Kinetics of zirconium ions adsorption on activated charcoal from aqueous solutions

The batch kinetics of adsorption of the zirconium ions from aqueous solutions on activated charcoal has been investigated over a wide range of concentration of zirconium ions (1.0–5.0 g/l) and temperatures (10–50°C). The adsorption process of zirconium ions proceeds via two stages; the first stage is rather fast, followed by a much slower one. The Bangham equation was used to study the kinetics of the zirconium ions' adsorption on activated charcoal. It is observed that the diffusion of zirconium ions into the pores of the activated charcoal controls the kinetics of the adsorption process. Moreover, zirconium ion adsorption obeys the Freundlich and Langmuir isotherms in the concentration range studied. The adsorption equilibrium constant (k_c) values for zirconium ions adsorption on activated charcoal have also been calculated at different temperatures. Various thermodynamic quantities, ΔG, ΔH, and ΔS were computed from k_c values. The results showed that the adsorption of zirconium ions on activated charcoal is an endothermic process.     

Synthesis and spectroscopic studies on novel Cu(II)–Cu(II) binuclear adducts. EPR evidence for ferromagnetic interactions

EPR investigations on two solid complexes [Cu(1-amidino-O-2-methoxyethylurea)₂]₂(H₂O)₂(SO₄)₂ (1) and [Cu(1-amidino-O-2-ethoxyethylurea)₂]₂(H₂O)₂(SO₄)₂ (2) indicated the formation of ferromagnetically coupled binuclear complexes (S = 1) having the isotropic exchange interaction constant J values of 59 and 50 cm⁻¹. The angle between the Cu–Cu direction and the parallel direction (ξ) of the complex 1 has been evaluated. The IR studies suggest the presence of tetrahedral sulfate ion in the complexes. When the EPR spectra were recorded in the temperature range 300–475 K, it was observed that the triplet-state EPR signal disappeared completely and irreversibly at ca. 450 K for complex 1 and at ca. 475 K for complex 2 with the appearance of a new signal attributable to the mononuclear complex (S = 1/2).     

Oxidation of demineralized coal and coal free of pyrite examined by EPR spectroscopy

The influence of oxidation on complex paramagnetic centres system of demineralized coal and coal free of pyrite was compared. Polish orthocoking coal with a carbon content of 87.8 wt% was studied. This coal was oxidized with nitric acid (HNO₃), peroxyacetic acid (PAA) and in O₂/Na₂CO₃ system. Multi-component structure of X-band EPR spectra of the coal samples was numerically analysed. The lineshape and the parameters of the component lines: linewidths and g-factors, were determined. Concentrations of paramagnetic centres were measured. The three groups of paramagnetic centres belonging to different molecular units were found in the studied samples. They were responsible for broad Gauss (ΔB_pp: 0.49-0.84 mT), broad Lorentz 1 (ΔB_pp: 0.18-0.35 mT), and narrow Lorentz 3 (ΔB_pp: 0.04-0.08 mT) EPR lines. Properties of paramagnetic centres of the simple molecular units with broad Gauss and Lorentz 1 lines were changed during demineralization of coal and after pyrite removing from coal. g-Values of Gauss and Lorentz 1 lines increased, Lorentz 1 lines were broadened and concentrations of paramagnetic centres with Lorentz 1 lines increased. Oxidation of both demineralized coal and coal free of pyrite with nitric acid led to the highest decrease of the concentration of paramagnetic centres with Gauss lines, narrowing of these lines and increase of g-factor. The higher effects of oxidation on paramagnetic centres responsible for broad lines were observed for coal free of pyrite. Paramagnetic centres with narrow Lorentz 3 lines belonging to multi-ring aromatic units in demineralized coal and coal free of pyrite were not susceptible for oxidation.     

Adsorption of methylene blue on kaolinite

Methylene blue was adsorbed on kaolin from a local deposit. The raw kaolin itself was a relatively good adsorbent. The adsorption capacity was improved by purification and by treatment with NaOH solution. Calcination of the kaolin reduced the adsorption capacity. The adsorption data could be fitted by the Freundlich and Langmuir equations. Also, the thermodynamic parameters such as ΔH⁰, ΔS⁰ and ΔG⁰ were determined.     

Influence of surfactants on the electroreduction of oxygen to hydrogen peroxide in acid and alkaline electrolytes

The effect of surfactants on the electroreduction of O₂ to H₂O₂ was investigated by cyclic voltammetry and batch electrolysis on vitreous carbon electrodes. The electrolytes were either 0.1 M Na₂CO₃ or 0.1 M H₂SO₄ at 295 K, under 0.1 MPa O₂. Electrode kinetics and mass transport parameters showed the influence of surfactants on the O₂ electroreduction mechanism. The cationic surfactant (Aliquat 336^®, tricaprylmethylammonium chloride), at mM levels, increased the standard rate constant of O₂ electroreduction to H₂O₂ 15 times in Na₂CO₃ and 1900 times in H₂SO₄, to 1.8 × 10^–6 m s^–1 and 9.9 × 10^–10 m s^–1, respectively. This effect on the reaction rate might be due to an increase of the surface pH, induced by the Aliquat 336^® surface film. The nonionic (Triton X-100) and anionic (sodium dodecyl sulfate) surfactants retarded the O₂ electroreduction, presumably by forming surface structures, which blocked the access of O₂ to the electrode. Ten hour batch electrosynthesis experiments performed at 300 A m^–2 superficial current density, 0.1 MPa O₂, 300 K, on reticulated vitreous carbon (30 ppi), showed that compared to the values obtained in the absence of surfactant, mM concentrations of Aliquat 336^® increased the current efficiency for peroxide from 12% to 61% (0.31 M H₂O₂) in 0.1 M Na₂CO₃ and from 14% to 55% (0.26 M H₂O₂) in 0.1 M H₂SO₄, respectively.     

Adsorption of thorium(IV) on MX-80 bentonite: Effect of pH, ionic strength and temperature

The adsorption of Th(IV) on MX-80 bentonite as a function of pH, ionic strength, Th(IV) concentration and temperature was studied by using batch technique. The results indicated that the adsorption of Th(IV) on bentonite depended on pH, ionic strength and temperature. The adsorption of Th(IV) decreased with increasing temperature, indicating that the adsorption process of Th(IV) on bentonite was exothermic. The experimental data of Th(IV) adsorption isotherms were obtained at T = 293, 303, 313, and 323K, and were analyzed with the Langmuir and Freundlich models, showing that the Langmuir model fitted the adsorption data better than the Freundlich model. Thermodynamic parameters, such as ΔH^o, ΔS^o, and ΔG^o, were calculated from the slope and intercept of the linear plot of lnK_d against 1000/T.     

Quantitative in-situ EPR spectroelectrochemical studies of doping processes in poly(3,4-alkylenedioxythiophene)s: Part 1: PEDOT

Quantitative in-situ EPR spectroelectrochemical studies of poly(3,4-ethylenedioxythiophene) (PEDOT) have been carried out with an aim to gain new insights into the doping processes taking place in this polymer. Corroborating the findings made during previous studies of this polymer, absolute measurements conducted in this study provided new detailed information regarding some of the basic parameters characterising the doping process of this conjugated polymer. It was found that concentrations of paramagnetic centres in PEDOT vary from 0.02 spin per mer in the dedoped state up to a maximum of 0.12 spin per mer at 0.15 [e⁻/mer] doping level, corresponding to 1 spin per ca. 8.5 meric units. Such notable concentration values indicate that polarons represent a numerous charge carrier group in PEDOT, contrary to observations made for other members of polythiophene family. Furthermore polarons do not disappear at high doping levels of PEDOT but rather decrease their numbers gradually down to 0.08 spins per mer at a maximum doping level of 0.55 [e⁻/mer] attained in this study. Based on information about concentrations of spins and polymer doping charges, concentrations of bipolarons have been evaluated as a function of doping level. Results indicate that bipolaron formation starts at ca. 0.06 [e⁻/mer] doping level when spin generation efficiency begins to deviate from 1 and interspin interactions emerge as evidenced by doping level dependency of EPR signal linewidth (ΔB_pp). Decomposition of complex EPR spectra of PEDOT in its doped state corroborated the presence of two groups of paramagnetic centres in this polymer. Based upon doping level dependencies of their spectroscopic parameters (concentration, ΔB_pp linewidth and g-factor), the identity of these centres has been redefined compared to our previous reports, linking their properties with the type of polymer phase (crystalline or amorphous) they reside in.     

EPR study of solid solutions La1 ? 0.33yBa0.33yMnyAl1 ? yO3 (y = 0.02, 0.04, 0.10)

Solid solutions La_{1 − 0.33y} Ba_0.33y Mn _y Al_{1 − y} O₃ (y = 0.02, 0.04, 0.10) prepared using the ceramic technique have been investigated by the EPR method at temperatures of 77 and 300 K. By comparing with the calculated spectra, the experimental spectra have been assigned to Mn²⁺ ions (g = 2.04 and line width ΔH _pp = 64 × 10⁻⁴ T at T = 77K) and Mn⁴⁺ ions (g = 1.97 and ΔH _pp = 76 × 10⁻⁴ T at T = 77 K) and the broad line (ΔH _pp = 500 × 10⁻⁴ T at T = 77 K) has been attributed to clusters. The dilution of manganese ions as a result of the dissolution of La_0.67Ba_0.33MnO₃ in LaAlO₃ has allowed one to trace the cluster formation and the spin dynamics of Mn ions. It has been established that, at room temperature, compared to the system in which the Sr²⁺ ion with a smaller ionic radius is the replacing element, the localized states are more stable at all three manganese concentrations (the EPR lines are more intense). The La_0.67Ba_0.33MnO₃ clusters dissolved in LaAlO₃ retain some properties of a concentrated compound even upon dilution to y = 0.02.     

Adsorption of cationic dye from aqueous solutions by activated carbon

Batch sorption experiments were carried out to remove a cationic dye, methylene blue (MB), from its aqueous solutions using a commercial activated carbon as an adsorbent. Operating variables studied were pH, stirring speed, initial methylene blue concentration and temperature. Adsorption process was attained to the equilibrium within 5 min. The adsorbed amount MB dye on activated carbon slightly changed with increasing pH, and temperature, indicating an endothermic process. The adsorption capacity of methylene blue did not significantly change with increasing stirring speed. The experimental data were analyzed by various isotherm models, and found that the isotherm data were reasonably well correlated by Langmuir isotherm. Adsorption measurements showed that the process was very fast and physical in nature. Thermodynamic parameters such as the adsorption entropy (ΔS^o) and adsorption enthalpy (ΔH^o) were also calculated as 0.165 kJ mol⁻¹ K⁻¹ and 49.195 kJ mol⁻¹, respectively. The ΔG^o values varied in range with the mean values showing a gradual increase from −0.256 to −0.780 to −2.764 and −7.914 kJ mol⁻¹ for 293, 313, 323 and 333 K, respectively, in accordance with the positive adsorption entropy value of the adsorption process.     

Examination of the use of synthetic Zeolite NaA–X blend as backfill material in a radioactive waste disposal facility: Thermodynamic approach

The underground disposal of radioactive waste is based upon a multibarrier concept. For long-term performance assessment of radioactive repositories, knowledge concerning the sorption of radionuclides in backfill materials is required. As a part of the multibarrier system for effective isolation of radioactive waste in a repository, Zeolite NaA–X blend was prepared from fly ash, characterized, and evaluated to be used as a backfill material. In this concern, the sorption behavior of Cs⁺ on the prepared material as a function of pH, initial ion concentration and temperature was studied by batch technique. The sorption isotherm data was interpreted by Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models. The application of the Langmuir isotherm yielded monolayer capacity of 1546 mmol/kg at 298 K while the maximum sorption capacity predicted by D–R isotherm was of 2446 mmol/kg. Thermodynamic parameters for the sorption system were determined at three different temperatures. The enthalpy (ΔH°), entropy (ΔS°) and free energy (ΔG°) of sorption at 298 K were found to be 25.43 kJ/mol, 93 J/mol K and −2.316 kJ/mol, respectively. The positive value of ΔH° corresponds to the endothermic nature of the sorption process. The numerical value of ΔG° decreases with an increase in temperature indicating that the sorption was spontaneous and more favorable at higher temperatures.     

Adsorption of Pb(II) from aqueous solution to MX-80 bentonite: Effect of pH, ionic strength, foreign ions and temperature

The adsorption of Pb(II) from aqueous solution to MX-80 bentonite was studied using batch technique under ambient conditions. Removal percent (%) and distribution coefficient (K_d) were determined as a function of shaking time, pH, ionic strength and temperature. The results showed that the adsorption behavior of Pb(II) on bentonite was strongly dependent on pH and ionic strength. The presence of complementary cations depressed the adsorption of Pb(II) on bentonite in the order of Li⁺ ≈ Na⁺ > K⁺ at pH 2–5. The adsorption isotherms were simulated by the Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) models very well. The thermodynamic parameters (ΔH⁰, ΔS⁰, and ΔG⁰) for the adsorption of Pb(II) were determined at three different temperatures of 291 K, 308 K and 328 K. The adsorption reaction was exothermic and the process of adsorption was favored at low temperature. The results suggest that bentonite is suitable as a sorbent material for the recovery and adsorption of Pb(II) from aqueous solution.     

An EPR investigation of conductive polyaniline–poly(methyl methacrylate‐co‐acrylic acid) blends

A conductive blend of polyaniline (PANI) with sodium form poly(methyl methacrylate‐co‐acrylic acid) copolymer (PMMAA) was prepared by in situ dispersion polymerization. The PANI‐PMMAA blends were characterized with UV–vis, FTIR, and electron paramagnetic resonance (EPR) spectra. The effects of PANI and temperature on the electronic properties of the PANI‐PMMAA blends were studied with EPR technique. The PANI and temperature affect the intermolecular interaction between PANI and PMMAA and then determines the EPR parameters (A/B ratio, g factor, T₂, ΔH_pp, N_s, and lineshape). POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Interaction of metal ions with clays: I. A case study with Pb(II)

Pb(II) adsorption was studied under different conditions (pH, time, metal ion concentration, clay amount, temperature) on kaolinite, montmorillonite, and their poly(hydroxo)zirconium (ZrO–kaolinite, ZrO–montmorillonite) and tetrabutylammonium (TBA–kaolinite, TBA–montmorillonite) derivatives. All samples were calcined (ZrO-derivatives at 773 K, TBA-derivatives at 973 K) before using as adsorbents. The data were interpreted assuming first- and second-order kinetics. The rate constants including the pore diffusion rate constant are reported. The adsorption data could be fitted with Freundlich and Langmuir isotherms, and the coefficients indicated favorable adsorption of Pb(II) on the clays. Determination of the thermodynamic parameters, ΔH, ΔS, and ΔG showed the adsorption to be exothermic accompanied by decrease in entropy and Gibbs energy.     

Formation and electrochemical properties of composites of the C60–Pd polymer and multi-wall carbon nanotubes

Preparation and electrochemical properties of a novel type of the composite made of multi-wall carbon nanotubes (MWCNTs) and two-component polymer of palladium and C₆₀ (C₆₀–Pd) were investigated using cyclic voltammetry, electrochemical impedance spectroscopy, and piezoelectric microgravimetry. A composite film was prepared by electrochemical deposition of C₆₀–Pd on the layer of MWCNTs immobilized on the electrode surface. The polymer forms islands of shells on the carbon multi-wall core. This composite is electrochemically active in the negative potential range due to the electroreduction of the fullerene moiety. In this potential range, specific pseudo-capacitance of the film of the MWCNT/C₆₀–Pd composite is 425 F g⁻¹ in the acetonitrile solution of tetra(n-butyl)ammonium perchlorate. The presence of MWCNTs makes the composite conductive also at potentials less negative than potentials of the C₆₀ electroreduction. The double-layer specific capacitance of this film is close to 15 F g⁻¹.     

Model-evaluation of the erosion behavior of activated sludge under shear conditions using a chemical-equilibrium-based model

The primary particles would erode from the sludge surface under shear conditions. As the primary particles have significant effects on the solid–liquid separation process, the erosion behaviors of activated sludge in biological wastewater treatment processes under shear conditions were investigated using a chemical-equilibrium-based model. The equilibrium dispersed mass concentration of the primary particles in the sludge solution was found to nonlinearly increase with the solid content and shear intensity, and could be well described by the model. Compared with other sludge reported in literatures, the activated sludge used in this study was found to be more stable during the shear test, with a high equilibrium constant K⁰ of 30.2 and a low Gibbs’ free energy of adhesion (ΔG⁰) of −3.41 at a shear intensity of 800 s⁻¹. The two parameters could be used to evaluate the strength of the sludge. The negative value of ΔH indicates the energy demand for the erosion process. The low value of ΔH for the activated sludge used in this study indicates that the erosion process was more energy demanding and the erosion process was less shear dependent for the activated sludge used in this study.     

Biosorption of Pb(II) ions from aqueous solution by pine bark (Pinus brutia Ten.)

The biosorption potential of pine (Pinus brutia Ten.) bark in a batch system for the removal of Pb(II) ions from aqueous solutions was investigated. The biosorption characteristics of Pb(II) ions on the pine bark was investigated with respect to well-established effective parameters including the effects of solution pH, initial Pb(II) concentration, mass of bark, temperature, and interfering ions present, reusability, and desorption. Initial solution pH and contact time were optimized to 4.0 and 4 h, respectively. The Langmuir and Freundlich equilibrium adsorption models were studied and observed to fit well. The maximum adsorption capacity of the bark for Pb(II) was found to be 76.8 mg g⁻¹ by Langmuir isotherms (mass of bark: 1.0 g L⁻¹). The kinetic data fitted the pseudo-second-order model with correlation coefficient greater than 0.99. The thermodynamic parameters Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) changes were also calculated, and the values indicated that the biosorption process was spontaneous. Reutilization of the biosorbent was feasible with a 90.7% desorption efficiency using 0.5 M HCl. It was concluded that pine bark can be used as an effective, low cost, and environmentally friendly biosorbent for the removal of Pb(II) ions from aqueous solution.     

Effect of Schiff Bases Containing Pyridyl Group as Corrosion Inhibitors for Low Carbon Steel in 0.1 M HCl

The inhibiting effect of four newly synthesised Schiff bases containing pyridyl group was investigated on the corrosion of low carbon steel in 0.1 M hydrochloric acid solution under various conditions by potentiodynamic polarisation method and impedance measurements. The Schiff bases used were 2-((1Z)-1-aza-2-(2-pyridyl)vinyl)benzene-1-thiol, (1Z)-1-aza-1,2- di(2-pyridyl)ethene, [((1Z)-1-aza-2-(2-pyridyl)vinyl)amino]benzene-1-thione and 2-((1Z)-1-aza-2-(2-pyridyl)vinyl)benzothiazole. All the Schiff bases inhibit corrosion of low carbon steel and their inhibition efficiencies increase with decrease in temperature and increase in concentration. The difference in protection actions of the inhibitors can be attributed to the presence of substituents in the structures that increase or decrease the electron density on the azomethine (–C=N–) group. Polarisation curves indicate that the Schiff bases act as anodic inhibitors. AC impedance and potentiodynamic polarisation measurements reveal that the compounds are adsorbed on the steel surface and the adsorption obeys the Temkin isotherm. Activation parameters (E_a, ΔH*, ΔS*) for the corrosion of low carbon steel in 0.1 M HCl were calculated and showed that corrosion was much reduced in the presence of inhibitors.     

Nonkinetic changes in heat-treated glasslike carbons part I: Pore size and bulk dimensions

Small-angle X-ray scattering measurements have been used to characterize the radius of gyration R_g of the pores in a glasslike carbon heat treated between 1000 and 2800°C for periods up to 150 hours. Measurements were also made of the irreversible bulk dimensional changes Δl. In both cases, a nonkinetic increase occurs when the heat treatment temperature is increased stepwise to a higher value. The relative changes ΔR_g/R_g and Δl/l exhibit a similar three-region behavior: an initial increase with the annealing temperature up to 1600°C, a plateau up to about 2200°C, and thereafter an increase again. However, the maximum dilatation Δl/l is scarcely 3% whereas the increase in ΔR_g/R_g is twofold. The first region is attributed to a gas pressure mechanism, and the highest-temperature region results from strain relief due to the mismatch of the thermal expansion coefficients in the directions perpendicular and parallel to the layers in graphitic materials. The intermediate region is explained by a combination of both mechanisms.     

Switching on the photochemical reactivity in heterodimetallic Os–Ru bipyridyl complexes containing a bis(bidentate) phosphine

For the first time the excited states of the RuP₂N₄ moiety belonging to a new heterodimetallic Os^II–Ru^II bipyridyl complex are successfully designed in order to introduce photochemical reactivity. This dramatic effect is achieved via the use of the sterically demanding bis(bidentate) phosphine cis, trans, cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb). Thus, the temperature dependence of the luminescence lifetimes ranging from 77 to 298 K for the novel homodimetallic species meso-(ΔΛ/ΛΔ)-[Os₂(dppcb)(bpy)₄](PF₆)₄ (1) and rac-(ΔΔ/ΛΛ)-[Os₂(dppcb)(bpy)₄](PF₆)₄ (2) clearly indicates that the d–d state responsible for photochemistry is not populated. By contrast, the analogous temperature dependence for the new heterodimetallic species ΔΛ/ΛΔ-[Os(bpy)₂(dppcb)Ru(bpy)₂](PF₆)₄ (3) and ΔΔ/ΛΛ-[Os(bpy)₂(dppcb)Ru(bpy)₂](PF₆)₄ (4) unequivocally shows that as a consequence of the population of the d–d state the photochemical reactivity is switched on. Since single crystal X-ray structure analyses are a major clue to the understanding of photophysical and photochemical properties, also the X-ray structures of 1–3 are given.     

Effects of catalysts and steam gasification on e.s.r. of carbon black

The effects of temperature and steam concentration on Spheron-6 carbon black with and without impregnated K₂C0₃ and diluted with alumina have been measured by in-situ electron spin resonance (e.s.r.). For samples in flowing helium, heating from 290 to 1070 K results in a small increase in the carbon black resonance linewidth but a large and mostly irreversible increase in the resonance linewidth of carbon black with K₂C0₃ at >650 K. The effect of steam concentration on the e.s.r. spectra of the carbon black at 875 K has been studied; an effect is observed only for carbon black with K₂C0₃. Increasing the steam concentration from 0 to 6.5 vol% results in reversible narrowing of the linewidth while hardly changing the free radical concentration. The mechanism of the line-broadening of the resonance resulting from heating the K₂C0₃-impregnated carbon black may be due to one of two processes: an unresolved nuclear hyperfine interaction between the unpaired electron of the carbon free radical and potassium, or an increased mobility of charge carriers produced by the potassium. The reversible effects of steam are attributed to a modificartion of these processes and may be related to the mechanism of catalysed gasification of coal.