Sorption behavior of nano-TiO2 for the removal of selenium ions from aqueous solution

Titanium dioxide nanoparticles were employed for the sorption of selenium ions from aqueous solution. The process was studied in detail by varying the sorption time, pH, and temperature. The sorption was found to be fast, and to reach equilibrium basically within 5.0 min. The sorption has been optimized with respect to the pH, maximum sorption has been achieved from solution of pH 2–6. Sorbed Se(IV) and Se(VI) were desorbed with 2.0 mL 0.1 mol L⁻¹ NaOH. The kinetics and thermodynamics of the sorption of Se(IV) onto Nano-TiO₂ have been studied. The kinetic experimental data properly correlate with the second-order kinetic model (k₂ = 0.69 g mg⁻¹ min⁻¹, 293 K). The overall rate process appears to be influenced by both boundary layer diffusion and intraparticle diffusion. The sorption data could be well interpreted by the Langmuir sorption isotherm. The mean energy of adsorption (14.46 kJ mol⁻¹) was calculated from the Dubinin–Radushkevich (D–R) adsorption isotherm at room temperature. The thermodynamic parameters for the sorption were also determined, and the ΔH⁰ and ΔG⁰ values indicate exothermic behavior.     

Interactive behavior of caffeine at a platinum electrode surface

Interactive behavior of caffeine at a charged platinum/solution interface was investigated in a wide temperature range, from 295 to 333 K, in a phosphate buffer solution pH 7.0. It was shown that the amount of adsorbed caffeine (surface concentration) is directly proportional to the measured adsorption surface charge density resulting from caffeine oxidation to theophilline. At low temperatures, a monolayer of caffeine molecules laying in a flat orientation on the Pt surface is adsorbed, while at higher temperatures, conformational changes occur, resulting in tilting of the adsorbed molecules to allow for higher surface concentrations to be achieved. A highly negative Gibbs energy of adsorption, ranging from −51.1 kJ mol⁻¹ at 295 K to −60.6 kJ mol⁻¹ at 333 K, demonstrated a high affinity of caffeine for the Pt surface. Although the adsorption process was found to be endothermic (ΔH_ADS = 20 kJ mol⁻¹), it was determined that a large positive change in the adsorption entropy (TΔS_ADS = 75 ± 3 kJ mol⁻¹) represents the driving force for the strong interaction of caffeine with Pt.     

Cr(VI) sorption behavior from aqueous solutions onto polymeric microcapsules containing a long-chain quaternary ammonium salt: Kinetics and thermodynamics analysis

This work studies the adsorption of Cr(VI) ions from an aqueous acid solution on hydrophobic polymeric microcapsules containing a long-chain quaternary ammonium salt-type extractant immobilized in their pore structure. The microcapsules were synthesized by adding the extractant Aliquat 336 during the in situ radical copolymerization of the monomers styrene (ST) and ethylene glycol dimethacrylate (EGDMA). The microcapsules, which had a spherical shape with a rough surface, behaved as efficient adsorbents for Cr(VI) at the tested temperatures. The results of kinetics experiments carried out at different temperatures showed that the adsorption process fits well to a pseudo-second-order with an activation energy of 82.7 kJ mol⁻¹, confirming that the sorption process is controlled by a chemisorption mechanism. Langmuir's isotherms were found to represent well the experimentally observed sorption data. Thermodynamics parameters, namely, changes in standard free energy (ΔG⁰), enthalpy (ΔH⁰), and entropy (ΔS⁰), are also calculated. The results indicate that the chemisorption process is spontaneous and exothermic. The entropy change value measured in this study shows that metal adsorbed on microcapsules leads to a less chaotic system than a liquid–liquid extraction system.     

Direct oxidation route from metal to ceramic: Study on cobalt oxide

The study deals with the direct-oxidation kinetics of micronic-cobalt metal particles and its simulation for the complete transition from metal to ceramic. The simulation was also experimentally verified. All the three possible interfaces, Co/CoO, CoO/Co₃O₄ and Co₃O₄/O₂ (air), have been taken into consideration for the simulation. The complete oxidation kinetics has been investigated from the thermogravimetric studies under isothermal conditions in the temperatures 973–1173 K. A quantitative interpretation based on the diffusion of Co or oxygen ions through the grown oxide layer has been proposed. The activation energy for the oxidation kinetics calculated from the Arrhenius law was 161 ± 20 kJ mol⁻¹.     

Growth of hafnium and zirconium silicides by reactive diffusion

Diffusion controlled growth of the phases in Hf–Si and Zr–Si systems are studied by bulk diffusion couple technique. Only two phases grow in the interdiffusion zone, although several phases are present in both the systems. The location of the Kirkendall marker plane, detected based on the grain morphology, indicates that disilicides grow by the diffusion of Si. Diffusion of the metal species in these phases is negligible. This indicates that vacancies are present mainly on the Si sublattice. The activation energies for integrated diffusion coefficients in the HfSi₂ and ZrSi₂ are estimated as 394 ± 37 and 346 ± 34 kJ mol⁻¹, respectively. The same is calculated for the HfSi phase as 485 ± 42 kJ mol⁻¹. The activation energies for Si tracer diffusion in the HfSi₂ and ZrSi₂ phases are estimated as 430 ± 36 and 348 ± 34 kJ mol⁻¹, respectively.     

Cu diffusion kinetics in (Cu, Ni)3Sn intermetallic compound nanolayers investigated by an Energy-Dispersive-X-ray-based permeation test

The Energy-Dispersive-X-ray-based permeation and oxidation test has been further developed by an improved theoretical analysis, in which chemical potential gradients rather than concentration gradients are employed. The developed test is able to characterize diffusion kinetics in diffusion barriers at the nanometer scale. The Cu flux coefficient in (Cu, Ni)₃Sn intermetallic compound nanolayers was determined from the test to be 8.48 × 10^− 15 mol·(m·s·J/mol)^–1 exp(− 52.3 kJ·mol^− 1/RT) in a temperature range of 250 °C–400 °C.     

Preparation and gases storage capacities of N-doped porous activated carbon materials derived from mesoporous polymer

In this report, the chemical activation of mesoporous carbon derived from mesoporous polymer is used to prepare N-doped carbon materials with high surface area and narrow pores size distribution. The porous carbons derived from the activation of mesoporous carbon generally possess high surface area up to 2400 m² g⁻¹ and narrow micropores/super-micropore size distribution and exhibit H₂ uptake capacity of up to 4.8 wt% at −196 °C and 20 bar and CO₂ sorption capacity of up to 3.7 mmol g⁻¹ at 25 °C and 1 bar. The measured isosteric heat of adsorption for H₂ sorption is 10 kJ mol⁻¹ and 58 kJ mol⁻¹ for CO₂ sorption, indicating a strong interaction between the carbon surface and adsorbed hydrogen and carbon dioxide respectively.     

Isothermal and non-isothermal sublimation kinetics of zirconium tetrachloride (ZrCl4) for producing nuclear grade Zr

Sublimation of ZrCl₄ is important for the production of nuclear grade metallic Zr in Kroll's process. The sublimation kinetics of ZrCl₄ was investigated by thermogravimetric analysis under both isothermal and non-isothermal conditions. The sublimation rate of ZrCl₄ increased with increasing temperature under isothermal conditions. ZrCl₄ sublimation was confirmed to be a zero-order process under isothermal conditions, whereas it was first-order kinetics under non-isothermal conditions. The activation energy of ZrCl₄ sublimation under isothermal conditions was 21.7 kJ mol⁻¹. The activation energy for non-isothermal sublimation was 101.4 kJ mol⁻¹ and 108.1 kJ mol⁻¹ with the Kissinger method and Flynn–Wall–Ozawa method, respectively. These non-isothermal activation energies were very close to the heat of sublimation (103.3 kJ mol⁻¹). Sublimation occurs by two elementary steps: surface reaction and desorption. Therefore, the overall activation energy of ZrCl₄ sublimation is 104.8 (±3.4) kJ mol⁻¹. The activation energy of the surface reaction and desorption steps are proposed to be 83.1 kJ mol⁻¹ and 21.7 kJ mol⁻¹, respectively.     

The removal of an anionic red dye from aqueous solutions using chitosan beads-the role of experimental factors on adsorption using a full factorial design

A factorial design was employed to evaluate the quantitative removal of an anionic red dye from aqueous solutions on epichlorohydrin-cross-linked chitosan. The experimental factors and their respective levels studied were the initial dye concentration in solution (25 or 600 mg L⁻¹), the absence or the presence of the anionic surfactant sodium dodecylbenzenesulfonate (DBS) and the adsorption temperature (25 or 55 °C). The adsorption parameters were analyzed statistically using modeling polynomial equations. The results indicated that increasing the dye concentration from 25 to 600 mg L⁻¹ increases the dye adsorption whereas the presence of DBS increases it. The principal effect of temperature did not show a high statistical significance. The factorial results also demonstrate the existence of statistically significant binary interactions of the experimental factors. The adsorption thermodynamic parameters, namely Δ_adsH, Δ_adsG and Δ_adsS, were determined for all the factorial design results. Exothermic and endothermic values were found in relation to the Δ_adsH. The positive Δ_adsS values indicate that entropy is a driving force for adsorption. The Δ_adsG values are significantly affected by an important synergistic effect of the factors and not by the temperature changes alone.     

Transient flow behaviour in a near alpha titanium alloy Timetal 834 in the dynamic strain aging regime

The transient flow behaviour in Timetal 834 titanium alloy was studied in the temperature range between 400 °C and 475 °C by means of stress relaxation and reloading during tensile testing at a strain rate of 6.67 × 10⁻⁴ s⁻¹. The increment in flow stress during reloading (Δσ_f) and the decrement in flow stress during stress relaxation (Δσ_r) were measured at different strains at each temperature. The observation of maximum value of Δσ_f and Δσ_r, normalized with respect to the Young's modulus at the corresponding temperature, confirmed that the maximum dynamic strain aging (DSA) effect in this alloy occurs at 450 °C.     

Rib waveguides based on Zn-substituted LiNbO3 films grown by liquid phase epitaxy

The fabrication of epitaxially grown Zn-substituted LiNbO₃ (Zn:LiNbO₃) waveguide films and rib waveguides is reported and detailed investigations about microstructure, morphology and optical waveguide properties are provided. Zn:LiNbO₃ films were grown on congruent X-cut LiNbO₃ substrates by a modified liquid phase epitaxy in solid–liquid coexisting solutions. The homogeneously Zn-substituted films exhibit high crystalline perfection and extremely flat surfaces with averaged surface roughness of rms = 0.2–0.3 nm. At the film/substrate interface a Zn-containing transient layer has been observed, which allows the growth of elastically strained Zn:LiNbO₃ film lattices. X-ray diffraction reciprocal-space measurements prove the pseudomorphic film growth. The refractive index difference between substrate and film depends on the zinc substitution content, which increase with rising growth temperatures. For films with 5.3 mol% Zn (Δn_o ≈ +5 × 10⁻³) only ordinary ray propagation was observed, while for films with 7.5 mol% Zn (Δn_o ≈ +8 × 10⁻³, Δn_e ≈ +5 × 10⁻³) both modes, TM and TE propagate. Stress-induced refractive index changes are in the order of Δn ≈ 10⁻⁴. In rib waveguide microstructures singlemode propagation with nearly symmetrical field distribution has been observed. To demonstrate the potential of the proton exchange-assisted dry-etching technique interferometer microstructures were fabricated.     

Oxidation of Urea with Nitrous Acid in Nitric Acid Solutions

The kinetics of the reaction between urea and HNO₂ in nitric acid solution was studied spectrophotometrically. It was found that, at a constant ionic strength of the solution μ = 2, in the range of the initial concentrations of urea from 0.01 to 0.1 M, HNO₂, from 0.003 to 0.012 M, and hydrogen ions, from 0.1 to 1.5 M, the rate constant of the reaction is described by the equation -d[HNO₂]/dt = k[HNO₂][CO(NH₂)₂][H⁺] · K([H⁺]K +1)⁻¹, where the rate constant k = 15.6±0.3 l mol⁻¹ min⁻¹ and the protonation constant of urea K = 1.38 l mol⁻¹ at 15°C. From the temperature dependence of the reaction rate in the range of 15–35°C, the activation energy was determined to be 61±5 kJ mol⁻¹. The reaction mechanism involving the reaction of nondissociated HNO₂ molecules and protonated urea species NH₂CONH ₃ ⁺ was suggested.__________Translated from Radiokhimiya, Vol. 47, No. 1, 2005, pp. 57–60.Original Russian Text Copyright © 2005 by Dvoeglazov, Marchenko.     

Oxidation of U(IV) in HNO<Subscript>3</Subscript> Solutions Containing Urea and Tc(VII)

The kinetics of U(IV) oxidation with nitric acid in aqueous solutions containing urea, catalyzed with technetium ions, were studied by sampling with subsequent colorimetric determination of the U(IV) concentration. At the constant ionic strength of the solution μ = 2 in the range of the initial concentrations of U(IV) from 2 × 10⁻³ to 1.28 × 10⁻², Tc(VII) from 5 × 10⁻⁵ to 1 × 10⁻³, urea from 0.01 to 0.1, and hydrogen ions from 0.4 to 1.96 M, the reaction rate is described by the equation -d[U(IV)]/dt = k ₁[U(IV)][Tc]^0.5[CO(NH₂)₂] × {[H⁺]² + β₁[H⁺] + β₂}⁻¹ - k ₂[U(IV)]₂[H⁺]^0.4[CO(NH₂)₂]^1.6{ [H⁺]² + β₁[H⁺]+ β₂}⁻², where k ₁ = 172 ± 10 mol^0.5 l^−0.5 min⁻¹ and k ₂ = (9.4±1.2)×10² mol l⁻¹ min⁻¹ at 25°C, β₁ and β₂ are the hydrolysis constants of U⁴⁺ ions. The activation energy is 63±2 kJ mol⁻¹. A reaction mechanism is proposed, in which in the slow stages the complex ion U(OH) ₂ ²⁺ ·CO(NH₂)₂ reacts with TcO²⁺ and TcO²⁺ · CO(NH₂)₂ ions.__________Translated from Radiokhimiya, Vol. 47, No. 1, 2005, pp. 61–66.Original Russian Text Copyright © 2005 by Dvoeglazov, Marchenko, Koltunov.     

Kinetics and Mechanism of Np(IV) Oxidation with Nitric Acid

Neptunium (IV) is oxidized to Np(V) with nitric acid in the presence of U(VI) under conditions of low acidity (<∼0.1 M). The reaction rate is described by the equation d[Np(V)]/dt = k ₁[Np(IV)]/[H⁺]² + k ₂[Np(IV)]²[U(VI)]/[H⁺]³, in which k ₁ = (2.0±0.3) × 10⁻⁵ mol² l⁻² min⁻¹ and k ₂ = (5.50±0.47) × 10⁻² mol l⁻¹ min⁻¹ at 50°C and solution ionic strength μ = 0.5. The activation energies of the two pathways are 148±31 and 122±12 kJ mol⁻¹. The reaction along the main pathway (with the rate constant k ₂) is limited by disproportionation of Np(IV) involving NpOH³⁺ and Np(OH)₂UO ₂ ⁴⁺ complex ions.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 228–233.Original Russian Text Copyright © 2005 by Koltunov, Taylor, Marchenko, Savilova, Dvoeglazov, Zhuravleva.     

Jatropha curcas: A potential crop for phytoremediation of coal fly ash

A greenhouse pot experiment was conducted to test the heavy metal phytoremediation capacity of Jatropha curcas from fly ash. Both natural accumulation by J. curcas and chemically enhanced phytoextraction was investigated. Plants were grown on FA and FA amended with fertile garden soil, in presence and absence of chemical chelating agent EDTA at 0.1 g kg⁻¹ and 0.3 g kg⁻¹ of soil. EDTA enhanced the uptake of all five elements (Fe, Al, Cr, Cu and Mn) tested. Fe and Mn were retained more in roots while Cu, Al and Cr were translocated more to the shoot. Metal accumulation index indicates that the effect of EDTA at 0.3 g kg⁻¹ was more pronounced than EDTA at 0.1 g kg⁻¹ in terms of metal accumulation. Biomass was enhanced up to 37% when FA was amended with GS. Heavy metal uptake was enhanced by 117% in root, 62% in stem, 86% in leaves when EDTA was applied at 0.3 g kg⁻¹ to FA amended with GS. Study suggest that J. curcas has potential of establishing itself on FA when provided with basic plant nutrients and can also accumulate heavy metals many folds from FA without attenuating plant growth.     

Kinetics of zero-valent iron reductive transformation of the anthraquinone dye Reactive Blue 4

The effect of operational conditions and initial dye concentration on the reductive transformation (decolorization) of the textile dye Reactive Blue 4 (RB4) using zero-valent iron (ZVI) filings was evaluated in batch assays. The decolorization rate increased with decreasing pH and increasing temperature, mixing intensity, and addition of salt (100 g L⁻¹ NaCl) and base (3 g L⁻¹ Na₂CO₃ and 1 g L⁻¹ NaOH), conditions typical of textile reactive dyebaths. ZVI RB4 decolorization kinetics at a single initial dye concentration were evaluated using a pseudo first-order model. Under dyebath conditions and at an initial RB4 concentration of 1000 mg L⁻¹, the pseudo first-order rate constant (k_obs) was 0.029 ± 0.006 h⁻¹, corresponding to a half-life of 24.2 h and a ZVI surface area-normalized rate constant (k_SA) of 2.9 × 10⁻⁴ L m⁻² h⁻¹. However, as the initial dye concentration increased, the k_obs decreased, suggesting saturation of ZVI surface reactive sites. Non-linear regression of initial decolorization rate values as a function of initial dye concentration, based on a reactive sites saturation model, resulted in a maximum decolorization rate (V_m) of 720 ± 88 mg L⁻¹ h⁻¹ and a half-saturation constant (K) of 1299 ± 273 mg L⁻¹. Decolorization of RB4 via a reductive transformation, which was essentially irreversible (2–5% re-oxidation), is believed to be the dominant decolorization mechanism. However, some degree of RB4 irreversible sorption cannot be completely discounted. The results of this study show that ZVI treatment is a promising technology for the decolorization of commercial, anthraquinone-bearing, spent reactive dyebaths.     

Application of natural and modified hectorite clays as adsorbents to removal of Cr(VI) from aqueous solution–Thermodynamic and equilibrium study

A hectorite (H) clay sample has been modified with 2-mercaptobenzimidazole (MBI) using homogeneous and heterogeneous routes. Both modification methodologies resulted in similar products, named H_HOM and H_HET, respectively. These materials were characterized by CO₂ gas adsorption, elemental analysis, nuclear magnetic nuclei of carbon-13 and silicon-29. The effect of two variables (contact time and metal concentration) has been studied using batch technique at room temperature and pH 2.0. After achieving the best conditions for Cr(VI) adsorption, isotherms of this adsorbate on using the chosen adsorbents were obtained, which were fitted to non-linear Sips isotherm model. The maximum number of moles adsorbed was determined to be 11.63, 12.85 and 14.01 mmol g⁻¹ for H, H_HOM and H_HET, respectively, reflecting the maximum adsorption order of H_HET > H_HOM > H. The energetic effects (Δ_intH°, Δ_intG° and Δ_intS°) caused by chromium ion adsorption were determined through calorimetric titrations.     

Metal availability in heavy metal-contaminated open burning and open detonation soil: Assessment using soil enzymes, earthworms, and chemical extractions

The effects of heavy metal contamination on soil enzyme activity and earthworm health (bioaccumulation and condition) were studied in contaminated soils collected from an formerly open burning and open detonation (OBOD) site. Soil extraction methods were also evaluated using CaCl₂ and DTPA solutions as surrogate measures of metal bioavailability and ecotoxicity. Total heavy metal content of the soils ranged from 0.45 to 9.68 mg Cd kg⁻¹, 8.96 to 5103 mg Cu kg⁻¹, 40.21 to 328 mg Pb kg⁻¹, and 56.61 to 10,890 mg Zn kg⁻¹. Elevated metal concentrations are assumed to be primarily responsible for the reduction in enzyme activities and earthworm health indices. We found significant negative relationships between CaCl₂- and DTPA-extractable metal content (Cd, Cu, and Zn) and soil enzyme activity (P < 0.01). Therefore, it could be concluded that soil enzyme activity and metal bioaccumulation by earthworms can be used as an ecological indicator of metal availability. Furthermore, CaCl₂ and DTPA extraction methods are proved as promising, precise, and inexpensive surrogate measures of Cd, Cu, Pb, and Zn bioavailability from heavy metal-contaminated soils.     

The structural and electrical property of CuCr1 − xNixO2 delafossite compounds

A series of CuCr_1 − xNi_xO₂ (0 ≤ x ≤ 0.06) polycrystalline samples was prepared. The electrical conductivity was measured in the temperature range of 160–300 K. It was found that the electrical conductivity (σ) increases rapidly with the doping of Ni²⁺ ions. At room temperature, the σ is 0.047 S cm^− 1 for the sample with x = 0.06, which is two orders of magnitude larger than that of the CuCrO₂ sample (9.49E− 4 S cm^− 1). The Seebeck coefficients are positive for all samples, which indicate p-type conducting of the samples. The experimental results imply that it is possible to get higher electrical conductivity p-type transparent conducting oxides (TCO) from CuMO₂ by doping with divalent ions.