Quantitative analysis of hydrolysis of carbaryl in tap water and river by excitation-emission matrix fluorescence coupled with second-order calibration

A novel method was proposed to determine simultaneously carbaryl and its degradation product 1-naphthol in river and tap water in this paper. The parallel factor analysis (PARAFAC) algorithm was adopted to analyze the excitation–emission matrix (EEM) fluorescence data. The second-order advantage of the PARAFAC-based second-order calibration algorithm was exploited, which make it possible that calibration can be performed even in the presence of unknown interferences. Good recoveries were obtained although the excitation and emission spectral profiles of the analytes were overlapped with background in the river water. It was also applied to investigate the hydrolysis kinetics of carbaryl in river water and tap water. The rate equation, the rate constant and the half life were calculated.     

Preparation and characterization of manganese(IV) in aqueous acetic acid

Mn(IV) acetate was generated in acetic acid solutions and characterized by UV-vis spectroscopy, magnetic susceptibility, and chemical reactivity. All of the data are consistent with a mononuclear manganese(IV) species. Oxidation of several substrates was studied in glacial acetic acid (HOAc) and in 95:5 HOAc-H(2)O. The reaction with excess Mn(OAc)(2) produces Mn(OAc)(3) quantitatively with mixed second-order kinetics, k (25.0 °C) = 110 ± 4 M(-1) s(-1) in glacial acetic acid, and 149 ± 3 M(-1) s(-1) in 95% AcOH, ΔH(?) = 55.0 ± 1.2 kJ mol(-1), ΔS(?) = -18.9 ± 4.1 J mol(-1) K(-1). Sodium bromide is oxidized to bromine with mixed second order kinetics in glacial acetic acid, k = 220 ± 3 M(-1) s(-1) at 25 °C. In 95% HOAc, saturation kinetics were observed.     

Modeling adsorption rate of organic micropollutants present in landfill leachates onto granular activated carbon

The overall adsorption rate of single micropollutants present in landfill leachates such as phthalic acid (PA), bisphenol A (BPA), diphenolic acid (DPA), 2,4-dichlorophenoxy-acetic acid (2,4-D), and 4-chloro-2-methylphenoxyacetic acid (MCPA) on two commercial activated carbons was studied. The experimental data obtained were interpreted by using a diffusional model (PVSDM) that considers external mass transport, intraparticle diffusion, and adsorption on an active site. Furthermore, the concentration decay data were interpreted by using kinetics models. Results revealed that PVSDM model satisfactorily fitted the experimental data of adsorption rate on activated carbon. The tortuosity factor of the activated carbons used ranged from 2 to 4. The contribution of pore volume diffusion represented more than 92% of intraparticle diffusion confirming that pore volume diffusion is the controlling mechanism of the overall rate of adsorption and surface diffusion can be neglected. The experimental data were satisfactorily fitted the kinetic models. The second-order kinetic model was better fitted the experimental adsorption data than the first-order model.     

From Langmuir kinetics to first- and second-order rate equations for adsorption

So far, the first- and second-order kinetic equations have been most frequently employed to interpret adsorption data obtained under various conditions, whereas the theoretical origins of these two equations still remain unknown. Using the Langmuir kinetics as a theoretical basis, this study showed that the Langmuir kinetics can be transformed to a polynomial expression of dtheta t /d t = k 1(theta e - theta t ) + k 2(theta e - theta t ) (2), a varying-order rate equation. The sufficient and necessary conditions for simplification of the Langmuir kinetics to the first- and second-order rate equations were put forward, which suggested that the relative magnitude of theta e over k 1/ k 2 governs the simplification of the Langmuir kinetics. In cases where k 1/ k 2 is greater than theta e or k 1/ k 2 is very close to theta e, adsorption kinetics would be reasonably described by the first-order rate equation, whereas the Langmuir kinetics would be reduced to the second-order equation only at k 1/ k 2 < theta e. It was further demonstrated that both theta e and k 1/ k 2 are the function of initial adsorbate concentration ( C 0) at a given dosage of adsorbent, indicating that simplification of the Langmuir kinetics indeed is determined by C 0. Detailed C 0-depedent boundary conditions for simplifying the Langmuir kinetics were also established and were verified by experimental data.     

Rank annihilation factor analysis method for spectrophotometric study of second-order reaction kinetics

In this study several methods are described to determine the rate constant of a second-order reaction in the form of A+B→C. These approaches allow circumventing a rank deficiency inherent of a second-order reaction when the spectroscopic data is influenced by additional source of variance. Classically, to determine the unknown rate constant in this kind of systems, one needs to have extra knowledge about the system, including the spectra of the reactants or product and the exact kinetics. In the case of the presence of an unknown phenomenon in the data set that cannot be explained by the model, such as baseline drift, the estimated rate constant might be erroneous. Present work is a modification of the rank annihilation factor analysis (RAFA) algorithm by inclusion of I) pure spectra of reactants, or IIA) mean centering step, or IIB) mean spectrum. The proposed methods can interestingly be applied on a single kinetic run. The performances of the new methods have been evaluated by applying them to analysis of simulated and experimental data.     

Experimental study of non-linear second-order analytical data with focus on the second-order advantage

Three different experimental systems have been studied regarding the determination of analytes in complex samples, using non-linear second-order instrumental data, which are intrinsically able to provide the second-order advantage. This permits the quantitation of calibrated analytes in the presence of unexpected sample components, although a suitable algorithm is required. The recently described combination of artificial neural networks with post-training residual bilinearization has been applied to the three data sets, with successful results concerning prediction accuracy and precision, as well as profile recovery for the potential interferents in test samples. The studies involve: (1) the determination of two pharmaceuticals in the presence of an unexpected excipient by absorbance-pH matrix measurements, (2) the quantitation of iron(II) by its catalytic effect on the kinetics of the bromate oxidation of a colorant in the presence of a second interfering organic dye, and (3) the analysis of the antibiotic amoxicillin by fluorescence excitation-emission matrices in the presence of a fluorescent anti-inflammatory. The prediction results were compared and shown to be significantly better than those yielded by the unfolded partial least-squares/residual bilinearization model, due to the non-linear nature of the studied data.     

ABSORPTION OF METAL IONS AND SWELLING PROPERTIES OF POLY(ACRYLIC ACID-CO-ITACONIC ACID) HYDROGELS

Hydrogels of acrylic acid and itaconic acid has been synthesized with different monomers ratios. The swelling process of the different xerogels immersed in water and salt solutions has been studied. The swelling of hydrogels loaded with metal cations (Cu²⁺, Zn²⁺) was also investigated. The swelling process was monitored by the increase in the weight of hydrogel as a function of time. The absorption properties of metal ions were studied by using the hydrogel, and different concentrations of copper and zinc solutions (prepared from sulphate salts). The influence of pH on the absorption process was studied. For the absorption of metal ions, the amount of ions absorbed within the hydrogel can be calculated from the initial and equilibrium concentrations of the metal ions in aqueous phase, the weight of the hydrogel, and the volume of solution used. Metal absorption increased when pH, salt concentration in external solution and itaconic acid content is levelled.

The swelling isotherms which consisted of an initial fast increase levelled off asymptotically to the equilibrium swelling limit. The experimental data clearly suggest that our hydrogels follow a second-order kinetics for both cases (unload and metal loaded). The kinetics rate constant and the equilibrium water content, K, have been calculated for every monomer ratio from the experimental data according to the kinetics equation. Both magnitudes decreased as the itaconic acid content decreases in the xerogels.     

Autocatalysis and equilibrium in polyimide synthesis

Model compounds have been used to determine the mechanism of the reaction of aromatic diamines with aromatic cyclic dianhydrides to form poly(amic acids). Phthalic anhydride was used to model the anhydride functionality, while either 4,4′-diaminodiphenyl ether or aniline was used for the amine functionality. The reaction between these materials was shown to follow second-order, autocatalytic, and reversible kinetics. The rate constants for the mechanism were determined using a Runge–Kutta numerical integration of the rate equation and a Fibonacci technique to determine the reverse rate constant which minimzed the sum of squared deviations of the experimental data from the predicted line. Autocatalytic reversible kinetics are also followed by the formation of the poly(amic acid) precursor to a thermoplastic polyimide. In this polymerizing system, pyridine shifts the equilibrium to higher degrees of conversion to give higher molecular weights, while the opposite effect is obtained with acetic acid. Similarly, low temperatures favor higher equilibrium conversion and higher molecular weights. Thus the molecular weight of polyimides can be systematically controlled by manipulating factors which control the equilibrium conversion during the original formation of the poly(amic acid) precursor.     

Energetics of the Acid-Catalyzed o-Cresol-Formaldehyde Reaction

The acid-catalyzed reaction of o-cresol with formaldehyde follows second-order kinetics. The reaction was carried out at 65, 70, 75, and 80°C and at pH values of 1.30, 1.80, 2.00, 2.50, and 3.00, using hydrochloric acid as a catalyst. The rate was found to increase with decreasing pH. The overall rate constant (k) has been resolved into stepwise rate constants (k₁ and k₂) for the formation of monomethylol and methylene derivatives. Values of Arrhenius parameters and of the entropy of activation for the overall reaction were also calculated. A mechanism consistent with our kinetic data is given.     

Kinetics and mechanism of oxidation of L-ascorbic acid by platinum(IV) in aqueous acid medium

The oxidation of l-ascorbic acid (H₂A) by platinum(IV) in aqueous acid medium exhibits overall second-order kinetics, being first order with respect to each reactant. Increasing both hydrogen and chloride ion concentrations inhibits the rate. The stoichiometry involves reaction of one platinum(IV) ion with H₂A to give dehydroascorbic acid. A reaction mechanism consistent with all the experimental observations is proposed.     

Palladium η3-allyl complex with sorbic acid: Kinetics and mechanism of protodemetalation in aqueous solutions

The allyl complex di-μ-chloro-bis[(1,2,3-η)-1-carboxy-3-(1-hydroxyethyl)allyl]dipalladium (which is a hydroxyl-containing palladium η³-allyl complex based on sorbic acid) has been synthesized from trans,trans-2,4-hexadienic (sorbic) acid and Na₂PdCl₄ in an aqueous solution. The complex has been isolated from the reaction solution and has been characterized by IR, ¹H NMR, and ¹³C NMR spectroscopy. Its composition has been determined by elemental analysis. The protodemetalation kinetics of the complex in aqueous solutions has been studied. The rate of this reaction obeys a second-order equation, first-order with respect to each reactant. A reaction mechanism has been derived from protodemetalation kinetics and data characterizing the state of the reactants.     

The effect of electron-withdrawing properties of substituents on the hydrolysis of some Schiff bases

The dissociation kinetics of the Schiff bases investigated in the present paper [N,N-bis(X-benzylidenes)ethylenediamine], have been examined under basic and acidic conditions, in aqueous medium 25% acetone in water (wt-wt). The base hydrolysis reaction of these compounds was found to follow second-order kinetics, first-order with respect to each of the Schiff base and the hydroxide ions. The rate-determining step is suggested to be the hydroxide ions attack on the free base. The effect of acetone ratio, in hydrolysis medium, has been studied under alkaline conditions. It is deduced that both the hydrogen bonding formation and solvent-solvent interaction have a pronounced role in such hydrolysis reactions. The acid hydrolysis reaction is strictly second-order kinetics, first-order with respect to the Schiff base and also to the hydrogen ions, and the attack of water molecules on the protonated substrate becomes the rate-determining step. A slower rate of the base hydrolysis was observed through the Schiff base II (p-NO₂), on the other hand, a fast acid hydrolysis rate was detected in the case of compound III (p-COOH). Furthermore, from the effect of temperature on the reaction rate, the various thermodynamic parameters have been also calculated and discussed.     

PREPARATION AND CHARACTERIZATION OF NOVEL CHITOSAN DERIVATIVES:ADSORPTION EQUILIBRIUM OF IRON(Ⅲ)ION

The adsorption of Fe(Ⅲ)ions from aqueous solution by chitosan alpha-ketoglutaric acid(KCTS)and hydroxamated chitosan alpha-ketoglutaric acid(HKCTS)was studied in a batch adsorption system.Experiments were carried out as function of pH,temperature,agitation rate and concentration of Fe(Ⅲ)ions.The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and isotherm constants were determined.The Langmuir model agrees very well with experimental data.The pseudo-first-order and second-order kinetic models were used to describe the kinetic data and the rate constants were evaluated.The dynamical data fit well with the second-order kinetic model.The pseudo second-order kinetic model was indicated with the activation energy of 19.61 and 7.98 KJ/mol for KCTS and HKCTS,respectively.It is suggested that the overall rate of Fe(Ⅲ)adsorption is likely to be controlled by the chemical process.Results also showed that novel chitosan derivatives(KCTS and HKCTS)were favorable adsorbents.     

The maintenance of the second-order advantage: second-order calibration of excitation-emission matrix fluorescence for quantitative analysis of herbicide napropamide in various environmental samples

A rapid non-separative spectrofluorometric method based on the second-order calibration of excitation-emission matrix (EEM) fluorescence was proposed for the determination of napropamide (NAP) in soil, river sediment, and wastewater as well as river water samples. With 0.10 mol L⁻¹ sodium citrate-hydrochloric acid (HCl) buffer solution of pH 2.2, the system of NAP has a large increase in fluorescence intensity. To handle the intrinsic fluorescence interferences of environmental samples, the alternating penalty trilinear decomposition (APTLD) algorithm as an efficient second-order calibration method was employed. Satisfactory results have been achieved for NAP in complex environmental samples. The limit of detection obtained for NAP in soil, river sediment, wastewater and river water samples were 0.80, 0.24, 0.12, 0.071 ng mL⁻¹, respectively. Furthermore, in order to fully investigate the performance of second-order calibration method, we test the second-order calibration method using different calibration approaches including the single matrix model, the intra-day various matrices model and the global model based on the APTLD algorithm with nature environmental datasets. The results showed the second-order calibration methods also enable one or more analyte(s) of interest to be determined simultaneously in the samples with various types of matrices. The maintenance of second-order advantage has been demonstrated in simultaneous determinations of the analyte of interests in the environmental samples of various matrices.     

Ultratrace kinetic measurements of the reduction of methylene blue

The kinetics of methylene blue reduction by ascorbic acid in acetonitrile was investigated by cavity ring-down spectroscopy. Because of our high sensitivity we were able to use very low concentrations (1-10 nM) of the dye. Under these conditions, we observed a second-order loss of dye as well as a competing back reaction with dissolved oxygen. The use of an inexpensive diode laser and a relatively simple setup should make ultratrace kinetic studies more accessible.     

PREPARATION AND CHARACTERIZATION OF NOVEL CHITOSAN DERIVATIVES: ADSORPTION EQUILIBRIUM OF IRON(Ⅲ) ION

The adsorption of Fe(Ⅲ)ions from aqueous solution by chitosan alpha-ketoglutaric acid(KCTS)and hydroxamated chitosan alpha-ketoglutaric acid(HKCTS)was studied in a batch adsorption system.Experiments were carried out as function of pH,temperature,agitation rate and concentration of Fe(Ⅲ)ions.The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and isotherm constants were determined.The Langmuir model agrees very well with experimental data.The pseudo-first-order and second-order kinetic models were used to describe the kinetic data and the rate constants were evaluated.The dynamical data fit well with the second-order kinetic model.The pseudo second-order kinetic model was indicated with the activation energy of 19.61 and 7.98 kJ/mol for KCTS and HKCTS,respectively.It is suggested that the overall rate of Fe(Ⅲ)adsorption is likely to be controlled by the chemical process.Results also showed that novel chitosan derivatives(KCTS and HKCTS)were favorable adsorbents.     

Kinetics of anhydride formation in poly(acrylic acid) and its effect on the properties of a PAA-alumina composite

The kinetics of anhydride formation of poly(acrylic acid) (PAA) in porous PAA–alumina composites have been investigated by using a thermogravimetric technique (TGA). Three distinct reaction peaks at 200°C (I), 250°C (II), and 390°C (III) were identified in the dynamic TGA thermogram. These peaks were attributed to bound water removal (I), anhydride formation (II), and polymer degradation (III). The kinetics of the anhydride reaction were studied in a temperature range of 220–240°C and found to follow a second-order mechanism with an activation energy of approximately 38 kcal/mole. In addition, the bound water was found to inhibit the onset of anhydride formation. The degree of conversion to anhydride was correlated with the equilibrium swelling level attained by the composite in water.     

Kinetics and mechanism of the comproportionation of hypothiocyanous acid and thiocyanate to give thiocyanogen in acidic aqueous solution

The kinetics of comproportionation of hypothiocyanous acid (HOSCN) and thiocyanate (SCN-) to give thiocyanogen ((SCN)2) in acidic aqueous solutions have been determined by double-mixing stopped-flow UV spectroscopy. Hypothiocyanite (OSCN-) was generated at pH 13 by oxidation of excess SCN- with hypobromite (OBr-), followed by a pH jump to acidic conditions ([H+] = 0.20-0.46 M). The observed pseudo-first-order rate constants exhibit first-order dependencies on [H+] and [SCN-] with overall third-order kinetics. The corresponding kinetics of hydrolysis of (SCN)2 have also been examined. Under conditions of high (and constant) [H+] and [SCN-], the kinetics exhibit second-order behavior with respect to [(SCN)2] and complex inverse dependences on [H+] and [SCN-]. Under conditions of low [H+] and [SCN-], the kinetics exhibit first-order behavior with respect to [(SCN)2] and independence with respect to [H+] and [SCN-]. We attribute this behavior to a shift in the rate-limiting step from disproportionation of HOSCN (second-order dependency on [(SCN)2]) to rate-limiting hydrolysis (first-order dependency on [(SCN)2]). Thus, we have determined the following equilibrium constant by the kinetic method: (SCN)2 + H2O HOSCN + SCN- + H+; Khyd = [HOSCN][SCN-][H+]/[(SCN)2] = khyd/kcomp = 19.8(+/-0.7) s-1/ 5.14(+/-0.07) x 103 M-2 s-1 = 3.9 x 10-3 M2.     

复合改性膨胀石墨的制备及对酸性艳蓝染料的吸附

采用相同反离子协同磷酸活化法, 以十六烷基三甲基溴化铵(CTAB)-KBr为复合改性剂, 制备了一种高效吸附剂复合改性膨胀石墨(M-EG), 通过扫描电子显微镜(SEM)、 傅里叶变换红外光谱(FTIR)及X射线电子能谱(XPS)等对膨胀石墨(EG)和改性膨胀石墨(M-EG)的形貌结构、 组成和价态进行了表征, 考察了EG和M-EG对酸性艳蓝染料废水的处理效果. 结果表明, 复合改性后的膨胀石墨孔隙度变大, 表面含氮和溴官能团增多. 吸附剂M-EG对酸性艳蓝染料废水具有较高的吸附性能, 在pH=1.0及30 ℃条件下对染料的去除率达到94.13%; EG符合二级动力学吸附模型, 用Langmuir等温线方程拟合效果较好; M-EG符合二级吸附动力学方程, 同时符合Langmuir和Freundlich等温吸附模型; M-EG的吸附动力学常数大于EG吸附动力学常数.     

pH快速响应PNIPAAm-co-PAAc水凝胶的制备及溶胀动力学

pH快速响应PNIPAAm-co-PAAc水凝胶的制备及溶胀动力学;N-异丙基丙烯酰胺;pH敏感性;溶胀历史