Metal chelate absorption coupled with microbial reduction for the removal of NOx from flue gas

A novel process for the removal of NO_x from flue gas by a combined Fe(II)EDTA absorption and microbial reduction has been demonstrated. Fe(II)EDTA–NO and Fe(III)EDTA (EDTA: ethylenediaminetetraacetate) can be effectively reduced to the active Fe(II)EDTA in the reactor containing microorganisms. In a steady‐state absorption and regeneration process, the final removal efficiency of NO is up to 88%. The effects of four main parameters (i.e. NO, O₂ and SO₂ concentrations, and the amount of cyclic solution) on NO_x removal efficiency were experimentally investigated at 50 °C. The results provide some insight into conditions required for the successful removal of NO_x from flue gas using the approach of Fe(II)EDTA absorption combined with microbial reduction. Copyright © 2005 Society of Chemical Industry     

Denitrification in aqueous FeEDTA solutions

The biological reduction of nitric oxide (NO) in aqueous solutions of FeEDTA is an important key reaction within the BioDeNOx process, a combined physico‐chemical and biological technique for the removal of NO_x from industrial flue gasses. To explore the reduction of nitrogen oxide analogues, this study investigated the full denitrification pathway in aqueous FeEDTA solutions, ie the reduction of NO₃^?, NO₂^?, NO via N₂O to N₂ in this unusual medium. This was done in batch experiments at 30 °C with 25 mmol dm^?3 FeEDTA solutions (pH 7.2 ± 0.2). Also Ca²⁺ (2 and 10 mmol dm^?3) and Mg²⁺ (2 mmol dm^?3) were added in excess to prevent free, uncomplexed EDTA. Nitrate reduction in aqueous solutions of Fe(III)EDTA is accompanied by the biological reduction of Fe(III) to Fe(II), for which ethanol, methanol and also acetate are suitable electron donors. Fe(II)EDTA can serve as electron donor for the biological reduction of nitrate to nitrite, with the concomitant oxidation of Fe(II)EDTA to Fe(III)EDTA. Moreover, Fe(II)EDTA can also serve as electron donor for the chemical reduction of nitrite to NO, with the concomitant formation of the nitrosyl‐complex Fe(II)EDTA–NO. The reduction of NO in Fe(II)EDTA was found to be catalysed biologically and occurred about three times faster at 55 °C than NO reduction at 30 °C. This study showed that the nitrogen and iron cycles are strongly coupled and that FeEDTA has an electron‐mediating role during the subsequent reduction of nitrate, nitrite, nitric oxide and nitrous oxide to dinitrogen gas. Copyright © 2004 Society of Chemical Industry     

Oxidation of 4‐nitrophenol in water over Fe(III), Co(II), and Ni(II) impregnated MCM41 catalysts

BACKGROUND: Nitrophenols are toxic constituents of the effluents of petroleum, textile, dye, iron and steel, foundries, pharmaceutical and electrical manufacturing industries. Aromatic nitro compounds are particularly resistant to normal chemical or biological oxidation making them environmentally persistent. Advanced oxidation using appropriate catalysts mineralize these organics to harmless final products. In this work, MCM41‐based catalysts incorporating Fe(III)‐, Co(II)‐ and Ni(II)‐ cations were used for oxidizing 4‐nitrophenol in water under variable conditions of reaction time, pH, mole ratio of the reactant and the oxidant, catalyst load, feed concentration, and temperature. RESULTS: The catalysts prepared were characterized with X‐ray diffraction (XRD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), cation exchange capacity (CEC) and atomic absorption spectrometry (AAS) measurements. In typical reaction conditions of temperature 353 K, time 300 min, catalyst load 2 g L^?1 and 10^?3 mol L^?1 4‐nitrophenol, the oxidation was 48.7, 52.2 and 55.2% with H₂O₂ and 42.5, 56.6 and 60.2% without H₂O₂ for Fe(III)‐, Co(II)‐ and Ni(II)‐MCM41, respectively. Pseudo‐first‐order kinetics with kinetic constant of 2.0 × 10^?3 to 5.5 × 10^?3 Lg^?1 min^?1 was proposed along with a possible mechanism. 4‐nitrocatechol, 4‐nitropyrogallol, 1,2,4‐trihydroxybenzene, hydroquinone, acrylic acid, malonic acid, and oxalic acid were identified in the oxidation products. CONCLUSION: Introduction of Fe(III)‐, Co(II)‐ and Ni(II)‐ into MCM‐41 by impregnation produced effective catalysts for wet oxidation of 4‐nitrophenol. The catalysts were able to oxidize 4‐NP even without the presence of an oxidizing agent. The results suggest that the transition metal loaded MCM41 brings about a more effective interaction between 4‐NP molecules and OH radicals. Copyright © 2008 Society of Chemical Industry     

Reductive transformation of 2-nitrophenol by Fe(II) species in γ-aluminum oxide suspension

Fe(II) adsorption onto γ-Al₂O₃ surfaces was studied in view of its high reactivity towards the aqueous reductive transformation of 2-NP. Kinetic measurements demonstrated that rates of 2-NP reduction were highly sensitive to pH, Fe(II) concentration and reaction temperature. An increase in pH, Fe(II) concentration or reaction temperature gave rise to an elevated density of Fe(II) adsorbed to mineral surfaces, which further resulted in an enhanced reaction rate of 2-NP reduction. By using the diffuse double layer (DDL) surface complexation model, the dominant Fe(II) surface complex that was responsible for the high reactivity was predicted to be the strongly bound ≡ SOFe⁺ functional group (represented by ≡ Al_stOFe⁺) onto γ-Al₂O₃ surfaces. In addition, cyclic voltammetry tests showed that the enhanced activity of Fe(II) species was attributed to the negative shift of the redox potential of Fe(III)/Fe(II) couple, resulted from the enhanced concentration of ≡ Al_stOFe⁺ complex.     

Nitrosylmetallochelates—III. Rotating ring disk electrode study of redox reaction of Fe(II)EDTA with NO−2

The oxidation process of the nitrosyliron(II)EDTA complex which was produced by the reaction of Fe(II)EDTA and NO^?₂ has been studied by the rotating disk electrode and the spectroscopic methods. The oxidation of Fe(II)(NO)_xEDTA proceeds via two steps occurring at different potentials. The first step is the oxidation of Fe(II)EDTA to Fe(III)EDTA which is limited by the rate of chemical reaction, and the second is oxidation of NO to NO^?₃ which corresponds to surface controlled process. This result suggests the possibility that the noxious species can be transferred to the innocuous ion.     

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.     

Influence of ionic speciation on electrocatalytic performance of polyaniline coated platinum electrode: Fe(III)/Fe(II) redox reaction

Porous-polyaniline coated Pt electrode (PANI/Pt) was electro-synthesized potentiodynamically in 0.1 M aniline + 0.5 M H₂SO₄ and morphologically characterized by scanning electron microscopy (SEM). Nature of predominant Fe-species in HCl and H₂SO₄ was checked by UV-vis spectrophotometry. Electrocatalysis of Fe(III)/Fe(II) reaction was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) for three different solution compositions viz. (i) FeCl₃/FeCl₂ in 1 M HCl, (ii) FeCl₃/FeCl₂ in 0.5 M H₂SO₄ and (iii) Fe₂(SO₄)₃/FeSO₄ in 0.5 M H₂SO₄. For different thicknesses of PANI, the peak current increased irrespective of the nature of the Fe-species, but the polarity of the charge on the Fe-species showed great influence on reversibility of electrocatalysis by PANI/Pt. The Donnan interaction of the polyaniline modified electrode for the three compositions was investigated with respect to [Fe(CN)₆]³⁻/H₂[Fe(CN)₆]²⁻ which are believed to be the predominant species present in K₃[Fe(CN)₆]/K₄[Fe(CN)₆] solution in 0.5 M H₂SO₄. The electrocatalytic performance of PANI/Pt for Fe(III)/Fe(II) redox reaction was found superior in HCl compared to that in H₂SO₄.     

Use of deep eutectic solvent as extractant for separation of Fe (III) and Mn (II) from aqueous solution

In this work, we used deep eutectic solvent (DES) composed of decanoic acid and lidocaine, which is characterized as a green solvent, for separation of Fe (III), which is the most-used metal in the world, and Mn (II), which is currently being used in many industries. We found that the pH of the initial metal solution strongly influenced the extraction mechanism. Fe (III) can be extracted at pH 1.0–2.0 due to the ion pair reaction between Fe³⁺ and decanoic anion, while at higher pH, the extraction mechanism cannot be evaluated due to formation of precipitation at the aqueous phase. In the case of Mn (II), the ion pair reaction occurred at pH of lower than 2.2 and higher than 3.5, while from pH 2.2 to 3.5, the cation exchange between Mn²⁺ and lidocaine cation probably dominated the extraction process. The DES concentration needed to reach the complete separation of Fe (III) was about 25 g/L, while Mn (II) was completely extracted using about 300 g/L of DES. The selectivity of this method was very high when was applied in the separation of Fe (III) from Mn (II).     

Calcined tetrabutylammonium kaolinite and montmorillonite and adsorption of Fe(II), Co(II) and Ni(II) from solution

Kaolinite and montmorillonite were modified with tetrabutylammonium (TBA) bromide, followed by calcination. The structural changes were monitored with XRD, FTIR, surface area and cation exchange capacity measurements. The modified clay minerals were used for adsorption of Fe(III), Co(II) and Ni(II) ions from aqueous solution under different conditions of pH, time and temperature. The uptake of the metal ions took place by a second order kinetics. The modified montmorillonite had a higher adsorption capacity than the corresponding kaolinite. The Langmuir monolayer capacities for the modified kaolinite and montmorillonite were Fe(III): 9.3 mg g^− 1 and 22.6 mg g^− 1; Co(II): 9.0 mg g^− 1 and 22.3 mg g^− 1; and Ni(II): 8.4 mg g^− 1 and 19.7 mg g^− 1. The modified kaolinite interacted with Co(II) in an endothermic manner, but all the other interactions were exothermic. The decrease of the Gibbs energy in all the cases indicated spontaneous adsorption.     

Application of crosslinked carboxymethyl konjac glucomannan in speciation of dissolved Fe(II) and Fe(III) in water samples

A new solid‐phase extraction technique has been developed for the speciation of trace dissolved Fe(II) and Fe(III) in environmental water samples with a microcolumn packed with crosslinked carboxymethyl konjac glucomannan (CCMKGM) prior to its determination by flame atomic absorption spectrometry (FAAS). Various influencing factors on the separation and preconcentration of Fe(II) and Fe(III), such as the acidity of the aqueous solution, sample flow rate and volume, and eluent concentration and volume, have been investigated systematically and optimized. Fe(III) could be quantitatively retained by CCMKGM in the pH range of 3.0–7.0, then the retained Fe(III) on the CCMKGM was eluted with 5.0 mol L^?1 HCl after cleaning with 0.01 mol L^?1 HCl to eliminate Fe(II) and determined by FAAS. Total Fe was determined after the oxidation of Fe(II) to Fe(III) by H₂O₂, and Fe(II) concentration was calculated by subtracting Fe(III) from total iron. The adsorption capacity of CCMKGM for Fe(III) was found to be as high as 162.3 mg g^?1. The detection limit (3σ) for Fe(III) was 1.5 μg L^?1 and the RSD was 3.5% (n = 11, c = 20 μg L^?1) with an enrichment factor of 50. The proposed method has been applied to the speciation of iron in water samples with satisfactory results. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Polycarbonateurethane films containing complex of copper(II) catalyzed generation of nitric oxide

Nitric oxide (NO) is a well known potent antiplatelet agent, and its continuous release will effectively prevent the adhesion of platelets on artificial blood vessel walls. In this paper, polycarbonateurethane (PCU) with lipophilic Cu(II)‐complex (Cu(II)‐DTTCT) blending films were prepared and used as catalyst to generate NO from nitrite. The mechanical properties of PCU films blended with Cu(II)‐DTTCT were characterized by tensile strength measurement. The tensile stress and Young's modulus of PCU films blending with Cu(II)‐DTTCT increased, however, the elongation at break decreased compared with corresponding PCU films. The NO generation was investigated in vitro in the presence of NaNO₂ and ascorbic acid in PBS (pH = 7.4) at 37°C. The flux of NO generation was quantitatively measured by Griess assay. NO flux and velocity increased with the increase of NaNO₂ concentration, the concentration of ascorbic acid in PBS and the amount of Cu(II) in the films. The loss of Cu(II) from blending film surfaces was found during the in vitro NO generation experiments, which resulted in the decrease of NO flux in the second run. The PCU film could catalyze continually generation of NO for two days, which will provide a promising approach that enable endogenous NO generation on the surface of the medical devices. The generation of biologically active level of NO at the blood/polymer interface can reduce the risk of thrombosis on the implants. Polycarbonateurethane films with NO generation function may be used as high thromboresistant blood contacting materials or coating. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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.     

Removal of Cu(II) and Fe(III) from aqueous solutions by dead sulfate reducing bacteria

The biosorption properties of dead sulfate reducing bacteria (SRB) for the removal of Cu(II) and Fe(III) from aqueous solutions was studied. The effects of the biosorbent concentration, the initial pH value and the temperature on the biosorption of Cu(II) and Fe(III) by the SRB were investigated. FTIR analysis verified that the hydroxyl, carbonyl and amine functional groups of the SRB biosorbent were involved in the biosorption process. For both Cu(II) and Fe(III), an increase in the SRB biosorbent concentration resulted in an increase in the removal percentage but a decrease in the amount of specific metal biosorption. The maximum specific metal biosorption was 93.25 mg?g^–1 at pH 4.5 for Cu(II) and 88.29 mg?g^–1 at pH 3.5 for Fe(III). The temperature did not have a significant effect on biosorption. In a binary metal system, the specific biosorption capacity for the target metal decreased when another metal ion was added. For both the single metal and binary metal systems, the biosorption of Cu(II) and Fe(III) onto a SRB biosorbent was better represented by a Langmuir model than by a Freundlich model.     

Role of Iron and Chromium Complexes in Environmental Self‐cleaning Processes

Abstract

The present research includes solar‐light‐driven photocatalytic cycles based on the photoreductions of Fe(III), Cr(VI), and Cr(III) compounds with EDTA, oxalate and other ligands. Molecular oxygen is needed to close the photocatalytic cycles in which the metal species plays a role of photocatalyst; it affects the reaction mechanism and rate. The photoinduced electron transfer was also investigated in the presence of some external electron donors, such as EDTA, aliphatic alcohols, phenol, and its halogen derivatives, oxalate, nitrate(III), sulfate(IV). The results apply to the removal of such hazardous environmental pollutants as chromate(VI) or phenol derivatives and such recalcitrant pollutants as EDTA.     

Synthesis,Characterization, and Antimicrobial Activity of Silver(I) and Copper(II) Complexes of Phosphate Derivatives of Pyridine And Benzimidazole

Two silver(I) complexes—{[Ag(4‐pmOpe)]NO₃}_n and [Ag(2‐bimOpe)₂]NO₃—and three copper(II) complexes—[Cu₄Cl₆O(2‐bimOpe)₄], [CuCl₂(4‐pmOpe)₂], and [CuCl₂(2‐bis(pm)Ope]—were synthesized by reaction of silver(I) nitrate or copper(II) chloride with phosphate derivatives of pyridine and benzimidazole, namely diethyl (pyridin‐4‐ylmethyl)phosphate (4‐pmOpe), 1H‐benzimidazol‐2‐ylmethyl diethyl phosphate (2‐bimOpe), and ethyl bis(pyridin‐2‐ylmethyl)phosphate (2‐bis(pm)Ope). These compounds were characterized by ¹H, ¹³C, and ³¹P NMR as well as IR spectroscopy, elemental analysis, and ESIMS spectrometry. Additionally, molecular and crystal structures of {[Ag(4‐pmOpe)]NO₃}_n and [Cu₄Cl₆O(2‐bimOpe)₄] were determined by single‐crystal X‐ray diffraction analysis. The antimicrobial profiles of synthesized complexes and free ligands against test organisms from the ATCC and clinical sources were determined. Silver(I) complexes showed good antimicrobial activities against Candida albicans strains (MIC values of ～19 μM ). [Ag(2‐bimOpe)₂]NO₃ was particularly active against Pseudomonas aeruginosa and methicillin‐resistant Staphylococcus epidermidis, with MIC values of ～5 and ～10 μM , respectively. Neither copper(II) complexes nor the free ligands inhibited the growth of test organisms at concentrations below 500 μg mL^?1.     

Bioaccumulation and biosorption of copper(II) and chromium(III) from aqueous solutions by Pichia stipitis yeast

BACKGROUND: Bioaccumulation and biosorption by Pichia stipitis yeast has not yet been explored. This paper evaluates, for the first time, the use of both viable and nonviable P. stipitis yeast to eliminate Cu(II) and Cr(III) from aqueous solutions. The effect of Cu(II) and Cr(III) ions on the growth and bioaccumulation properties of adapted and nonadapted biomass is investigated as a function of initial metal concentration. Binding capacity experiments using nonviable biomass are also performed as a function of temperature. RESULTS: The addition of Cu(II) and Cr(III) had a significant negative effect on the growth of yeast. Nonadapted cells could tolerate Cu(II) and Cr(III) ions up to a concentration of 75 ppm. The growth rate of nonadapted and adapted cells decreased with the increase in Cu(II) and Cr(III) concentration. Adapted P. stipitis biomass was capable of removing Cu(II) and Cr(III) with a maximum specific uptake capacity of 15.85 and 9.10 mg g⁻¹, respectively, at 100 ppm initial Cu(II) and Cr(III) concentration at pH 4.5. Adsorption data on nonviable cells were found to be well modeled by the Langmuir and Temkin isotherms. The maximum loading capacity of dry biomass predicted from Langmuir isotherm for Cu(II) and Cr(III) at 20 °C were 16.89 and 19.2 mg g⁻¹, respectively, at pH 4.5. Biosorptive capacities were dependent on temperature for Cu(II) and Cr(III) solutions. CONCLUSION: Cu(II)‐ and Cr(III)‐adapted cells grow and accumulate these ions at high ratios. On the other hand, nonviable P. stipitis was found to be an effective biosorbent for Cu(II) and Cr(III) biosorption. Copyright © 2008 Society of Chemical Industry     

The hydrothermal synthesis and structure of a one-dimensional Fe(II)molybdophosphate

A new one-dimensional Fe(II)molybdophosphate of the formula, [(C₁₀H₈N₂)H₂]₂[Fe₄^(II)Mo₁₂^(V)(HPO₄)₆(PO₄)₂(H₂O)₈(OH)₆O₂₄]·8H₂O, (1), has been synthesized by employing hydrothermal methods and characterized by single crystal X-ray diffraction. The structure consists of a network of MO₆ (M = Fe, Mo) octahedra and (H)PO₄ tetrahedra linked through their vertices. The connectivity between the polyhedral units gives rise to one-dimensional chains with eight-membered apertures. The hydrogen bonded interactions between the chains form pseudo two-dimensional layers. Extensive hydrogen bonding also exists between the amine molecule, 4,4^′-bipyridine, water molecule and framework oxygen atoms. Crystal data for 1: monoclinic, space group = P2₁ (no. 4), a=12.549(3) (Å), b=23.496(5) (Å), c=14.551(3) (Å), β=114.87(3)°, , and Z=2.     

Effect of sulfite on reduction kinetics of Fe(III)NTA chelate

The reduction of Fe(III)NTA (ferric ion coordinated to nitrilotriacetic acid) by sulfite has been found to be first-order with respect to Fe(III)NTA and of order minus one with respect to Fe(II)NTA (one of the reaction products). The order of reaction with respect to HSO^?₃ has been determined to be unity when the molar ratio of Na₂SO₃ to total Fe(III) is less than five. In this paper, the role of sulfite in the reduction scheme is reconsidered, and the reduction rate expression in which the coordination of Fe³⁺ to HSO^?₃ is incorporated, is newly presented. The proposed rate equation covers all reaction data for molar ratios of Na₂SO₃ to total Fe(III) in the range of 1 to 25.     

Cobalt(II) and nickel(II) complexes bearing mono(imino)pyridyl and bis(imino)pyridyl ligands: preparation,structure and ethylene polymerization/oligomerization behaviors

BACKGROUND: Ethylene oligomerization is the major industrial process to produce linear α‐olefins. Recently much work has been devoted to late transition metal catalysts used in this process, especially those with 2,6‐bis(imino)pyridyl dihalide ligands. Considering that most work has focused on simple modification to the substituents in imino‐aryl rings based on the symmetric bis(imino)pyridyl framework, here we expand this work to the asymmetric mono(imino)pyridyl ligands. RESULTS: The preparation, structure and ethylene polymerization/oligomerization behavior of series of mono(imino) pyridyl–MCl₂ and bis(imino)pyridyl–MX_n complexes are presented. The systematic studies were focused on the relationship between the catalytic behavior of these complexes for ethylene polymerization/oligomerization and reaction conditions, ligand structures, metal centers and counter‐anions. The influence of the coordination environment on catalyst behavior is also discussed. CONCLUSION: For mono(imino)pyridyl–Co(II) and ? Ni(II) catalysts bearing the Cl^? counter‐anion, good activities ranging from 0.513 × 10⁵ to 1.58 × 10⁵ g polyethylene (mol metal)^?1 h^?1 atm^?1 are afforded, and the most active catalysts are those with methyl in both ortho‐ and para‐positions of the imine N‐aryl ring. For bis(imino)pyridyl–Co(II) and ? Ni(II) catalysts bearing the SO₄^2? and NO₃^? counter‐anions, the low activities for ethylene oligomerization are in sharp contrast to those of their chloride analogues. Copyright © 2009 Society of Chemical Industry     

Study of the Daughter Products of Akardite‐II

In this work, five akardite‐II (AK‐II) daughter products were produced and isolated. Their respective MS, NMR, IR and UV spectra were recorded. These five products were positively identified as: N‐NO‐AK‐II, 2‐NO₂‐AK‐II, 4‐NO₂‐AK‐II, N‐NO‐2‐NO₂‐AK‐II and N‐NO‐4‐NO₂‐AK‐II. An HPLC method giving baseline separation of 6 AK‐II family products and 10 diphenylamine (DPA) family products is also described. Finally, preliminary results concerning the stability of AK‐II daughter products are discussed.