Selective sorption of Fe(III) using modified forms of chitosan beads

Modified chitosan beads (CB) were prepared and used for the removal of Fe(III) ions from aqueous solution. The advantages of modified CB than raw CB have been explored. The sorption capacity (SC) of the modified forms of CB namely, protonated CB, carboxylated CB, and grafted CB were found to be 3533, 3905, and 4203 mg kg^?1, respectively, while the raw CB showed the SC of 2913 mg kg^?1 only. Batch adsorption studies were conducted to optimize various equilibrating conditions like contact time, pH, and coions. The sorbents were characterized by FTIR, WDXRF, and SEM with EDAX analysis. The sorption process has been explained with Freundlich and Langmuir isotherms. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were calculated to understand the nature of sorption. Modified CB are more selective for Fe(III) than Cu(II), which inturn higher than Cr(VI). A suitable mechanism for iron sorption onto modified CB was established. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Absorption of nitrogen monoxide in aqueous solutions containing sulfite and transition-metal chelates such as Fe (II)-EDTA,Fe (II)-NTA,Co (II)-Trien and Co (II)-Treten

For wet denitrification processes nitrogen monoxide is the crucial component owing to its low water solubility. By addition of transition-metal complexes, able to form nitrosyls, the effective NO concentration in the liquid phase is enhanced. Kinetic (reaction orders and rate constants) as well as thermodynamic (stability constants) data for nitrosylation have been established. It has been found that Fe(II)-EDTA and Fe(II)-NTA react very fast to form stable NO complexes and are widely pH independent. The formation of Fe(III)-EDTA nitrosyl is found to be rapid, but the large deviation in the measured data prevents reliable evaluation. While the equilibrium constants of the Co(II)-trien and Co(II)-tetren nitrosyls are largely pH independent, the rate of formation is influenced markedly by pH. Each nitrosyl shows individual behavior towards sulfite. Fe(II)-EDTA and Fe(III)-EDTA exhibit the highest absorption capacities. The CO(II) polyamines convert the absorbed NO mainly to gaseous N₂O rather than to liquid-phase products.     

Adsorption of Fe(II) and Fe(III) from aqueous solution by using sepiolite: speciation studies with MINEQL+ computer program

ABSTRACT

As a low-cost adsorbent, sepiolite has been used for the adsorption of Fe(II) and Fe(III) from aqueous solutions. The proposed method was applied to the determination of iron in tap water, employing standard addition. The results reported with a confidence interval for the 95% confidence level show the applicability of the proposed method to water analysis. Speciation studies are very important for understanding of the toxicity, bio-availability, bio-accumulation, and transport of an element in different environmental media. In this study, Fe(II) and Fe(III) speciation was investigated for optimum concentration and pH in aqueous solutions with MINEQL+ computer program.     

Crosslinking of carboxylated nitrile rubber (XNBR) induced by coordination with anhydrous copper sulfate

BACKGROUND: Crosslinking induced by non‐covalent interactions in rubber materials is currently attracting a great deal of interest because of its perceived reversibility. Some thermoplastic elastomers and ionic elastomers, which are crosslinked by physical entanglements and ionic bonds, respectively, have already been investigated. The present work is centred on the study of the influence of coordination bonds on the physical properties of crosslinked materials. These bonds are formed on addition of copper sulfate. RESULTS: In this context, the effect of crosslinking of carboxylated nitrile rubber (XNBR) by anhydrous copper sulfate (CuSO₄) on crosslink reaction and mechanical and mechano‐dynamic properties is studied. The influence of different levels of CuSO₄ and the addition of conventional filler, carbon black, on the network is studied. The presence of nitrile (? CN) in the elastomeric chains leads to the formation of coordination bonds with the nitrile groups. The formation of ionic bonds between copper ions and carboxylic groups can be deduced from X‐ray photoelectron, attenuated total reflectance Fourier transform infrared and NMR analyses and vulcanization measurements. The dynamic response of the material does not show a secondary transition, the so‐called ionic transition typical of ionic elastomers, since ionic bonds do not lead to a separated ionic microphase, immersed in the elastomeric matrix. CONCLUSION: As expected, the crosslink density of the polymer network increases with the amount of crosslinking agent. Because of the presence of polymer–filler interactions, an increase in crosslink density is observed. However, these interactions seem not to affect the formation of coordination or ionic bonds. Copyright © 2008 Society of Chemical Industry     

Studies on chromium(III) complexes with active nitrogen,oxygen and sulfur donor ketimines synthesized under microwave conditions

Heterocyclic ketimines, 1-(2-furanyl)ethanonehydrazincarbothioamide (L¹H), 1-(2-furanyl)ethanone- hydrazincarboxamide (L²H), 1-(2-thienyl)ethanone hydrazincarbothioamide (L³H) and 1-(2-thienyl) ethanonehydrazincarboxamide (L⁴H), were prepared by the condensation of thiosemicarbazide and semicarbazide hydrochloride (in the presence of sodium acetate) in ethanol with the respective ketones by using microwave as well as conventional methods. Chromium(III) complexes have been prepared by mixing CrCl₃·6H₂O in 1:1 and 1:2 molar ratios with monobasic bidentate ketimines. The authenticity of the ligands and their complexes has been established by elemental analyses, melting point determinations, molecular weight determinations, EPR, infrared and UV spectral and X-ray powder diffraction studies. These studies showed that the ligands coordinated to the metal atom in a monobasic bidentate mode, coordinating through the nitrogen and sulfur/oxygen donor system. Thus, an octahedral environment around the metal atoms has been proposed. The growth-inhibiting potential of the ligands and complexes has been assessed against a variety of fungal and bacterial strains.     

Electrical properties of macromolecular complexes of coordinated polymers with mixed valence of Co(II), Co(III) and Co(II–III)

Electrical properties of bis‐ethylenediamine Co(II), Co(III) and Co(II–III) mixed valence complexes and polyethylenediaminecarbosilazane (PEDCSZ) [Co(II), Co(III) and Co(II–III)] macromolecules were measured at room temperature in a frequency range between 1 Hz and 10⁶ Hz. Electrical modulus, permittivity and ac conductivity were calculated using ac impedance and phase‐angle measurements. It was found that the overall conductivity of PEDCSZ macromolecules with Co is much higher than that for Co monomers. In addition, the conductivity of PEDCSZ Co(III) and Co(II–III) mixed valence compounds are higher than those containing Co(II) where the electronic conduction is dominant. The relaxation time increases from about 2.7 × 10^?6 s for Co(II) chloride to a value of 2.9 × 10^?4 s for Co(II–III) chloride monomers. Copyright © 2003 Society of Chemical Industry     

Porous Spherical Cellulose Carrier Modified with Polyethyleneimine and Its Adsorption for Cr(III) and Fe(III) from Aqueous Solutions

abstract An efficient porous spherical polyethyleneimine-cellulose (PEI-cell) absorbent was synthesized and char-acterized. The main influencing factors and adsorption mechanism for two typical metal i...     

Separation and concentration processes of solutions of Co(II), Ni(II), Cr(III), Fe(III) and Mn(II) by extraction with toluene-dissolved rosin

The extraction and stripping of Co(II), Ni(II), Cr(III) and Fe(III) from aqueous solutions by rosin dissolved in toluene has been investigated. Results obtained show that rosin is better extractant than abietic or n-lauric acids under comparable conditions. From these results, and the data of Mn(II) solvent extraction studied previously under the same conditions, a separation and concentration process for these five cations in aqueous solutions has been designed. Saturated solutions of Fe(III), Cr(III), Mn(II) and finally Co(II) and Ni(II) have been obtained successively by extraction and stripping, by addition of ammonium hydroxide to obtain the appropriate pH value, and by modifying adequately the organic phase/aqueous phase volume ratio.     

Electrochemical technique to measure Fe(II) and Fe(III) concentrations simultaneously

An electrochemical technique is presented to simultaneously determine the concentrations of Fe(II) and Fe(III) ions using a rotating disk electrode. The method consists of using a steady state polarization technique where the developed limiting currents are measured and related to the concentration of the cations present in solution. Two linear equations were derived which correlate the limiting currents with the concentrations of the pair cations. The equations are used to easily and simultaneously determine the concentrations of the multivalent species. The precision and accuracy of the technique were found to be comparable to other advanced methods for the quantification of cations, such as capillary zone electrophoresis and spectro-photometric sequential injection analysis.     

Extraction of Fe(III) from phosphoric acid by HDDNSA

A study was conducted on the stoichiometry of the reaction that takes place on the extraction of ferric ions by didodecyl naphthalene sulphonic acid (HDDNSA) from phosphoric acid solutions. The experimental results were numerically analyzed by nonlinear regression. It was found that ferric forms two compounds with HDDNSA, namely Fe(DDNSA)₃, and FeHPO₄-DDNSA. The values of the equilibrium constants of the reactions involved were also calculated.     

Interaction of nitrogen with iron surfaces: II. Fe(110)

Previous work on the interaction of N₂ with Fe(100) and (111) single-crystal planes was extended to the most densely packed (110) face. The dissociative chemisorption proceeds even slower than with the two other planes and is associated with an activation energy of about 7 kcal/mole at low coverages. At 683 K the initial rates of adsorption have a ratio of about 60:3:1 for Fe(111):(100):(110). The activation energy for desorption is estimated to be about 50 kcal/mole and is thus slightly smaller than on Fe(100)(58 kcal/mole), but higher than on Fe(111) (51 kcal/mole). The formation of two ordered surface structures (I and II) was observed. Their unit cell vectors b₁, b₂ are related with the (unreconstructed) substrate lattice vectors a₁, a₂ through: b₁ = 3a₁, b₁ = 2a₁ (I) (which may also be designated as 2 × 3 structure), and b₁ = 4a₁, b₁ = a₁ + 3a₂ (II). Both phases appear with two equivalent domain orientations with the mirror plane along the [001] direction. Structure I appears at lower surface concentrations than structure II; however their kinetics of formation is also influenced by the concentration of dissolved nitrogen. It is most probably that these large unit cells reflect the reconstruction of the topmost layer of Fe atoms [as in the case of the (111) plane]. For both surface structures quasihexagonal arrangements of Fe atoms may be constructed the nearest-neighbor distances for which agree to within ±3% with those in the (111) plane of fcc Fe₄N. Thus the concept of the formation of “surface nitrides” is further supported. Dissolution of nitrogen atoms in the bulk again interferes with the surface processes.     

Tetrachloroethylene and hexachloroethane degradation in Fe(III) and Fe(III)–citrate catalyzed Fenton systems

BACKGROUND: Tetrachloroethylene (PCE) and hexachloroethane (HCA) degradation, individually and in mixture, is investigated by Fe(III) or Fe(III)‐citrate initiated Fenton reaction under a range of hydrogen peroxide (H₂O₂) concentrations to illustrate the applicability and constraints of Fenton chemistry in degrading contaminants in polluted groundwater. RESULTS: In individual solutions Fe(III) rapidly degraded PCE for all H₂O₂ concentrations, but HCA at ≥ 0.2 mol L^?1 H₂O₂; the apparent PCE degradation rate initially increased but then decreased with increasing H₂O₂, while the HCA degradation rate was either unaffected or increased. With Fe(III)‐citrate PCE degradation was lower and no HCA degradation occurred. PCE degradation was lower in PCE‐HCA mixture, but the trend with H₂O₂ concentration was similar to the individual chemical; for HCA the residual was smaller for higher H₂O₂ concentration, but the apparent degradation rate constant was unaffected. CONCLUSION: Fe(III) catalyzed reactions can potentially degrade chemicals through reductive as well as oxidative transformations. Degradation of chemicals in mixtures occurs at a slower rate due to competition for radical moieties. The Fe(III)‐citrate complex further slowed chemical transformation. This study expands on the use of different forms of iron to catalyze the Fenton reaction to degrade chemicals. Copyright © 2012 Society of Chemical Industry     

Novel two-dimensional Co(II) and Cd(II) coordination polymers with intriguing net topologies

Three new two-dimensional coordination polymers were constructed from 2,6-bis(imidazole-1-yl)pyridine (2.6-bip), terephthalic acid (1,4-bdcH₂), and M(NO₃)∙nH₂O (M = Co, Cd). [M(2,6-bip)(1,4-bdc)] (1: M = Co; 2: M = Cd) were prepared under hydrothermal condition, whereas [Cd(2,6-bip)(1,4-bdc)∙xDMF] (3) was obtained under solvothermal condition in DMF solvent. Single-crystal X-ray analyses revealed the first example of a 2D 4-connected net of 6⁶ topology in 1 and 2 and a rare 2D 4,5-connected net of 4,5 L20 topology in 3. All these complexes were thermally robust and emissive in solid-states. This work confirmed the versatility of using hingelike 2,6-bip as a linker and the importance of solvent effect in the process of framework formation.     

Synthesis and characterization of unusual heterotrinuclear Co(III)Ni(II)Co(III) hydrotris(3,5-dimethylpyrazolyl)borate complex with mixed 1,1-azide and pyrazolate bridges

An unusual heterotrinuclear complex [LCo(μ-L₁, 1-N₃)₂(μ-L₁)Ni(μ-1, 1-N₃)₂(μ-L₁)CoL] (1) was obtained by the reaction of the precursor of half-sandwich nickel(II) complex [LNi(HL₁)₂(N₃)] (2) and CoCl₂ · 6H₂O (L = hydrotris(3,5-dimethylpyrazolyl)borate; L₁ = 3,5-dimethylpyrazolate), the complex 1 was characterized by X-ray single-crystal diffraction, elemental analysis, IR, UV–vis spectra and magnetic properties.     

Removal of reactive dyes from wastewater using Fe(III) coagulant

The coagulation-flocculation process was employed for the treatment of reactive dye wastewaters, with ferric chloride hexahydrate employed as the coagulant. The process was found to be very effective with a more than 99.5% colour removal. Typical representatives of monochlorotriazine reactive dyes, with azo and anthraquinone chromophores, were CI Reactive Red 45 and CI Reactive Green 8, which were chosen as the model dyes. In order to determine the optimum pH range and coagulant concentration, a series of jar tests was done. Further experiments were conducted using a square flocculation tank with turbine impeller applying rapid and slow mix operations. The optimisation of initial rapid mixing, which has an important role in the overall coagulation process efficiency, was carried out. The optimum combination of velocity gradient and time of rapid mix was suggested for reactive dye wastewater treatment. Sedimentation curves for both model dyes were also obtained.     

活性炭负载Fe(III)吸附剂去除饮用水中的As(V)

利用活性炭负载水合铁氧化物制备了复合吸附剂,并用于饮用水中As(V)的去除. 研究了活性炭种类、粒度、溶液pH值、Fe(III)盐浓度和干扰离子等对As(V)去除的影响. 结果表明,煤质活性炭作为基质负载水合铁氧化物比椰壳炭和果壳炭具有更好的除砷效果. 随着炭粒度降低,除砷效率显著增加. 在pH 3~9范围内,活性炭负载水合铁氧化物可有效吸附As(V). F-, Cl-, SO42-的加入对As(V)的去除效率基本无影响,而SiO32-和PO43-则明显抑制As(V)的去除. Langmuir模型比Freundlich模型能更好地描述复合吸附剂对As(V)的吸附平衡. 动力学研究表明,As(V)吸附反应可用二级速率方程描述.     

Fe(III)-humate complexes from Megalopolis peaty lignite: A novel eco-friendly fertilizer

Fe(III)-humate complexes were synthesized from Greek peaty lignite of the Megalopolis Basin. The preparation was carried out under mild and low-energy conditions producing a biodegradable, eco-friendly and effective material to substitute the synthetic chelates Fe-EDDHA, Fe-EDTA and Fe-DTPA. Due to both the existing expanded configuration of the humic substances (that make binding sites accessible to the metal ions) and the ionization of functional groups, alkaline environment facilitates the association between Fe(III) ions and the lignite-derived humic substances. UV-vis and IR spectra revealed coordination of the metal ions with the carboxylic and phenolic groups of the oxygen-rich humic substances. Fe(III)-humate complexes were proved stable in a wide pH range similar to Fe-EDDHA synthetic chelates. Furthermore, the presence of K⁺ and humic matter increases the agronomic value of this material establishing alternative applications for Megalopolis peaty lignite.     

Chromotropic ferrocenyl chalcone with two pyrenyl groups: Solvatochromism and molecular chemosensor for Fe(III)/Fe(II) ions

A chromotropic ferrocenyl chalcone with two pyrenyl groups (Fc-dPyr) is prepared and spectroscopically characterized. The X-ray structure analysis shows that the two pyrenyl groups are almost parallel to each other with a torsion angle of 5.57° and adopt a dimeric mode with a distance of 3.776 Å between them, ready to form an excimer. The solvatochromic fluorescence spectra indicate that the emission maxima observed in hydrogen-bonding donor (HBD) solvents (CHCl₃, EtOH and MeOH) exhibit a strictly linear relationship with the normalized E_T^N value, while those in a non-HBD solvent (CH₃CN) do not. The molecular chemosensor activity of Fc-dPyr is highly selective toward Fe(III) ions over Fe(II) ions. The fluorescence emission intensity of Fc-dPyr steeply decreases in the presence of Fe(III) ions as an oxidant, but not in the presence of Fe(II) ions.