Thermal stability and degradation of Co(II), Cd(II), and Zn(II) complexes with <Emphasis Type="Italic">N</Emphasis>-benzyloxycarbonylglycinato ligand

Thermal behavior of Co(II), Cd(II), and Zn(II) complexes with N-benzyloxycarbonylglycinato ligand was investigated using the results of TG, DSC and DTG analysis obtained at different heating rates (2.5 to 30 °C min⁻¹), from room temperature to about 900 °C. Mechanisms of complex degradation, as well as enthalpies of the degradation processes were determined. It is shown that thermal stability of investigated complexes correlates with their crystal structures, especially with the presence of crystallization and coordinated water molecules. The values of dehydration enthalpies are discussed and correlated with composition of the complexes. Kissinger’s, Ozawa’s, and Friedman’s isoconversion methods were used for the determination of kinetic parameters: the pre-exponential factor A and the apparent activation energy E _a. For all three complexes and all steps of degradation, the values of kinetics parameters obtained by Kissinger’s and Ozawa’s methods are in good agreement. The results obtained by Friedman’s method showed that some decomposition steps are simple and some others are complex ones.     

Bioproduction of Food Additives Hexanal and Hexanoic Acid in a Microreactor

Hexanal and hexanoic acid have number of applications in food and cosmetic industry because of their organoleptic characteristics. Problems like low yields, formation of unwanted by-products, and large quantities of waste in their traditional production processes are the reasons for developing new production methods. Biotransformation in a microreactor, as an alternative to classical synthesis processes, is being investigated. Because conditions in microreactors can be precisely controlled, the quality of the product and its purity can also be improved. Biocatalytic oxidation of hexanol to hexanal and hexanoic acid using suspended and immobilized permeabilized whole baker’s yeast cells and suspended and immobilized purified alcohol dehydrogenase (ADH) was investigated in this study. Three different methods for covalent immobilization of biocatalyst were analyzed, and the best method for biocatalyst attachment on microchannel wall was used in the production of hexanal and hexanoic acid.     

Thermal degradation kinetics of poly(methylphenylsiloxane) containing methacryloyl groups

The kinetics of the thermal degradation of polymethylphenylsiloxane containing methacryloyl groups (PMPS-M) were investigated by thermogravimetric analysis (TGA). Thermal degradation of PMPS-M had two different processes: “unzipping degradation” and “rearrangement degradation”. The corresponding kinetic parameters of the two degradation stages were determined by using Friedman and Flynn-Wall-Ozawa methods, respectively. Coats-Redfern and Phadnis-Deshpande methods were also used to discuss the probable degradation mechanisms of the two different stages. The results showed that the activation energy obtained from Friedman method was in good agreement with the value obtained using Flynn-Wall-Ozawa method. The solid-state decomposition mechanism followed by the first degradation stage of PMPS-M was a decelerated D₄ type (three-dimensional diffusion controlled reaction). However, as for the second degradation stage of PMPS-M, its solid-state decomposition mechanism corresponded to a sigmoidal A₃ type, a nucleation and growth mechanism.     

Use of NIR spectroscopy in the production of modified industrial resins

Natural resins are scarcely used, but after appropriate modification processes they acquire characteristics of viscosity, point of softening, stability, etc. that facilitate their application in fields such as paintings, varnishes, cosmetic, etc. The complexity of resins makes it very difficult to monitor the reactions involved in their modification, the extent of which is usually determined via more experimentally accessible parameters. However, the methods typically used to determine such parameters are slow and produce environmentally unfriendly waste.In this work, we assessed the potential of NIR spectroscopy, as an alternative to the traditional analytical methods, for monitoring the industrial processes involved in the production of modified resins. To this end, we developed PLS calibration models that were used to quantify physical (viscosity and cloud point) and chemical parameters (acid and hydroxyl numbers), with a view to characterize the evolution of the resins during the reaction that take place throughout the fabrication process.Samples were withdrawn at different times stages of the process for analysis with the proposed quantitation models; the data thus obtained were compared with those provided by reference methods. Based on the results, NIR spectroscopy is an effective choice for the accurate, expeditious monitoring of industrial resin modification processes.     

Application of polyurethane foam as a sorbent for trace metal pre-concentration — A review

The first publication on the use of polyurethane foam (PUF) for sorption processes dates back to 1970, and soon after the material was applied for separation processes. The application of PUF as a sorbent for solid phase extraction of inorganic analytes for separation and pre-concentration purposes is reviewed. The physical and chemical characteristics of PUF (polyether and polyester type) are discussed and an introduction to the characterization of these sorption processes using different types of isotherms is given. Separation and pre-concentration methods using unloaded and loaded PUF in batch and on-line procedures with continuous flow and flow injection systems are presented. Methods for the direct solid sampling analysis of the PUF after pre-concentration are discussed as well as approaches for speciation analysis. Thermodynamic proprieties of some extraction processes are evaluated and the interpretation of determined parameters, such as enthalpy, entropy and Gibbs free energy in light of the physico-chemical processes is explained.     

Development of Methods to Determine the Infrared-Optical Properties of Polymer Films

Summary: In this paper, two methods for the determination of infrared optical properties of thick polymer films, based on FTIR spectroscopy, were implemented and used. Complex index of refraction data were generated for various ethylene copolymer films. Transmittance and reflectance spectra were measured in the mid infrared range using a gold-coated 100 mm-diameter integrating sphere. For the investigated films n and k values ranging from 1.3 to 1.6 and from 10⁻⁴ to 0.25 were determined, respectively. Regarding n, a good agreement was obtained for both methods, the transmittance/reflectance procedure (T/R method) used for transparent and semitransparent regions, and Single Substractive Kramers-Kronig (SSKK) algorithm applied for non-transparent regions. The highest k values were determined for the CH₂ stretching vibration. The k values are dependent on comonomer content and film thickness. The combination of both methods allows for an accurate determination of n and k in the entire IR region relevant for solar application.     

Application of advanced oxidation processes for removing salicylic acid from synthetic wastewaters

<正>In this study,advanced oxidation processes(AOPs) such as anodic oxidation(AO),UV/H_2O_2 and Fenton processes(FP) were investigated for the degradation of salicylic acid(SA) in lab-scale experiments.Boron-doped diamond(BDD) film electrodes using Ta as substrates were employed for AO of SA.In the case of FP and UV/H_2O_2,most favorable experimental conditions were determined for each process and these were used for comparing with AO process.The study showed that the FP was the most effective process under acidic conditions,leading to the highest rate of SA degradation in a very short time interval.However,the results showed that Ta/BDD films had high electrocatalytic activity for complete degradation of SA;even if it employs more time for complete elimination of the SA respect to FP.Additionally,AO led to a sixfold acceleration of the oxidation rate compared with the UV/H_2O_2 process.Finally a rough comparison of the specific energy consumption shows that AO process reduced the energy consumption by at least 90%compared with the UV/H_2O_2 process.     

Thermal analysis and kinetics of the copper-lead matte roasting process

In this paper, the results of copper-lead matte investigations are presented. Investigated copper-lead matte is intermediate product of the lead production in TREPCA-Zvečan. In the first part of the paper characterization of starting material is presented, consisting of: chemical composition analysis (XRQ), scanning electron microscopy (SEM) and diffractometry (XRD). Thermal properties of investigated matte were determined using differential thermal analysis (DTA) at characteristic temperatures. Using results of induced analysis, mechanism of matte oxidation process was determined. In the second part of the paper kinetic parameters describing oxidative roasting of copper-lead matte are presented. For activation energy calculations, non-isothermal methods defined by Kissinger and Ozawa were used [1, 2]. Kinetic equation describing oxidation process was determined using Sharps method of reduced half time of reaction [3].     

Instrumental Dependent Dissociations of n-Propyl/Isopropyl Phosphonate Isomers: Evaluation of Resonant and Non-Resonant Vibrational Activations

Structural elucidation and distinction of isomeric neurotoxic agents remain a challenge. Tandem mass spectrometry can be used for this purpose in particular if a “diagnostic” product ion is observed. Different vibrational activation methods were investigated to enhance formation of diagnostic ions through consecutive processes from O,O-dialkyl alkylphosphonates. Resonant and non-resonant collisional activation and infrared multiphoton dissociation (IRMPD) were used with different mass spectrometers: a hybrid quadrupole Fourier transform ion cyclotron resonance (Qh-FTICR) and a hybrid linear ion trap-Orbitrap (LTQ/Orbitrap). Double resonance (DR) experiments, in ion cyclotron resonance (ICR) cell, were used for unambiguous determination of direct intermediate yielding diagnostic ions. From protonated n-propyl and isopropyl O-O-dialkyl-phosphonates, a diagnostic m/z 83 ion characterizes the isopropyl isomer. This ion is produced through consecutive dissociation processes. Conditions to favor its formation and observation using different activation methods were investigated. It was shown that with the LTQ, consecutive experimental steps of isolation/activation with modified trapping conditions limiting the low mass cut off (LMCO) effect were required, whereas with FT-ICR by CID and IRMPD the diagnostic ion detection was provided only by one activation step. Among the different investigated activation methods it was shown that by using low-pressure conditions or using non-resonant methods, efficient and fast differentiation of isomeric neurotoxic agents was obtained. This work constitutes a unique comparison of different activation modes for distinction of isomers showing the instrumental dependence characteristic of the consecutive processes. New insights in the dissociation pathways were obtained based on double-resonance IRMPD experiments using a FT-ICR instrument with limitation at low mass values.

Study on the equilibria of the complex formation of molybdenum(VI) with 3,5-dinitrocatehol and 3-(2-naphthyl)-2,5-diphenyl-2H-tetrazolium chloride

The formation of an ion-associated complex between the anionic chelate of Mo(VI)–3,5-dinitrocatehol (3,5-DNC) and the cation of 3-(2-naphthyl)-2,5-diphenyl-2H-tetrazolium chloride (TV) in the liquid–liquid extraction system Mo(VI)–3,5-DNC–TV–H₂O–CHCl₃ was studied by spectrophotometry. The optimum conditions for the complex formation and extraction of the ion-associated complex were established. The effect of co-existing ions and reagents on the process of complex formation was investigated under optimum extraction conditions. The validity of Beer’s law was checked and some analytical characteristics were calculated. The association process in aqueous phase and the extraction equilibria were investigated and quantitatively characterized. The following key constants of the processes were calculated: association constant, distribution constant, extraction constant and recovery factor. The molar ratio of the reagents was determined by independent methods. Based on this, a reaction scheme, a general formula and a structure of the complex were suggested.     

High Sensitive Sensor Based on Carbon Nanotube Electrode for Determination of Lanthanum in the Presence of Calcon Carboxylic Acid

In this paper we have investigated the electrochemical activity of lanthanum chloride (La (III)) in the presence of calcon carboxylic acid (CCA) using a multi-walled carbon nano tube/carbon paste electrode (CNT/CPE). The peak current increases linearly with increasing of the La (III) concentration. For this purpose, a few electrochemical methods such as cyclic, differential pulse voltammetry, linear sweep and hydrodynamic voltammetry, and chronoamperometry were used. The results show that calcon carboxylic acid as a ligand was useful for determination of La (III) and was able to improve its sensitivity. Cyclic voltammetry was used for study of reduction reaction of La (III) at the surface of modified electrode. The electrochemical parameters for La (III) at the surface of CNT/CPE, such as diffusion coefficient (D/ cm² s ^?1 = 5.26 × 10^?6), the electron transfer coefficient, (α = 0. 43), and the reduction rate constant, (k/ M s^?1 = 2.33 (±0.015) × 10²), were determined using voltammetry methods, which with the detection limit of La (III) by differential pulse voltammetry was found to be 1.3 nM. The combination of CCA with CNT as mediators in carbon paste electrode showed that this electrode is capable, sensitive, and simple to quantify La (III) in real samples with an average recovery of 97.64%.     

Application of isoconversional and multivariate non-linear regression methods for evaluation of the degradation mechanism and kinetic parameters of an epoxy resin

The thermo-oxidative degradation of an epoxy resin obtained by curing of an industrially produced DGEBA mixture with 4,4′-methylene-dianiline (MDA) and used as electric insulator has been investigated by TG + DTG + DSC simultaneous analyses performed in static air atmosphere, at five heating rates. TG, DTG and DSC curves showed that, in the temperature range 25-900 °C, a glass transition followed by three thermo-oxidative processes occur. The processing of the non-isothermal data corresponding to the first process of thermo-oxidation was performed by using Netzsch Thermokinetics - A Software Module for Kinetic Analysis. The dependence of the activation energy, evaluated by isoconversional methods, on the conversion degree and the relative high standard deviations of this quantity show that the investigated process is a complex one. The mechanism and the corresponding kinetic parameters were determined by multivariate non-linear regression program and checked for quasi-isothermal data. It was pointed out that the first process of thermo-oxidation of the investigated resin consists in four steps, each step having a specific kinetic triplet. The obtained results were used for prediction of the thermal lifetime of the material corresponding to some temperatures of use and the end point criterion 5% and 10% mass loss.     

Fundamentals of 2, 4 Dichlorophenoxyacetic Acid Removal from Aqueous Solutions

Herbicides are widely used in farmlands worldwide. However, after their application on farmlands, they accumulate in high amounts in continental and marine waters. Herbicides are endocrine disruptors, and are known to cause toxicity, carcinogenicity and mutagenicity. Besides, they also spoil the taste and odor of water bodies. To prevent these effects, it is necessary to perform an in-depth study on various herbicide removal methods. This review discusses the various methods of herbicide removal from aqueous body, using a commonly used herbicide (2,4-dichlorophenoxyacetic acid) as a representative chemical. This paper includes a systematic tabulated review of all reported removal methods with important parameters and their mechanism. Adsorption, biological degradation, electrochemical treatment, Fenton degradation, oxidation, ozonation and photocatalytic degradation are investigated and compared for removal of 2,4-D. The advantages and disadvantages and the factors influencing selection of the aforementioned processes are discussed.     

Thermal and kinetic analyses of 2,5-bis(2-hydroxyphenyl)thiazolo[5,4-d]thiazole

Thermal behavior and UV–Vis absorption properties of 2,5-bis(2-hydroxyphenyl)thiazolo[5,4-d]thiazole were investigated in the present study. It was found that decomposition occurs in two stages which correspond to removal of both phenolic rings and degradation of remaining core structure, respectively. After the characterization of decomposition stages, apparent activation energy values of each stage were calculated using model-free isoconversional methods (FWO and KAS). Apparent activation energies of decomposition stages are determined by both methods. Their averages are calculated as 98.232 and 123.253 kJ mol^?1 in consecutive order. UV–Vis absorption properties of this compound have been determined with using different solvents.     

NMR measurements of gaseous sulfur hexafluoride (SF6) to probe the cross-linking of EPDM rubber

The effects of embedding gaseous SF6 into EPDM rubber were investigated using NMR methods. It was found that observed sorption and desorption processes follow the behavior of the dual mode sorption model. A strong correlation was found between EPDM cross-linking and transversal relaxation time of embedded SF6. EPDM samples with different cross-link densities, preliminarily determined by 1H transversal relaxation using the Gotlib model and Litvinov's method, were investigated using embedded SF6. The sensitivity of the 19F transversal relaxation rate of SF6 to the EPDM cross-link density variation was found to be at least 10 times higher than for 1H in the polymer chain. First experiments on probing the swelling effects in EPDM due to its contact with polar liquids have been performed.     

Relationships between strain,microstructure and oxide growth at the nano‐ and microscale

In the present article, the relationships between oxidation processes, surface strains and the microstructure of duplex stainless steels were investigated. Specimens were oxidized at 500 °C under secondary vacuum for 1 h to form a thin oxide film (thickness in the range of 20–50 nm). Such specimens were considered as the model system for developing novel methods of analysis in understanding the behavior of passive films. The interfacial strain field after oxidation was measured experimentally at the microscale using the point grid method. On the other hand, the chemical composition of the oxide film was determined at the submicroscopic scale by means of local scanning Auger spectroscopy (with a spot diameter of 50 nm). Local variations of the chemical composition of the oxide film were analyzed according to the specimen microstructure and the strain field. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of dissolution processing of PVA blends on the characteristics of their hydrogels synthesized by radiation—Part I: Gel fraction,swelling, and mechanical properties

In this work several hydrogels were obtained with two different poly(vinyl alcohol)s/PVAs as the main polymer in aqueous solutions containing 10% of PVA, 0.6% of agar, and 0.6% of κ-carrageenan (KC), cross-linked by gamma-rays from a ⁶⁰Co irradiation source. The PVAs tested have different degrees of hydrolysis and viscosities at 4% with values closed to 30 mPa s. The aqueous polymeric solutions were prepared using two distinct processes: the simple process of heating–stirring and that of making use of an autoclave. The purpose of this study was to evaluate the influence of the dissolution process by means of both methods on the hydrogels’ properties obtained. These were investigated by means of degree of cross-linking/gel fraction, degree of swelling in water, and some mechanical properties. The results that are obtained for hydrogels synthesized from solutions of PVA, agar, KC, and blends thereof prepared by both dissolution processes showed higher degrees of swelling for hydrogels from the autoclaved polymer solutions than those from the solutions prepared by simple heating–stirring process. Furthermore, their hydrogels containing totally hydrolyzed PVA displayed higher tensile strength and lower elongation properties.     

在线富集-微乳液毛细管电动色谱法分析食品塑料袋中邻苯二甲酸酯类化合物

建立了微乳液毛细管电动色谱(MEEKC)模式下,采用常规样品堆积模式(normal stacking mode, NSM)和反向极性堆积模式(reversed electrode polarity stacking mode, REPSM)两种在线富集邻苯二甲酸酯类化合物(phthalate esters, PAEs)的简便、有效方法。与常规MEEKC方法相比,REPSM-MEEKC方法使4种PAEs的检测灵敏度提高了937.5～7143倍。考察了常规MEEKC的分离条件,分别对影响两种富集过程的一些因素进行了研究,同时对两种富集方法的重现性和检出限等进行了考察。NSM-MEEKC和REPSM-MEEKC对邻苯二甲酸酯类化合物的检出限(按信噪比(S/N)=3计)分别为0.021～0.33 mg/L和0.7～4 μg/L。其中,灵敏度更高的REPSM-MEEKC方法已成功应用于食品塑料袋中邻苯二甲酸酯类化合物的测定,加标回收率为89.1%～105.6%,结果令人满意。