The annealing of chemical radiation damage in acetatopentamminecobalt/III/nitrate

The kinetics of isothermal annealing of NO ₂ ⁻ in γ-irradiated acetatopentamminecobalt/III/ nitrate in the range 95–115 °C is a combination of a first order process affecting 28% of the damage fragments and a second order process, governing the behaviour of the remainder. The annealing data have also been analyzed on the basis of models developed by Fletcher and Brown and by Waite.     

Kinetic study of Cr(VI) sorption on MnO2

The kinetics of adsorption of chromate ions has been investigated radiometrically over a wide range of concentration of chromate ions (10^–6–10^–2M) and temperature (303–323 K). The kinetics of the process follows essentially a first order rate law with respect to adsorptive concentration and obeys the Freundlich adsorption isotherm in the concentration range studied. In addition, the kinetics of desorption of the preadsorbed species also follows a first order rate law and the activation energy for desorption is greater than that of the adsorption process. On the basis of an adsorption kinetic study, the thermodynamic parameters have been calculated. Infrared spectroscopy has shown the chemical interaction of chromate ions on the surface of MnO₂.     

Adsorption properties of amidoximated porous acrylonitrile/methyl acrylate copolymer beads for Ag (I)

Porous a crylonitrile (AN)/methyl acrylate (MA) copolymer beads were synthesized by suspended emulsion polymerization and amidoximated for the purpose of Ag⁺ adsorption. Optimum amidoximation temperature and time were determined by following the adsorption capacity for Ag⁺. The results showed that amidoximated AN/MA (AO AN/MA) with the amidoximation temperature 70°C and amidoximation time 20 hr had a relatively higher adsorption capacity for Ag⁺. The effect of pH on adsorption for Ag⁺ was studied; the highest adsorption capacity presented at pH 5.0. Adsorption kinetics and isotherms of AO AN/MA copolymer beads for Ag⁺ were also investigated. The kinetics data indicated that the adsorption process was governed by the film diffusion and followed both pseudo‐first‐order and pseudo‐second‐order rate model. The isotherms indicated that adsorption capacities increased with equilibrium concentration and temperature. The Langmuir model and Sips model could describe the isothermal process. Thermodynamic analysis revealed that the adsorption behaviors of Ag⁺ ions on AO AN/MA could be considered as endothermic and physical sorption process. Copyright © 2010 John Wiley & Sons, Ltd.     

Kinetics and mechanism of the catalytic epoxidation of cyclohexene with tert-butyl hydroperoxide in the presence of molybdenum–squarate complex

The kinetics of the catalytic epoxidation of cyclohexene with tert-butyl hydroperoxide (TBHP) in the presence of a novel molybdenum–squarate complex was studied. Both the kinetics and mechanism of the process were found to be similar to those established with the “classical” homogeneous catalysts for epoxidation.     

Sorption kinetics of selenium on humic acid

This study investigated selenium sorption kinetics on humic acid (HA) as a function of initial Se concentration (10–300 μg·1⁻¹) and solid/liquid ratio (0.01–0.1). From the result, it was clear that the Se sorption kinetics on HA could be expressed by a pseudo-second order equation. This was possible because the sorption mechanism on HA is a multiple sorption process including specific and non specific mechanisms. Additionally, the 3-D empirical equation for the amount of sorbed Se could be determined as a function of the initial Se concentration and solid/liquid ratio.     

Mechanism of complex formation between [AuCl4] and l-methionine

The kinetics of the reaction between the tetrachloroaurate(III) ion and l-methionine (l-Met) (0.1 M HClO₄, pH 1.0–2.5) have been studied spectrophotometrically using a stopped-flow technique at different temperatures. Initially, the fast substitution reaction was ascribed to the formation of the short-lived square-planar Au(III)–(l-Met) that was followed by the replacement of a Cl⁻ ligand and a subsequent, slower reduction to Au(I)–(l-Met). This is an intermolecular process, involving attack on the [AuCl₄]⁻ complex by an outer-sphere l-methionine. The activation parameters (ΔH^≠ and ΔS^≠) for substitution and reduction were determined. IR spectroscopy indicates that l-methionine acts as a bidentate ligand, most likely coordinating via the S and N atoms, while ¹H and ¹³C NMR data indicate methionine sulfoxide as the final product. Finally, the components of the reaction were treated thermally in order to investigate the solid phase synthesis of the resulting complex.     

Kinetics study of the UV-initiated cationic polymerization of cycloaliphatic diepoxide resins

Photo-differential scanning calorimetry (photo-DSC) was used to study the cure kinetics of UV-initiated cationic photo-polymerization of epoxy resin monomers in presence of different photoinitiators and to investigate the photo-reactivity with respect to their chemical structure. Two cycloaliphatic diepoxy monomers - 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate and bis-(3,4-epoxycyclohexyl) adipate - were studied. Both monomers have two terminal epoxy functional groups and differ only in the number of, so-called, “space” carboxylate group and thus the overall length of the molecule. Different kinetics analysis results, including enthalpy of the reaction, induction time, peak maximum, percentage conversion were obtained for both epoxy systems for different amounts of added photoinitiator and at different isothermal temperatures (30-70 °C). Two kinetic parameters - rate coefficient (k) and the order of the initiating reaction (m) - were determined, using an autocatalytic kinetics model. Activation energy for the two epoxies curing process using the Arrhenius equation was calculated as well. Results show that photochemical reactivity is influenced by the chemical structures of monomers.     

Temperature and pH effects on the kinetics of 2-aminophenol auto-oxidation in aqueous solution

The kinetics of the auto-oxidation of 2-aminophenol (OAP) to 2-amino-phenoxazin-3-one (APX) was followed in air-saturated aqueous solutions and the influence of temperature and pH on the auto-oxidation rate was studied. The kinetic analysis was based on a spectrophotometric method following the increase of the absorbance of APX. The process follows first order kinetics according to the rate law—d[OAP]/dt=k′[OAP]. The experimental data, within the pH range 4–9.85, were analyzed using both differential and incremental methods. The temperature variation of the overall rate constant was studied at pH=9.85 within the range 25–50°C and the corresponding activation energy was evaluated.     

Influence of the addition of erbium and ytterbium triflates in the curing kinetics of a DGEBA/<Emphasis Type="Italic">o</Emphasis>-tolybiguanide powder mixture

Solid bisphenol-A epoxy resin (DGEBA) of medium molecular mass was cured using o-tolylbiguanide (TBG) as cross-linking agent. In order to improve the kinetics of the reactive system, two Lewis acid catalysts (erbium(III) and ytterbium(III) trifluoromethanesulfonates) were added in proportions of 1 phr. The kinetic study was performed by dynamic scanning calorimetry (DSC) and the complete kinetic triplet (E, A and g(α)) determined. The kinetic analysis was performed with an integral isoconversional procedure (model-free), and the kinetic model was determined by the Coats-Redfern method and through the compensation effect (IKR). All the systems followed the m=1.5/n=0.5 isothermal curing model simulated from non-isothermal experiments. The addition of a little proportion of ytterbium or erbium triflates accelerated the curing process. In order to extract further information about the role of the lanthanide triflates added to epoxy/TBG systems, the kinetic results were compared with our previous kinetic studies made on DGEBA/lanthanide triflates initiated systems.     

Synthesis of poly(methyl methacrylate) via ARGET ATRP and study of the effect of solvents and temperatures on its polymerization kinetics

This investigation reports the synthesis of poly(methyl methacrylate) via activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) and studies the effect of solvents and temperature on its polymerization kinetics. ARGET ATRP of methyl methacrylate (MMA) was carried out in different solvents and at different temperatures using CuBr₂ as catalyst in combination with N,N,N′,N″,N″‐pentamethyldiethylenetriamine as a ligand. Methyl 2‐chloro propionate was used as ATRP initiator and ascorbic acid was used as a reducing agent in the ARGET ATRP of MMA. The conversion was measured gravimetrically. The semilogarithmic plot of monomer conversion versus time was found to be linear, indicating that the polymerization follows first‐order kinetics. The linear polymerization kinetic plot also indicates the controlled nature of the polymerization. N,N‐Dimethylformamide (DMF), tetrahydrofuran (THF), toluene, and methyl ethyl ketone were used as solvents to study the effect on the polymerization kinetics. The effect of temperature on the kinetics of the polymerization was also studied at various temperatures. It has been observed that polymerization followed first‐order kinetics in every case. The rate of polymerization was found to be highest (k_app = 6.94 × 10⁻³ min⁻¹) at a fixed temperature when DMF was used as solvent. Activation energies for ARGET ATRP of MMA were also calculated using the Arrhenius equation.     

Investigation of Electrochemical Properties of Metalloporphyrin Species at the Liquid/Liquid Interface by Switching Substitutes on the Porphyrin Ring

In order to investigate the electrochemical properties of porphyrin complexes species in biological systems, metalloporphyrin with different substitutes was applied to observe the process of heterogeneous electron transfer (ET) at the interface between two immiscible electrolyte solutions (ITIES) by scanning electrochemical microscopy (SECM). Experimental results demonstrated that the process of electron transfer was affected dramatically by the presence of different substitutes. Our results also show that the rate constant follows Bulter? Volmer kinetics where the rate increases with increasing force at the low driving force, and Marcus inverted region kinetics at the high driving force where the rate decreases.     

Investigation of the electrosurface properties of NiO and Fe2O3 in azole solutions

The electrokinetic study of heterogeneous system consisting of Ni(II) and Fe(III) oxide powders in aqueous azole solutions is presented. Diazole, triazole and tetrazole were used in our experiments. Various combinations of operating conditions such as pH, electrolyte and azole concentrations were employed. Zeta-potentials of powders with adsorbed azoles were obtained in order to investigate the interactions occurring between azoles and the oxide surfaces. In the presence of azoles the equilibration process of zeta-potential of oxide surfaces has a very special “damping oscillation” character and the equilibration process continues for around a week. However, kinetics of adsorption of azoles is completed in approximately 3 h. The latter shows a complex behaviour of adsorbed azoles on oxide surfaces.     

Nanocrystallization of anatase in amorphous TiO2

The kinetics of nanocrystallization in amorphous TiO₂ has been studied in non-isothermal conditions by DSC. It was found that this process could be well described by standard Johnson-Mehl-Avrami-Kolmogorov (JMA) model with kinetic exponent m≅1. The kinetic parameters were calculated by simultaneous analysis of experimental data taken at different heating rates. These parameters were used as a basis for prediction of crystallization kinetics in isothermal conditions. The agreement between the JMA model prediction and experimental data depends on the method of preparation of amorphous TiO₂.     

Atom transfer radical polymerization with activators regenerated by electron transfer of acrylonitrile from silica nanoparticles,and adsorption properties of the resin for Hg2+ after amidoximation with hydroxylamine

Polyacrylonitrile (PAN) was grafted from surfaces of chloro‐modified silica‐gel with their surface chlorines as initiation sites, using an iron (III)‐mediated surface‐initiated atom transfer radical polymerization (ATRP) with activators regenerated by electron transfer (SI‐ARGET ATRP) method. The graft reaction exhibits first‐order kinetics with respect to the polymerization time in the low‐monomer‐conversion stage. The conversion of monomer (C%) and the percentage of grafting (PG%) increased with increasing of the polymerizing time and reached 23 and 730% after a polymerizing time of 24 hr, respectively. Hydroxylamine (NH₂OH·HCl) was used to modify the cyano groups of SG‐g‐PAN to obtain amidoxime (AO) groups. The AO SG‐g‐PAN was used to remove Hg²⁺. The adsorption kinetics indicated that the pseudo‐second‐order model was more suitable to describe the adsorption kinetics of AO SG‐g‐PAN for Hg²⁺. The adsorption isotherms demonstrated that Langmuir model was much better than Freundlich model to describe the isothermal process. Copyright © 2010 John Wiley & Sons, Ltd.     

Kinetic studies on the extraction of U(IV) by TBP in kerosene from nitrate medium

The kinetics of extraction of U(IV) by TBP in kerosene was investigated using a stirred Lewis cell. The effect of the different parameters affecting the extraction rate as well as temperature were separately investigated. The rate equation deduced from the experimental results show that the extraction of U(IV) is first order dependent on TBP concentration while it is of zero order with respect to U(IV), H⁺, NO ₃ ^– and HNO₃ concentrations. The data obtained show that the extraction process is governed by chemical reactions taking place at teh interface.     

活性炭/CoFe2O4复合物的制备及其对亚甲基蓝的吸附性能

通过低温回流法制备了具有磁分离响应的活性碳(AC)与CoFe₂O₄的复合物AC/CoFe₂O₄（MAC）。采用批式吸附实验法对MAC吸附溶液中偶氮染料亚甲基蓝（MB）的吸附动力学过程及吸附平衡进行了研究,考察了溶液初始pH值对MAC吸附MB的影响。结果表明,MAC吸附MB的过程很快,20 min几乎达到平衡。MAC吸附MB过程可以用准二级动力学方程描述。等温吸附过程服从Langmuir方程,MAC对MB的饱和吸附容量为120.48 mg/g。在较低pH值时,MB吸附量较小。随着pH值的升高,MAC对MB的吸附量增大。     

Gelation kinetics of PAM/PEI system

Excess water production in oil and gas wells causes serious productivity and environmental problems in the oilfield. A mixture composed of a polymer, cross-linker, and water is usually injected into the reservoir to block unwanted water by forming a three-dimensional structure. This transition process from solution to gel is a function of temperature, time, salinity of mixing water, and concentration of the various components. The gelling solution was prepared by mixing polyacrylamide (PAM) with distilled water, and then polyethylenimine (PEI) was added as a cross-linker. The injection process was simulated and investigated by differential scanning calorimeter (DSC) over the temperature range of 80–120 °C. The DSC dynamic scan showed two consecutive peaks. An endothermic peak was observed at low temperature due to PAM alkaline hydrolysis which ends at around 60 °C. Another exotherm was observed at ~70 °C which corresponds to the onset of cross-linking of PAM and PEI. It was found that high temperatures lead to high release of heat due to gelation. The effect of salts on the cross-linking was also examined. More delay in cross-linking was observed in the case of NH₄Cl compared to NaCl. The gelation kinetics was modeled using a rate process model that relates fractional gelation with time. Further, Avrami model, usually used to study crystallization kinetics, was also used to model the gelation process. Kinetic parameters were obtained from the two different models, and the results showed good agreement with experimental data. The presence of salts in seawater leads to a drop of 60–80 % in the rate constant without influencing the order of the gelation reaction.     

Dsc Evaluations in F.c.c. Solid Solutions of Short-range-order Kinetics As Influenced by Bound Vacancies

A modified first order kinetic law, which describes the roles of bound and unbound vacancies, is proposed in order to predict defect decay and short-range-order kinetics of quenched binary alloys during linear heating experiments. The model has been applied to differential scanning calorimetry (DSC) curves of Cu–5 at%Zn quenched from different temperatures. Activation energy for migration of solute-vacancy complexes was also assessed from the kinetics of short-range-order using DSC traces. A value of 89.5±0.32 kJ mol^–1 was obtained. The relative contribution of bound and unbound vacancies to the ordering process as influenced by quenching temperature was determined. In conjunction, a parametric study of the initial total defect concentration and effective energy for defect migration was performed in order to envisage their influence on the calculated DSC profiles. This revised version was published online in August 2006 with corrections to the Cover Date.     

Adsorption equilibrium and kinetics on N-lauroyl-N-methylglucamide at air/water interface

The adsorption equilibrium and kinetics of N-lauroyl-N-methylglucamide (MEGA-12) aqueous solution were studied. The critical micelle concentration, the maximum surface excess, and the minimum area per molecule of MEGA-12 were obtained as 2.48 × 10⁻⁴ mol/l, 4.883 × 10⁻⁶ mol/m², and 0.34 nm², respectively. The adsorption kinetics of MEGA-12 was studied by the maximum bubble pressure method. The result shows that in the initial stage or at small MEGA-12 concentrations, the adsorption process is diffusion-controlled; however, it changes to become adsorption-controlled at the end of the process. The effects of temperature, inorganic salts, alcohols, and ionic liquid on the adsorption kinetics were also discussed. The text was submitted by the authors in English.