Nonisothermal decomposition kinetics of chromium–polyacrylate complexes prepared from aged Cr(III) solutions

Thermogravimetric studies of poly(acrylic acid) (PAA) and its chromium–polyacrylate complexes prepared from Cr(III) solutions aged for different times were undertaken. Six kinetic methods were used to investigate the thermal decomposition behavior of these materials. The applied methods were the Coats–Redfern, Horowitz–Metzger, MacCallum–Tanner, van Krevelen, Madhusudanan–Krishnan–Ninan, and Criado methods. The activation energy values obtained with the Coats–Redfern, Horowitz–Metzger, and MacCallum–Tanner methods were in good agreement with one another, and those obtained with the van Krevelen and Madhusudanan–Krishnan–Ninan methods were found to be 10–20 kJ/mol larger. The apparent activation energies increased for the complexes prepared from Cr(III) solutions aged for longer times. An analysis of the experimental results suggested that the actual decomposition mechanisms of PAA and the metal–polymer complexes were a D_n deceleration type. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Studies on interaction of Cr(III) polypyridyl complexes with DNA

Two chromium(III) complexes containing derivatives of 1,10-phenanthroline were synthesized and characterized using different spectroscopic methods. The interaction of the synthesized complexes with DNA was performed. From the absorption titration data, the binding constant for the complexes [Cr(imiphen)₂Cl₂]⁺ (1) and [Cr(furphen)₂Cl₂]⁺ (2) with DNA were found to be 5.69 ± 0.3 × 10⁴ M^− 1 for 1 and 3.7 ± 0.2 × 10⁴ M^− 1 for 2, respectively. The viscosity studies show that both the complexes bind to DNA in a partial intercalative mode. The results of competitive binding assay reveal that both complexes displace EB from DNA marginally. Gel electrophoresis data show that both the complexes 1 and 2 requires co-reagent to induce DNA cleavage but complex 2 exhibit better nuclease activity compared to complex 1. The results from this study describe the role of ligand structure in the binding and cleavage of DNA as furan based ligand exhibit better cleaving ability compared to imidazole moiety.     

Microwave-assisted urea-modified sorghum biomass for Cr (III) elimination from aqueous solutions

The present study concentrated on the use of an agro-waste biodegradable sorghum biomass in its simple and modified forms for the binding of Cr (III) ions. A relatively new method of modification was adopted using urea under microwave irradiation. FTIR analysis showed the presence of oxygen and nitrogen bearing functional groups in unmodified (UMS) and modified (MS) sorghum biomass. The appearance of new bands and shifts in the peaks confirmed the modification. The influence of different process parameters such as the adsorbent dose, solution pH, contact time, agitation speed and initial metal ion concentration was studied thoroughly to evaluate optimum conditions for adsorption. Maximum adsorption for Cr (III) ions occurred at pH 5.0–6.0 using UMS and MS. Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models in a non-linear fashion were used to explain the phenomenon. Maximum adsorption capacity was 7.03 and 16.36 mg of Cr (III) per gram of UMS and MS, respectively. Adsorption mechanism was explored by pseudo-first- and pseudo-second-order kinetic models, and it was found that the process followed pseudo-second-order kinetics. Thermodynamic study indicated the process favorability. The study concluded that urea modification under microwave irradiation produces a non-toxic and more effective adsorbent for Cr (III) remediation by inducing new nitrogen bearing functional groups to sorghum biomass.     

Rapid Solvent Extraction of Indium(III) and Its Separation from Gallium(III) and Aluminum(III)

Abstract

Mesityl oxide (4-methyl-3-pentene-2-one) has been used extensively for the solvent extraction separation of several transition elements (l). In the present communication, solvent extraction behavior of indium (III) toward mesityl oxide as a function of HCl or HBr concentrations has been studied and a simple and rapid method for the solvent extraction separation of gallium, indium, and aluminum has been proposed.     

Kinetics and mechanism of chromium electrodeposition from formate and oxalate solutions of Cr(III) compounds

Kinetics of multistep reaction of Cr(III) ions discharge to metal was studied on a stationary electrode and on a rotating disk electrode from the solutions containing formic acid or oxalic acid. The electroreduction of Cr(III) complex ions in aqueous solutions is shown to proceed via the formation of relatively stable intermediates—Cr(II) compounds which are partially removed into bulk solution. The effect of pH, organic ligand concentration and disk rotation velocity on the partial current density of chromium electroplating was demonstrated. The kinetic equations of the studied process were derived and compared with the experimental data. Kinetic parameters for the discharge of Cr(II) ions were calculated. The mechanism of chromium electrodeposition reaction was proposed. The electrodeposition of chromium from formate bath is suggested to proceed with the participation of hydroxocomplexes of bivalent chromium. The oxalate complexes of bivalent chromium directly discharge in the electrolytes containing oxalic acid. The partial polarization curves of chromium electrodeposition exhibit a current peak which may be caused by blocking the electrode surface with poorly soluble Cr(III) hydroxide.     

Interactions of Cr(VI) and Cr(III) with isolated rat liver mitochondria

The mechanism of interaction of Cr(VI) with isolated rat liver mitochondria was investigated in this study. The results suggest that Cr(VI) induces the opening of the membrane permeability transition pore (MPT). The phenomenon is cyclosporine-sensitive and is in agreement with the cyclosporine-sensitive apoptosis observed in the cells incubated with this compound. Moreover the action of Cr(III), that is formed in the cells by a reduction of Cr(VI), has been also analysed. The results obtained demonstrated that the Cr(III) does not induce the opening of the MPT in isolated mitochondria, but it has a protective effect in preventing Cr(VI) MPT opening. Therefore, these results suggest that apoptosis is regulated by a balance between Cr(VI) accumulation in the cytoplasm and Cr(III) formation.     

Gallium(III) and indium(III) complexes of cross-bridged tetraamine ligands

Gallium(III) and indium(III) complexes of cross-bridged cyclam and cyclen tetraaza macrocyclic ligands have been prepared and structurally characterized. In the crystalline state, both the GaCl₃ (cross-bridged cyclam) and InBr₃ (cross-bridged cyclen) complexes feature hexacoordinate cations in cis-folded tetradentate ligand clefts with ancillary cis-dihalides. These represent the first well-characterized gallium and indium halide complexes of tetraazamacrocycles.     

Complexation of Ho(III) with tetraalkyl-diglycolamide in aqueous solutions and a solid state compared in organic solutions of solvent extraction

The complexation of Ho(III) with tetramethyl-diglycolamide (TMDGA) and N,N′-dimethyl-N,N′-dioctyl-diglycolamide (DMDODGA) were investigated with spectrophotometry and X-ray crystallography. Single crystals of a solid compound HoL₃(ClO₄)₃ (L = TMDGA) were grown from aqueous solutions by slow evaporation. The crystal structure of HoL₃(ClO₄)₃ shows that in the solid compound Ho(III) is coordinated by nine oxygen atoms from three tridentate TMDGA molecules in a distorted tricapped trigonal prism (TCTP) geometry. In aqueous solution, three successive complex species, HoL^3 +, HoL₂^3 +, and HoL₃^3 + (L = TMDGA) were identified and their stability constants were determined to be 2.20 ± 0.09, 4.48 ± 0.18, 5.88 ± 0.18, respectively, with spectral titration method at 25 °C and 1 M ionic strength (1 M NaNO₃). The UV–Vis absorption/reflection spectra of the 1:3 species HoL₃^3 + (L = TMDGA) in aqueous solution/solid state HoL₃(ClO₄)₃ compound were very well comparable to the absorption spectra of the extracted samples of Ho(III) with DMDODGA in various organic solvents in solvent extraction. The similarity in the spectra suggest that Ho(III) in the extracted samples is also coordinated by three tridentate DMDODGA with similar coordination geometry as that in HoL₃^3 + (L = TMDGA) in aqueous solution/solid HoL₃(ClO₄)₃ compound. In the organic phase of solvent extraction with DMDODGA as extractant, the nitrate anions do not directly bond to Ho(III) in the extracted complex but just act as far away counter-ion to neutralize the positive charge of HoL₃^3 + (L = DMDODGA), and the diluents do not have much influence on the formation of the extracted Ho(III)-DMDODGA complex.     

Electrometric study of La(III), Ce(III), Pr(III) and Sm(III) complexes of n-glycylglycine

Saxena and co-workers have made extensive study on the complexing tendencies of several thiols and some of the aminoacids with various metals[1–4]. This paper reports the determination of composition and stabilities of La(III), Ce(III), Pr(III) and Sm(III) complexes of N-Glycylglycine at 30° C and 40° C by applying potentiometric and conductometric titration techniques and also the values of ΔG, ΔH and ΔS at 30° C accompanying the complexation reactions. There is however, no reference in the literature on the study of the present system.     

Bulk solvent-free ring-opening copolymerization of CHO and MA catalyzed by series of Cr(III) asymmetrical bis-Schiff-base complexes

Using each of the Cr(III) asymmetrical bis-Schiff-base complexes with different substituents as the catalyst, bulk solvent-free copolymerization of CHO (cyclohexene oxide) and MA (maleic anhydride) is efficiently realized, where besides high catalytic activity and polymeric chain-growth owe to the introduction of substituent ortho and/or para to the phenoxide group, low catalyst concentration is helpful for the formation of perfectly alternating polyester.     

New bis-o-iminosemiquinonate aluminium(III) complexes

The first aluminium(III) complexes based on sterically hindered 4,6-di-tert-butyl-N-(2,6-di-iso-propyl-phenyl)-o-iminobenzoquinone (imQ) of general formula imSQ₂AlR (where imSQ — is a radical anion of imQ, R = I (1), NCS (2) and N₃ (3)) were synthesized. Compounds 1–3 demonstrate biradical X-band EPR spectra in frozen toluene matrix. The crystalline samples of 1–3 were characterized using magnetic susceptibility measurements. The antiferromagnetic coupling between spins of o-iminosemiquinonate radicals in 1–3 is predominant and, as the result, the singlet ground state for pentacoordinated biradical compounds is observed. The molecular structures of all the complexes obtained have been established by the single crystal X-ray analysis.     

Optical properties of PMMA doped with erbium(III) and ytterbium(III) complexes

In this article, we report the fabrication and optical/spectroscopic properties of polymethylmethacrylate (PMMA) doped with rare earth (RE) (Er³⁺ and Er³⁺/Yb³⁺) ions. Infrared spectroscopy revealed only very weak O? H stretching vibration peaks in the samples, which is important if satisfactory photoluminescence is to be observed at 1530 nm. Measurement of transmission spectra in the wavelength ranges from 300 to 700 nm for Er³⁺‐doped samples and from 900 to 1050 nm for Yb³⁺‐doped samples enabled us to observe the ⁴G_11/2 (377 nm) and ²H_11/2 (519 nm) transmission bands typical for Er³⁺‐doped samples, as well as the ²F_5/2 (975 nm) band typical for Yb³⁺‐doped samples. Under excitation at 980 nm, at room temperature, the characteristic Er³⁺ emission at 1530 nm was also observed with improving trend when the higher RE concentrations were applied. The results indicate that the PMMA reveals very low tendency to the RE clustering, which together with low cost and easy fabrication make it a material with a great potential in the active photonics devices. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

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.     

Simultaneous recovery of Cr(III) and Cr(VI) from the aqueous phase with ion-exchange membranes

The simultaneous recovery of trivalent and tetravalent chromium ions through charged ion-exchange membranes by using three detachable cells was tested at different current densities. The effect of mono- and divalent valence ions corresponding to trivalent and hexavalent chromium ions in the feed phase was investigated. The recovery factor values of chromium (III) and (VI) ion without current density were obtained and found that it was higher in the absence of binary monovalent and divalent ions, but increased with increasing current density and decreased in the presence of the binary mono- and divalent ions. The transport of both oxidation states of chromium ions through membranes was also correlated with the flux data.     

Cr(III) oxidation with lead dioxide-based anodes

A procedure for preparing PbO₂-based electrodes with a titanium substrate is proposed. A platinum underlayer is first deposited on Ti by metal organic chemical vapor deposition (MOCVD), followed by the electrodeposition of the PbO₂ layer. The prepared Ti/Pt/PbO₂ anodes were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) before being used for oxidation of Cr(III) in sulphuric acid. The current efficiency was determined for that electrodes and the results were compared with those obtained with Pb/PbO₂ and Ebonex^®/PbO₂ electrodes with different pH conditions. The Ti/Pt/PbO₂ were found to have a very good electrochemical behaviour (current efficiency: φ=0.93 for pH 2), and may be used as dimensionally stable anodes for the oxidation of Cr(III).     

Solvent extraction kinetics of Sm(Ⅲ),Eu(Ⅲ) and Gd(Ⅲ) with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester

Solvent extraction kinetics of Sm(Ⅲ), Eu(Ⅲ) and Gd(Ⅲ) from hydrochloric acid have been focused on using2-ethylhexyl phosphoric acid-2-ethylhexyl ester(P507) with Anordning for Kontinuerlig Undersokning av Fordelningsfaktore vid Vatske Extraction(AKUFVE). Compared with the conventional set-up, some advantages emerge obviously, for example, fast phase separation, easy operation and convenience of kinetic data acquisition.First of all, the extraction mechanism was discussed based on the dimeric model of P507. Secondly, the effects of stirring speed were investigated and 420 r·min~(-1) was determined of the following experiments. The effects of pH, concentration of rare earth elements(REEs) and P507 on the extraction rate were analyzed. The results indicated that the extraction mechanism changed with the increasing concentration of P507. Then, the experiments with different temperature were carried out. It turned out that the values of apparent activation energy(E_a) for Sm(Ⅲ), Eu(Ⅲ) and Gd(Ⅲ) extracted by P507 were 26.80 kJ·mol~(-1), 13.40 kJ·mol~(-1) and11.10 kJ·mol~(-1) respectively, the resistance of the entire process was limited by diffusion or both of diffusion and reaction. Finally, the correlation equations were obtained, and the theoretical results fit with the experimental data well, most relative error was within ±30%.     

Solvent Extraction and Separation of Gallium(III) using Hexaacetato Calix(6)Arene

Gallium(III) was extracted at pH 3.5 by equilibrating eight min with 10 mL of 0.0001 M acetyl derivative of calix(6)arene in xylene. Gallium(III) was stripped quantitatively with 0.1 N hydrochloric acid and determined spectrophotometrically with 0.01% PAR at 510 nm. The nature of the extracted species was determined from the log-log plots and its stoichiometry was confirmed by numerical treatment to experimental data. The IR analysis of Ga(III) loaded organic phase was also studied. The conformational change of reagent during complex formation was studied from the ¹H NMR treatment. The temperature dependence of the extraction equilibrium and metal loading capacity of the reagent was also evaluated. The proposed method was successfully applied for the extraction and separation of multicomponent mixtures, synthetic mixtures, and binary and ternary separation of gallium from the associated elements. The results obtained were reproducible and accurate.     

Modulated Cr(III) oxidation in KOH solutions at a gold electrode: Competition between disproportionation and stepwise electron transfer

The electrochemical oxidation of aqueous Cr(III) was examined using cyclic voltammetry with a polycrystalline Au electrode in KOH solutions of varying pH and Cr(III) concentration. The mechanism and kinetics for the oxidation of Cr(III) is a quasi-reversible diffusion-controlled reaction and is largely dependent on the solution pH. The reaction mechanism is initiated by an irreversible electrochemical electron transfer to form Cr(IV) which is the rate-determining step (RDS). Following the RDS, subsequent oxidation of Cr to its hexavalent state occurs by the disproportionation of Cr(IV) at low KOH concentrations and electron transfer at high KOH concentrations due to the involvement of OH⁻ in the disproportionation reaction. As the solution pH increases, the Cr(III) oxidation peak potential shifts negatively owing to the involvement of OH⁻ in the RDS. The competitive adsorption of OH⁻ and CrO₂⁻ on the electrode surface also plays an important role in the oxidation behavior.