxidation of nitric oxide and nitrite by high-valent manganese porphyrins at an ITO electrode

Catalytic oxidation of nitric oxide and nitrite by water-soluble manganese(III) meso-tetrakis(N-methylpyridinium-4-yl) porphyrin (Mn(III)(4-TMPyP) was first studied at an indium-tin oxide (ITO) electrode in pH 7.4 phosphate buffer solutions. A stepwise oxidation of Mn(III)(4-TMPyP) through high-valent manganese porphyrin species has been observed by electrochemical and spectroelectrochemical (OTTLE) techniques. The formal potential of 0.63 V for the formation of OMn(IV)(4-TMPyP) has been estimated from OTTLE data. The product, oxoMn(IV) porphyrin, was relatively stable decaying slowly to Mn(III)(4-TMPyP) with a first-order rate constant of 3.7 × 10⁻³ s⁻¹. OMn(IV)(4-TMPyP) has been found to oxidize NO catalytically at potentials about 70 mV more negative than that previously reported for OFe(IV)(4-TMPyP) with good selectivity against nitrite. Nitrite was catalytically oxidized at potentials higher than 1.1 V presumably by OMn(V)(4-TMPyP). OMn(IV)(4-TMPyP) was observed as an intermediate species. Nitrate has been confirmed to be a final product of the electrolysis at 1.2 V, while at 0.8 V nitrite left unchanged, demonstrating that OMn(IV)(4-TMPyP) could not oxidize nitrite. A possible schemes of the catalytic oxidation of NO by OMn^IV(4-TMPyP) and NO₂⁻ by OMn(V)(4-TMPyP) have been proposed.     

气液传质理论研究进展

文内对气液传质的理论研究进行了评述，并预测了未来的发展方向     

新型卟啉及其金属配合物的合成与性能

通过琥珀酰基、马来酰基和邻苯二甲酰基对四-(4-氨基苯基)卟啉进行修饰改性,合成不同结构的新型卟啉及其铜配合物。对合成的新型结构卟啉配体进行核磁共振、质谱和红外表征,对其铜配合物进行质谱表征,结果表明,所合成的化合物是目标产物。通过紫外-可见、荧光发射、热重、循环伏安法进行性质测试,计算出HOMO和LUMO能级。结果表明,新型化合物具有良好的可见光区吸收和纯红光发射光谱,热稳定性高,可以作为红光材料的备选材料。     

几种含羧基的不对称卟啉化合物的微波合成及其光谱性质

羧基苯基卟啉是一种重要的水溶性卟啉化合物,在分析化学、仿生化学等领域具有潜在应用价值。利用微波加热法,以4-甲酰基苯甲酸、吡咯及对位R取代苯甲醛(R=H、Cl、OCH3)为原料分别合成了3种含羧基的不对称卟啉化合物。微波辐射时间8～10 min,产物收率分别为5%、5.8%、2.8%。目标化合物结构分别经UV-Vis、IR、1HNMR表征,并讨论了取代基结构及其电子效应对光谱性质的影响。     

Some catalytic properties of silica‐supported base and metal porphyrins for hydrocarbon cracking and hydrogenation

A base porphyrin, etioporphyrin (EPI), has been synthesised and a number of metal–etioporphyrin compounds have been derived from EPI by metal insertion, these being nickel, vanadyl, palladium and platinum. The metal–etioporphyrins were supported on silica gel with loadings of 0.5–5.0% (w/w) to be employed as catalysts for hydrocarbon cracking and to a minor extent for hydrogenation. The porphyrins themselves were characterised using temperature programmed decomposition (TPD), temperature programmed reduction (TPR), mass spectroscopy (MS) and infra‐red (IR) spectroscopy. TPD studies up to 550 °C indicated complete stability and TPR studies (20–500 °C) showed interaction with hydrogen, nickel–EPI and Pd–EPI especially showing strong interaction. MS studies showed that metal insertion had occurred for VO–EPI and Ni–EPI and Pd insertion was demonstrated to have occurred using an analytical method. IR spectroscopy carried out on VO–EPI and Ni–EPI showed an absence of ? NH linkages, again confirming metal insertion. The behaviour of the catalysts for hydrocarbon cracking was studied using 2,2‐dimethylbutane (2,2‐DMB) as the model reactant in the temperature range 440–550 °C and thermally in the temperature range 440–600 °C and at 1 at, m (101.3 kPa) pressure. All porphyrins, even the base porphyrin, exhibited cracking activity and the catalysed reaction had an energy of activation, depending on the porphyrin, in the range 78–113 kJ/mol^?1, compared with a value of 210 kJ mol^?1 for the thermal reaction. The product distribution was dominated by C₁ and C₂ hydrocarbons and is typical of a free radical reaction, the thermal reaction giving a similar product distribution, so that the porphyrin catalyst acts as a free radical initiator. Hydrogenation studies using hex‐1‐ene at 150 °C and at 1 atm. pressure showed that Pd–EPI/SiO₂ was an active and possibly stable hydrogenation catalyst, whereas Ni–EPI/SiO₂ while of only slightly lower activity initially, lost that activity so that the Pd–EPI catalyst was over 16 times more active at the end of a 2 h period. © 2001 Society of Chemical Industry     

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.     

The isotherm,kinetic and thermodynamic studies of the cadmium uptake by colpomenia sinuosa

ABSTRACT

A number of isotherm models were studied and modeled for colpomenia sinuosa. The experimental data were fitted among the 12 biosorption kinetic models. Thermodynamic studies indicated a spontaneous and endothermic process. The morphology of the biosorption process was revealed by Fourier transfer infrared (FT-IR) analysis and scanning electron microscope (SEM). The isotherm and kinetic parameters were compared with other microorganisms.     

Structural and magnetic characterization of norbornene-deuterated norbornene dicarboxylic acid diblock copolymers doped with iron oxide nanoparticles

A series of iron oxide doped norbornene (NOR)/deuterated norbornene dicarboxylic acid (NORCOOH) diblock copolymers were synthesized and characterized by X-ray photoelectron spectroscopy (XPS), small angle neutron scattering (SANS) and superconducting quantum interference device (SQUID) experiments. γ-Fe₂O₃ nanoparticles were synthesized within the microdomains of diblock copolymers with volume fractions of NOR/NORCOOH 0.64/0.36, 0.50/0.50 and 0.40/0.60. A spherical nanoparticle morphology was displayed in the polymer with 0.64/0.36 volume fraction. Polymers with 0.50/0.50 and 0.40/0.60 volume fractions exhibited interconnected metal oxide nanostructures. The observed changes in the shape and peak positions of the small-angle neutron scattering profiles of polymers after metal doping were related to the scattering from the metal oxide particles and to the possible deformed morphologies due to the strong interparticle interactions between metal particles, which may influence the polymer microphase separation. The combined scattering from both polymer domains and magnetic particles was depicted in SANS profiles of metal oxide doped polymers. γ-Fe₂O₃ containing block copolymers were superparamagnetic at room temperature. An increase in the blocking temperature (T_b) of interconnected nanoparticles was observed and was related to the interparticle interactions, which depends on the average distance (d) between particles and individual particle diameter (2R). The sample with volume fraction of 0.4/0.6 have the lowest d/(2R) ratio and exhibit the highest T_b at 115 K.