Adsorption and thermodynamic characteristics of Hg(II)-SCN complex onto polyurethane foam

The sorption of Hg(II) in the presence of sodium thiocyanate solution onto polyurethane (PUR) foam, an excellent sorbent, has been investigated in detail. Maximum sorption of Hg(II) is achieved from 0.1 M hydrochloric acid solution containing 7.5x10(-2) M sodium thiocyanate in 5 min. The sorption data followed both Freundlich and Langmuir adsorption isotherms. The Freundlich constants 1/n and sorption capacity, C(m), are evaluated to be 0.44+/-0.02 and (3.86+/-0.89)x10(-3) mol g(-1). The saturation capacity and adsorption constant derived from Langmuir isotherm are (6.88+/-0.28)x10(-5) mol g(-1) and (5.6+/-0.37)x10(4) dm(3) mol(-1) respectively. The mean free energy (E) of Hg(II)-SCN sorption onto PUR foam computed from D-R isotherm is 12.4+/-0.3 kJ mol(-1) indicating ion-exchange type mechanism of chemisorption. The variation of sorption with temperature yields thermodynamic parameters of DeltaH=-30.7+/-1.2 kJ mol(-1), DeltaS=-70.1+/-4.1 J mol(-1) K(-1) and DeltaG=-9.86+/-0.77 kJ mol(-1) at 298 K. The negative value of enthalpy and free energy reflects the exothermic and spontaneous nature of sorption. On the basis of the sorption data, sorption mechanism has been proposed.     

Adsorption syntax of Au(III) on unloaded polyurethane foam

The nature of adsorption behavior of Au(III) on polyurethane (PUR) foam was studied in 0.2M HCl aqueous solution. The effect of shaking time and amount of adsorbent were optimized for 3.16·10⁻⁵M solution of Au(III) in 0.2M HCl. The classical Freundlich and Langmuir adsorption isotherms have been employed successfully. The Freundlich parameters 1/n and adsorption capacityK are 0.488±0.016 and (1.40±0.22)·10⁻² mol·g⁻¹, respectively. The Langmuir constants of saturation capacityM and binding energyb are (1.66±0.08)·10⁻⁴mol·g⁻¹ and 40294±2947 l·g⁻¹, respectively, indicating the monolayer chemical sorption. The mean free energy (E) of adsorption of Au(III) on PUR foam has been evaluated using D-R isotherm and found to be 11.5±0.16 kJ·mol⁻¹ reflecting the ion exchange type of chemical adsorption. The effect of temperature on the adsorption has also been studied. the isosteric heat of adsorption was found to be 44.03±1.66 kJ·mol⁻¹. The thermodynamic parameters of ΔG, ΔH, ΔS and equilibrium constantK _c have been calculated. The negative values of ΔG, ΔH and ΔS support that the adsorption of Au(III) on PUR foam is spontaneous, exothermic and of ion exchange chemisorption. The nature of the Au(III) species sorbed on PUR foam have been discussed.     

Adsorption profile and thermodynamic parameters of the preconcentration of Eu(III) on 2-thenoyltrifluoroacetone loaded polyurethane (PUR) foam

The adsorption studies of Eu(III) was investigated on 2-thenoyltrifluoroacetone (HTTA) loaded PUR foam. The adsorption conditions were optimized with respect to pH, shaking time, loading capacity and adsorbent weight. The adsorption data followed the classical Freundlich and Langmuir type isotherms successfully. The Freundlich constant (1/n) is estimated to be 0.35±0.02, reflects a surface heterogeneity of the PUR foam. Langmuir isotherm gives a saturated capacity of 0.082±0.002 mmol^.g^-1 suggests a monolayer coverage of the surface. The Dubinin-Radushkevich (D-R) isotherm is applied and the sorption mean free energy (E) is calculated and found to be 13.36±0.12 kJ^.mol^-1 suggesting that chemisorption involving chemical bonding is responsible for the adsorption process. The thermodynamic parameters such as enthalpy (H), entropy (S) and Gibbs free energy (G) were calculated and interpreted. The positive value of H indicates that the adsorption of metal ions on HTTA-loaded PUR foam is an endothermic process. A possible explanation of this endothermicity has been given. The selectivity and sensitivity of the adsorbent was also studied. The sorption of Eu(III) is greatly affected in the presence of oxalate and fluoride. The sorptive affinity of different cations towards HTTA loaded PUR foam was also discussed.     

Adsorption modeling of antimony(V) on diphenylthiocarbazone loaded polyurethane foam

The uptake behavior of Sb(V) onto diphenylthiocarbazone (H2DZ) loaded polyurethane foam (PUF) from aqueous solutions of different acids in the presence of KI have been studied. The maximum adsorption was found from 0.5N HNO₃ containing 0.2M KI. The maximum equilibrium was achieved within twenty minutes shaking time. The sorption behavior followed the Freundlich and Langmuir adsorption isotherms. The Freundlich constants 1/n and K_f are 0.57 and 3.26^.10^-2 mol^.g^-1, respectively. The Langmuir constants M and b are 2.18^.10^-4 mol^.g^-1 and 2.4^.10⁴ l^.g^-1, respectively. The value of sorption free energy (E) evaluated from D-R isotherm is 10.8 kJ^.mol^-1 indicating the ion exchange type chemisorption of Sb(V) on H2DZ loaded PUF. The thermodynamic parameters of enthalpy (H), entropy (S) and Gibbs free energy (G) have also been investigated and found to be -51.8 kJ^.mol^-1, -127.3 J^.mol^-1.deg^-1 and -13.8 kJ^.mol^-1, respectively. The negative values of (H) and (G) indicate that the sorption is exothermic and spontaneous in nature. The effect of anions and cations and sorption mechanism are discussed.     

Biotechnology of Cr(VI) transformation into Cr(III) complexes

The dose-dependent formation of Cr(III) complexes and uptake of chromium by Arthrobacter oxydans — a Gram-positive bacterium from contaminated Columbian basalt rocks (USA) — were studied along with the testing under aerobic conditions of two bacterial strains of Arthrobacter genera isolated from the polluted basalts from the Republic of Georgia. Instrumental neutron activation analysis (INAA) was used to track the accumulation of chromium in the bacterial cells. To monitor and identify Cr(III) complexes in these bacteria, electron spin resonance (ESR) spectrometry was employed.     

Photoredox reactions of Cr(III) mixed-ligand complexes

Irradiation of chromium(III) complexes with oxalate and pyridinedicarboxylate ligands (pda = 2,3-, 2,4-, or 2,5-dicarboxylate) leads to diverse behaviors, dictated by light energy, presence of oxygen and the ligand nature. Irradiation within the MC bands is unaffected by O₂ and results in ligand substitution. The LMCT excitation is effective only when oxalate is coordinated to Cr(III); then electron transfer from oxalate to central ion generates an intermediate, consisted of a Cr(II)species and the C₂O₄^? radicals. The species undergo fast redox reactions dependent on the presence of O₂ and the pda ligand.(1) In anoxic medium the fast outersphere electron transfer from Cr(II) to solvent, generates hydrated electrons and re-oxidizes the chromium centre to Cr^III. Then geminate recombination regenerates substrate, whereas competitive release of the C₂O₄^? radical leads to substitution of one oxalate ligand by two water molecules (aquation induced by the LMCT excitation). In the presence of the pda ligand the outersphere electron transfer is accompanied by the innersphere CT, generating Cr(III) coordinated to two radical ligands: C₂O₄^? and pda^3?; the intermediate releases also e_aq^?, but this reaction is slower than that of the homoleptic oxalate complex. Hydrated electrons are scavenged also by the released radicals. All these processes are completed within microseconds and in consequence, the Cr(III) complexes irradiated in deoxygenated solutions are insensitive to subsequent oxygenation.(2) When UV-irradiation is carried out in oxygenated medium reaction of Cr(II) species with molecular oxygen competes with the outer- or inner electron transfer observed in anoxic medium. Both these pathways result in generation of chromate(VI). Quantum yield of the Cr(VI) production is sensitive to the presence and structure of pda ligand, decreasing within the series 2,3-pda > 2,4-pda > 2,5-pda.     

Mutual separation of Co(II), Fe(III), Eu(III) and Tb(III) on HTTA-loaded polyurethane foam

The selectivity of the 2-thenoyltrifluoroacetone (HTTA) loaded polyurethane (PUR) foam as adsorbent was studied. The influence of various anions on the adsorption indicated that permanganate, oxalate, EDTA, and citrate formed strong complexes with the metal ions and masked completely, while phosphate, thiosulphate, cyanide, ascorbate, tartrate and fluoride hindered the sorption of Fe(III). The sorption of Co(II) is also prohibited in presence of anions like cyanide, ascorbate and tartrate. The sorption of Eu(III) and Tb(III) is greatly affected in the presence of phosphate and fluoride. A group separation of different metals has been proposed on the basis of selectivity of the foam.     

Thermal decomposition of dinitrogen complexes of Cr(III)

The thermal behaviour of two dinitrogen complexes of chromium with EDTA and CDTA have been studied using DTA and TG. IR spectroscopy is used for the characterization of intermediate products. The loss of dinitrogen occurs at 240°C in both cases.     

Photochemistry and photophysics of Cr(III) macrocyclic complexes

The phosphorescence and photochemical behavior of the macrocyclic complexes (1,4,7,10,13,16-hexaazacyclooctadecane)chromium(III) (Cr([18]-aneN(6))(3+); 1) and (4,4',4'-ethylidynetris(3-azabutan-1-amine)) chromium(III) (Cr(sen)(3+); 2) have been compared to each other and to the complex Cr(en)(3)(3+). For both macrocyclic complexes, phosphorescence from room temperature aqueous solutions is too weak to be observed, contrasting with Cr(en)(3)(3+), though both had somewhat longer 77 K lifetimes than Cr(en)(3)(3+). Phosphorescence lifetimes for these macrocyclics decreased with increasing temperature much faster than for Cr(en)(3)(3+) and a conventional extrapolation based on a fit of reciprocal lifetimes (corrected for the low-temperature contribution) to the Arrhenius equation gave estimated room temperature phosphorescence lifetimes of a few nanoseconds, consistent with the failure to observe room temperature emission. Fitting of the nonlinearity of the data seen in these plots suggested that two high-temperature processes were occurring with estimated activation parameters (E in kJ mol(-1) and A in s(-1)) for Cr([18]-aneN(6))(3+): E(1) = 40, A(1) = 1 x 10(16); E(2) = 24, A(2) = 1 x 10(14): Cr(sen)(3+); E(1) = 45, A(1) = 2 x 10(15); E(2) = 29, A(2) = 7 x 10(11). Cr([18]-aneN(6))(3+) was photochemically inert on irradiation. On irradiation into the lowest quartet ligand field absorption band, Cr(sen)(3+) photolyzes with a quantum yield of 0.098 +/- 0.001 at room temperature. Laser flash photolysis with conductivity detection showed that this photoreaction occurred faster than protonation of the liberated amine ligand at all practical proton concentrations. The quantum yield for irradiation directly into the doublet absorption band of Cr(sen)(3+) was 0.077 +/- 0.003. Photoaquation of Delta-Cr(sen)(3+) led to loss of optical activity and product analysis by capillary electrophoresis showed that both racemic and Delta-Cr(sen)(3+) photoaquate to a single main product, trans-Cr(sen-NH)(H(2)O)(4+). The product stereochemistry is shown to be consistent with predictions based on the angular overlap model for Cr(III) photochemistry, recognizing the additional constraints imposed by the ligand. The abnormally short room temperature solution lifetime of the doublet state is a result of a radiation-less process that competes with other processes depleting the doublet state. However, this doublet-state deactivation process does not lead to photoaquation but competes with BISC and photoaquation via the quartet state, resulting in an unprecedented reduction in photoaquation quantum yield on direct irradiation into the doublet state.     

The thermal decomposition of some Cr(III) complexes

The thermal decomposition reactions of the following chromium(III) complexes were investigated: Cr(CH₃COO)₃·2 H₂O, [C_r3O(CH₃COO)₆(H₂O)₃]Cl·2 H₂O and [Cr₃O(CH₂ClCOO)₆(H₂O)₃]Cl·6H₂O. Simultaneous TG/DTG/DTA were applied nonisothermal conditions. From the recorded curves, the activation energiesE _a were calculated for all the thermal decomposition steps. Appropriate chemical reactions were attributed to the thermal effects, with consideration to the X-ray diffraction and IR spectra results.

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Zusammenfassung Für die Untersuchung der thermischen Zersetzungsreaktion der Chrom(III)-Komplexe Cr(CH₃COO)₃·2H₂O [C_r3O(CH₃COO)₆·(H₂O)₃]Cl2H₂O und [C_r3O(CH₂ClCOO)₆·(H₂O)₃]C₁₆H₂O wurde simultane TG/DTG/DTA unter nichtisothermen Bedingungen eingesetzt. Ausgehend von den aufgezeichneten Kurven wurden für alle Schritte der Zersetzungsreaktion die E_a-Werte berechnet. In Übereinstimmung mit röntgenographischen und IR-spektroskopischen Ergebnissen wurden den thermischen Effekten passende chemische Reaktionen zugeordnet.

     

Adsorption Studies of Cr(III) & Cr(VI) on Lead Sulphide,Copper Sulphide & Zinc Sulphide-Determination Cr(III) in the Presence of Cr(VI)

Abstract

The adsorption studies of Cr(VI) in presence of Cr(III) on the sulphide of Lead, Zinc and Copper has been studied. It has been found that in case of lead sulphide 100% adsorption of Cr(VI) took place at pH 4.0 and of Cr(III) at pH 7.0. While in case of zinc sulphide the 100% adsorption of Cr(VI) took place at pH 4.5 and of Cr(III) at pH 6.5. In case of copper sulphide 100% adsorption of Cr(VI) took place at pH 5.0 and of Cr(III) at pH 7.0. This difference in adsorption at different pH values forms the basis for the determination of these ions. The method is accurate.     

Kinetics and thermodynamic aspect of the adsorption of Fe(III) on HTTA-imbedded polyurethane foam

The batch kinetics of Fe(III) adsorption on HTTA-loaded polyurethane (PU) foam have been investigated. The rate of controlling the adsorption is found to be intraparticle diffusion. The reaction rate of adsorption and desorption was also evaluated and found to increase and decrease with temperature, respectively. This indicates an endothermic adsorption behavior of Fe(III) on HTTA loaded PU foam. The activation energy of adsorption (80±10 kJ·mol^–1) and of desorption (–45±±2 kJ· mol^–1) indicates the chemical adsorption rather than physical adsorption. The isosteric heat of adsorption (H _ads) was found to be –82.7±5.05 kJ·mol^–1. This shows the formation of new chemical bonds among Fe(III)-HTTA-PU foam. The thermodynamic parameters of G, H and S, and equilibrium constantK _c have been calculated. These functions further support that the process of adsorption of Fe(III) on HTTA-loaded PU foam is endothermic and chemisorption, stabilized through thermodynamic functions.     

Redox reactions of V(III) and Cr(III)picolinate complexes in aqueous solutions

Reactions of e_aq⁻, H-atoms, OH, (CH₃)₂COH, and CO₂⁻ radicals with V(III)picolinate and Cr(III)picolinate have been studied by the pulse radiolysis technique. The spectra of V(II)picolinate, V(IV)picolinate, Cr(II)picolinate, OH adduct of Cr(III)picolinate and Cr(IV)picolinate have been obtained and the rate constants of the reactions of various radicals with V(III) and Cr(III)picolinate have been determined. The implications of these results to the chemical decontamination of nuclear reactor systems are discussed.     

Optimization of the Conditions for the Cr (III) Adsorption on Activated Carbon

In order to understand the patterns of the adsorption equilibrium of Cr (III) on activated carbon, the adsorption process was studied by two different ways: classical batch experiments on commercial Norit and Merck activated carbons and their oxidized forms in a wide range of pHs; and extended time-based tests at the same pH values on the same adsorbents. This approach allowed us to understand the role of texture, chemical carbon surface functionality and experimental conditions (initial pH of the solution, contact time and adsorbate/adsorbent ratio) on the effectiveness of Cr (III) removal. The adsorption process of Cr (III) at (24 ± 1^∘C) on Merck and Norit activated carbons and their oxidized forms were studied at pH values between 1.5 and 5 (either adjusted or buffered). Chromium concentration was fixed at 200 ppm. The carbon loading ranged from 1.2 to 20 g/l. The carbon/Cr (III) solution contact time was varied from 0.5–1 month to 5 months, to ensure that the saturation of the carbon level was reached. According to the data obtained, the presence of carboxylic groups on carbon surface seems to enhance Cr (III) uptake at initial pH of the solution in the range between 2 and 4. Depending on the nature of the adsorbent surface chemistry, the contact time to reach equilibrium may range from 3 to 5 months. There is an optimum carbon loading which limits the Cr (III) uptake/removal at given pH value. In order to understand the adsorption process, an ion exchange, surface complex and surface precipitation were considered. This paper was presented in the 5th Brazilian Meeting on Adsorption, held at Natal, Brazil, 18-21 July, 2004.     

Studies on Cr(III) complexes with glycilglycine in the solid state

Two isomers of the trinuclear Cr(III) complex with glycilglycine have been separated in the solid state. Their properties have been examined by spectroscopic, EPR, and magnetic methods, and the structures of these compounds are suggested.     

The synthesis of organo-imido complexes of Cr(IV) and Fe(III)

The reaction of p-tolylazide with (5,10,15,20- tetraphenylporphyrinato) chromium(II) (Cr(TPP)) yields the high spin chromium(IV) organo-imido complex, CH₃C₆H₄N=Cr(TPP). N,N′-ethylene- bis-(salicylideneiminato)iron(II), (Fe(salen)), however reacts with arylazides to produce iron(III) organo-imido-bridged compounds of general formula, [Fe(salen)]₂NR showing magnetic coupling between the Fe(III) centres.     

Adsorption of Cr(III) from wastewater by wine processing waste sludge

Wine processing waste sludge has been shown to be an effective adsorbent for the adsorption of Cr(III) from aqueous solution. The sludge has been characterized by scanning electron microscopy (SEM) and energy dispersive X-rays (EDX). The effect of pH, initial concentration of Cr(III), sludge particle size, and temperature on the adsorption studied. The equilibrium data could be described well by the Langmuir and Freundlich isotherm equations. A separation factor was used to judge the favorable adsorption. The calculated thermodynamic parameters, deltaH0 and deltaS0, are 1.95 kJ/mol and 27.16 J/molK, respectively. The deltaG0 values range from -5.98 to -6.79 J/mol, which shows the physical adsorption properties of the sludge. Adsorption dynamics had been successfully studied by the Lagergren model and an intraparticle diffusion model.     

Thermal decomposition of Cr(III) complexes with urea and thiourea

The thermal decompositions of Cr(III) complexes with urea and thiourea were investigated. The courses of the decompositions were found to be anion- and ligand-dependent. Suggestions for a mechanism of decomposition of these complexes are presented. The final product of decomposition of the complexes investigated was chromium(III) oxide (Cr₂O₃).

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Zusammenfassung Die thermische Zersetzung der Komplexe von Cr(III) mit Karbamid und Thiokarbamid wurde untersucht. Der Verlauf der Zersetzung wurde für Anionen- und Liganden-abhängig gefunden. Vorstellungen über eine mechanische Zersetzung dieser Komplexe werden gegeben. Das Endprodukt der Zersetzung der untersuchten Komplexe war jeweils Chrom(III)oxid (Cr₂O₃).

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Résumé On a étudié la décomposition thermique des complexes du chrome(III) avec l'urée et la thiourée. On a trouvé que le processus de la décomposition dépend de l'anion et du ligand. On propose un mode de décomposition mécanique pour ces complexes. Le produit final de la décomposition des complexes étudiés est l'oxyde de chrome(III), Cr₂O₃.

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Cr (111) . , . . (111) (Cr₂O₃).