利用目标试验因子分析法确定化学反应的级数及速率常数

利用目标试验因子分析(TTFA)结合数值遗传算法(NGA).解析反应过程中在线测得的动力学谱-光谱数据矩阵,可在未知各组分纯光谱及动力学模型情况下同时求解出各组分的纯光谱、反应级数及速率常数。提出用近似计算法计算各组分的动力学谱,使该方法能适用于任意反应级数的体系。针对两步连续反应模型,对反应物、中间体和最终产物均有吸收及某一种组分没有吸收的体系的模拟实验数据矩阵进行了处理,表明该方法均能适用。利用该方法对邻苯二甲酸二甲酯在碱性介质中的水解反应及日落黄水溶液的电解降解反应过程中测得的数据矩阵进行解析,均获得了可靠结果。     

利用减秩因子分析法同时优化确定化学反应级数和速率常数

通过对反应过程中在线测得的动力学谱-光谱二维数据矩阵进行主成分分析，可确定化学反应过程存在的组分数。提出用优化动力学参数-减秩因子分析法解析二维数据矩阵，对未知动力学模型的复杂反应可同时优化求解第一步反应的级数和速率常数。模拟二维数据验证了该方法的可行性。该方法用于高锰酸钾氧化溴化钠的反应过程中测得的二维数据的解析，结果表明：高锰酸钾的还原过程符合0级反应模型。     

原位紫外-可见光谱和电化学方法研究苯胺聚合过程中的降解

用电化学及光谱电化学研究了硫酸溶液中苯胺在玻碳电极上的聚合降解过程 ,在 - 0 2～ 1 0V电位范围 ,循环伏安图显示了四对氧化还原峰 .通过比较聚苯胺 (PAn)膜在硫酸空白溶液和含对氨基苯酚 (PAP)的硫酸溶液中的循环伏安曲线及电化学聚合时溶液的紫外 可见吸收光谱 ,证明了PAn膜的降解产物PAP的存在 ,同时原位现场紫外 可见吸收光谱法初步研究了苯胺聚合降解的动力学过程 .     

几种典型有毒有机污染物的光催化降解研究

本文研究了氯代苯酚和苯胺类化合物的光催化降解,探讨了这些有机污染物分子的氯取代和化合物毒性与光催化降解之间的关系.研究表明,氯代苯酚和苯胺类化合物的光催化降解均符合表观一级反应动力学模型.有机物分子中氯取代基的引入加快了化合物的光催化降解,且反应速率随氯取代基个数的增多而增大.光催化降解的表观速率常数与正辛醇-水分配系数之间存在有较好的线性关系:logk=alogKow+b,该模型可以用于有机污染物的光催化降解性预测.     

电聚合苯胺过程的在线紫外-可见光谱

用在线紫外-可见光谱电化学的方法对0.5mol/L硫酸水溶液中苯胺在ITO导电玻璃电极上的电化学聚的过程进行了研究.结果表明在循环伏安条件下苯胺发生了电聚合,聚合速率与苯胺浓度成正关系;而且在线紫外-可见电化学光谱表明,在0.01mol/L苯胺溶液的电聚合过程的诱导期较长.恒电位条件下的在线紫外-可见电化学光谱显示苯胺浓度为0.05mol/L,电位为0.8V时,在ITO电极上苯胺低聚合物中间体可能产生于聚苯胺形成之前;而0.01mol/L苯胺在0.8V电位下不发生聚合,但在线紫外-可见光谱又显示此时在电极上可能存在小的苯胺低聚物的中间体;在线紫外-可见光谱表明这种中间体是可能产生并存在电极表面上的.     

未知动力学模型的化学反应过程的解析

采用迭代目标转换因子分析法(ITTFA)解析动力学模型未知的化学反应过程中的动力学-光谱数据矩阵,获得了各组分的动力学谱.基于体系中各组分间的等吸收点等光谱特征,提出并建立了一种新的初始迭代矢量的方法.利用该方法解析了动力学模型未知且各组分均有吸收的两步连续反应的模拟数据矩阵,并对最终产物无吸收的水杨酸水溶液电降解反应过程中测得的数据矩阵进行解析,获得了可靠的结果.     

气相苯在TiO2光催化剂上吸附常数和光催化反应常数测定

采用溶胶-凝胶法制备TiO2光催化剂以及掺杂Fe3 和Ce3 的TiO2光催化剂,进行间歇式光催化降解气相苯动力学实验,基于光催化Langmuir-Hinshelwood反应动力学模型(L-H模型),测定气相苯在3种光催化剂上的降解动力学常数和吸附平衡常数.根据光催化降解气相苯实验动力学曲线和L-H模型,估算出TiO2、Fe3 /TiO2和Ce3 /TiO2光催化剂光催化降解苯的反应速率常数k和Langmuir吸附常数K分别为0.5247g/m3·min、1.523g/m3·min、1.010g/m3·min和8.605×10-2m3/g、2.390×10-2m3/g、3.928×10-2m3/g.掺杂Fe3 和Ce3 可明显提高光催化剂光催化降解苯的反应速率常数k,其中Fe3 /TiO2,的反应速率常数k最大.     

MnO_2对TiO_2光催化降解苯胺的影响

采用动力学方法研究了MnO2颗粒物对TiO2光催化降解苯胺活性的影响,对比考察了光催化降解过程中苯胺溶液的UV吸收光谱的变化,并用HPLC方法鉴别了中间产物.结果表明,少量MnO2颗粒物就能使TiO2光催化降解苯胺的活性受到明显的抑制,不同结构的二氧化锰致毒效应由大到小的顺序为:δ-MnO2α-MnO2β-MnO2;降解不同时间后溶液的UV吸收光谱的变化也反映了MnO2颗粒物具有同样的致毒效应;MnO2颗粒物不改变TiO2光催化降解苯胺的途径,但对生成中间产物的基元步骤的抑制程度不同。     

反相胶束中辣根过氧化物酶的停流光谱研究

用停流光谱法研究了HRP在AOT、CTAB和SDS反相胶束中的吸收光谱和反应动力学，实验结果显示在AOT反相胶束中，HRP的吸收峰位置与水相中相同；而另外两种反相胶束对HRP的分子结构产生了较大影响，快速反应动力学研究显示在反相胶束中HRP形成化合物Ⅰ的速率常数远远高于化合物Ⅰ形成HRP—Ⅱ的反应速率常数，推测这是反相胶束的特殊性质造成的结果。     

银纳米颗粒的绿色可控合成及光催化性能的研究

以桑葚植物提取液为还原剂和稳定剂,合成了单分散的类球形、多晶银纳米颗粒。采用紫外-可见分光光度计、透射电子显微镜和选区电子衍射,对银纳米颗粒的形貌、成分及微观结构进行了表征。在可控合成的基础上,以2-、3-、4-硝基苯酚(2-、3-、4-NP)为目标污染物,考察了银纳米颗粒的光催化性能。结果表明,在太阳光照射下,银纳米颗粒展现出了高的光催化活性和稳定性(90天)。2-、3-、4-NP降解反应的动力学速率常数关系如下:K_(4-NP)K_(2-NP)K_(3-NP)。其中,4-NP降解反应的动力学速率常数最大可达0.33 min~(-1),并可由降解体系中银纳米颗粒的添加量来线性调控。     

Determination of rate constants from two-way kinetic-spectral data by using rank annihilation factor analysis

Rank annihilation factor analysis (RAFA) is applied to resolve the two-way kinetic-spectral data measured from spectroscopic reactions and acquire rate constants and the absorption spectrum of each component. A two-step first-order consecutive reaction is studied in this paper. When the first step rate constant acts as an optimizing object, and simply combined with the pure spectrum of reactant, the rank of the original data matrix can be reduced by one by annihilating the information of reactant from the original data matrix. The residual standard deviation (R.S.D.) of the residual matrix after bilineaization of the background matrix is regarded as the evaluation function. Owing to the correlation between kinetic functions of species in the reaction, two optimal resolutions, corresponding to the rate constants of the first and second step, respectively, can both be obtained in one computing process. Given the kinetic parameters, the absorption spectrum of each component including the intermediate can be obtained through least square regression. This approach can also be applied to reaction systems where the intermediate or the final product doesnot absorb. The performance of the method has been evaluated by using synthetic data. Electrodegradation of phenol solution and alkaline hydrolysis of dimethyl phthalate were also studied by the present method.     

Rank annihilation factor analysis for multicomponent kinetic‐spectrophotometric determination using difference spectra

In this work rank annihilation factor analysis (RAFA) is used to analyze difference spectra of kinetic‐spectrophotometric data. Annihilation of the contribution of one chemical component from the original data matrix is a general method in RAFA. However, sometimes RAFA is not suitable for studying rank deficient data such as kinetic‐spectrophotometric measurements. On the other hand, in order to apply RAFA for the determination of an analyte in an unknown sample, a standard two‐way matrix of the analyte with rank one should generally be available. This is not usually attainable for kinetic‐spectrophotometric monitoring of complexation reactions. Processes monitored by difference spectroscopy always have the spectrum of the initial stage subtracted from each spectrum in the data matrix. In this work we show that, for kinetic‐spectrophotometric data of complexation reactions, the spectrum of ligand (reactant) itself can be used as initial spectrum for subtraction. The obtained difference matrix of sample and that of analyte of interest will be full‐rank and rank 1, respectively. Therefore the system can be analyzed by RAFA. The proposed method was investigated with simulated data at the first stage. The method was then applied in the analysis of experimental kinetic‐spectrophotometric data of a complexation reactions of Co(II) and Ni(II) with chromogenic reagent 1‐(2‐pyridylazo) 2‐naphthol in order to do multi‐component determination of these ions in various real samples. Copyright © 2009 John Wiley & Sons, Ltd.     

Photodegradation study of decabromodiphenyl ether by UV spectrophotometry and a hybrid hard- and soft-modelling approach

This work presents an exploratory study of the photochemical degradation process of decabromodiphenyl ether (decaBDE) and gives an interpretation of the kinetic pathway, species and effects of the key factors involved in the degradation process. Use of lowly brominated diphenyl ethers (PBDE) has been banned by the EU and there seems to be evidence of the photolytic degradation of highly brominated PBDEs into lowly brominated congeners. Hence, the importance of knowing the photodegradation process of decaBDE.The photodegradation was investigated under UV light by UV-spectrophotometric monitoring. A novel hybrid data analysis approach, based on the combination of hard- and soft-spectrophotometric multivariate curve resolution, was applied to elucidate the mechanism of the degradation process, to resolve kinetic profiles and pure spectra of the photodegradation products and to evaluate the rate constants. The photodegradation process could be described with a kinetic model based on three consecutive first-order reactions and a decrease of the degradation process was observed as solvent polarity increased. Complementary identification of photodegradation products by gas chromatography coupled to mass spectrometry using negative chemical ionization (GC-NCI-MS) is attempted.This work presents a novel attempt of describing in a comprehensive way the photochemical degradation process of decaBDE, with all successive steps and related rate constants. This study proves also the potential of the proposed hybrid data analysis methodology as a general strategy to interpret the evolution of these photochemical reactions.     

Reaction Schemes That Are Easily Confused with a Reversible First–Order Reaction

A detailed kinetic analysis of two schemes, one involving coupled consecutive processes and another featuring the simultaneous association reaction and decay of a component, is presented here using Taylor series expansion. It is shown that both of these schemes are easily confused with the reversible second–order reaction in a routine kinetic study. The kinetic traces predicted by both schemes are sufficiently close to pseudo–first–order curves so that it is practically impossible to identify the deviations based on data with the usual experimental errors, which was also demonstrated by fitting simulated theoretical curves to exponential functions. The dependence of the pseudo–first–order rate constants on the concentration of the excess reagent features the same trend as in the case of a reversible reaction: A straight line with an intercept is observed. This analysis emphasizes that the reversible nature of reactions should be demonstrated by direct equilibrium studies when elements of reversibility are implied by kinetic results.     

Estimation of the rate constants of second order reactions using mean centering of ratio spectra

A new application of the mean centering of ratio spectra method is proposed for estimation of the rate constants of second order reactions, using kinetic-spectrophotometric data. The method is based on the mean centering of the ratio spectra to obtain a kinetic profile of the product. Using computational fitting, the rate constant can be obtained without any ambiguity. An interesting feature of second-order reactions is that the number of steps in the reaction is less than the number of absorbing species, resulting in a rank-deficient response matrix. Through using row mean centering of ratio spectra, the pure response of the product of the reaction could be obtained, and thus an accurate estimation of rate constant would be possible. The applicability of the method was evaluated by using several model data. The reaction of 1,2-naphthoquinone-4-sulfonate sodium (NQS) and 3-nitroaniline (TNA) in ethanol as a real system was also studied applying the proposed method.     

Application of chemometrics methods with kinetic constraints for estimation of rate constants of second order consecutive reactions.

To determine the rate constants for the second order consecutive reactions of the form U + V -(k1)--> W -(k2)--> P, a number of chemometrics and hard modeling-based methods are described. The absorption spectroscopic data from the reaction were utilized for performing the analysis. Concentrations and extinctions of components were comparable, and all of them were absorbing species. The number of steps in the reaction was less than the number of absorbing species, which resulted in a rank-deficient response matrix. This can cause difficulties for some of the methods described in the literature. The standard MATLAB functions were used for determining the solutions of the differential equations as well as for finding the optimal rate constants to describe the kinetic profiles. The available knowledge about the system determines the approaches described in this paper. The knowledge includes the spectra of reactants and products, the initial concentrations, and the exact kinetics. Some of this information is sometimes not available or is hard to estimate. Multiple linear regression for fitting the kinetic parameters to the obtained concentration profiles, rank augmentation using multiple batch runs, a mixed spectral approach which treats the reaction using a pseudo species concept, and principal components regression are the four groups of methods discussed in this study. In one of the simulated datasets the spectra are quite different, and in the other one the spectra of one reactant and of the product share a high degree of overlap. Instrumental noise, sampling error are the sources of error considered. Our aim was the investigation of the relative merits of each method.     

Two novel procedures for automatic resolution of two-way data from coupled chromatography

In order to deal with the problem of simultaneous qualitative and quantitative analysis of the complicated samples in analytical chemistry, two novel procedures for automatic resolution of two-way data from coupled chromatography were developed in this work. The first can be used to determine automatically the number of components involved in a certain peak cluster. The second method is an iterative resolution procedure named the stepwise key spectrum selection which has also been developed to resolve automatically the spectra and chromatographic profiles of every component in the peak cluster investigated. The results obtained from simulated and real data show that the proposed methods perform fairly well.     

Kinetic calculations of the Ni anodic dissolution from EIS

Anodic nickel dissolution in acid media has been analyzed by means of electrochemical quartz crystal microbalance and electrochemical impedance spectroscopy techniques. The experimental impedance spectra have been fitted to an equivalent circuit which is related to a mechanism of two consecutive electron transfers followed by a Ni²⁺ mass transfer step. That way, an estimation for values of rate constants and surface concentrations of the Ni(0), Ni(I) and Ni(II) species has been obtained.