A polyaniline-magnetite nanocomposite as an anion exchange sorbent for solid-phase extraction of chromium(VI) ions

This work describes a novel polyaniline-magnetite nanocomposite and its application to the preconcentration of Cr(VI) anions. The material was obtained by oxidative polymerization of aniline in the presence of magnetite nanoparticles. The parameters affecting preconcentration were optimized by a Box-Behnken design through response surface methodology. Extraction time, amount of magnetic sorbent and pH value were selected as the main factors affecting sorption. The sorption capacity of the sorbent for Cr(VI) is 54 mg g^?1. The type, volume and concentration of the eluents, and the elution time were selected as main factors in the optimization study of the elution step. Following sorption and elution, the Cr(VI) ions were reacted with diphenylcarbazide, and the resulting dye was quantified by HPLC with optical detection at 546 nm. The limit of detection is 0.1 μg L^?1, and all the relative standard deviations are <6.3 %. The nanocomposite was successfully applied to the rapid extraction and determination of trace quantities of Cr(VI) ions in spiked water samples. Figure

A schematic procedure of magnetic solid phase extraction     

Chromium(VI) Accumulation and Tolerance by Tradescantia pallida: Biochemical and Antioxidant Study

Tradescantia pallida (Wandering jew)—a succulent perennial herb—was screened to be a potent chromium (Cr) accumulator. Its ability to grow under Cr stress was examined by studying biochemical changes and physiological response of the plant in presence of 5–20 mg L^?1 Cr(VI) concentration in hydroponic environment for up to ca. 90 days. Average Cr(VI) bioaccumulation in plant roots reached about 408 μg g^?1 dry weight (dw) after 30 days and up to 536 μg g^?1dw after 60 days of culture. Biochemical changes in the plant exposed to Cr(VI) indicated a reduction in the total carbohydrate and protein content. Furthermore, lipid peroxidation, catalase, peroxidase and ascorbate peroxidase activity were measured in different parts of the plant exposed to Cr(VI). Increased activities of these enzymes showed their important role in overcoming the Cr-induced oxidative stress on the plant.     

Biosorptive profile of synthetic and natural humiresin for the remediation of metallic water pollutants

To evaluate the bioremediation efficiency of natural humic substances, over it’s synthetic counterpart, a comparative batch equilibration biosorption assay have been carried out employing radiotracers on different humi-resins. The biosorptive profile of various humiresins as devised hereby, attempts to justify an innovative and concrete role of dry cow dung powder (DCP), in ‘as it is form’, for the bioremediation of metal pollutants such as Cr(III), Cr(VI), Cd(II), Hg(II) and Sr(II). Our comparative results conclude that, with all other optimized parameters as obtained 100 mg of DCP removes Cr(III) at pH 6, Cd(II) at pH 3 and Hg(II) at pH 3 to 70–75 and 80–85 % respectively. Also, at pH 1 with 250 mg of DCP 70–75 % Cr(VI) is removed. Similarly, 90–95 % of Sr(II) is sequestered at pH 6, with 350 mg of DCP. The study on thermodynamic, kinetic and isotherm modelling of DCP indicates feasible, eco-friendly and efficient process.     

Parameter evaluation,kinetics, and energy consumption for Cr(VI) photocatalytic reduction under mild conditions

Photocatalytic reduction of hexavalent chromium, Cr(VI), ions in aqueous solutions was studied using remarkably low doses of commercial titania nanoparticles at conventional temperature range of 15–45 °C. A direct imposed irradiation photo-reactor, equipped with ultrasonic source was utilized. Design of experiments, correlating and process optimization were performed using central composite design of response surface methodology. Accordingly, a reduced quadratic expression was developed to predict the reduction efficiency as a function of involved parameters. Analysis of variance shows the agreement of the provided model with experimental data. At the found optimum conditions of titania concentration: 33.1 mg/L, pH: 2.50, temperature: 36 °C and reaction time: 120 min; 81 % efficiency was achieved for reduction of initial 5 mg/L of Cr(VI). The process revealed proceeding through parallel branches of photolysis and photocatalysis, and only UV irradiation was promising for reaction progress. Based on differential method of analysis, the relevant kinetic model, jointed with the Arrhenius equation, was introduced. Energy (electrical and thermal) consumption evaluations revealed that treatment at higher temperatures provides a significant cost reduction. Meantime, a criterion was proposed for a more valid assessment of photocatalytic processes.     

Interaction of ozone with variable-valence metal ions in concentrated silicate solutions

Spectrophotometric studies have revealed that ozone oxidizes Cr(III) into Cr(VI), Fe(III) into Fe(VI), Mn(VI) into Mn(VII), and Np(VI) into Np(VII) in the concentrated aqueous silicate solutions. Cr(III) oxidation is accelerated in alkaline-silicate and alkaline solutions as compared to neutral silicate solution. Ferrate and permanganate ions are unstable in Na₂SiO₃ solutions (0.5–1.3 mol/L of the silicate). Neptunium(VII) ions formed in the course of ozonation are stable in Na₂SiO₃ solution (1 mol/L) upon drying in air to form solid vitreous mass.     

Sequential determination of nickel(II) and zirconium(IV) with dimethylglyoxime and arsenazo III after adsoprtion on one substrate disc

The possibility of the sequential determination of nickel with dimethylglyoxime and zirconium with arsenazo III from a single aliquot portion using polyacrylonitrile fiber as a solid phase impregnated with a KU-2 cation exchanger is studied. Conditions for the simultaneous adsorption of nickel and zirconium in the dynamic mode from 0.01 M HNO₃ are found as along with the ones for their sequential determination on one disc. The calibration functions are linear in the range 5–50 ng/mL, the detection limits for both elements are 2 ng/mL. In their simultaneous presence, the determination of nickel and zirconium is not affected by 10-fold weight amounts of Fe(III), Cu(II), Co(II), Al, Mn(II), Pb, Zn, Cd, Cr(VI), Mo(VI), and V(V). A method is proposed for determining nickel and zirconium from a single aliquot portion on a single substrate disc at their ratios from 1: 1 to a 5-fold excess of each element.     

Search for optimal conditions for the extraction of thiosulfate complexes of Cu(II) by 4-(5-nonyl)pyridine from aqueous mineral acid solutions

Solvent extraction of Cu(II) by 4-(5-nonyl)pyridine (NPy) in benzene from mineral acid solutions containing thiosulfate ions has been studied at room temperature (23±2°C). Mineral acid solutions alone constitute an aqueous phase from which Cu(II) is not extracted. Addition of small amounts of thiosulfate ions augments the extraction to an extent that quantitative recovery is possible. Stoichiometric studies reveal the involvement of ion-pair type complexes (NPy·H)₂·Cu(S₂O₃)₂ which are responsible for extraction. Stability constants lg K_ex for this complex are 7.2±0.2; 9.1±0.2 and 9.5±0.2 for HCl, HNO₃ and H₂SO₄, respectively. The presence of 0.01 mol/l of some complexing ions like ascorbate, acetate, citrate, oxalate, tartrate or iodide does not affect the extraction, thus allowing the recovery of the metal from diverse matrices. Under optimal conditions (0.1M NPy in benzene-0.1M HNO₃ or H₂SO₄+0.01M S₂O ₃ ^?2 or 0.5M HCl+0.05 M S₂O ₃ ^?2 ) a clean separation from some elements, e.g. Cs(I). Co(II), Fe(III), Eu(III), Ce(III), Se(IV) and Cr(VI) can be achieved.     

The reaction of ammonium tetra(isothiocyanato)diamminechromate(III) with ?-caprolactam in aqueous solution. Revised refinement of the structure of (HCpl2)3[Cr(NCS)6]

A reaction of ammonium tetra(isothiocyanato)diamminechromate(III) (ammonium reineckate) with ?-caprolactam in aqueous solution at different pH values gave the novel complexes (NH₄)[Cr(NH₃)₂(NCS)₄] · 7Cpl (I), (NH₄)[Cr(NH₃)₂(NCS)₄] · 2.5Cpl · 0.5(H₂O) (II), and (HCpl₂)[Cr(NH₃)₂(NCS)₄] (III), where Cpl is ?-caprolactam (?-C₆H₁₁NO). The crystals of complexes I?CIII are triclinic, space group $P\bar 1$ ; I: a = 12.7058(4) ?, b = 13.2544(4) ?, c = 19.4487(7) ?, ?? = 105.2360(10)°, ?? = 106.6410(10)°, ?? = 91.5290(10)°, V = 3009.37(17) ?³, ??_calc = 1.245 g/cm³, Z = 2; II: a = 12.3144(5) ?, b = 12.6518(5) ?, c = 23.3300(8) ?, ?? = 75.4580(10)°, ?? = 80.0760(10)°, ?? = 61.0830(10)°, V = 3074.1(2) ?³, ??_calc = 1.358 g/cm³, Z = 4; III: a = 6.4701(4) ?, b = 12.5973(9) ?, c = 16.5556(12) ?, ?? = 108.769(2)°, ?? = 98.543(2)°, ?? = 90.345(2)°, V = 1261.36(15) ?³, ??_calc = 1.437 g/cm³, Z = 2. The structure refinement for (HCpl₂)₃[Cr(NCS)₆] (IV) was revised. Like complex III, complex IV contains the cation (HCpl₂)⁺ stabilized by a strong hydrogen bond between the O atoms of the ?-caprolactam molecules; the cation was structurally characterized for the first time.     

Influence of the bridging coordination of DMSO on the exchange interaction character in the binuclear copper(II) complex with the nonsymmetrical exchange fragment

The binuclear copper(II) complex [Cu₂L(CH₃COO)] (I), where L^3? is the azomethine trianion based on 3-methyl-4-formyl-1-phenylpyrazol-5-one and 1,3-diaminopropan-2-ol, and its DMSO adduct (II) in which the DMSO molecule acts as an additional bridging ligand are synthesized. The structure of complex II is determined by X-ray diffraction analysis, and the structure parameters of the coordination unit of complex I are determined by EXAFS spectroscopy. The μ²-coordination of the DMSO molecule in compound II results in a change in the sign of the exchange interaction parameter. In complex I, the antiferromagnetic exchange interaction (2J = ?169 cm^?1) occurs between the copper(II) ions. The exchange interaction of the ferromagnetic type (2J = 174 cm^?1) is observed in complex II. The quantum-chemical calculations of the magnetic exchange parameters by the density functional theory method show that the role of the DMSO molecule as a switch of the exchange interaction character is exclusively the stabilization of the “broken” conformation of the metallocycles.     

Salt-assisted liquid-liquid microextraction of Cr(VI) ion using an ionic liquid for preconcentration prior to its determination by flame atomic absorption spectrometry

We report on the salt-assisted liquid-liquid microextraction of cationic complexes of Cr(VI) ion using the hydrophilic ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoraborate and potassium hydrogen phosphate. This is a novel, simple, non-toxic and effective technique for sample pretreatment technique that displays large extraction efficiency and represents a new platform where Cr(VI) is complexed with 1,5-diphenylcarbazide (DPC) in sulfuric acid medium. It was applied to the extraction of Cr(VI) in the form of the Cr(VI)-DPC complex prior to its determination by flame atomic absorption spectrometry. Cr(III) ion also can be determined by this procedure after oxidation to Cr(VI). Extraction is mainly affected by the amount of water-soluble IL, the kind and quantity of inorganic salts, by pH and the concentration of DPC. Calibration plots are linear in the range from 3 to 150?μg?L^?1 of Cr(VI), and the limit of detection is 1.25?μg?L^?1. The method was successfully applied to the speciation and determination of trace levels of Cr(III) and Cr(VI) in environmental water samples containing high levels of dissolved salts or food grade salts.

A solid state Cr(VI) ion-selective electrode based on polypyrrole

We report on a graphite electrode onto which polypyrrole was electrodeposited and then doped with chromate ion. This electrode can serve as a Cr(VI)-selective solid-state electrode. Electropolymerization of pyrrole was performed potentiostatically at 0.80?V (vs. SCE) using battery graphite as the working electrode in a solution containing 0.10?M of pyrrole and 20?mM of chromate. A platinum wire was used as an auxiliary electrode. The new electrode displays high selectivity, a very wide dynamic range, a sufficiently fast response time and a good shelf lifetime. It shows a linear Nernstian response over 1.0?×?10^?6 to 1.0?×?10^?1?M concentration range (with a slope of 26.55?±?0.20?mV per log of concentration). The detection limit is 0.5?μM, and the pH optimum is 7.0.

Manganese(II), nickel(II), and cadmium(II) coordination polymers with tetrafluoroterephthalate: syntheses,crystal structures,and luminescence properties

Three new coordination polymers, [Mn(BDC-F₄)(DMF)₂(H₂O)₂] _n (1), [Ni(BDC-F₄)(DMF)(EtOH)] _n (2), and [Cd(BDC-F₄)(DMF)(EtOH)] _n (3), have been synthesized by assembling transition metal salts with the rigid ligand tetrafluoroterephthalic acid (H₂BDC-F₄) in mixed EtOH/DMF solvent at pH ca. 2. For complex 1, the octahedral coordination geometry of the Mn^II center is provided by two oxygen atoms from two dianionic BDC-F₄ ligands, two DMF ligands and two aqua ligands, giving a 1-D linear chain array. For complex 2, the Ni^II center is coordinated by two dianionic BDC-F₄ ligands, two EtOH ligands and two DMF ligands, resulting in a 1-D chain structure. For complex 3, the Cd^II center is coordinated by four dianionic BDC-F₄ ligands, one EtOH ligand and one DMF ligand, generating a 2-D layered structure. The results suggest that both the metal and the solution pH play an important role in the formation of the complexes. The spectroscopic, thermal, and luminescence properties of the complexes have been investigated.     

Synthesis of tyrosine-involved corrole Cu(III), Mn(IV), and Mn(III) complexes as biomimetic models of oxygen evolving complex in photosystem II

Boc-protected tyrosine-attached corrole ligand on the “ortho” position compound 3, its corresponding copper (III) 4a, manganese (IV) 4b, and manganese (III) 4c complexes have been designed and synthesized based on the structures of active-centers of related biological systems. ¹H NMR and electronic absorption spectra of these metal complexes are investigated. The crystal structure of 4a displays the relative position of TyrOH unit to the high valent metal center. Electrochemistry investigations display the possibilities of intramolecular electron or energy transfer between TyrOH group and metal corrole group.     

Titanium dioxide nanoparticle based solid phase extraction of trace Alizarin Violet,followed by its specrophotometric determination

Nanometer-sized titanium dioxide (nano-TiO₂) is shown to be a viable material for the preconcentration of Alizarin Violet (AV, a common dye and biological stain). In the preconcentration step, a 5-ring cyclic ester is formed between the ortho-dihydroxy groups of AV and two hydroxy groups of the titanic acid on the surface of the nano-TiO₂. Under optimized conditions, the adsorption capacity of nano-TiO₂ is?~?20 μg?·?mg^?1, the adsorption efficiency is 98 %. The adsorbed AV can be eluted with 5 mL of 5 mol?·?L^?1 5-sulfosalicylic acid with an elution efficiency of more than 91.8 %. The preconcentration factor is 50 in case of 250 mL samples. Spectrophotometric determination of AV in the eluate gives a linear calibration plot in the range between 18.8 μg?·?L^?1 and 10 mg?·?L^?1 and a detection limit (3 s; for n?=?11) of 18.8 μg?·?L^?1. The method is simple and fast. It was successfully applied to the analysis of AV in spiked natural waters, and recoveries were found to range between 94.2 and 97.3 %.

Nanometer-sized titanium dioxide is a viable material for the preconcentration of Alizarin Violet (AV), before its spectrophotometrical determination. The method is simple and fast. It was successfully applied to the analysis of AV in spiked natural waters, and recoveries were found to range between 94.2 and 97.3 %.     

A turn-on fluorescence-sensing technique for glucose determination based on graphene oxide–DNA interaction

Graphene is a two-dimensional carbon nanomaterial one atom thick. Interactions between graphene oxide (GO) and ssDNA containing different numbers of bases have been proved to be remarkably different. In this paper we propose a novel approach for turn-on fluorescence sensing determination of glucose. Hydrogen peroxide (H₂O₂) is produced by glucose oxidase-catalysed oxidation of glucose. In the presence of ferrous iron (Fe²⁺) the hydroxyl radical (?OH) is generated from H₂O₂ by the Fenton reaction. This attacks FAM-labelled long ssDNA causing irreversible cleavage, as a result of the oxidative effect of ?OH, producing an FAM-linked DNA fragment. Because of the weak interaction between GO and short FAM-linked DNA fragments, restoration of DNA fluorescence can be achieved by addition of glucose. Due to the excellent fluorescence quenching efficiency of GO and the specific catalysis of glucose oxidase, the sensitivity and selectivity of this method for GO-DNA sensing are extremely high. The linear range is from 0.5 to 10 μmol L^?1 and the detection limit for glucose is 0.1 μmol L^?1. The method has been successfully used for analysis of glucose in human serum. Figure

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The use of stable isotopes for Cr(VI) determination in silty-clay soil solution

In assessing the environmental hazard of Cr(VI) present in soil, exchangeable Cr(VI) is important, since it can be easily washed out from the upper part of the soil into subsurface soil, surface and ground water, and taken up by plants. The aim of this study was to evaluate the degree of species interconversion that may occur during the extraction of exchangeable Cr(VI) from silty-clay soil with phosphate buffer in order to establish an extraction method that would be effective, accurate and with minimal or no species interconversions. The Cr(VI) concentration in soil extracts was determined by speciated isotope dilution inductively coupled plasma mass spectrometry (SID-ICP-MS). The study was performed on soil samples from a field treated with tannery waste for 17 years. Samples were spiked by enriched stable isotopic solutions of ⁵⁰Cr(VI) and ⁵³Cr(III) that were added to phosphate buffers (0.1 M KH₂PO₄-K₂HPO₄ (pH 7.2) and/or 0.1 M K₂HPO₄ (pH 8)). To optimize extraction, mechanical shaking and/or ultrasound-assisted extraction were compared. The separation and detection of Cr species was performed by high-performance liquid chromatography (HPLC) ICP-MS. When mechanical shaking was applied, 90 % reduction of Cr(VI) was induced by extraction with 0.1 M KH₂PO₄-K₂HPO₄, while with 0.1 M K₂HPO₄ reduction was around 40 %. To shorten the extraction time and the possibility of species interconversions, ultrasound-assisted extraction was further applied only with 0.1 M K₂HPO₄. For total extraction of exchangeable Cr(VI) with a maximum 10 % reduction of Cr(VI), five consecutive ultrasound-assisted extractions were needed.

Determination of nitrite, nitrate, bromide, and iodide in seawater by ion chromatography with UV detection using dilauryldimethylammonium-coated monolithic ODS columns and sodium chloride as an eluent

A method was developed for determination of inorganic anions, including nitrite (NO ₂ ^? ), nitrate (NO ₃ ^? ), bromide (Br^?), and iodide (I^?), in seawater by ion chromatography (IC). The IC system used two dilauryldimethylammonium bromide (DDAB)-coated monolithic ODS columns (50?×?4.6?mm i.d. and 100?×?4.6?mm i.d.) connected in series for separation of the ions. Aqueous NaCl (0.5?mol/L; flow rate, 3?mL/min) containing 5?mmol/L phosphate buffer (pH 5) was used as the eluent, and detection was with a UV detector at 225?nm. The monolithic ODS columns were coated and equilibrated with a 1-mmol/L DDAB solution (in H₂O/methanol, 90:10 v/v). The hydrophilic ions (NO ₂ ^? , NO ₃ ^? , and Br^?) were separated within 3?min and the retention time of I^? was 16?min. No interferences from matrix ions, such as chloride and sulfate ions, were observed in 35?‰ artificial seawater. The detection limits were 0.6?μg/L for NO ₂ ^? , 1.1?μg/L for NO ₃ ^? , 70?μg/L for Br^?, and 1.6?μg/L for I^? with a 200-μL sample injection. The performance of the coated columns was maintained without addition of DDAB in the eluent. The IC system was successfully applied to real seawater samples with recovery rates of 94–108?% for all ions.

Enantioselective Supramolecular Carriers for Nucleoside Drugs. A Thermodynamic and Kinetic Gas Phase Investigation

The enantioselective interactions between chiral tetra-amidic receptors and nucleosides have been investigated by the ESI-IT-MS and ESI-FT-ICR-MS methodologies. Configurational effects on the CID fragmentation of diastereomeric [M ^H ₂ ?H?A]?⁺ aggregates (A?=?2'-deoxycytidine dC, citarabine (ara-C) were found to be mostly offset by isotope effect in [S ^X ₂ ?H?A]?⁺ (X?=?H, D) differently from the results obtained on the analogues (A?=?cytidine C and gemcitabine G). This result points the involvement of two different nucleoside/tetraamide isoforms. The structural differences of the [M ^H ₂ ?H?A]?⁺ (A?=?C and G) complexes vs. the [M ^H ₂ ?H?A]?⁺ (dC and ara-C) ones is fully confirmed by the kinetics of their uptake of the 2-aminobutane enantiomers, measured by FT-ICR mass spectrometry. Indeed, uptake of the 2-aminobutane enantiomers by [M ^H _n ?H?A]?⁺ (n?=?1,2; A?=?dC and ara-C) complexes is reversible, while that by [M ^H _n ?H?A]?⁺ (n?=?1,2; A?=?C and G) is not. The most encouraging result concerning the measured fragmentation and kinetic differences between C and ara-C, that are just epimers, indicates the possibility to subtly modulate the non-covalent drug/receptor interactions, through the electronic properties of the 2'-substituent on the nucleoside furanose ring, and furthermore on its three-dimensional position.     

Through bond mechanism versus exciplex formation in the photochemistry of fullerene / ferrocene donor-bridge-acceptor dyads

A systematic fluorescence and flash photolytic investigation of a series of covalently linked fullerene / ferrocene based donor-bridge-acceptor dyads is reported as a function of the nature of the bridge between the donor site and acceptor site. The fluorescence of the investigated dyads 2 (Φ_rel = 0.17 × 10^?4, 3 (Φ_rel = 0.78 × 10^?4), 4 (Φ_rel = 1.5 × 10^?4), 5 (Φ_rel = 0.7 × 10^?4), and 6 (Φ_rel = 2.9 × 10^?4) were substantially quenched, relative to N-methyl fulleropyrrolidine (1) (Φ_rel = 6.0 × 10^?4). Photolysis of N-methyl fulleropyrrolidine (1) in toluene revealed formation of the excited singlet state which was followed by a rapid intersystem crossing to the excited triplet state. On the other hand, the fate of the excited singlet state of 2, 3, 4, 5, and 6 was found to be governed by rapid intramolecular quenching, with rate constants of 28×10⁹ s^?1, 6.9×10⁹ s^?1, and 3.4×10⁹ s^?1, 14×10⁹ s^?1, 2.3×10⁹ s^?1 respectively. The electron transfer process and the charge separation were confirmed by monitoring the characteristic π-radical anion bands at λ_max = 400 and 1055 nm in degassed benzonitrile with τ_1/2 = 1.8 μs (3) and 2.5 μs (4).     

The conditions of formation of heterometallic complexes in the GeCl4 (SnCl4)-citric acid-M(CH3COO)2-H2O systems. The crystal and molecular structures of [M(H2O)6][Ge(HCit)2] · 4H2O (M = Mg, Mn, Co, Cu, Zn) and [M(H2O)6][Sn(HCit)2] · 4H2O (M = Mg, Co, Ni)

Fourteen bis(citrato)germanates(IV) and bis(citrato)stannates(IV) were prepared, in particular, [M(H₂O)₆][Ge(HCit)₂] · 4H₂O (M = Mg (I), Mn (II), Fe (III), Co (IV), Ni (V), Cu (VI), Zn (VII)) and [M(H₂O)₆][Sn(HCit)₂] · nH₂O (M = Mg, n = 4 (VIII); Mn, n = 2 (IX); Fe, n = 4 (X); Co, n = 4 (XI); Ni, n = 4 (XII); Cu, n = 4 (XIII); Zn, n = 3 (XIV)) (H₄Cit is citric acid). The purity and the composition of the products were determined by a set of physicochemical methods including elemental analysis, thermogravimetry, and IR spectroscopy. The structures of I, II, IV, VI, VII, VIII, XI, and XII were determined by X-ray diffractometry. All eight crystals composed of centrosymmetrical octahederal [M(H₂O)₆]²⁺ cations, [Ge(HCit)₂]^2? (or [Sn(HCit)₂]^2?) anions, and crystal water molecules are isostructural. The structural units in I, II, IV, VI, VII, VIII, XI, and XII are connected by systems of hydrogen bonds to form a three-dimensional framework.