Retention profile and subsequent chemical speciation of chromium (III) and (VI)) in industrial wastewater samples employing some onium cations loaded polyurethane foams

The retention of chromium (VI) from aqueous media onto tetraphenylarsonium chloride (TPAs⁺Cl⁻) or tetraphenylphosphonium bromide (TPP⁺Br⁻) immobilized polyurethane foams (PUFs) was fast and followed first order reaction. The kinetic data of the retention step were subjected to Weber-Morris, Lagergren, Bhattacharya and Venkobachar and Bt kinetic models. The results revealed that, film and intraparticle transport might be the two steps controlling the rate of chromium (VI) sorption from the aqueous acid solutions of pH ∼ zero. The positive values of the Δ H of chromium (VI) retention by the reagents loaded PUFs were interpreted as an endothermic process. Under the optimum pH (pH ∼ zero ) of the aqueous solution, the proposed TPAs⁺Cl⁻ or TPP⁺Br⁻ immobilized PUFs was successfully used in a series of medical syringe (30, 50 mL capacity) as pulse columns for complete collection of chromium (VI) species present in fresh and industrial wastewater samples at ultra trace low level of chromium (VI) (≤ 0.05 μg mL^− 1). The collected chromium (VI) species onto TPAs⁺Cl⁻ or TPP⁺Br⁻-PUFs was then stripped quantitatively (98-102 ± 2.6%) from the pulse columns with NaOH (2.0 mol L^− 1) and subsequently analyzed photometrically. The chromium (VI) ions could be pre concentrated up to 100-fold from large volume of water samples. The proposed pulse foam columns were applied successfully for complete collection, recovery (97.5 ± 2.6%, n = 5) and subsequent chemical speciation of chromium (III) and (VI) in wastewater samples. The results are in good agreement with the reported and standard methods at 95% confidence.     

Nucleophilic attack by bromide ions as a first step of conversion of Se(VI) to Se(IV)

Numerous commonly used analytical methods allow only determination of a total amount of selenium in a given sample. Electroanalytical methods as well as those based on hydride generation or on formation of piazselenol allow only determination of Se(IV). To determine Se(VI) by these procedures, present alone or in mixtures with Se(IV), it is first necessary to convert Se(VI) to Se(IV). Such conversion is effective in the presence of excess of halides in acidic media or by photoreduction. In the often used conversion of Se(VI) in the presence of chlorides or less frequently of that of bromides, it has been assumed that the halide ion acts as a reducing agent. Kinetic studies of conversion of Se(VI) in acidic solutions containing an excess of bromide ions indicated that the rate determining first step of the reaction with Se(VI) is a nucleophilic substitution of the OH₂⁺ group in the protonated form of H₂SeO₄ by bromide ions. For the overall reaction with rate −d[Se(VI)]/dt = k₁[H⁺][Br⁻]^1.15[Se(IV)] the rate constant 1 × 10⁻³ L² mol⁻² s⁻¹ was found. The following formation of Se(IV) from the bromo derivative is a fast reaction probably resulting in elimination of HBrO.     

Sorptive potential of sunflower stem for Cr(III) ions from aqueous solutions and its kinetic and thermodynamic profile

The sorptive potential of sunflower stem (180-300 μm) for Cr(III) ions has been investigated in detail. The maximum sorption (≥85%) of Cr(III) ions (70.2 μM) has been accomplished using 30 mg of high density sunflower stem in 10 min from 0.001 M nitric and 0.0001 M hydrochloric acid solutions. The accumulation of Cr(III) ions on the sorbent follows Dubinin-Radushkevich (D-R), Freundlich and Langmuir isotherms. The isotherm yields D-R saturation capacity X_m = 1.60 ± 0.23 mmol g⁻¹, β = −0.00654 ± 0.00017 kJ² mol⁻², mean free energy E = 8.74 ± 0.12 kJ mol⁻¹, Freundlich sorption capacity K_F = 0.24 ± 0.11 mol g⁻¹, 1/n = 0.90 ± 0.04 and of Langmuir constant K_L = 6800 ± 600 dm³ mol⁻¹ and C_m = 120 ± 18 μmol g⁻¹. The variation of sorption with temperature (283-323 K) gives ΔH = −23.3 ± 0.8 kJ mol⁻¹, ΔS = −64.0 ± 2.7 J mol⁻¹ K⁻¹ and ΔG_298k = −4.04 ± 0.09 kJ mol⁻¹. The negative enthalpy and free energy envisage exothermic and spontaneous nature of sorption, respectively. Bisulphate, Fe(III), molybdate, citrate, Fe(II), Y(III) suppress the sorption significantly. The selectivity studies indicate that Cr(III), Eu(III) and Tb(III) ions can be separated from Tc(VII) and I(I). Sunflower stem can be used for the preconcentration and removal of Cr(III) ions from aqueous medium. This cheaper and novel sorbent has potential applications in analytical and environmental chemistry, in water decontamination, industrial waste treatment and in pollution abatement. A possible mechanism of biosorption of Cr(III) ions onto the sunflower stem has been proposed.     

Synthesis,structural characterization and catalytic potential of oxidovanadium(IV) and dioxidovanadium(V) complexes with thiazole-derived NNN-donor ligand

Reaction between the tridentate NNN donor ligand, (E)-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)benzo[d]thiazole (HL), and V₂O₅ in ethanol gave a new vanadium(V) complex, [VO₂L] (1), while the similar reaction by using [V^IVO(acac)₂] as the metal source gave two different types of crystals related to compounds [VO₂L] (1) and [V^IVO(acac)L] (2). The molecular structures of the complexes were determined by single-crystal X-ray diffraction and spectroscopic characterization was carried out by means of FT-IR, UV–vis and NMR experiments as well as elemental analysis. The oxidovanadium(IV) and dioxidovanadium(V) species were used as catalyst precursors for olefin oxidation in the presence of hydrogen peroxide (H₂O₂) as an oxidant. Under similar experimental conditions, the presence of 1 resulted in higher oxidation conversion than 2.     

Application of Doehlert matrix to the study of flow injection procedure for selenium (IV) determination

A method for the rapid determination of selenium is reported. It is based on the injection of selenium sample into a stream of KI and subsequent measurement of the increase of the absorption at 290 nm due to the formation of I₃⁻. A Doehlert matrix was applied for the determination of the optimal working conditions. With the developed method, a linear calibration curve from 1 to 10 ppm was obtained. For the analysis of semiconducting thin layers of CuInSe₂ (CIS), a cationic resin was added to the sample solution in order to eliminate the effect of copper and indium on the absorbance values. With the developed procedure a sample throughput of 36 samples per hour and a relative standard deviation 1.1% was achieved.     

Sequential determination of Se(IV) and Se(VI) by flow injection-hydride generation-atomic absorption spectrometry with HCl/HBr microwave aided pre-reduction of Se(VI) to Se(IV)

In this study a flow injection (FI) system used in conjunction with hydride generation (HG), atomic absorption spectrometry (AAS) and microwave (MW) aided pre-reduction of selenite (Se(IV)) to selenate (Se(IV)) with HCl:HBr has been developed in order to differentiate both inorganic selenium species. As full control of the MW reduction step is possible, the experimental approach allows the use of milder acidic conditions (10% v/v of HCl and HBr) than those conventionally accomplished with hydrochloric acid alone (≥50% v/v). Experimental parameters were optimized by the univariate optimization method. In either case, the linear range was from 1.0 to 30 μg l⁻¹. The detection limits based on 3σ of the blank signal were 0.25 μg l⁻¹ for Se(IV) and 0.30 μg l⁻¹ for Se(VI). The reproducibility, about 3% RSD and recoveries of different amounts of Se(VI) and Se(IV) added to water and orange juice samples (97–103%) were good. The main advantage of the proposed method is that the sequential determination of Se(IV) and Se(VI) is performed at a high sampling frequency (ca. 50 samples per h) in a closed system without Se losses, and with a minimum sample waste, operator attention, and sample manipulation.     

Unsymmetrical mononuclear and insoluble polynuclear oxo-vanadium(IV) Schiff-base complexes

Unsymmetrical and symmetrical mononuclear and insoluble polynuclear oxo-vanadium(IV) Schiff-base complexes were prepared and characterized. The complexes [VO(5-x-6-y-Sal)(5-x′-6-y′-Sal)en)] (where x, x′ = H, Br and y, y′ = H, OMe) were obtained in monomeric form while for x or x′ = NO₂ polymers were produced. In the case of [VO(5-x-6-y-Sal)(5-x′-6-y′-Sal)pn)] with a six-member N–N chelating ring, oxo-vanadium(IV) complexes were polynuclear. The tetradentate N₂O₂-Schiff-base ligands are coordinated in the equatorial plane of oxo-vanadium(IV). Electrochemical and spectroscopic data (UV–Vis and IR) suggest importance of coordination geometry and the substiuents on phenyl rings and the bridge group. Electron density of the vanadium center decreases by the electron-withdrawing groups on the ligand while electron density on vanadium increases via σ-donation of phenolic oxygen.     

Flow-injection simultaneous determination of selenium(IV) and selenium(IV + VI) using photooxidative coupling of p-hydrazinobensenesulfonic acid with N-(1-naphthyl)ethylenediamine

A flow-injection spectrophotometric method has been developed for the simultaneous determination of selenium(IV) and (IV + VI) at nanogram per milliliter levels. It is based on the catalytic effect of selenium(IV) on the photooxidative coupling of p-hydrazinobenzenesulfonic acid (HBS) with N-(1-naphthyl)ethylenediamine (NED) to form an azo dye (λ_max = 538 nm). In this reaction, bromide acted as an activator for the catalysis of selenium(IV) and an reducer for selenium(VI) to selenium(IV) in an acidic medium which allowed the determination of selenium(IV + VI). A sample solution, being split by Y-piece into two portions, passed through the low-temperature coil (4 m, 25 °C) and the high-temperature coil (20 m, 100 °C). By monitoring the absorbance of the dye produced in the two portions, selenium(IV) and (IV + VI) in the range of 0.2–6 ng ml⁻¹ were determined simultaneously. The relative standard deviations for 3 ng ml⁻¹ selenium(IV) and (VI) (n = 10) were 1.2 and 1.3%, respectively. There were few interfering ions in the selenium determination. The proposed method was applied to the determination of selenium(IV) and (VI) in natural water samples.     

Flow injection for the determination of Se(IV) and Se(VI) by hydride generation atomic absorption spectrometry with microwave oven on-line prereduction of Se(VI) to Se(IV)

An on-line flow injection system has been developed for the selective determination of Se(IV) and Se(VI) in citric fruit juices and geothermal waters by hydride generation atomic absorption spectrometry with microwave-aided heating prereduction of Se(VI) to Se(IV). The samples and the prereductant solutions (4 mol l⁻¹ HCl for Se(IV) and 12 mol l⁻¹ HCl for Se(VI)) which circulated in a closed-flow circuit were injected by means of a time-based injector. This mixture was displaced by a carrier solution of 1% v/v of hydrochloric acid through a PTFE coil located inside the focused microwave oven and mixed downstream with a borohydride solution to generate the hydride. The linear ranges were 0–120 and 0–100 μg l⁻¹ of Se(IV) and Se(VI), respectively. The detection limits were 1.0 μg l⁻¹ for Se(IV) and 1.5 μg l⁻¹ for Se(VI). The precision (about 2.0–2.5% RSD) and recoveries (96–98% for Se(IV) and 94–98% for Se(VI)) were good. Total selenium values were also obtained by electrothermal atomic absorption spectrometry which agreed with the content of both selenium species. The sample throughput was about 50 measurements per hour. The main advantage of the method is that the selective determination of Se(IV) and Se(VI) in citric fruit juices and geothermal waters is performed in a closed system with a minimum sample manipulation, exposure to the environment, minimum sample waste and operator attention.     

Sorption characteristics and separation of tellurium ions from aqueous solutions using nano-TiO2

Titanium dioxide nanoparticles (nano-TiO₂) were employed for the sorption of Te(IV) ions from aqueous solution. A detailed study of the process was performed by varying the sorption time, pH, and temperature. The sorption was found to be fast, equilibrium was reached within 8 min. When the concentration of Te(IV) was below 40 mg L⁻¹, at least 97% of tellurium was adsorbed by nano-TiO₂ in the pH range of 1-2 and 8-9. The sorbed Te(IV) ions were desorbed with 2.0 mL of 0.5 mol L⁻¹ NaOH. The sorption data could be well interpreted by the Langmuir model with the maximum adsorption capacity of 32.75 mg g⁻¹ (20 ± 0.1 °C) of Te(IV) on nano-TiO₂. The kinetics and thermodynamics of the sorption of Te(IV) onto nano-TiO₂ were also studied. The kinetic experimental data properly correlated with the second-order kinetic model (k₂ = 0.0368 g mg⁻¹ min⁻¹, 293 K). The overall rate process appeared to be influenced by both boundary layer diffusion and intra-particle diffusion. The mean energy of adsorption was calculated to be 17.41 kJ mol⁻¹ from the Dubinin-Radushkevich (D-R) adsorption isotherm at room temperature. Moreover, the thermodynamic parameters for the sorption were estimated, and the ΔH⁰ and ΔG⁰ values indicated the exothermic and spontaneous nature of the sorption process, respectively. Finally, Nano-TiO₂ as sorbent was successfully applied to the separation of Te(IV) from the environmental samples with satisfactory results (recoveries >95%, relative standard deviations was 2.0%).     

Electron transfer reactions of nickel(III) and nickel(IV) complexes

This review narrates the electron transfer reactions of various nickel(III) and nickel(IV) complexes reported during the period 1981 until today. The reactions have been categorized mainly with respect to the type of nickel complexes. The reactivity of nickel(III) complexes of macrocycles, 2,2′-bipyridyl and 1,10-phenanthroline, peptides and oxime–imine, and of nickel(IV) complexes derived from oxime–imine, oxime and miscellaneous ligands with various organic and inorganic electron donors have been included. Kinetic and mechanistic features associated with such interactions have been duly analyzed. The relevance of Marcus cross-relation equations in the delineation of the electron transfer paths has also been critically discussed.     

Preconcentration and determination of ultra-trace amounts of U(VI) and Th(IV) using titan yellow-impregnated Amberlite XAD-7 resin

A simple and sensitive method for the determination of ultra trace amounts of U(VI) and Th(IV) ions by spectrophotometric method after solid-phase extraction on a new extractant-impregnated resin (EIR) has been reported. The new EIR was synthesised by impregnating a weakly polar polymeric adsorbent, Amberlite XAD-7, with titan yellow (TY) as extractant. The analytical method is based on the simultaneous adsorption of analyte ions in a mini-column packed with TY/XAD-7 and performing sequential elution with 0.5% (w/v) Na₂CO₃ for uranium and 2.0 M HCl for thorium. The influences of the analytical parameters including pH, salting out agent and sample volume were investigated. The interference effects of foreign ions on the retention of the analyte ions were also explored. The limits of detection for U(VI) and Th(IV) were as low as 50 and 25 ng L^?1, respectively. Relative standard deviations (n = 7) for U(VI) and Th(IV) were 3.1% and 2.9%, respectively. The method was successfully applied to the determination of ultra trace amounts of U(VI) and Th(IV) in different real matrices including industrial wastewater samples and environmental waters. The proposed method was validated using three certified reference materials and the results were in good agreement with the certified values.     

Structural studies on 3-acetyl-1,5-diaryl and 3-cyano-1,5-diaryl formazan chelates with cerium(III), thorium(IV) and uranium(VI)

Summary Solid complexes of 3-acetyl-1,5-diaryl and 3-cyano-1,5-diaryl formazans were prepared and characterized by elemental analysis, IR, NMR, TGA and DTA analyses. Based on these studies, the suggested general formula for the complexes is [M(HL) _m (OH^–) _n or (NO ₃ ^– or Cl^–) _x ·(H₂O) _y or (C₂H₅OH orDMSO) _z , where HL=formazanM=Ce³⁺, Th⁴⁺, and UO ₂ ²⁺ ,m=1–2,n=0–3,x=0–3,y=0–4 andz=0–3. The metal ions are expected to have coordination numbers 6–8.

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Strukturuntersuchungen an 3-Acetyl-1,5-diaryl- und 3-Cyan-1,5-diaryl-formazan-Chelaten mit Cer(III), Thorium(IV) und Uran(VI)

Zusammenfassung Die hergestellten Chelate wurden mittels Elementaranalyse, IR, NMR, TGA und DTA charakterisiert. Darauf basierend wird die generelle Formel [M(HL) _m (OH^–) _n bzw. (NO ₃ ^– oder Cl^–) _x ·(H₂O) _y oder (C₂H₅OH bzw.DMSO) _z ] vorgeschlagen, wobei HL=Formazan,M=Ce³⁺, Th⁴⁺ oder UO ₂ ²⁺ ,m=1–2,n=0–3,x=0–3,y=0–4 undz=0–3. Die Metallionen haben Koordinationszahlen von 6–8.

     

A novel extractant-impregnated resin containing carminic acid for selective separation and pre-concentration of uranium(VI) and thorium(IV)

The present work proposes the use of a novel extractant-impregnated resin (EIR) as an adsorbent in trace separation and pre-concentration of U(VI) and Th(IV) ions. The new EIR was prepared by impregnating carminic acid onto Amberlite XAD-16 resin beads. The morphology of new EIR was studied by BET surface area measurements and SEM micrographs. A column packed with CA/XAD-16 was used for selective separation and pre-concentration of the metal ions. Maximum adsorption of Th(IV) and U(VI) ions occurred at pHs of 3.50–5.75 and 3.75–6.50, respectively. The adsorbed metals could be eluted sequentially using 0.55?mol?L^?1 HCl for U(VI) and 2.25?mol?L^?1 HCl for Th(IV). The dynamic capacity of EIR was found to be 0.832 and 0.814?mmol?g^?1 for Th(IV) and U(VI), respectively. The tolerance limit of some foreign ions was also studied. The proposed method showed a good performance in analyzing geological reference materials and a synthetic seawater sample. Furthermore, the above procedure was successfully employed for the analysis of natural water samples.     

Oxidation of glyoxylic acid by a mononuclear manganese(IV) complex of 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane: A kinetics and mechanistic study

The oxidation of glyoxylic acid (HGl) by Mn^IVL {L⁴⁻ = tetra deprotonated 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane} was investigated in the pH range 1.67-10.18, at 25-45 °C and 0.5 M ionic strength. The reaction exhibited biphasic kinetics with Mn^IIIL⁻ as the reactive intermediate. Mn^IV was reduced to Mn^II. The products of oxidation of HGl were identified as formic acid and CO₂ in acidic medium, and oxalate in basic medium, consistent with the stoichiometry: −Δ[Mn^IV]/−Δ[HGl] = 1. In acidic medium, both Mn^IVL and Mn^IIIL⁻ formed outer-sphere adducts with the neutral HGl {HC(OH)₂COOH} molecule, with an association constant Q_av of 28 and 70 M⁻¹, respectively. A similar adduct formation was not observed for the glyoxylate mono anion {Gl⁻, CH(OH)₂(CO₂⁻)} and glyoxylate dianion {Gl²⁻, CH(OH)(O⁻)CO₂⁻}. The rate and activation parameters for the various paths are reported and an outer-sphere electron transfer mechanism is suggested.     

Reactivity investigations of some chosen peroxo-vanadium(V), manganese(III) and chromium(VI) compounds

An interpretative account of the results of reactions in aqueous medium of a highly peroxygenated vanadium(V) complex, K [V(O_{2 3}]·3H₂O, with different organic and inorganic substrates is presented. The reactions were monitored by solution EPR spectroscopy and isolation of products at different stages of the reactions. Redox reactions between diperoxide, K[VO(O₂)₂(H₂O)] and VOSO₄ were conducted. The results of the investigation suggest that secondary oxygen exchange-reaction occurs which not only depends on but also utilises the intermediates in the primary reaction during diperoxovanadate-dependent oxidation of VOSO₄. In an interesting reactiontris(acetylacetonato)-manganese(III), Mn(acac)₃, on being reacted with a hydrogen peroxide adduct, KF·H₂O₂, and bpy and phen afforded crystalline [Mn(acac)₂(bpy)] and [Mn(acac)₂(phen)], respectively. The X-ray structural analysis of [Mn(acac)₂(phen)] showed that the compound crystallised in orthorhombic space groupPbcn. The structure consists of a pseudooctahedral Mn(II) ion being bound to two acac⁻(C₅H₅O ₂ ⁻ ) and a phen ligand with the molecule lying on two-fold axis. Reactivity profiles of two new chromium(VI) reagents viz., pyridinium fluorochromate, C₅H₅NH[CrO₃F] (PFC), and quinolinium fluorochromate C₉H₇NH [CrO₃F] (QFC), have been presented. The compounds are capable of acting as both electron-transfer and oxygen-atom-transfer agents. The X-ray analysis of PFC crystals reveals that the compound crystallises in the orthorhombic space group CmcZ₁. The structure consists of discrete pyridinium cations and CrO₃ F anions with no significant hydrogen bonding. This results in total disorder of the pyridinium cation. The tetrahedral [CrO₃ F]⁻ ion lies on a crystallographic mirror plane.     

Convenient and efficient stereoselective synthesis of (2Z)-2-(chloromethyl)alk-2-enoates using iron(III) or indium(III) chloride

The stereoselective synthesis of (2Z)-2-(chloromethyl)alk-2-enoates has been achieved efficiently and in high yields and in short reaction times from Baylis-Hillman adducts, 3-hydroxy-2-methylene-alkanoates, by treatment with FeCl₃ or InCl₃ at room temperature.     

A highly efficient stereoselective synthesis of (Z)- and (E)-allyl iodides from Baylis-Hillman adducts

A highly efficient synthesis of (Z)- and (E)-allyl iodides has been accomplished by treatment of Baylis-Hillman adducts with iodine and triphenylphosphine in methylene chloride at room temperature. The method is associated with mild reaction conditions, high yields and excellent stereoselectivity.     

Solid phase extraction and preconcentration of uranium(VI) and thorium(IV) on Duolite XAD761 prior to their inductively coupled plasma mass spectrometric determination

A simple and effective method is presented for the separation and preconcentration of thorium(IV) and uranium(VI) by solid phase extraction on Duolite XAD761 adsorption resin. Thorium(IV) and uranium(VI) 9-phenyl-3-fluorone chelates are formed and adsorbed onto the Duolite XAD761. Thorium(IV) and uranium(VI) are quantitatively eluted with 2 mol L⁻¹ HCl and determined by inductively coupled plasma-mass spectrometry (ICP-MS). The influences of analytical parameters including pH, amount of reagents, amount of Duolite XAD761 and sample volume, etc. were investigated on the recovery of analyte ions. The interference of a large number of anions and cations has been studied and the optimized conditions developed have been utilized for the trace determination of uranium and thorium. A preconcentration factor of 30 for uranium and thorium was achieved. The relative standard deviation (N = 10) was 2.3% for uranium and 4.5% for thorium ions for 10 replicate determinations in the solution containing 0.5 μg of uranium and thorium. The three sigma detection limits (N = 15) for thorium(IV) and uranium(VI) ions were found to be 4.5 and 6.3 ng L⁻¹, respectively. The developed solid phase extraction method was successively utilized for the determination of traces thorium(IV) and uranium(VI) in environmental samples by ICP-MS.     

二羟基二过碘酸合镍(IV)氧化氨基丙酸的动力学

在碱性介质中研究了二羟基二过碘酸合镍（Ⅳ）配离子（DDN）氧化α－氨基丙酸的动力学，结果表明，反应对DDN为一级，对α－氨基丙酸为正分数级，准一级速率常数，k_(obs)，随［OH~－］增加而增加，随［IO~-_4］增加而减小，无盐效应也未检出自由基1/k_(obs)对［IO~-_4］有直线关系，表明二羟基一过碘酸合镍（Ⅳ）（DMN）是氧化剂的活性物种，据此很出了一个包括DDN与DMN存在前期平衡和内层一步双电子转移的反应机理．导出的速率方程园满地解释了全部实验现象，并且计算出速控步聚的速率常数，前期平衡常数和活化参数．