Adsorption of arsenite and arsenate on amorphous iron hydroxide

Adsorption isotherms in solutions with ionic strengths of 0.01 at 25°C were measured over the arsenite and arsenate concentration range 10−7−10−3 M and the pH range 4–10. At low concentrations, these isotherms obeyed equations of the Langmuir type. At higher concentrations the adsorption isotherms were linear, indicating the existence of more than one type of surface site on the amorphous iron hydroxide adsorbent. Removal of arsenite and arsenate by amorphous iron hydroxide throughout the concentration range were determined as a function of pH. By careful selection of the relative concentration of arsenic and amorphous iron hydroxide and pH, removals on the order of 92% can be achieved.

Specific Adsorption of Trace Amounts of Calcium and Strontium by Hydrous Oxides of Iron and Aluminum1

Freshly prepared Fe and Al hydrous oxide gels and the amorphous product of heating gibbsite selectively adsorbed traces of Ca and Sr from solutions containing a large excess (∼1M) of NaNO3. The fraction of the added Ca (Sr) adsorbed depended principally on the suspension pH, the amount of solid present, and to a lesser extent on the NaNO3 concentration. Significant Ca and Sr adsorption occurred on the Fe and Al gels, and heated gibbsite, at pH values below the points of zero charge (8.1, 9.4, and 8.3±0.1, respectively), indicating specific adsorption. The pH (± 0.10) at which 50% of the Ca was adsorbed (pH50) occurred at pH 7.15 for the Fe gel (0.093M Fe), 8.35 for the Al gel (0.093M Al), and 6.70 for the heated gibbsite (0.181M Al); for Sr, the pH50 values were 7.10, 9.00, and 6.45, respectively. For the Fe gel and heated gibbsite, an empirical model based on the law of mass action described the pH dependence of adsorption reasonably well and suggested that for each Ca or Sr fraction adsorbed, approximately one proton was released. Failure of the Al gel to fit this model may have resulted from its rapid aging.

Magnetic control of bioelectrocatalytic processes based on assembled iron oxide particles

A facile magnetic control system was designed in bioelectrocatalytic process based on functionalized iron oxide particles. The iron oxide particles were modified with glucose oxidase, and ferrocene dicarboxylic acid was used as electron transfer mediator. Functionalized iron oxide particles can assemble along the direction of applied magnetic field, and the directional dependence of the assembled iron oxide particles can be utilized for device purposes. We report here how such functionalized magnetic particles are used to modulate the bioelectrocatalytic signal by changing the orientation of the applied magnetic field. (C) 2008 Elsevier B.V. All rights reserved.

Phosphonate-Functionalized Polyfluorene as a Highly Water-Soluble Iron(III) Chemosensor

An anionic, phosphonate-functionalized polyfluorene, i.e., poly(9,9-bis(3'-phosphatepropyl)fluorene-alt-1,4-phenylene) sodium salt (PFPNa), has been synthesized by copolymerization of phosphonic acid-substituted 2,7-dibromofluorene and phenyldiboronic ester via direct Suzuki polycondensation reaction in DMF/water. Polymer PFPNa is highly soluble and emissive in water with a solubility of 60 mg/mL and a photoluminescence quantum yield of 75%. The absorption and fluorescence spectra of PFPNa are strongly dependent on pH value owing to the partial protonation of phosphate groups and the aggregation of the polymer chains.

The mechanism of formic acid electro oxidation on iron tetrasulfophthalocyanine-modified platinum electrode

The mechanism of formic acid electrooxidation on iron tetrasulfophthalocyanine (FeTSPc) modified Pt electrode was investigated with electrochemical methods. It was found that a "third-body" effect of FeTSPc on Pt electrode predominates during the electrooxidation process based on unusual electrochemical results. The modification leads formic acid electrooxidation to take place through a desired direct pathway, in which the mechanism is proposed to be the gradual dehydrogenation of formic acid and the reaction of formate with hydroxyl species.

Syndiotactically enriched 1,2-selective polymerization of 1,3-butadiene initiated by iron catalysts based on a new class of donors

A series of phosphoryl (P=O) contained compounds: triethylphosphate (a), diethyl phenyl phosphate (b), ethyldiphenylphosphate (c) triarylphosphates (d and h-m), triphenylphosphine oxide (e), phenyl diphenylphosphinate (f) and diphenyl phenylphosphonate (g) have been prepared. Iron catalysts, which are generated in situ by mixing the compounds with Fe(2-EHA)(3) and (AlBu3)-Bu-i in hexane, are tested for butadiene polymerization at 50 degrees C. Phosphates donated catalysts have been, unprecedently, found to conduct extremely high syndiotactically (pentad, rrrr=46.1-94.5%) enriched 1,2-selective (1,2-structure content=56.2-94.3%) polymerization of butadiene.

Living polymerization of 1,3-butadiene by a Ziegler-Natta type catalyst composed of iron(III) 2-ethylhexanoate, triisobutylaluminum and diethyl phosphite

Living characteristics of facilely prepared Ziegler-Natta type catalyst system consisting of iron(III) 2-ethylhexanoate, triisobutylaluminum and diethyl phosphite have been found in the polymerization of 1,3-butadiene in hexane at 40 degrees C. The characteristics have been well demonstrated by: a first-order kinetics with respect to monomer conversion, a narrow molecular weight distribution (M-w/M-n = 1.48-1.52) of polybutadiene in the entire range of polymerization conversion and a good linearity between M-n and the yield of polymer. Feasible post-polymerization of 1,3-butadiene and block co-polymerization of 1,3-butadiene and isoprene further support the living natures of the catalyst bestowed with.

Fabrication of Iron Oxide Core/Gold Shell Submicrometer Spheres with Nanoscale Surface Roughness for Efficient Surface-Enhanced Raman Scattering

A method to synthesize Fe3O4 core/Au shell submicrometer structures with very rough surfaces on the nanoscale is reported. The Fe3O4 particles were first modified with uniform polymers through the layer-by-layer technique and then adsorbed a lot of gold nanoseeds for further Au shell formation. The shell was composed of a large number of irregular nanoscale An particles arranged randomly, and there were well-defined boundaries between these Au nanoparticles. The Fe3O4 core/Au shell particles showed strong plasmon resonance absorption in the near-infrared range, and can be separated quickly from solution by an external magnet.

The adsorption of dopamine on gold and its interactions with iron(III) ions studied by microcantilevers

The adsorption of dopamine (DA) molecules on gold and their interactions with Fe3+ were studied by a microcantilever in a flow cell. The microcantilever bent toward the Au side with the adsorption of DA due to the change Of Surface stress induced by the intermolecular hydrogen bonds of DA or the charge transfer effect between adsorbates and the Substrate. The interaction process between DA adsorbates and Fe3+ was revealed by the deflection curves of microcantilever. As indicated by the appearance of a variation during the decline of curves, two steps were observed in the curve at relative high concentrations of Fe3+. In this case, Fe3+ reacted with DA molecules only in the outer layers and the complexes removed with solution. Then Fe3+ reacted further with DA molecules forming the surface complex in the first layer next to the gold. At this stage, the stability Of Surface complexes was time dependent, i.e., unstable initially and stable finally. This may be due to the surface complexes change from mono-dentate to bi-dentate complexes. In another case, i.e., at relative low concentration of Fe3+, only the first step was observed as indicated by the absence of a variation.

Antioxidant Sensors Based on Iron Diethylenetriaminepentaacetic Acid, Hematin, and Hemoglobin Modified TiO2 Nanoparticle Printed Electrodes

Antioxidant amperometric sensors based on iron-containing complexes and protein modified electrodes were developed. Indium tin oxide glass was printed with TiO2 nanoparticles, onto which iron-containing compounds and protein were adsorbed. When applied with negative potentials, the dissolved oxygen is reduced to H2O2 at the electrode surface, and the H2O2 generated in situ oxidizes Fe-II to Fe-III, and then electrochemical reduction of Fe-III therefore gives rise to a catalytic current. In the presence of antioxidants, H2O2 was scavenged, the catalytic current was reduced, and the decreased current signal was proportional to the quantity of existing antioxidants. A kinetic model was proposed to quantify the H2O2 scavenging capacities of the antioxidants. With the use of the sensor developed here, antioxidant measurements can be done quite simply: put the sensor into the sample solutions (in aerobic atmosphere), perform a cathodic polarization scan, and then read the antioxidant activity values. The present work can be complementary to the previous studies of antioxidant sensor techniques based on OH radicals and superoxide ions scavenging methods, but the sensor developed here is much easier to fabricate and use.

Two-Step Spin-Transition Iron(III) Compound with a Wide [High Spin-Low Spin] Plateau

A new iron(III) coordination compound exhibiting a two-step spin-transition behavior with a remarkably wide [HS-LS] plateau of about 45 K has been synthesized from a hydrazino Schiff-base ligand with an N,N,O donor set, namely 2-methoxy-6-(pyridine-2-ylhydrazonomethyl) phenol (Hmph). The single-crystal X-ray structure of the coordination compound {[Fe(mph)(2)](ClO4)(MeOH)(0.5)(H2O)(0.5)}(2) (1) determined at 150 K reveals the presence of two slightly different iron(III) centers in pseudo-octahedral environments generated by two deprotonated tridentate mph ligands. The presence of hydrogen bonding interactions, instigated by the well-designed ligand, may justify the occurrence of the abrupt transitions. 1 has been characterized by temperature-dependent magnetic susceptibility measurements, EPR spectroscopy, differential scanning calorimetry, and Fe-51 Mossbauer spectroscopy, which all confirm the occurrence of a two-step transition. In addition, the iron(III) species in the high-spin state has been trapped and characterized by rapid cooling EPR studies.

Bis[tris(2,2 '-bipyridyl-kappa N-2,N ')iron(II)] cyclo-tetravanadate decahydrate

The hydrothermal reactions of metavanadate and divalent iron salts in the presence of nitrogen-donor chelating ligands yield the complex [Fe(C10H8N2)(3)](2)[V4O12].10H(2)O, which consists of one centrosymmetric eight-membered ring [V4O12](4-) anion cluster, formed by four VO4 tetrahedra sharing vertices, two discrete octahedral [Fe(C10H8N2)(3)](2+) cations, formed by three 2,2'-bipyridyl ligands coordinated to Fe-II, and ten water molecules of solvation. The anion and coordination cations are isolated and form anion and cation layers, respectively. In the anion layers, these anions and water molecules of solvation are linked to each other, in a two-dimensional motif, through hydrogen-bonding interactions.

Polymerization of methyl methacrylate by iron(II) pyridinebisimine complexes

Fe(II) pyridinebisimine complexes activated with trialkylaluminium or modified methylaluminoxane (MMAO) as catalysts were employed for the polymerization of methyl methacrylate. Polymer yields, activities and polymer molecular weights as well as molecular weight distributions can be controlled over a wide range by the variation of the structures of the Fe(II) pyridinebisimine complexes and the reaction parameters such as Al/Fe molar ratio, monomer/catalyst molar ratio, monomer concentration, reaction temperature and time applied to the polymerization of methyl methacrylate. Under optimum condition, the catalytic activity of Fe(II) complex is of up to 74.5 kg(polym)/mol(Fe)h.